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Tectonic Plate Motion, Convergent Boundaries - Pass My Exams: GSCE Physicss

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Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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Geothermal heat flux (GHF) is the amount of heat flowing outward from the interior of the Earth as measured at different points on the surface. GHF can play an important role in the motion of glaciers in places like Greenland, but the ice can also make GHF difficult to measure directly. The ice sheet covering Greenland is up to three kilometers thick, so GHF there has been measured in only a few places where deep boreholes have been drilled through the ice.

In a paper published in Geophysical Research Letters, NASA Goddard research scientist Yasmina Martos and her coauthors describe a method of mapping GHF across Greenland using a map of magnetic anomaly, the local variations in the Earth's magnetic field. Temperature affects the magnetic record stored in minerals in the Earth's crust, and using this fact, Martos et al. were able to infer a high-resolution map of GHF for Greenland and neighboring Ellesmere Island. Crustal thickness data derived from gravity measurements supports the conclusions.

The GHF map contains at least two surprises. The overall GHF is lower than expected, and the map reveals a warm swath across Greenland from the northwest to the southeast. The swath is likely to be the track of the Iceland hotspot, a plume of magma rising from deep within the Earth's mantle. The hotspot is responsible for the formation of Iceland, beginning roughly 20 million years ago, in a manner similar to the formation of the Hawaiian islands. The track of the hotspot through Greenland actually records the motion of Greenland over the last 100 million years as plate tectonics moved it north and west.

This visualization shows the GHF map, the hotspot track, and the motion of Greenland.

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This page was originally published on Wednesday, August 1, 2018.
This page was last updated on Monday, January 6, 2025 at 12:13 AM EST.

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		Ernie Wright
	
		 and Yasmina Martos
	

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NASA Scientific Visualization Studio | Geothermal Heat Flux Reveals the Iceland Hotspot Track underneath Greenland

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This visualization shows the Greenland geothermal heat flux map, the track of the Iceland hotspot through Greenland, and the plate tectonic motion of Greenland over the hotspot during the past 100 million years.This video is also on the NASA YouTube channel.

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Tectonic Plate Motion, Divergent Boundaries - Pass My Exams: Easy exam revision notes for GSCE Physics

# data[].attributes.attachment_link.description
Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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Oceanographer Bob Ballard explores thermal vents in Iceland. Graphics illustrate the layers of Earth’s crust, mantle, outer and inner core.

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How Iceland’s fiery mantle plume scattered ancient volcanoes across the North Atlantic

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What do the rumblings of Iceland’s volcanoes have in common with the now peaceful volcanic islands off Scotland’s western coast and the spectacular basalt columns of the Giant’s Causeway in Northern Ireland?

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Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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Tectonic Plate Motion

Convergent Boundaries

The Earth's size has remained relatively the same since shortly after its formation 4.6 billion years ago. This implies that the Earth's crust must be destroyed at the same rate it is being created. The destruction or recycling of the Earth's crust takes place at convergent boundaries. Convergent boundaries are the zones where two tectonic plates moving towards each other come together at their plate boundaries. At convergent boundaries tectonic plates collide and crust is destroyed as one plate is pulled beneath the other, the type of collision depends on the types of plates involved. These can be categorised as:

Oceanic - Continental Plate Convergence

Oceanic - Oceanic Plate Convergence

Continental - Continental Plate Convergence

Oceanic-Continental Plate Convergence

When an oceanic plate collides with a continental plate the crust forming the oceanic plate gets bent and pulled under the continental crust. This is because the rocks that form the oceanic crust are denser and thinner than the rocks that form the continental crust. The process by which the oceanic crust is pulled under the continental crust is called subduction and the zone at which this occurs at the plate boundaries is called the subduction zone. At the subduction zone where the oceanic crust sinks beneath the continental crust a deep oceanic trench or valley is created. These can be many of thousands of kilometres long and 8 to 10 kilometres deep making them the deepest part of the ocean floor.

Oceanic and continental plate collisions result in mountain and volcano formation. Mountains are formed as the overriding continental plate gets lifted up over the oceanic plate. An example of this is found at the boundary between the South American continental plate and the Nazca oceanic plate. The South American continental plate is being lifted over the subducted Nazca oceanic plate creating the Andes mountain range.

The formation of volcanoes is a result of the subduction of the oceanic crust. As the oceanic crust gets forced deeper into the Earth the increasing heat and pressure releases trapped water and gases, the combing effect of which is the crust melting to form magma. This magma rises and accumulates in magma chambers which then feeds and creates volcanoes on the overriding continental plate.

Earthquakes are also common at oceanic and continental plate boundaries. These occur when the deepest part of the subducting oceanic plate break into smaller pieces. Some of the pieces become locked in place for long periods and when they are suddenly released they generate large earthquakes.

Oceanic-Oceanic Plate Convergence

This is similar to oceanic-continental convergence in that one of the plates is subducted under the other during the collision. At the subduction zone a very deep trench is formed in the ocean floor.

Oceanic and oceanic plate convergence result in the formation of volcano chains. The crust that is pulled under or subducted melts to form magma. This magma rises to the top of the overriding oceanic plates and erupts on the ocean floor. Over millions of years, the lava and debris from the volcanic eruptions pile up on the ocean floor until the volcano rises above sea level to form a volcanic island. These types of islands are usually formed as chains called island arcs, which run parallel to the trench at the subduction zone.

Oceanic-oceanic plate convergence experience similar powerful earthquakes to oceanic-continental convergences.

Continental - Continental Plate Convergence (Collisions)

When two continental plates collide they resist downwards motion or subduction because the continental rocks that make them up are of similar density. Instead, the crust tends to buckle and gets pushed upwards and sideways. Thus, when two continental plates collide mountains are formed.

Approximately 200 million years ago when Pangaea broke apart the Indian plate began its journey northwards. About 50 million years ago the Indian plate collided with the Eurasian plate. This collision caused the crust to buckle upwards and the Eurasian plate to crumple up over the Indian plate. Over millions of years the continuous collisions between the two plates has resulted in the formation of the Himalayan mountain range and the Tibetan Plateau. The Himalayas are the highest continental mountains in the world holding many peaks at 8000 meters above sea-level, the highest being Mount Everest at 8848 meters. Since the Indian Plate is continuing in its northward movement into the Eurasian plate the Himalayas continue to grow at a rate of approximately 5mm to 20mm a year.

# data[].attributes.attachment_link.title
Tectonic Plate Motion, Convergent Boundaries - Pass My Exams: GSCE Physicss

# data[].attributes.attachment_link.description
Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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Skip to main content

Official websites use .gov
A.gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock () or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

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This tectonic map of the Turkey region shows the tectonic plates in the area and their direction of motion (arrows). The red lines indicate the plate boundaries and the small black arrows next to the red lines show the relative motion across the plate boundaries.

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The Anatolian transform fault system is probably the most active in the world.

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North Anatolian Fault, Turkey

Regional faults in Turkey: © Mike Norton, Wikimedia Commons

The North Anatolian fault stretches across northern Turkey and its movement is strike-slip in nature just like the ancient movement seen at the Great Glen Fault in Scotland. The fault runs along the boundary between the Eurasian plate and the smaller Anatolian plate but movement in the area is controlled by collision of the larger Arabian plate to the south and the Eurasian plate to the north. The fault is a transform fault with the Anatolian Plate and the Eurasian Plate sliding past each other

The fault is 1500 kilometres long and stretches from the junction with the East Anatolian fault in eastern Turkey all the way across northern Turkey and into the Aegean Sea. Most concerning for earthquake geologists is that it passes within 20km of Istanbul; the most populated city in Turkey.

This fault has been the site of a number of disastrous earthquakes including the 1939 Erzincan earthquake which resulted in the death of more than 32,000 people and injured more than 100,000. Since then, there have been seven further earthquakes measuring over 7.0 in magnitude including the7.6-magnitude Golcuk-Kocaeli earthquake which directly struck the city of Izmit in 1999, killing over 17,100 people, and displacing 250,000 others.

Regional plate tectonics: © Molear 3

Seismologists think that earthquakes are progressing along the fault from west to east with each one triggering the next further west along the fault. Over the past century earthquake events have been moving in a broadly westerly direction and this create significant concern around the potential for a major earthquake in the vicinity of Istanbul, a city with a population of more than 14 million people, which was also suffered heavy damage in the 1999 earthquake despite being 110km away from the epicentre.

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News and updates for members of the public and policy makers interested in how the geosciences interact with society. Find updates about outreach activities and policy related meetings, consultation responses and position statements.

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An Introduction to the Geology of the Aleutian Islands - NOAA Ocean Exploration

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Ocean exploration is vital for mapping and characterizing geologic features and biologic communities in the ocean, some of which have not been previously described. However, the impacts of ocean exploration extend well beyond the ocean, with impacts reaching to rock layers in the high mountains and deep subsurface. By investigating modern tectonic margins and deep-ocean environments, we improve interpretations of ancient rock layers that record the geologic history of our planet.

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Editor's note:In the summer and fall of 2014, Paul Salopek hiked 800 miles across Anatolia, Turkey, documenting the beautiful region's ancient roots and its peoples' warmth, hospitality-and struggles with war and refugee crises. Walking partner Deniz Kilic trekked more than 300 miles of that route. He now sends us a report from the earthquakes that leveled parts of Turkey and Syria this week.

When two massive earthquakes struck Turkey on Monday, I was traveling with friends in a distant city called Ardahan near the Caucasus mountains in the northeast of the country. We immediately left that remote area by four-wheel-drive to render help.

The trip wasn't easy. We drove about 500 miles to the hardest-hit regions, centered around the province of Kahramanmaras, in the southeast. It took us 12 hours. Police at checkpoints only admitted emergency vehicles. But they let me and my friends through because we are trained volunteers for an emergency rescue team in Bodrum, my hometown on the Aegean Sea. By the time we got to the actual disaster zone, it was already 11 p.m.

First, we went to the provincial governor's building in Adiyaman, one of the cities ravaged by the quakes. Seeing us in our yellow Disaster and Emergency Management Agency vests, the local officials immediately gave us our first assignment: to join other crews in rescuing people trapped inside two collapsed buildings.

Friends on social media also began sending tips about where aid was needed most.

The earthquakes smashed Turkey on one of the coldest days of the year. One early request came in to rescue three families stranded in cars in heavy snows. We saved them from freezing. We gave them gasoline and pulled them out of the drifts.

Then it was a new mission at one of the local hotels. It was reduced to rubble. We helped gently pull about 80 people out of this massive wreck. We literally disentangled living survivors from beneath huge piles of concrete and bricks.

On the third day after the catastrophe, we got some good news: There were people still alive in the ruins. We tried to save them. But with each passing day of freezing temperatures, hope has grown thinner.

These two quakes, the biggest registering 7.8 on the Richter scale, may be among the most devasting in Turkey's history. And the country was unfortunately not ready.

Thousands of buildings have collapsed. There are only about 200 organized rescue teams in all of Turkey. Even if we deploy 100 percent of these resources, it won't be enough to save all the victims.

The main problem, in my opinion, is not listening to the scientists who for years have warned authorities not to build on Turkey's active earthquake fault lines. Or, if they must build something, then only allow earthquake-resistant structures. In recent days, I saw only one such building that had been designed correctly and stood undamaged. It didn't even have a scratch. (See photo.) But far more buildings, roads, and airports were constructed without safeguards and are now destroyed and unusable. Viaducts are damaged. Today, this substandard infrastructure actually forms a deadly barrier that prevents people from being rescued. Of course, the unbelievably terrible weather conditions don't help.

Thousands of shipments of relief materials are arriving now in Turkey from all around the world. The most important task ahead is to be organized in distributing these lifesaving goods. Many shattered cities will desperately need help: Kilis, Diyarbakır, Adana, Osmaniye, Gaziantep, Şanlıurfa, Adıyaman, Malatya, and Hatay.

I hope everybody will take a serious lesson from this catastrophe. We must face the reality that a big earthquake hitting Istanbul is likely coming. All the country must prepare. We must be ready from now on.

Here are a few of the organizations working in the disaster zone:
A veteran traveler, motorcycle rider, and mountaineer, Deniz Kilic owns a travel agency called Ibex Adventure Club, in the city of Bodrum. He has volunteered for disaster relief missions in earthquake zones before, including the Erzincan quake in Turkey in 1992.

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A Walking Partner in Turkey Offers a Glimpse of his Earthquake-Pummeled Country-and a Warning About the Future

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Pulitzer Prize-winning journalist and National Geographic Fellow Paul Salopek is retracing on foot the global migration of our ancestors in a 38,000 km, multi-year odyssey that begins in Ethiopia and ends in Tierra del Fuego.

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Plate Tectonics theory: Geography UPSC - UPSC Notes » LotusArise

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According to the plate tectonics theory, the earth’s lithosphere is broken into distinct plates which are floating on a ductile layer called asthenosphere.

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In plate tectonics, a divergent boundary is a linear feature that exists between two tectonic plates that are moving away from each other. An example of a divergent boundary is a mid ocean ridge, a…

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Shaded relief map of United States, highlighting National Park Service sites at Hotspots. Letter codes are abreviations for park names listed in tectonic settings pages linked below. Sites in Hawaii and American Samoa lie on thin oceanic crust, whereas thicker continental crust is associated with the hotspot track in the Columbia Plateau of Oregon and Washington, the Snake River Plain of Idaho, and the current position of the Yellowstone Hotspot beneath Yellowstone National Park.
Modified from "Parks and Plates: The Geology of our National Parks, Monuments and Seashores," by Robert J. Lillie, New York, W. W. Norton and Company, 298 pp., 2005, www.amazon.com/dp/0134905172.

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Hotspots - Geology (U.S. National Park Service)

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Volcanoes - Hawaiʻi Volcanoes National Park (U.S. National Park Service)

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Volcanoes are monuments to Earth’s origins, evidence that its primordial forces are still at work. Over time, these prodigious land builders have created the Hawaiian island chain itself. Kīlauea and Mauna Loa are still adding to the island of Hawaiʻi and put this incredible phenomenon on full display.

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Tectonic Plate Motion, Divergent Boundaries - Pass My Exams: Easy exam revision notes for GSCE Physics

# data[].attributes.attachment_link.description
Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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Tectonic Plate Motion

Convergent Boundaries

The Earth's size has remained relatively the same since shortly after its formation 4.6 billion years ago. This implies that the Earth's crust must be destroyed at the same rate it is being created. The destruction or recycling of the Earth's crust takes place at convergent boundaries. Convergent boundaries are the zones where two tectonic plates moving towards each other come together at their plate boundaries. At convergent boundaries tectonic plates collide and crust is destroyed as one plate is pulled beneath the other, the type of collision depends on the types of plates involved. These can be categorised as:

Oceanic - Continental Plate Convergence

Oceanic - Oceanic Plate Convergence

Continental - Continental Plate Convergence

Oceanic-Continental Plate Convergence

When an oceanic plate collides with a continental plate the crust forming the oceanic plate gets bent and pulled under the continental crust. This is because the rocks that form the oceanic crust are denser and thinner than the rocks that form the continental crust. The process by which the oceanic crust is pulled under the continental crust is called subduction and the zone at which this occurs at the plate boundaries is called the subduction zone. At the subduction zone where the oceanic crust sinks beneath the continental crust a deep oceanic trench or valley is created. These can be many of thousands of kilometres long and 8 to 10 kilometres deep making them the deepest part of the ocean floor.

Oceanic and continental plate collisions result in mountain and volcano formation. Mountains are formed as the overriding continental plate gets lifted up over the oceanic plate. An example of this is found at the boundary between the South American continental plate and the Nazca oceanic plate. The South American continental plate is being lifted over the subducted Nazca oceanic plate creating the Andes mountain range.

The formation of volcanoes is a result of the subduction of the oceanic crust. As the oceanic crust gets forced deeper into the Earth the increasing heat and pressure releases trapped water and gases, the combing effect of which is the crust melting to form magma. This magma rises and accumulates in magma chambers which then feeds and creates volcanoes on the overriding continental plate.

Earthquakes are also common at oceanic and continental plate boundaries. These occur when the deepest part of the subducting oceanic plate break into smaller pieces. Some of the pieces become locked in place for long periods and when they are suddenly released they generate large earthquakes.

Oceanic-Oceanic Plate Convergence

This is similar to oceanic-continental convergence in that one of the plates is subducted under the other during the collision. At the subduction zone a very deep trench is formed in the ocean floor.

Oceanic and oceanic plate convergence result in the formation of volcano chains. The crust that is pulled under or subducted melts to form magma. This magma rises to the top of the overriding oceanic plates and erupts on the ocean floor. Over millions of years, the lava and debris from the volcanic eruptions pile up on the ocean floor until the volcano rises above sea level to form a volcanic island. These types of islands are usually formed as chains called island arcs, which run parallel to the trench at the subduction zone.

Oceanic-oceanic plate convergence experience similar powerful earthquakes to oceanic-continental convergences.

Continental - Continental Plate Convergence (Collisions)

When two continental plates collide they resist downwards motion or subduction because the continental rocks that make them up are of similar density. Instead, the crust tends to buckle and gets pushed upwards and sideways. Thus, when two continental plates collide mountains are formed.

Approximately 200 million years ago when Pangaea broke apart the Indian plate began its journey northwards. About 50 million years ago the Indian plate collided with the Eurasian plate. This collision caused the crust to buckle upwards and the Eurasian plate to crumple up over the Indian plate. Over millions of years the continuous collisions between the two plates has resulted in the formation of the Himalayan mountain range and the Tibetan Plateau. The Himalayas are the highest continental mountains in the world holding many peaks at 8000 meters above sea-level, the highest being Mount Everest at 8848 meters. Since the Indian Plate is continuing in its northward movement into the Eurasian plate the Himalayas continue to grow at a rate of approximately 5mm to 20mm a year.

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Tectonic Plate Motion, Convergent Boundaries - Pass My Exams: GSCE Physicss

# data[].attributes.attachment_link.description
Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

# data[].attributes.attachment_link.description
Comprehensive revision notes for GCSE exams for Physics, Chemistry, Biology

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The Hawaiian Emperor seamount chain is a well-known example of a large seamount and island chain created by hot-spot volcanism. Each island or submerged seamount in the chain is successively older toward the northwest. Near Hawaii, the age progression from island to island can be used to calculate the motion of the Pacific Oceanic plate toward the northwest. The youngest seamount of the Hawaiian chain is Loihi, which presently is erupting from its summit at a depth of 1000 meters. Image courtesy of U.S. Geological Survey.

The Earth's outer crust is made up of a series of tectonic plates that move over the surface of the planet. In areas where the plates come together, sometimes volcanoes will form. Volcanoes can also form in the middle of a plate, where magma rises upward until it erupts on the seafloor, at what is called a "hot spot."

The Hawaiian Islands were formed by such a hot spot occurring in the middle of the Pacific Plate. While the hot spot itself is fixed, the plate is moving. So, as the plate moved over the hot spot, the string of islands that make up the Hawaiian Island chain were formed.

The Hawaiian Islands form an archipelago that extends over a vast area of the North Pacific Ocean. The archipelago is made up of 132 islands, atolls, reefs, shallow banks, shoals, and seamounts stretching over 1,500 miles from the island of Hawaii in the southeast to Kure Atoll in the northwest.

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national oceanic and atmospheric administration

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The Hawaiian Islands were formed by volcanic activity

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The long trail of the Hawaiian hotspot

Over the past 70 million years, the combined processes of magma formation, volcano eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian "hot-spot" have left a long trail of volcanoes across the Pacific Ocean floor. The Hawaiian Ridge-Emperor Seamounts chain extends some 6,000 km from the "Big Island" of Hawaii to the Aleutian Trench off Alaska. The Hawaiian Islands themselves are a very small part of the chain and are the youngest islands in the immense, mostly submarine mountain chain composed of more than 80 volcanoes. The length of the Hawaiian Ridge segment alone, from the Big Island northwest to Midway Island, is about equal to the distance from Washington, D.C. to Denver, Colorado (2,600 km). The amount of lava erupted to form the Hawaiian-Emperor chain is calculated to be at least 750,000 cubic kilometers-more than enough to blanket the entire State of California with a layer of lava roughly 1.5 km thick.

Map of part of the Pacific basin showing the volcanic trail of the Hawaiian hotspot-- 6,000-km-long Hawaiian Ridge-Emperor Seamounts chain. (Base map reprinted by permission from World Ocean Floor by Bruce C. Heezen and Marie Tharp, Copyright 1977.)

A sharp bend in the chain indicates that the motion of the Pacific Plate abruptly changed about 43 million years ago, as it took a more westerly turn from its earlier northerly direction. Why the Pacific Plate changed direction is not known, but the change may be related in some way to the collision of India into the Asian continent, which began about the same time.

As the Pacific Plate continues to move west-northwest, the Island of Hawaii will be carried beyond the hotspot by plate motion, setting the stage for the formation of a new volcanic island in its place. In fact, this process may be under way. Loihi Seamount, an active submarine volcano, is forming about 35 km off the southern coast of Hawaii. Loihi already has risen about 3 km above the ocean floor to within 1 km of the ocean surface. According to the hotspot theory, assuming Loihi continues to grow, it will become the next island in the Hawaiian chain. In the geologic future, Loihi may eventually become fused with the Island of Hawaii, which itself is composed of five volcanoes knitted together-Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea.

URL: https://pubs.usgs.gov/publications/text/Hawaiian.html
Last updated: 05.05.99
Contact: bhanks@usgs.gov

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Hawaiian hotspot [This Dynamic Earth, USGS]

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Over the past 70 million years, the combined processes of magma formation, volcano eruption and growth, and continued movement of the Pacific Plate over the stationary Hawaiian "hot-spot" have left a long trail of volcanoes across the Pacific Ocean floor.

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Volcano - Yellowstone National Park (U.S. National Park Service)

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Geologic History: Between 542 and 66 million years ago—long before the “supervolcano” became part of Yellowstone’s geologic story—the area was covered by inland seas.

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What is a hotspot and how do you know it's there?

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Most volcanic eruptions occur near the boundaries of tectonic plates, but there are some exceptions. In the interior of some tectonic plates, magma has been erupting from a relatively fixed spot below the plate for millions of years. As the plate continuously moves across that spot, a trail of progressively older volcanic deposits is left at the surface.

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In the early twentieth century, when the Earth scientist Alfred Wegener proposed that the planet's continents drift - joining to form giant landmasses and retreating away again over long spans of time - most researchers weren't having it. "Wegener's hypothesis in general is of the footloose type," scoffed one geologist, and "takes considerable liberty with our globe."

That viewpoint was common. Though some scientists accepted Wegener's proposal, it failed to gain much traction during his lifetime. Much of the Earth science community continued to believe that continents were fixed in place, thanks to a combination of elitism and some genuine scientific weaknesses with Wegener's theory, like the lack of a plausible explanation for how continents might move across the Earth's surface.

Today, however, the notion that continents shift their positions over time - though modified since Wegener's day - is fundamental to the theory of plate tectonics. So, what gives? How did dynamic continents transform from an object of ridicule to a fixture of Geology 101 textbooks?

Much of the answer lies in what might seem an unlikely place: the bottom of the ocean. In the 1950s and 1960s, scientists pieced together several lines of evidence to identify vast, volcanic stretches of the seafloor where lava cools to form Earth's hard outer crust. It was more than a fascinating find: understanding these areas where crust is born, along with the zones where it dips back into the planet's interior, allowed scientists to develop the modern theory of plate tectonics and marked a sea change in the field of Earth science.

Earth scientists now see the layered planet as an intensely dynamic system. The Earth's rigid outer layer, called the lithosphere, is made up of the crust and the shallowest part of the mantle (the shell of rock that lies below the crust). The lithosphere is divided into several rocky puzzle pieces- the tectonic plates -that rest atop the deeper mantle. These plates are constantly shifting, colliding or retreating or sliding past one another, pushed along by the motion of rock in the mantle below.

(NOAA)

"This rock, while solid, is also flowing on long timescales," said Elizabeth Cottrell, a geologist at the Smithsonian National Museum of Natural History. That can be tough to visualize, so Cottrell offers an analogy. "Imagine you tipped a jar of honey on its side in the freezer," she said. "You could smash the frozen honey with a hammer and shatter it, because on short timescales it behaves like a solid. But on long timescales, the honey would slowly flow and pool in the freezer, behaving like a liquid."

Earth's mantle behaves similarly. Even though it's solid, it flows very slowly, with warmer, deeper rock rising toward the surface before cooling and sinking back down. This process, known as convection, acts like a conveyor belt for the lithosphere above it. As rock convects in the mantle, it shuttles the tectonic plates around the Earth's surface.

But even as recently as the mid-twentieth century, most scientists thought of the Earth as a far more static place. Many assumed that the seafloor, which we now know is rugged, active, and ever-changing, was like the bottom of a planetary bathtub, flat and featureless and ultimately uninteresting.

That assumption began to crumble in the 1950s, thanks in large part to the pioneering work of the oceanographic cartographer Marie Tharp. Using sonar data from ships that had entered the ocean in droves during World War II, Tharp mapped the topography of a seafloor that looked nothing like the bottom of a bathtub. Instead, it was a landscape as complex as the terrestrial one, complete with towering mountains, yawning trenches, and sprawling plains. One of Tharp's most stunning finds was the Mid-Atlantic Ridge, a gigantic mountain range that spans the Atlantic Ocean. We now know that this ridge marks the boundary where multiple pairs of tectonic plates pull away from one another at a few centimeters per year.

Tharp's colleagues ridiculed some of her work, including her hypothesis that new crust formed at sites like the Mid-Atlantic Ridge. But other scientists were coming to similar conclusions. In 1962, for instance, the geologist Harry Hess formally proposed the concept that would become known as seafloor spreading. At plate boundaries like the Mid-Atlantic Ridge, he thought, molten rock from deep inside the Earth would upwell to the surface and cool, producing new oceanic crust.

Today, Earth scientists accept seafloor spreading as an integral part of plate tectonics. "When you have two oceanic plates moving away from one another, that's called a spreading center," said Daniel Rasmussen, a volcanologist and Peter Buck postdoctoral fellow at the museum. As mantle rock convects upward, he said, the decreasing pressure will cause it to melt. "And then that melt will percolate up into the spreading center, and some of it will erupt at the surface." Bathed by ocean water, the lava cools, and you have new seafloor.

(NOAA Ocean Explorer)

That doesn't mean the planet is growing. "The crust is being consumed and recycled back into Earth's interior at an equal rate, at subduction zones," Cottrell said. At these zones, the boundaries where tectonic plates collide into each other, one plate slides beneath the other. As the descending plate churns and releases its water, it causes surrounding rock to melt into magma, meaning subduction zones are sites of intense volcanic activity.

None of these concepts had been solidified when scientists like Tharp and Hess were investigating the seafloor. Instead, the notion that the seafloor was full of ruptures, pulling apart and birthing new crust like so many planetary nurseries, was radical. It wasn't lost on the Earth science community that this process would provide a basis for the much-maligned theory of continental drift, since continental crust would move just like oceanic crust. Such a blow to the prevailing model would require some hefty evidence.

It didn't take long to arrive. Some of the most compelling evidence came in the 1960s, from distinctive patterns found in magnetic minerals embedded in the rock at deep-sea spreading centers.

When magnetic minerals in lava cool down, they orient themselves according to Earth's magnetic field, like tiny compasses. Because the direction of Earth's magnetic field has flipped several times over the planet's history, the orientation of the minerals differs depending on when they formed. That means spreading centers, where new minerals are constantly forming, should act like a logbook of the planet's magnetic history. Sure enough, these sites show symmetrical patterns of magnetic "stripes," as new minerals repeatedly lock in the direction of the field and spread outward.

(NOAA)

The magnetic stripe observations, combined with other lines of evidence - including volcanic activity, earthquakes, and data that Wegener had marshaled in support of his theory decades previously - started to convince scientists of the Earth's dynamic structure.

"There were all these ideas around that were consistent with plate tectonics, and the theory tied them all together," Rasmussen said. "Gaining an understanding of how seafloor is formed helped scientists understand what they had been seeing on land surfaces for many, many years."

Spreading centers like the Mid-Atlantic Ridge are a crucial part of the Earth system for a number of reasons. Their volcanism produces energy that supports vibrant deep-sea communities. They are sites of seawater circulation, playing a vital role in ocean chemistry. And they've been key players in the history of Earth science, helping scientists understand the workings of a planet in motion.

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How the Ocean Floor Helped Seal the Deal for Plate Tectonics

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In the early twentieth century, when the Earth scientist Alfred Wegener proposed that the planet's continents drift - joining to form giant landmasses and retreating away again over long spans of time - most researchers weren't having it. "Wegener's hypothesis in general is of the footloose type," scoffed one geologist, and "takes considerable liberty with our globe."

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The massive mid-ocean ridge system is a continuous range of underwater volcanoes that wraps around the globe like seams on a baseball, stretching nearly 65,000 kilometers (40,390 miles). The majority of the system is underwater, with an average water depth to the top of the ridge of 2,500 meters (8,200 feet).

Mid-ocean ridges occur along divergent plate boundaries, where new ocean floor is created as the Earth's tectonic plates spread apart. As the plates separate, molten rock rises to the seafloor, producing enormous volcanic eruptions of basalt. The speed of spreading affects the shape of a ridge - slower spreading rates result in steep, irregular topography while faster spreading rates produce much wider profiles and more gentle slopes.

Two well-studied mid-ocean ridges within the global system are the Mid-Atlantic Ridge and the East Pacific Rise. The Mid-Atlantic Ridge runs down the center of the Atlantic Ocean, slowly spreading at a rate of 2 to 5 centimeters (0.8 to 2 inches) per year and forming a rift valley that is about the depth and width of the Grand Canyon. In contrast, the East Pacific Rise is spreading quickly, at rates of 6 to 16 centimeters (3 to 6 inches) per year. Due to the fast spreading rates, there is no rift valley in the Pacific, just a smooth volcanic summit with a crack along the crest that is much smaller than the Atlantic rift valley.

Despite being such a prominent feature on our planet, much of the mid-ocean ridge system remains a mystery. By funding expeditions to spreading centers in the Atlantic and the Pacific, NOAA Ocean Exploration is helping scientists to draw connections between volcanic, tectonic, hydrothermal, and biological systems in order to better understand the Earth's remarkable, evolving geography.

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The massive mid-ocean ridge system is a continuous range of underwater volcanoes that wraps around the globe like seams on a baseball, stretching nearly 65,000 kilometers (40,390 miles). The majority of the system is underwater, with an average water depth to the top of the ridge of 2,500 meters (8,200 feet).

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lates of lithosphere move because of convection currents in the mantle. One type of motion is produced by seafloor spreading. Plate boundaries can be located by outlining earthquake epicenters. …

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An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

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Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean-and some of the deepest natural spots on Earth. Ocean trenches are found in every ocean basin on the planet, although the deepest ocean trenches ring the Pacific as part of the so-called "Ring of Fire" that also includes active volcanoes and earthquake zones.

How Ocean Trenches Form
Subduction Zones
When the leading edge of a dense tectonic plate meets the leading edge of a less-dense plate, the denser plate bends downward. This place where the denser plate subducts is called a subduction zone.

Oceanic subduction zones almost always feature a small hill preceding the ocean trench itself. This hill, called the outer trench swell, marks the region where the subducting plate begins to buckle and fall beneath the more buoyant plate.

Some ocean trenches are formed by subduction between a plate carrying continental crust and a plate carrying oceanic crust. Continental crust is always much more buoyant than oceanic crust, and oceanic crust will always subduct.

Ocean trenches formed by this continental-oceanic boundary are asymmetrical. On a trench's outer slope (the oceanic side), the slope is gentle as the plate gradually bends into the trench. On the inner slope (continental side), the trench walls are much more steep. The types of rocks found in these ocean trenches are also asymmetrical. The oceanic side is dominated by thick sedimentary rocks, while the continental side generally has a more igneous and metamorphic composition.

Some of the most familiar ocean trenches are the result of this type of convergent plate boundary. The Peru-Chile Trench off the west coast of South America is formed by the oceanic crust of the Nazca plate subducting beneath the continental crust of the South American plate. The Ryukyu Trench, stretching out from southern Japan, is formed as the oceanic crust of the Philippine plate subducts beneath the continental crust of the Eurasian plate.

More rarely, ocean trenches can be formed when two plates carrying oceanic crust meet. The Mariana Trench, in the South Pacific Ocean, is formed as the mighty Pacific plate subducts beneath the smaller, less-dense Philippine plate.

In a subduction zone, some of the molten material-the former seafloor-can rise through volcanoes located near the trench. The volcanoes often build volcanic arcs-island mountain ranges that lie parallel to the trench. The Aleutian Trench is formed where the Pacific plate subducts beneath the North American plate in the Arctic region between the U.S. state of Alaska and the Russian region of Siberia. The Aleutian Islands form a volcanic arc that swings out from the Alaskan Peninsula and just north of the Aleutian Trench.

Not all ocean trenches are in the Pacific, of course. The Puerto Rico Trench is a tectonically complex depression in part formed by the Lesser Antilles subduction zone. Here, the oceanic crust of the enormous North American plate (carrying the western Atlantic Ocean) is being subducted beneath the oceanic crust of the smaller Caribbean plate.

Accretionary wedges form at the bottom of ocean trenches created at some convergent plate boundaries. The rocks of an accretionary wedge are so deformed and fragmented they are known as melange-French for "mixture."

Accretionary wedges form as sediments from the dense, subducting tectonic plate are scraped off onto the less-dense plate. Sediments often found in accretionary wedges include basalts from the deep oceanic lithosphere, sedimentary rocks from the seafloor, and even traces of continental crust drawn into the wedge. The most common type of continental crust found in accretionary wedges is volcanic material from islands on the overriding plate.

Accretionary wedges are roughly shaped like a triangle with one angle pointing downward toward the trench. Because sediments are mostly scraped off from the subducting plate as it falls into the mantle, the youngest sediments are at the bottom of this triangle and the oldest are at the more flattened area above. This is the opposite of most rock formations, where geologists must dig deep to find older rocks.

Life in the Trenches

Ocean trenches are some of the most hostile habitats on Earth. Pressure is more than 1,000 times that on the surface, and the water temperature is just above freezing. Perhaps most importantly, no sunlight penetrates the deepest ocean trenches, making photosynthesis impossible.

Organisms that live in ocean trenches have evolved with unusual adaptations to thrive in these cold, dark canyons. Their behavior is a test of the so-called "visual interaction hypothesis," which states that the greater an organism's visibility, the more energy it must expend to catch prey or repel predators. In general, life in dark ocean trenches is isolated and slow-moving.

Pressure at the bottom of the Challenger Deep, the deepest spot on Earth, is about 12,400 tons per square meter (8 tons per square inch). Large ocean animals, such as sharks and whales, cannot live at this crushing depth.

Many organisms that thrive in these high-pressure environments lack gas-filled organs, such as lungs. These organisms, many related to sea stars or jellies, are made mostly of water and gelatinous material that cannot be crushed as easily as lungs or bones. Many of these creatures navigate the depths well enough to even make a vertical migration of more than 1,000 meters (3,281 feet) from the bottom of the trench-every day.

Even the fish in deep trenches are gelatinous. Several species of bulb-headed snailfish, for example, dwell at the bottom of the Mariana Trench. The bodies of these fishes have been compared to tissue paper.
Dark and Deep
Shallower ocean trenches have less pressure, but may still fall outside the photic or sunlight zone, where light penetrates the water.

Many fish species have adapted to life in these dark ocean trenches. Some use bioluminescence, meaning they produce their own "living light" in order to attract prey, find a mate, or repel a predator. Anglerfish, for instance, use a bioluminescent growth on the top of their heads (called an esca) to lure prey. The anglerfish then snaps up the little fish with its huge, toothy jaws.

Without photosynthesis, marine communities rely primarily on two unusual sources for nutrients.

Another source of nutrients for ocean-trench food webs comes not from photosynthesis, but from chemosynthesis. Chemosynthesis is the process in which producers in the ocean trench, such as bacteria, convert chemical compounds into organic nutrients. The chemical compounds used in chemosynthesis are methane or carbon dioxide ejected from hydrothermal vents and cold seeps, which spew these toxic, hot gases and fluids into the frigid ocean water. One common animal that relies on chemosynthetic bacteria for food is the giant tube worm.

Exploring Trenches

Ocean trenches remain one of the most elusive and little-known marine habitats. Until the 1950s, many oceanographers thought that these trenches were unchanging environments nearly devoid of life. Even today, most research on ocean trenches has relied on seafloor samples and photographic expeditions.

That is slowly changing as explorers delve into the deep-literally. The Challenger Deep, at the bottom of the Mariana Trench, lies deep in the Pacific Ocean near the island of Guam. Only three people have visited the Challenger Deep, the deepest ocean trench in the world: a joint French-American crew (Jacques Piccard and Don Walsh) in 1960 and National Geographic Explorer-in-Residence James Cameron in 2012. (Two other unmanned expeditions have also explored the Challenger Deep.)

Engineering submersibles to explore ocean trenches is presents a huge set of unique challenges. Submersibles must be incredibly strong and resilient to contend with strong ocean currents, no visibility, and intense pressure of the Mariana Trench. Engineering a submersible to safely transport people, as well as delicate equipment, is even more challenging. The sub that took Piccard and Walsh to the Challenger Deep, the remarkable Trieste, was an unusual vessel called a bathyscaphe.

The Deepsea Challenger, Cameron's submersible, successfully addressed engineering challenges in innovative ways. To combat deep-sea currents, the sub was designed to spin slowly as it descended. Lights on the sub were not incandescent or fluorescent bulbs, but arrays of tiny LEDs that illuminated an area of about 30 meters (100 feet). To adapt to the pressure of the deep, the sub was shaped like a sphere-the walls of a square or cylinder-shaped vessel would need to be at least three times thicker to avoid being crushed. The sub's fuel was augmented by seawater to prevent the oil from compressing. Perhaps most startlingly, the Deepsea Challenger itself was designed to compress. Cameron and his team created glass-based syntactic foam that allowed the vehicle to compress under the ocean's pressure-the Deepsea Challenger came back to the surface 7.6 centimeters (3 inches) smaller than when it descended.

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Ocean trenches are long, narrow depressions on the seafloor. These chasms are the deepest parts of the ocean-and some of the deepest natural spots on Earth.

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Convergent Boundaries
Places where plates crash or crunch together are called convergent boundaries. Plates only move a few centimeters each year, so collisions are very slow and last millions of years. Even though plate collisions take a long time, lots of interesting things happen. For example, in the drawing above, an oceanic plate has crashed into a continental plate. Looking at this drawing of two plates colliding is like looking at a single frame in a slow-motion movie of two cars crashing into each other. Just as the front ends of cars fold and bend in a collision, so do the "front ends" of colliding plates. The edge of the continental plate in the drawing has folded into a huge mountain range, while the edge of the oceanic plate has bent downward and dug deep into the Earth. A trench has formed at the bend. All that folding and bending makes rock in both plates break and slip, causing earthquakes. As the edge of the oceanic plate digs into Earth's hot interior, some of the rock in it melts. The melted rock rises up through the continental plate, causing more earthquakes on its way up, and forming volcanic eruptions where it finally reaches the surface. An example of this type of collision is found on the west coast of South America where the oceanic Nazca Plate is crashing into the continent of South America. The crash formed the Andes Mountains, the long string of volcanoes along the mountain crest, and the deep trench off the coast in the Pacific Ocean.

Are They Dangerous Places to Live?
Mountains, earthquakes, and volcanoes form where plates collide. Millions of people live in and visit the beautiful mountain ranges being built by plate collisions. For example, the Rockies in North America, the Alps in Europe, the Pontic Mountains in Turkey, the Zagros Mountains in Iran, and the Himalayas in central Asia were formed by plate collisions. Each year, thousands of people are killed by earthquakes and volcanic eruptions in those mountains. Occasionally, big eruptions or earthquakes kill large numbers of people. In 1883 an eruption of Krakatau volcano in Indonesia killed 37,000 people. In 1983 an eruption-caused mudslide on Nevada del Ruiz in Columbia killed 25,000 people. In 1976, an earthquake in Tangshan, China killed an astounding 750,000 people.

On the other hand, earthquakes and volcanoes occurring in areas where few people live harm no one. If we choose to live near convergent plate boundaries, we can build buildings that can resist earthquakes, and we can evacuate areas around volcanoes when they threaten to erupt. Yes, convergent boundaries are dangerous places to live, but with preparation and watchfulness, the danger can be lessened somewhat.

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Convergent Boundaries Places where plates crash or crunch together are called convergent boundaries. Plates only move a few centimeters each year, so collisions are very slow and last millions of years. Even though plate collisions take a long time, lots of interesting things happen.

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Geologists believe that the total accumulated displacement from earthquakes and creep is at least 350 miles along the San Andreas fault since it came into being about 15-20 million years ago.

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Introduction

Where tectonic plates slip horizontally past one another, lithosphere is neither created nor destroyed. Instead, blocks of crust are torn apart in a broad zone of shearing between the two plates. Such boundaries are called transform plate boundaries because they connect other plate boundaries in various combinations, transforming the site of plate motion. The grinding action between the plates at a transform plate boundary results in shallow earthquakes, large lateral displacement of rock, and a broad zone of crustal deformation.

Perhaps nowhere on Earth is such a landscape more dramatically displayed than along the San Andreas Fault in western California. The landscapes of Channel Islands National Park, Pinnacles National Park, Point Reyes National Seashore and many other NPS sites in California are products of such a broad zone of deformation, where the Pacific Plate moves north-northwestward past the rest of North America. Virgin Islands National Park in the U. S. Virgin Islands is located on another transform plate boundary, where the Caribbean Plate is sliding past the oceanic part of the North American Plate.

Lateral Movement along a Transform Plate Boundary

Point Reyes National Seashore, California. Tomales Bay is the surface expression of the San Andreas Fault, seen in the photo below. The granite rocks in the foreground are similar to those found in Yosemite National Park in the Sierra Nevada Mountains. They have been transported about 300 miles (500 kilometers) in a north-northwestward direction along the transform plate boundary. The sedimentary and metamorphic rocks across the fault line are similar to those found in Redwood National and State Parks on the North Coast of California. They were lifted out of the ocean as part of the accretionary wedge of an ancient subduction zone.

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Transform Plate Boundaries - Geology (U.S. National Park Service)

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Where tectonic plates slip horizontally past one another, lithosphere is neither created nor destroyed. Instead, blocks of crust are torn apart in a broad zone of shearing between the two plates. Such boundaries are called transform plate boundaries because they connect other plate boundaries in various combinations, transforming the site of plate motion.

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Image

Photograph by Bruce Beck

Hawai'i, that honeymoon destination known for stunning sunsets, has a dark secret-it's a geologically violent place. That's because the Hawaiian Islands were born from volcanic activity. In fact, that volcanism can still be observed today in Hawai'i.

The six largest Hawaiian Islands-the Big Island, Maui, Lanai, Molokai, Oahu, and Kauai-form a chain of islands running to the northwest. The islands appear in this pattern for a specific reason: They were formed one after the other as a tectonic plate, the Pacific Plate, slid over a plume of magma-molten rock-puncturing Earth's crust. These magma plumes aren't small-they can extend hundreds of kilometers below Earth's surface.

This upwelling of molten rock, known as a "hot spot," creates volcanoes that spew out lava (magma that reaches Earth's surface). The lava then cools and hardens to create new land. The Hawaiian Islands were literally created from lots of volcanoes-they're a trail of volcanic eruptions.

Hot-spot volcanism can occur in the middle of tectonic plates. That's unlike traditional volcanism, which takes place at plate boundaries. One explanation that scientists have proposed for hot-spot volcanism is that it occurs near unusually hot parts of Earth's mantle, the layer of the planet below the crust.

In the case of the Hawaiian Islands, the Pacific Plate is continually moving to the northwest over the Hawaiian hot spot. This movement caused the Hawaiian chain of islands to form. The Pacific Plate is just one of the Earth's roughly 20 tectonic plates, which are constantly in motion and are responsible for events like earthquakes.

There are many landforms around the Hawaiian Islands that formed from the same volcanic hot spot. Scientists believe this hot spot has been expelling lava for roughly 70 million years.

Many of these landforms created by volcanoes are still submerged. Also submerged are the peaks of the Emperor Seamount to the northwest of Hawai'i, which is part of the same chain of volcanic formations. A seamount is a submarine mountain. The Emperor Seamount extends for more than 6,000 kilometers (3,728 miles) from Hawai'i up to the Aleutian Trench in Alaska. In total, more than 750,000 cubic kilometers (180,000 cubic miles) of lava erupted to form all of the landforms in the Hawaiian-Emperor chain. That's enough to cover the entire state of California in a layer of lava more than one kilometer (0.62 mile) thick.

Volcanic activity is still occurring on the southern shore of the Big Island, the youngest of the Hawaiian Islands. In 2018, the Kilauea volcano erupted spectacularly and inundated over 30 square kilometers (30.5 square miles) of the Big Island with lava. The layer of lava was up to 24 meters (79 feet) thick in places-taller than a six-story building. Thousands of earthquakes accompanied the eruptions, and nearby residents and staff at the United States Geological Survey's Hawaiian Volcano Observatory near Kilauea were forced to evacuate.

Kilauea isn't the only volcano on the Big Island. There are also Kohala, Mauna Kea, Hualalai, and Mauna Loa. Of these four volcanoes, only Hualalai and Mauna Loa are active. Mauna Kea, a dormant volcano on the Big Island, is in fact the tallest mountain in the world measured from its base to its top. It's over 10,000 meters (32,800 feet) tall, significantly taller than Mt. Everest. But nearly 6,000 meters (19,700 feet) of its height is below the sea, so we only see about 4,000 meters (13,000 feet) of it.

The oldest of the major Hawaiian Islands, Kauai, doesn't have any active volcanoes because it's no longer over the Hawaiian hot spot. Instead, the dominant ecological process occurring there is erosion, which has sculpted Kauai's landscape into beautiful cliffs.

As the Pacific Plate continues to move at a rate of roughly seven centimeters (2.75 inches) per year-about the rate at which fingernails grow-new volcanic material is building up over the Hawaiian hot spot. This material will eventually form another Hawaiian island. Located about 35 kilometers (22 miles) off the southern coast of the Big Island, this future island already has a name: Loihi. But don't book a trip there just yet-Loihi is not visible as an island right now. It's grown by thousands of meters already, but it is still roughly 1,000 meters (3,280 feet) below the surface of the Pacific Ocean. As lava continues to be deposited on Loihi, scientists predict that it will rise above sea level sometime between 10,000 and 100,000 years from now.

Scientists think that seamounts like Loihi may resemble worlds in the outer solar system like Saturn's moon Enceladus. By studying the conditions in the deep sea around Loihi, researchers can better understand what other worlds in the solar system may look like.

Director

Author

National Geographic Society

Production Managers

Program Specialists

Last Updated

July 15, 2022

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The Hawaiian Islands were formed by a volcanic hot spot, an upwelling plume of magma, that creates new islands as the Pacific Plate moves over it.

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Why Mt. Everest keeps changing its height?

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Why Mt. Everest keeps changing its height?

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Climbers who make it to the top of Mount Everest may not know it, but under the snowpack sits an expanse of mottled gray rocks that once lay on the ocean floor.

The rocks arrived at this surprising spot, nearly 30,000 feet above sea level, due to the slow march of tectonic plates, slabs of solid rock that make up our planet's fractured outer shell. These plates continually jockey for position, shaping the array of features visible at the surface. In some places, the plates pull apart, creating valleys in the land. In others, they collide, shoving mountains into the sky.

Rising at the border of Tibet and Nepal, Mount Everest formed from a tectonic smashup between the Indian and Eurasian tectonic plates tens of millions of years ago. The collision crumpled the landscape, raising mountains along some 1,5000 miles, a range we know as the Himalaya. While mysteries remain about the precise steps happening in this continental crash, the collision continues to this day, which is, in part, why Everest's altitude is always changing. ( Find out results from the latest surveys for the height of Mount Everest.)

The birth of a mountain range

The story of the Himalaya begins some 200 million years ago, as the supercontinent of Pangea began to split into pieces. The Indian plate eventually broke free, trekking northward toward the landmass we now know as Asia. The Indian plate zipped along at surprisingly fast speeds, geologically speaking, shifting nearly 30 feet or more each century.

At the time, the vast Tethys ocean filled the gap between India and Eurasia, but as India moved northward, the ocean began to close. The plate under the water, made of dense oceanic crust, plunged beneath the southern edge of the more buoyant rocks that make up the Eurasian continental plate, creating a feature known as a subduction zone. The slow slip of the oceanic slab into the mantle scraped a thick layer of seafloor sediments into a pile at the edge of the Eurasian plate-and this sandy layer would later be squeezed into rock and end up on the mountainous peaks. ( See the summit of Everest and its surrounding peaks in 360 degrees.)

Around 50 million years ago, India's speed precipitously declined, a shift many scientists interpreted as the early stages of the plate's collision with Eurasia. Further evidence from marine sediments suggests the final swath of the Tethys ocean closed between 50 and 60 million years ago.

Unlike an oceanic plate, which is cold and dense, the Indian continental plate is thick and buoyant. So, as the continents compressed and India shoved its way under Asia, the surface buckled and the crust thickened to form what would eventually become the mighty Himalaya mountain range. Or, at least, that's long been the accepted version of the story.

But as scientists continue to pore over every bend, crack, and rock in this system, many mysteries have arisen. Study of ancient magnetic patterns in the rock allows researchers to chart a continent's position over time, and recent work using this method revealed that when the mountain-forming collision supposedly took place, some 55 million years ago, India would have been strikingly far south from Eurasia. That would leave a mysterious yawning gap between the two continents.

Did the Indian plate initially collide with a now long-gone landmass that sat between the two larger continental blocks? Could the Indian plate's northern edge have extended much farther than previously thought? Why was the Indian plate moving so fast before impact? These are among the many questions scientists are still working out.

Ever growing and shrinking

No matter when it started, though, the collision that formed Everest still continues today. India creeps northward a couple inches each year, and scientists estimate that the ongoing impact with Eurasia might force the mountains to ever greater heights, with an estimated average uplift of roughly 10 millimeters a year in the northwestern sections of the range, and around a millimeter a year at Everest. ( Learn why it's so difficult to measure Everest.)

The growth can happen in fits and starts, brought on by more violent shifts in the landscape. As India rams underneath Eurasia, it doesn't always slide smoothly by. When the land compresses, pressure builds until it hits a breaking point. The blocks of earth can then suddenly shift, rattling the ground in the jolt of an earthquake.

Yet the mountain doesn't necessarily get taller during earthquakes. Depending on exactly how and where the ground shifts, temblors can cause the mountain to either grow or shrink small amounts. This may have been the case during the 2015 Nepal earthquake, according to satellite data.

At the same time, as the rocks continue to rise toward the skies, erosion works against their upward progression. Wind and water scour away the surface, washing sediment into streams that race down the mountain's flanks. In the Himalaya, much of the sediment flushes through the Ganges and Brahmaputra rivers. Sand drops out of the water as the slope diminishes at the mountains' base in what is the largest river delta in the world, making up the land that sits under most of Bangladesh and the Indian state of West Bengal.

Even as erosion and gravity keep the mighty mountains in check, tectonic plates maintain their geologic dance, and Everest will continue to follow their lead.

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Why Mount Everest keeps changing its height

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An ancient geologic smashup raised the mighty Himalaya mountains-and the collision continues today.

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The Himalayas: Two continents collide

Among the most dramatic and visible creations of plate-tectonic forces are the lofty Himalayas, which stretch 2,900 km along the border between India and Tibet. This immense mountain range began to form between 40 and 50 million years ago, when two large landmasses, India and Eurasia, driven by plate movement, collided. Because both these continental landmasses have about the same rock density, one plate could not be subducted under the other. The pressure of the impinging plates could only be relieved by thrusting skyward, contorting the collision zone, and forming the jagged Himalayan peaks.

About 225 million years ago, India was a large island still situated off the Australian coast, and a vast ocean (called Tethys Sea) separated India from the Asian continent. When Pangaea broke apart about 200 million years ago, India began to forge northward. By studying the history -- and ultimately the closing-- of the Tethys, scientists have reconstructed India's northward journey. About 80 million years ago, India was located roughly 6,400 km south of the Asian continent, moving northward at a rate of about 9 m a century. When India rammed into Asia about 40 to 50 million years ago, its northward advance slowed by about half. The collision and associated decrease in the rate of plate movement are interpreted to mark the beginning of the rapid uplift of the Himalayas.

Artist's conception of the 6,000-km-plus northward journey of the "India" landmass (Indian Plate) before its collision with Asia (Eurasian Plate). Solid lines indicate present-day continents in the Indian Ocean region, but no geologic data exist to determine the exact size and shape of the tectonic plates before their present-day configurations. The dashed outlines for the "India" landmass are given for visual reference only, to show the inferred approximate locations of its interior part in the geologic past. The "India" landmass was once situated well south of the Equator, but its northern margins began to collide against the southward-moving Eurasian Plate about 40 to 50 million years ago (see text).
The Himalayas and the Tibetan Plateau to the north have risen very rapidly. In just 50 million years, peaks such as Mt. Everest have risen to heights of more than 9 km. The impinging of the two landmasses has yet to end. The Himalayas continue to rise more than 1 cm a year -- a growth rate of 10 km in a million years! If that is so, why aren't the Himalayas even higher? Scientists believe that the Eurasian Plate may now be stretching out rather than thrusting up, and such stretching would result in some subsidence due to gravity.

Sunset view of towering, snow-capped Mt. Everest, from the village of Lobuche (Solu-khumbu), Nepal. (Photograph by Gimmy Park Li.)
Fifty kilometers north of Lhasa (the capital of Tibet), scientists found layers of pink sandstone containing grains of magnetic minerals (magnetite) that have recorded the pattern of the Earth's flip-flopping magnetic field. These sandstones also contain plant and animal fossils that were deposited when the Tethys Sea periodically flooded the region. The study of these fossils has revealed not only their geologic age but also the type of environment and climate in which they formed. For example, such studies indicate that the fossils lived under a relatively mild, wet environment about 105 million years ago, when Tibet was closer to the equator. Today, Tibet's climate is much more arid, reflecting the region's uplift and northward shift of nearly 2,000 km. Fossils found in the sandstone layers offer dramatic evidence of the climate change in the Tibetan region due to plate movement over the past 100 million years.

At present, the movement of India continues to put enormous pressure on the Asian continent, and Tibet in turn presses on the landmass to the north that is hemming it in. The net effect of plate-tectonics forces acting on this geologically complicated region is to squeeze parts of Asia eastward toward the Pacific Ocean. One serious consequence of these processes is a deadly "domino" effect: tremendous stresses build up within the Earth's crust, which are relieved periodically by earthquakes along the numerous faults that scar the landscape. Some of the world's most destructive earthquakes in history are related to continuing tectonic processes that began some 50 million years ago when the Indian and Eurasian continents first met.
URL: https://pubs.usgs.gov/publications/text/himalaya.html
Last updated: 09.03.15
Contact: bhanks@usgs.gov

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The Himalayas [This Dynamic Earth, USGS]

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Among the most dramatic and visible creations of plate-tectonic forces are the lofty Himalayas, which stretch 2,900 km along the border between India and Tibet. This immense mountain range began to form between 40 and 50 million years ago, when two large landmasses, India and Eurasia, driven by plate movement, collided.

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Aurora Elmore was approaching Mount Everest's South Base Camp in Nepal. But rather than taking the traditional 12-day hiking route, she was soaring between the frozen peaks, the rotor blades of her helicopter slicing through the thin air with a whap, whap, whap.

It was April 2019, and she was delivering supplies to a team of scientists working on the slopes of the world's tallest mountain. Her reward was a spectacular view: the day was crystal clear, exposing the entire Himalayan range.

Over the next two months, researchers on the National Geographic and Rolex expedition she helped to organise would study the effects of climate change on this part of the Himalayas. Elmore, a geologist and at the time senior programme manager of the National Geographic Society in the US, supported the team installing the world's highest weather station on the flanks of Mount Everest. During the course of their expedition, her colleagues discovered the world's highest evidence of microplastic pollution in snow and stream water close to the summit.

Gliding closer to Everest's iconic peak, Elmore got a bird's-eye view of them. A miniature city of green and yellow tents, each sheltering mountaineers headed for the top, had formed at Everest Base Camp more than 5km (3 miles) above sea level. Thousands flock to Everest every spring to make an attempt to reach the roof of the world.

And while few of the climbers would have noticed, Everest grew a tiny bit bigger during their time on the mountain.

Mount Everest, along with the rest of the Himilayas, inches further skyward every year. It raises an interesting question - with enough time, just how tall can Mount Everest grow? There are mountains on other planets in our Solar System that dwarf those on our own, so are there limits to how big a mountain can get on Earth?

Mount Everest towers 8,848.86m (29,032ft) above sea level, according to the most recent official joint survey by China and Nepal, whose borders run across its summit. But it isn't the only giant in these lands - 10 of the world's 14 peaks higher than 8,000m (26,247ft) above sea level can be found in the Himalayan range. Everest, Elmore says, is among friends. "If you've ever flown over Greenland or the Canadian Rockies you can see big mountains, but [the Himalayas] are just on another level," she says.

Surrounded by so many other enormous peaks, is it possible to discern just what a monster Everest is? Elmore hesitates before answering. "It's kind of like trying to tell the tallest person on a basketball team," she says finally. "They're all tall, but which one is the teeny [bit taller]?"
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The history of measuring the tallest mountain in the world stretches back to 1852. In Europe, Charles Dickens was publishing serialised instalments of his novel Bleak House. North America had started testing its first steam-powered fire engine. In Asia, the height of Mount Everest was a mystery. It was known only as "Peak XV". Radhanath Sikdar, an Indian mathematician, had been employed by the British to work on their Great Trigonometrical Survey. They wanted to gather a more accurate geographical picture of the territory they were occupying so they could control it more effectively, be it for trade or military purposes.

Sikdar used trigonometry. He measured the horizontal and vertical angles of Everest's summit from other mountaintops whose positions and heights were already known. In doing so he made a momentous discovery: the tallest mountain ever recorded. According to his calculations, the mountain stood at 8,839.8m (29,002ft) tall.

Though the technology behind measuring mountains has advanced since the 1850s, his figure was astonishingly accurate, just nine metres off the latest official height. Despite Sikdar's findings, the mountain eventually was named after his previous boss, British surveyor Sir George Everest, who had retired several years before Sikdar's discovery.

Since then, teams have continued to work to understand Mount Everest's height. In 1954 an Indian survey determined Mount Everest to be 8,848m (29,029ft) tall, a figure which was accepted by the Nepalese government. But then, in 2005, the Chinese measured it at 8,844.43m (29,017ft) - nearly four metres (13ft) lower. In 2020, teams from China and Nepal jointly agreed upon a new officially accepted height that was 0.86m (2.8ft) higher than the Survey of India's original calculation.

While these changes in the measured height are partly due to improvements in the measuring technology available to surveyors, there has also been some politics involved. China and Nepal historically have argued over whether the snow cap on the summit should be included in the measurement or not.

But we mustn't ignore that Everest also grows a tiny little bit taller every year too.

Once, the craggy limestone peaks that skim the sky of Everest were on the ocean floor. Scientists believe it all began to change about 200 million years ago - at around the time the Jurassic dinosaurs were beginning to emerge - when the supercontinent of Pangea cracked into pieces. The Indian continent eventually broke free, journeying north across the vast swathe of Tethys Ocean for 150 million years until it smacked into a fellow continent - the one we now know as Asia - around 45 million years ago.

The crushing force of one continent hitting another caused the plate beneath the Tethys Ocean, made of oceanic crust, to slide under the Eurasian plate. This created what is known as a subduction zone. Then the oceanic plate slipped deeper and deeper into the Earth's mantle, scraping off folds limestone as it did so, until the Indian and Eurasian plates started compressing together. India began sliding under Asia, but because it's made of tougher stuff than the oceanic plate it didn't just descend. The surface started to buckle, pushing the crust and crumples of limestone upwards.

And so the Himalayan mountain range began to rise skyward. By around 15-17 million years ago, the summit of Everest had reached about 5,000m (16,404ft) and it continued to grow. The collision between the two continental plates is still happening today. India continues to creep north by 5cm (2in) a year, causing Everest to grow by about 4mm (0.16in) per year (although other parts of the Himalayas are rising at around 10mm per year [0.4in]).

But understanding how and why Everest's height changes is more complex than just this. While plate tectonics push the summit higher into the sky, erosion claws away at it.

To understand this process better, scientists studied another mountain some 8,700km (5,405 miles) away from Mount Everest, in Alaska.

Rachel Headley, an associate professor of geosciences at the University of Wisconsin-Parkside, was part of a scientific expedition to Mount Saint Elias on the border of Alaska and Canada between 2005-2008. The mission intended to understand the complex roles of tectonics and erosion in how mountains grow and shrink. The second largest mountain in both Canada and the US, Saint Elias faces the same effects as Everest, from tectonic activity to erosion, but across a far smaller, more manageable area. "In that region, Alaska, there were very particular weather patterns that had helped these large glaciers grow," Headley says. "And then both glaciers and rivers, landslides, and avalanches were all kind of the processes that connected to tear them down."

Headley's role on the team was to understand the thickness of the Seward Glacier, which runs through the Saint Elias mountains, and how fast it was moving. Both can impact the rate of erosion, which can affect how quickly a mountain's height is worn away. "If we have a thinner glacier, and it's moving super fast... we know there has to be some sliding, which we think is really important for erosion," she says. "Sliding" can cause glacial abrasion, which is when the glacier drags rock fragments across the surface as it moves, creating a sandpapering effect.

Weather can also cause significant erosion to a mountain. Elmore describes one of the weather stations she helped install during the 2019 Mount Everest expedition as being "damaged by rocks the size of cricket balls that were picked up by the wind and thrown at it". Buffetting by debris and ice picked up by the wind takes its toll after a while.

Many of the highest peaks in the world, including Everest, have permanent snow caps that help protect them from this wind-blown barrage. Rock covered in a soft blanket of snow suffers less weathering and erosion than bare rock, says Headley. It also protects the rock from chemical reactions with the air that can gradually degade the minerals in the limestone that comprises much of the uppermost parts of Mount Everest. But there are still places where the rock is exposed to the elements.

"For a tall mountain range, you can basically get to such a steep angle in the rock that it can't actually support ice, and snow, and then you start to get avalanches, and you get bare rock," says Elmore. Rock falls and land slides - a constant hazard on Everest and the surrounding area - both play a role in shaving away at Everest's height, and rivers too. They have been estimated to be cutting gorges into the rock at a rate of between 4-8mm (0.2-0.3in) a year.

But the exact impact erosion has on a mountain's height is still to be understood. Some scientists believe that reducing the weight of a mountain (by taking away the snow, ice and rock it's made of) might actually allow the tectonic plates to push the, now lighter, mountain even further into the sky.

Headley's colleague Terry Pavlis, who was the lead investigator on the St Elias Erosion Tectonics Project (Steep), explains that, on a large scale, "erosion attacking a landscape allows it to rise up".

In some parts of the world, entire landmasses are still rearing up after the last ice age - something known as isostatic rebound. Parts of North America and northern Europe, including Scotland, are rebounding after the rocky crust there was squashed by enormous continental ice sheets that waxed and waned during the Pleistocene. According to one study by researchers at Germany's University of Postdam, up to 90% of the uplift in the European Alps can be explained by this surprisingly elastic response to the end of the ice age. Experts believe similar glacial isostatic rebound may have taken place on the Tibetan Plateau and in the Himalaya as the ice age glaciers receeded - contributing between 1-4mm (0.04-0.16in) a year to the uplift.

"But there's some kind of equilibrium between how fast that landscape can erode and how high those peaks can get," adds Pavlis.

The exact details of this equilibrium are still being explored. In a region like the Appalachians in north-eastern North America, or the Scottish Highlands, erosive forces like rivers and landslides are cutting mountains down lower and lower, Headley says. "But in regions with tectonic activity, the tectonic force can be driving the mountains up slower, faster, or at around the same rate as the erosion is cutting it down. We don't fully understand all the drivers in those types of systems."

So how are mountains actually measured nowadays? One of the most common instruments used is the Global Navigation Satellite System (GNSS), which records the precise position of the mountain peak using a network of satellites. GNSS can "measure heights to the millimetre," according to Pavlis. The challenge, for a mountain like Everest, has always been the weight of the equipment. "It's hard enough to get to the peak - try adding a 30lb (13kg) instrument," he says.

A helicopter taxi to the top with the heavy luggage is out of the question - the thin air around Everest's summit means the engine can't produce enough power and there's too much drag from the rotor blades to operate safely. The strong winds and jagged creeks also make touching down anywhere near the summit dangerous. One helicopter pilot did set a world record by touching down briefly on top of Mount Everest in 2005, but only after the manufacturer stripped it bare of every unessential item to make it feather light.

Luckily, GNSS systems have gotten smaller over the years. Now they weigh more like 1.2kg (2.6lbs) and are "about the size of a lunchbox, maybe a little smaller", says Pavlis. But the devices still need batteries, which can struggle in cold temperatures. The average temperature at the summit of Everest during the summer monsoon months is a balmy -19C. And there are other complications too. "There's an antenna that's about, you know, half a metre in diameter. And those have to be set up somehow so that they are absolutely stationary," Pavlis explains.

To gather millimetre-accurate results the instrument then has to record for several hours. In the thin air of Everest's "death zone", operating these instruments can be hazardous for surveyors. Members of a Nepalese expedition to take GNSS measurements on Everest in 2019 spent two hours on the summit - far longer than most who make their way there - after arriving at 03:00 in the pitch black and biting cold.

Another option, often used in addition to GNSS for the most accurate readings, is Ground Penetrating Radar (GPR). "GPR uses radar pulses to image below the surface, so it can tell us the thickness and internal structure of snow and ice overlying the rocks on Everest's summit," says Elmore. "There's something like 4m (13ft) of snow and ice on the top of Mount Everest, but that can change depending on the climate."

While Elmore and her team were conducting their own scientific experiments on Everest they leant the Nepalese expedition a GPR device so they could take measurements from the summit. "It had to be a specific design of GPR, one that was super lightweight so [it could be carried] to the top of Everest, but that also had the right transmitter and receiver to measure the ice," says Elmore. The device had recently been used at the summit of Denali, the tallest mountain in the US, so they knew it was up to the job.

Despite the many hurdles they faced, the Nepalese team's expedition to measure the height of Everest was successful. They had hoped to answer questions about whether a deadly 7.8 magnitude earthquake that hit Nepal in April 2015 had affected Mount Everest's height. Initial reports indicated the mountain had shifted 3cm (1.9in) to the south-west by the large earthquake, which killed 9,000 people and damaged hundreds of thousands of homes, but had not changed its height.

The project, however, soon became muddied with international politics. A few months later a team of Chinese surveyors conducted their own measurements during an expedition from the other side of the mountain. They had their own figure, which didn't include the snow cap. The Nepalese figure, on the other hand, did. In October 2019, the two countries decided to combine their data and in December 2020 they released the figure for the new official height - 8,848.86m (29,032ft), including the snow on top.

As China and Nepal found, deciding exactly what you measure, and how you measure, is fundamental to establishing a mountain's height. For example, to agree upon how tall a mountain is, we must first agree on where the bottom is. But that's not as easy as it might sound.

For centuries mountains have been measured using sea level as the base from where their height is calculated. But the Earth is not perfectly round: it bulges along the equator. And sea level isn't static, it is pulled and changed by our planet's gravity. Plus, Everest isn't sticking out of the ocean, it's nestled among a landscape of other mountains. Many complex calculations have to be done to establish where sea level would actually be, and Everest's relative height to it. When that starting point is changed, everything changes.

But let's say scientists started their measurements from the core of the planet instead. Everest would no longer be considered the tallest mountain on Earth. The mountain that measures the greatest distance from the centre of Earth to its peak is Mount Chimborazo, in Equador at 10,920m (35,826ft). What about starting from the seabed? The accolade of tallest mountain would then go to Mauna Kea, a volcano in Hawaii that arches 10,000m (32,808ft) from the ocean floor.

Looking beyond our own planet, we can see examples of just how enormous mountains can become. Olympus Mons, a volcano on Mars, towers 21km (19.2 miles) into the sky and stretches 624km (388 miles) wide. It is roughly the size of the state of Arizona. Because gravity on Mars is weaker than on Earth, and because Mars doesn't have tectonic plates shifting and colliding beneath the surface, the ooze of lava that flowed out of the Martian volcano in the planet's past was able to grow to monstrous proportions.

Could Everest become a similar giant? In the 1980s, a researcher at the Cavendish Laboratory in Cambridge, UK, attempted to estimate what such a limit might be on Earth, taking into account the strength of gravity and the strength of the rock underlying the mountain. The calculations, which made "no presensions to serious geophysics" estimated the theoretical maximum height of a mountain range with a granite base - as Mount Everest largely has - to be 45km (28 miles) on Earth.

But there are a number of barriers - apart from our planet's relentless weather - that might stand in the way of this, according to Headley. For starters, "you would eventually run out of your tectonic forces, and then it would stop growing", she says. Scientists believe that eventually the Earth's mantle will cool to such a degree that the planet-wide dance of plate tectonics will end. Until then, earthquakes and landslides will also erode away the mountain too.

"At some point, [the mountain] becomes so steep that it's unstable and chunks start falling off," Elmore says.

With the wind, snow and ice buffeting, cracking and splitting the rock, Everest is unlikely to ever reach the sizes seen on Mars. "We have our weather systems, and weather is really good at creating erosional forces," Headley says. "Basically, the fact that we have water, whether in the form of ice or snow, or just rain, is what really can limit mountain growth."

For now, Everest keeps edging, bit by bit, into the sky as other forces try to tear it down. Elmore's 2019 team discovered global warming was yet another of these, driving considerable thinning of the snow and ice on the upper reaches of the mountain in recent decades and revealing more bare rock to the erosive impacts of weather.

Everest is also far from being the fastest-growing mountain on our planet. The closest contender for the top spot is perhaps Nanga Parbat, a neighbour to Everest located in the Pakistani Himalayan range, which is 8,126m (26,660ft) tall and growing at 7mm (0.27in) per year. In 241,000 years it could overtake Everest to be the tallest mountain on Earth, provided rates of erosion don't change.

Others, such as those in the Swiss Alps, are also growing rapidly thanks to an imbalance in the amount of erosion taking place. Scientists found that uplift is more than 50 times faster than any negative effects from erosion here. But the Swiss Alps are far shorter than Mount Everest and most studies suggest the mountains there are currently growing at 2-2.5mm (0.08-0.1 inches) per year.

Meanwhile, Everest retains its allure as a mountain at the extreme of what can be found and endured here on Earth. Its reputation as the highest peak on our planet continues to attract climbers from all over the world, even as its height continues to shift.

Over a video call I ask Billi Bierling, a mountaineering journalist who hiked Everest herself in 2009, whether an extra millimetre, metre or mile higher matters to people like her. She is relaxing on the sofa at her mother's house in Germany, preparing to head back to Nepal for the summer season in March.

"The exact measurement doesn't matter," she says, laughing warmly at my question. "What matters is that it's the highest, and that you go to the highest point. If you're having a bad day, or someone is not very nice to you, or they put you down, you can think to yourself, you know what? I've climbed Everest."

For most who reach the summit, it is simply being there that counts.

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How tall will Mount Everest get before it stops growing?

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Arching over 8,849 metres (29,032ft) into the sky, Everest is the world's tallest mountain. But will it always be? 8,848.86

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In the days before and after a rift opened in the Ethiopian Desert in September 2005, the ground shook with no fewer than 420 earthquakes. Volcanic activity bubbled across the landscape, sending ash into the sky. In the climactic event, the earth ripped itself apart like a pair of too-tight jeans, opening up a 35-mile fissure. Some 25,000 herders fled the first major new "dike intrusion" to hit land since the 1970s, according to .

Scientists rushed to the rift, hoping to study a process that typically occurs underwater, at the mid-ocean ridge, where volcanic material forms new oceanic crust. Exactly how this plays out on land, however, is poorly understood.

An early paper on the rift, led by Atalay Ayele, an associate professor at Addis Ababa University in Ethiopia, drew a parallel to the underwater variety, calling the new land one an "incipient oceanic rift," which could further divide the land.

Could a New Ocean Form In Africa?

Yes, but it would take millions of years, geologists say, and a lot of help from other land features on the continent.

East Africa Rift System

The rift that split in 2005 is part of the much larger East Africa Rift System (EARS), a network of rifts and valleys that first appeared about 25 million years ago as the first apes were evolving in Africa. Over time, the system branched out and spread south to where it ends today in Mozambique, near the Indian Ocean. Along the way, EARS skirted Lake Victoria by splitting into two different paths.

Tectonic Plates Shifting

Shifting tectonic plates underlie the system, including the Somali Plate to the East, the large African (or Nubian) Plate, and the Arabian Plate to the Northeast. Caught in the middle of these massive slabs of land is the smaller Victorian Plate, which is made of harder stuff and sits like a rock in a geologic stream. As the rift expands, sections of the Somali Plate could drift out to the Indian Ocean and open up a narrow sea within the continent.

Lake Tanganyika

Some of the valleys within EARS have already filled with water, most notably Lake Tanganyika, the second-deepest lake in the world. The rest could one day fill with ocean water, as they sink lower, but that would take the aforementioned millions of years.

"Remember it has taken over 30 million years for the [crust] thickness around the rift valley to reduce from 40 kilometers to 35 kilometers," geologist Edwin Dindi , "meaning that it will take many more years to shed off another 5 kilometers."

For this to happen, the African and Somali Plates must divide a great deal further, but they're currently separating at a rate of up to 0.5 inches a year .

Ocean Odds for Rift Valleys

Other forces could slow the separation and lead to a "failed" rift, one that fills with sediment instead of water, and stagnates. Dindi points to a failed rift in Kenya, while the most famous example, the Midcontinent Rift, runs for about 1,800 miles through Wisconsin, Minnesota, Iowa and Michigan and contains billion-year-old rocks. Volcanic eruptions spilled massive amounts of basalt on the land, but North America refused to divide.

Other researchers have cautioned against naming a new ocean just yet, however high the hopes.

A questions Ayele's conclusion that the rift amounted to an oceanic one or something close: "Whether these modern zones are the direct precursors to oceanic spreading centers remains unresolved."

And the PaleoMap project run by geologist Christopher Scotese, which maps future and past tectonic plates, predicts that over 100 million years the Somali and African plates will stay together and collide with Europe and Asia to create a huge landmass.

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Rift valleys have scientists rushing to understand the unpredictable forces that decide whether Africa splits in half or "fails" at rifting.

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The Earth's tectonic plates have always slowly shifted over billions of years of our planet's history, carving out seas and pressing mountain ranges into existence.

One change that is expected in the Earth's relatively near geological future is for a rift in the middle of Africa to open, forming a new ocean in the middle of the continent.

Douwe van Hinsbergen, the chair in global tectonics and paleogeography at Utrecht University in the Netherlands, told Newsweek: "The East African Rift has long been recognized as a rift that may develop into an ocean like the Red Sea and the Gulf of Aden have done before."

The Earth's crust is made up of between 15 and 20 pieces known as tectonic plates, that float gradually atop the molten magma mantle below, according to the National Oceanic and Atmospheric Administration. The heat of the Earth's core produces convection currents in the mantle, causing the plates to drift in certain directions, moving apart from each other, pressing into one another, or splitting in two. These movements occur over millions and millions of years and are the reasons for the ancient continent of Pangea breaking up 250 million years ago and forming the continents we know today.

Geologists can predict how the plates will shift in the future, and forecast that the East African Rift in Ethiopia, Kenya, and Tanzania, among other African countries, will split open, forming a new ocean. How long it will take for this new ocean to emerge depends entirely on how fast the rifting of the plates occurs.

New ocean could form in Africa as continent continues to split apart
Scientists say they can see continental crust become oceanic in the East Africa Rift pic.twitter.com/0blcOrF0W6
- Ben Buisson (@_7A_I) March 24, 2023

John Long, a strategic professor in paleontology at Flinders University in Australia, told Newsweek, "Based on tectonic spreading rates in East Africa that vary for 0.5-1 cm per year [0.2-0.4 inches per year], to open up a large enough rift to allow an ocean to come in, even a narrow one, say 5 km wide [3.1 miles], would take between 50,000-100,000 years coupled with what we know about sea levels rising."

"If seas rise by up to 0.7 m [2.3 feet] in the next hundred years or by 20-30m [65-100 feet] in the next 500 years with melting ice caps caused by the warming climate, it would happen much sooner," he said.

For comparison, human fingernails grow at a rate of around 4.2 cm per year, or 1.6 inches.

Different rifts move at different rates, with some plates moving apart from each other faster than others.

"The East African Rift formed already 30 million years ago, and its spreading is very slow. Normally, a true oceanic basin with ocean floor forms after about 300-400 km [186-248 miles] of extension, which, with the current rates, may take another 10 million years or more," van Hinsbergen said. "But in other cases, this occurred more rapidly, like in the Central Atlantic Ocean, where from initial breaking to oceanization took less than 15 million years, about 200 million years ago."

Scientists use signals transmitted from satellites to GPS receivers on land to measure plate movements and elevation changes.

"We don't have a lot of these continuously recording stations in Africa, but where we do have measurements, we can then use modern rates to predict where plates will be 1 million years or 5 million years from now," Cynthia Ebinger, a plate tectonics professor at Tulane University, Louisiana, told Newsweek. "We can also gain insight from dating rock units in ancient rift systems where we can get general opening rates."

"The general motions of the plates are predicted using global measurements from GPS and other space-based observations. These measurements give us estimates of modern plate motions that represent an 'instantaneous' motion, at least in terms of very slow geological processes. Are they representative of longer-term, or time-averaged processes over 100,000 or 1 million years? We use seafloor spreading anomaly patterns on the seafloor to track the motions of the plates over the past 180 million years, allowing us to see patterns in plate motion that then guide our future predictions," she said.

Predictions of the next 200 million years also indicate that Australia will move northwards, eventually colliding with East Asia.

If the East African rift did eventually become an ocean, it would have massive impacts on the geography and ecology of the continent we know today.

"Areas below sea level that are connected to the oceans will indeed flood with seawater. Already the Tanganyika rift has lake basins that lie below sea level, but they are filled by freshwater," Ebinger said.

Additionally, the parts of Africa to the east of the rift, including Somalia and other countries on the Horn of Africa, will shift further eastwards, eventually colliding with Asia.

"If the western branch of the East African Rift will become the new ocean, then there will be a new 'passive margin' forming," van Hinsbergen said. "The land that is now in the rift will subside, and the margins will become the site of big coral reef systems. The countries to the east of the rift will move with the new 'Somali Plate' towards India, and this actually may become kind of an Andes/Tibetan Plateau highland."

Neither we nor our children's generations will have to worry about this newfangled world geography, however, as the human lifespan is a mere blink in the eye of geographical time.
Do you have a tip on a science story that Newsweek should be covering? Do you have a question about plate tectonics? Let us know via science@newsweek.com.

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New ocean within Africa could take millions of years to form

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The East Africa Rift is slowly splitting apart and is expected to eventually fill with water, forming a brand new ocean.

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"It will pull apart, sink down deeper and deeper and eventually... parts of southern Ethiopia, Somalia will drift off, create a new island, and we'll have a smaller Africa and a very big island that floats out into the Indian Ocean."

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Africa 'witnessing birth of a new ocean'

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Africa is witnessing the birth of a new ocean which will eventually split the continent in two, say scientists.

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The Rift Valley of eastern Africa and Asia (sometimes called the Great Rift Valley [GRV] or East African Rift system [EAR or EARS]) is an enormous geological split in the crust of the earth, thousands of kilometers long, up to 125 miles (200 kilometers) wide, and between a few hundred to thousands of meters deep. First designated as the Great Rift Valley in the late 19th century and visible from space, the valley has also been a great source of hominid fossils, most famously in Tanzania's Olduvai Gorge.

Key Takeaways: Great Rift Valley

The Rift Valley is the result of an ancient series of faults, rifts, and volcanoes deriving from the shifting of tectonic plates at the junction between the Somalian and the African plates. Scholars recognize two branches of the GRV: the eastern half-which is that piece north of Lake Victoria that runs NE/SW and meets the Red Sea; and the western half-running nearly N/S from Victoria to the Zambezi river in Mozambique. The eastern branch rifts first occurred 30 million years ago, the western 12.6 million years ago. In terms of rift evolution, many parts of the Great Rift Valley are in different stages, from pre-rift in the Limpopo valley, to initial-rift stage at the Malawi rift; to typical-rift stage in the northern Tanganyika rift region; to advanced-rift stage in the Ethiopian rift region; and finally to oceanic-rift stage in the Afar range.

That means the region is still quite tectonically active: see Chorowicz (2005) for much more detail concerning the ages of the different rift regions.

Geography and Topography

The Eastern African Rift Valley is a long valley flanked by uplifted shoulders that step down to the central rift by more or less parallel faults. The main valley is classed as a continental rift, extending from 12 degrees north to 15 degrees south of our planet's​ equator. It extends a length of 3,500 km and intersects major portions of the modern countries of Eritrea, Ethiopia, Somalia, Kenya, Uganda, Tanzania, Malawi, and Mozambique and minor portions of others. The width of the valley varies between 30 km to 200 km (20-125 mi), with the widest section at the northern end where it links to the Red Sea in the Afar region of Ethiopia. The depth of the valley varies across eastern Africa, but for most of its length it is more than 1 km (3280 feet) deep and at its deepest, in Ethiopia, it is over 3 km (9,800 ft) deep.

The topographical steepness of its shoulders and the depth of the valley have created specialized microclimates and hydrology within its walls. Most rivers are short and small within the valley, but a few follow the rifts for hundreds of kilometers, discharging into deep lake basins. The valley acts as a north-south corridor for the migration of animals and birds and inhibits east/west movements. When glaciers dominated most of Europe and Asia during the Pleistocene, the rift lake basins were havens for animals and plant life, including early hominins.

History of the Rift Valley Studies

Following on the mid- to late-19th-century work of dozens of explorers including the famous David Livingstone, the concept of an East African rift fracture was established by Austrian geologist Eduard Suess, and named the Great Rift Valley of East Africa in 1896 by British geologist John Walter Gregory. In 1921, Gregory described the GRV as a system of graben basins which included the valleys of the Red and Dead Seas in western Asia, as the Afro-Arabian rift system. Gregory's interpretation of the GRV formation was that two faults had opened up and a central piece dropped down forming the valley (called a graben).

Since Gregory's investigations, scholars have re-interpreted the rift as the result of multiple graben faults organized over a major fault line at the plate juncture. The faults occurred in time from the Paleozoic to Quaternary eras, a time span of some 500 million years. In many areas, there have been repeated rifting events, including at least seven phases of rifting over the past 200 million years.

Paleontology in the Rift Valley

In the 1970s, paleontologist Richard Leakey designated the East African Rift region as the "Cradle of Mankind," and there is no doubt that the earliest hominids-members of the Homo species-arose within its boundaries. Why that happened is a matter of conjecture, but may have something to do with the steep valley walls and microclimates created within them.

The interior of the rift valley was isolated from the rest of Africa during the Pleistocene ice age and sheltered freshwater lakes located in savannahs. As with other animals, our early ancestors may have found refuge there when the ice covered much of the planet and then evolved as hominids within its tall shoulders. An interesting study on the genetics of frog species by Freilich and colleagues showed that the valley's micro-climates and topography are at least, in this case, a biogeographic barrier that resulted in the splitting of the species into two separate gene pools.

It is the eastern branch (much of Kenya and Ethiopia) where much of the paleontological work has identified hominids. Beginning about 2 million years ago, barriers in the eastern branch eroded away, a time which is coeval (as much as that clock can be called co-eval) with the spread of Homo species outside of Africa.

Rift Evolution

Analysis of the rift reported by German geologist Sascha Brune and colleagues in March 2019 (Corti et al. 2019) suggests that although the rift began as two overlapping disconnected rifts (Ethiopian and Kenyan), the lateral offset that lies in the Turkana depression has evolved and continues to evolve into a single oblique rift.

In March of 2018, a great crack measuring 50 feet wide and miles long opened up in the Suswa area of southwestern Kenya. Scientists believe the cause was not a sudden recent shift of the tectonic plates, but rather the abrupt erosion to the surface of a long-standing subsurface crack that developed over thousands of years. Recent heavy rains caused the soil to collapse over the crack, exposing it to the surface, rather like a sinkhole.

Selected Sources

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Rift Valley - The Crack in the Planet's Crust in Eastern Africa

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The Rift Valley of eastern Africa and Asia is an enormous geological split in the crust of the earth, where many of our early human ancestors lived.

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Home " Plate Tectonics " The East Africa Rift System

East Africa's Great Rift Valley: A Complex Rift System

by James Wood and Alex Guth - Michigan Technological University

Part I. The East African Rift System

The East African Rift System (EARS) is one of the geologic wonders of the world, a place where the earth's tectonic forces are presently trying to create new plates by splitting apart old ones. In simple terms, a rift can be thought of as a fracture in the earth's surface that widens over time, or more technically, as an elongate basin bounded by opposed steeply dipping normal faults.

Geologists are still debating exactly how rifting comes about, but the process is so well displayed in East Africa ( Ethiopia- Kenya- Uganda- Tanzania) that geologists have attached a name to the new plate-to-be; the Nubian Plate makes up most of Africa, while the smaller plate that is pulling away has been named the Somalian Plate (Figure 1). These two plates are moving away from each other and also away from the Arabian plate to the north.

The point where these three plates meet in the Afar region of Ethiopia forms what is called a triple-junction. However, all the rifting in East Africa is not confined to the Horn of Africa; there is a lot of rifting activity further south as well, extending into Kenya and Tanzania and the Great Lakes region of Africa. The purpose of this paper is to discuss the general geology of these rifts and highlight the geologic processes involved in their formation.

What is the East Africa Rift System?

The oldest and best defined rift occurs in the Afar region of Ethiopia and this rift is usually referred to as the Ethiopian Rift. Further to the South a series of rifts occur which include a Western branch, the "Lake Albert Rift" or "Albertine Rift" which contains the East African Great Lakes, and an Eastern branch that roughly bisects Kenya north-to-south on a line slightly west of Nairobi (Figure 2).

These two branches together have been termed the East African Rift (EAR), while parts of the Eastern branch have been variously termed the Kenya Rift or the Gregory Rift (after the geologist who first mapped it in the early 1900's). The two EAR branches are often grouped with the Ethiopian Rift to form the East Africa Rift System (EARS).

The complete rift system therefore extends 1000's of kilometers in Africa alone and several 1000 more if we include the Red Sea and Gulf of Aden as extensions. In addition there are several well-defined but definitely smaller structures, called grabens, that have rift-like character and are clearly associated geologically with the major rifts. Some of these have been given names reflecting this such as the Nyanza Rift in Western Kenya near Lake Victoria. Thus, what people might assume to be a single rift somewhere in East Africa is really a series of distinct rift basins which are all related and produce the distinctive geology and topography of East Africa.

How did these Rifts form?

The exact mechanism of rift formation is an on-going debate among geologists and geophysicists. One popular model for the EARS assumes that elevated heat flow from the mantle (strictly the asthenosphere) is causing a pair of thermal "bulges" in central Kenya and the Afar region of north-central Ethiopia. These bulges can be easily seen as elevated highlands on any topographic map of the area (Figure 1).

As these bulges form, they stretch and fracture the outer brittle crust into a series of normal faults forming the classic horst and graben structure of rift valleys (Figure 3). Most current geological thinking holds that bulges are initiated by mantle plumes under the continent heating the overlying crust and causing it to expand and fracture.

Ideally the dominant fractures created occur in a pattern consisting of three fractures or fracture zones radiating from a point with an angular separation of 120 degrees. The point from which the three branches radiate is called a "triple junction" and is well illustrated in the Afar region of Ethiopia (Figure 4), where two branches are occupied by the Red Sea and Gulf of Aden, and the third rift branch runs to the south through Ethiopia.

The stretching process associated with rift formation is often preceded by huge volcanic eruptions which flow over large areas and are usually preserved/exposed on the flanks of the rift. These eruptions are considered by some geologists to be "flood basalts" - the lava is erupted along fractures (rather than at individual volcanoes) and runs over the land in sheets like water during a flood.

Such eruptions can cover massive areas of land and develop enormous thicknesses (the Deccan Traps of India and the Siberian Traps are examples). If the stretching of the crust continues, it forms a "stretched zone" of thinned crust consisting of a mix of basaltic and continental rocks which eventually drops below sea level, as has happened in the Red Sea and Gulf of Aden. Further stretching leads to the formation of oceanic crust and the birth of a new ocean basin.

Part II. The East African Rift

If the rifting process described occurs in a continental setting, then we have a situation similar to what is now occurring in Kenya where the East African/Gregory Rift is forming. In this case it is referred to as "continental rifting" (for obvious reasons) and provides a glimpse into what may have been the early development of the Ethiopian Rift.

As mentioned in Part I, the rifting of East Africa is complicated by the fact that two branches have developed, one to the west which hosts the African Great Lakes (where the rift filled with water) and another nearly parallel rift about 600 kilometers to the east which nearly bisects Kenya north-to-south before entering Tanzania where it seems to die out (Figure 2).

Lake Victoria sits between these two branches. It is thought that these rifts are generally following old sutures between ancient continental masses that collided billions of years ago to form the African craton and that the split around the Lake Victoria region occurred due to the presence of a small core of ancient metamorphic rock, the Tanzania craton, that was too hard for the rift to tear through. Because the rift could not go straight through this area, it instead diverged around it leading to the two branches that can be seen today.

As is the case in Ethiopia, a hot spot seems to be situated under central Kenya, as evidenced by the elevated topographic dome there (Figure 1). This is almost exactly analogous to the rift Ethiopia, and in fact, some geologists have suggested that the Kenya dome is the same hotspot or plume that gave rise to the initial Ethiopian rifting. Whatever the cause, it is clear that we have two rifts that are separated enough to justify giving them different names, but near enough to suggest that they are genetically related.

Other Points of Interest:

What else can we say about the Ethiopian and Kenya Rifts? Quite a lot actually; even though the Eastern and Western branches were developed by the same processes they have very different characters. The Eastern Branch is characterized by greater volcanic activity while the Western Branch is characterized by much deeper basins that contain large lakes and lots of sediment (including Lakes Tanganyika, the 2nd deepest lake in the world, and Malawi).

Recently, basalt eruptions and active crevice formation have been observed in the Ethiopian Rift which permits us to directly observe the initial formation of ocean basins on land. This is one of the reasons why the East African Rift System is so interesting to scientists. Most rifts in other parts of the world have progressed to the point that they are now either under water or have been filled in with sediments and are thus hard to study directly. The East African Rift System however, is an excellent field laboratory to study a modern, actively developing rift system.

This region is also important for understanding the roots of human evolution. Many hominid fossil finds occur within the rift, and it is currently thought that the rift's evolution may have played an integral role in shaping our development. The structure and evolution of the rift may have made East Africa more sensitive to climate changes which led to many alternations between wet and arid periods. This environmental pressure could have been the drive needed for our ancestors to become bipedal and more brainy as they attempted to adapt to these shifting climates (see Geotimes 2008 articles: Rocking the Cradle of Humanity by Beth Christensen and Mark Maslin, and Tectonic Hypotheses of Human Evolution by M. Royhan Gani and Nahid DS Gani).

Conclusions:

The East African Rift System is a complicated system of rift segments which provide a modern analog to help us understand how continents break apart. It is also a great example of how many natural systems can be intertwined - this unique geological setting may have altered the local climate which may have in turn caused our ancestors to develop the skills necessary to walk upright, develop culture and ponder how such a rift came to be. Just like the Grand Canyon, the East African Rift System should be high on any geologist's list of geologic marvels to visit.

About the authors:

James Wood has a PhD from Johns Hopkins University and is currently Professor of Geology at the Michigan Technological University in Houghton, Michigan where he teaches Earth History, Geochemistry, Remote Mapping and conducts a field course every spring in East Africa. His main research interests are energy deposits, mainly gas and oil, and doing field work in rift valleys.

Alex Guth is currently a PhD candidate at Michigan Tech and is looking at the effects of climate on desert varnish on the exposed flows and alluvium in the East African Rift Valley. She assists Dr. Wood with the geology field camp. Her website can be viewed at: pages.mtu.edu/~alguth/.

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East Africa's Great Rift Valley: A Complex Rift System

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A description of the East Africa Rift System with maps and cross sections.

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The Red Sea - 50 years of geological and geophysical research

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The Red Sea - 50 years of geological and geophysical research

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Figure 1: The Afar triple junction. The red arrows show the movement of the African, Arabian and Somalian plates away from the Afar depression.

Red Sea and Gulf of Aden (non-technical)

The Red Sea and the Gulf of Aden were formed as the Arabian plate separated from Nubia, as Nubia obliquely collided with the Eurasian plate (Figure 1). NE-directed extension between 35-27million years ago lead to the continents rifting apart and the formation of new oceans along the line of the Red Sea and Gulf of Aden. At the same time as this, between about 31-29Ma, there was a massive eruption of lava - flood basalts - covering some 600,000km2 of the region. Along the margins of the Red Sea these lavas are up to 2000m thick. Sea floor spreading in the Gulf of Aden begun about 16Ma and about 4Ma in the Red Sea.

With the East African Rift System, the Red Sea and the Gulf of Aden form the Afar triple junction. The Red Sea runs roughly straight for 2000km northwards to where it joins the Aqaba-Dead Sea transform rift system (where the plates are sliding past each other). The Gulf of Aden is straight near the triple junction, before curving round to link in the with mid-ocean ridge system in the Indian Ocean (Figure 2).

Figure 2: Regional plate tectonic setting. Red arrows show approximate direction of opening of the rift systems.

Across both the Gulf of Aden mid-ocean ridge system and the southernmost part of the Red Sea the plates are moving not only apart but also sliding past each other with one side moving to the left with respect to the other.

For references used, please see technical version.

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Red Sea and Gulf of Aden (non-technical)

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Figure 1: The Afar triple junction. The red arrows show the movement of the African, Arabian and Somalian plates away from the Afar depression. The Red Sea and the Gulf of Aden were formed as the Arabian plate separated from Nubia, as Nubia obliquely collided with the Eurasian plate (Figure 1).

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The surface of the Earth is broken up into large plates. It's easy to confuse these plates with the Earth's crust - the thin outermost layer of the Earth. But there is more to the structure of the Earth than this simple image of a 'cracked egg-shell'.

The Earth's layers can be defined in two different ways - based on the chemical composition or the mechanical properties of the rock. To understand what plates are, it is important to understand both of these different models.

When we talk about tectonic or lithospheric plates, we mean the sections into which the lithosphere is cracked. The surface of the Earth is divided into 7 major and 8 minor plates. The largest plates are the Antarctic, Eurasian, and North American plates. Plates are on average 125km thick, reaching maximum thickness below mountain ranges. Oceanic plates (50-100km) are thinner than the continental plates (up to 200km) and even thinner at the ocean ridges where the temperatures are higher. Some plates are large enough to consist of both continental and oceanic crustal portions (e.g. the African or South American plates) whilst the Pacific Plate is almost entirely oceanic.

The Earth is roughly spherical, so these plates are fractured into curved sections which are in constant motion relative to each other and meet in various ways along their edges - these are the 'plate boundaries', where most volcanoes and earthquakes occur. The mechanism by which plates move is still a highly controversial subject amongst Earth scientists.

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An online resource from the Geological Society, outlining the chemical and mechanical properties of tectonic plates and how they move.

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Triple Junction: The Red Sea/East Africa

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Triple Junction: The Red Sea/East Africa

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News and updates for members of the public and policy makers interested in how the geosciences interact with society. Find updates about outreach activities and policy related meetings, consultation responses and position statements.

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Triple Junction: The Red Sea/East Africa

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Triple Junction: The Red Sea/East Africa

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News and updates for members of the public and policy makers interested in how the geosciences interact with society. Find updates about outreach activities and policy related meetings, consultation responses and position statements.

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The North American and Eurasian Plates are moving away from each other along the line of the Mid Atlantic Ridge. The Ridge extends into the South Atlantic Ocean between the South American and African Plates. The ocean ridge rises to between 2 to 3 km above the ocean floor, and has a rift valley at its crest marking the location at which the two plates are moving apart.

The Mid Atlantic Ridge, like other ocean ridge systems, has developed as a consequence of the divergent motion between the Eurasian and North American, and African and South American Plates. As the mantle rises towards the surface below the ridge the pressure is lowered (decompression) and the hot rock starts to partially melt. This produces basaltic volcanoes when an eruption occurs above the surface ( Eyjafjallajökull in Iceland) and characteristic basalt " pillow lava" in underwater eruptions. In this way, as the plates move further apart new ocean lithosphere is formed at the ridge and the ocean basin gets wider. This process is known as " sea floor spreading " and results in a symmetrical alignment of the rocks of the ocean floor which get older with distance from the ridge crest.

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Evidence for this process comes from the magnetic properties of the erupted basalt. The Earth's magnetic field has been shown to "flip" occasionally so that the North and South magnetic poles reverse with time. Basalt contains minute magnetic minerals that take on the direction of the Earth's magnetic field at the time of eruption.
Image courtesy of the Naked Science Society
These polarity reversals are therefore recorded in the rocks forming at the Mid Atlantic Ridge every time the Earth's magnetism changes from a normal field (as it is today) to a reversed field (as it was about 0.78 million years ago). When these variations in the magnetic rocks are mapped on the ocean bed they are seen to line up in a series of alternating " magnetic stripes ", rather like barcodes.

The significance of the magnetic stripes was only revealed when their ages were discovered from dating magnetic reversals in volcanic rocks accessible on land. The dates revealed that the Atlantic Ocean was opening by seafloor spreading from the Mid Atlantic Ridge at a rate of about 0.02 metres per year.

This means that North America and Europe are moving away from each other at about the rate it takes for your fingernails to grow.

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An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

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Whilst most volcanic activity happens at plate margins, there are cases of volcanoes erupting in the middle of plates. The Hawaiian Islands are formed by volcanic activity, despite the nearest plate margin being 3,200 km away.

Some geologists have suggested that a ' hot spot' in the mantle, which remains stationary as the Pacific Plate moves over it, explains the existence of the island chain. The hot spot may represent the top of a mantle plume which originated deep down at the outer core - lower mantle boundary. The plate moves in a north westerly direction due to sea floor spreading along the East Pacific Rise. As oceanic lithosphere moves away from the hot spot, volcanic activity ceases and it cools, becomes denser, and slowly subsides. As new oceanic lithosphere is positioned over the hot spot, a new island will begin to form above.

The islands extend for around 2,400 km, forming a chain that is progressively older from the south east end to the north west end. The volcanoes are often very wide, with gently sloping sides comprising many thin (1 to 5 metres thick) basaltic lava flows. These are referred to as 'shield volcanoes'. Kilauea and Mauna Loa on Big Island are currently active examples.

The next island to appear in the Hawaiian chain has already been identified, and named as Lo'ihi. It is currently 975 metres below sea level, and is estimated to emerge above sea level in the next 10,000 to 100,000 years.

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An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

# data[].attributes.attachment_link.description
An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

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An online resource from the Geological Society, outlining the three types of plate boundary and the activity that characterises them.

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On April 18, 1906, an earthquake struck near San Francisco, California, then the largest city on the West Coast.

On April 18, 1906, an earthquake struck near San Francisco, California, United States, then the largest city on the West Coast. The earthquake occurred offshore, at an outcropping called Mussel Rock, a little after 5:00 a.m.

Tremors were felt from the state of Oregon to Los Angeles, California, and inland toward the state of Nevada. The exact magnitude of the earthquake is disputed, but the most common estimate is about 7.9-a very damaging temblor. Fires immediately broke out in San Francisco due to broken gas lines, fallen power lines, and lanterns that had toppled over during the earthquake. Water lines were ruptured as well, which made it difficult to put the fires out.

It is estimated that 3,000 people were killed during the earthquake and its aftershocks, which lasted for days. The earthquake displaced even more people from their homes.

The earthquake occurred as a result of a shift along the San Andreas Fault, which bisects the San Francisco Peninsula just to the west of the city. The land on the eastern side of the fault, including the city and San Francisco Bay, moved southward, while the land on the western side was pushed northward. More than six meters (20 feet) of displacement occurred during the quake.

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March 1, 2023

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On April 18, 1906, an earthquake struck near San Francisco, California, then the largest city on the West Coast.

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A rift valley is a lowland region that forms where Earth's tectonic plates move apart, or rift. Rift valleys are found on land and at the bottom of the ocean, where they are created by the process of seafloor spreading. Rift valleys differ from river valleys and glacial valleys in that they are created by tectonic activity and not the process of erosion.

Tectonic plates are huge, rocky slabs of Earth's lithosphere-its crust and upper mantle. Tectonic plates are constantly in motion-shifting against each other in fault zones, falling beneath one another in a process called subduction, crashing against one another at convergent plate boundaries, and tearing apart from each other at divergent plate boundaries.

Many rift valleys are part of "triple junctions," a type of divergent boundary where three tectonic plates meet at about 120° angles. Two arms of the triple junction can split to form an entire ocean. The third, "failed rift" or aulacogen, may become a rift valley. The Atlantic Ocean, for instance, is a result of a triple junction that started in what is now the Gulf of Guinea on the west coast of Africa. Two arms of a triple junction on the supercontinent Pangaea "opened" the ocean, while the aulacogen formed the rift valley known as the Benue Trough through what is now southern Nigeria.

Rift valleys can also form at transform faults, where tectonic plates are grinding past each other. The Salton Trough, which stretches through the states of California (United States) and Baja California (Mexico), is a rift valley created in part by the San Andreas Fault. The San Andreas is a transform fault that marks the roughly northward movement of the Pacific plate and the roughly southern movement of the North American plate.

Many of Earth's deepest rift valleys are found underwater, dividing long mountain ranges called mid-ocean ridges. As tectonic plates move away from one another at mid-ocean ridges, molten rock from the mantle may well up and harden as it contacts the frigid sea, forming new oceanic crust at the bottom of the rift valley.

In the northern Mid-Atlantic Ridge, the North American plate and the Eurasian plate are splitting apart at a rate of about 2.5 centimeters (one inch) per year. Over millions of years, the Mid-Atlantic Ridge has formed rift valleys as wide as 15 kilometers (nine miles).

Continental Rift Valleys

Very few active rift valleys are found on continental lithosphere. The East African Rift, the Baikal Rift Valley, the West Antarctic Rift, and the Rio Grande Rift are Earth's major active continental rift valleys. The East African Rift is part of the "Great Rift Valley" system discussed below.

The Baikal Rift Valley (sometimes called the Baikal Rift Zone) cuts through 2,000 kilometers (1,200 miles) of Siberia, in eastern Russia. The Baikal Rift Valley is formed by a divergent plate boundary, where the Amur plate is slowly tearing itself away from the Eurasian plate, and has been doing so for about 25 million years. The Amur plate is moving eastward at a rate of about four to five millimeters (0.16 to 0.2 inch) a year.

The West Antarctic Rift is a series of smaller rifts that roughly separate the two regions of Earth's southernmost continent into West Antarctica and East Antarctica. The West Antarctic Rift is one of the most difficult rift valleys to study, because it lies beneath the massive Antarctic Ice Sheet, which can be more than 2 kilometers (1.2 miles) thick. The Rio Grande Rift is a series of rift valleys along faults in the Southwestern United States.

The Rio Grande Rift separates the Colorado Plateau, which is generally moving in a clockwise direction, from the older part (craton) of the North American plate. The Rio Grande Rift stretches from central part of the U.S. state of Colorado to the Mexican state of Chihuahua.

Great Rift Valley

The most well-known rift valley on Earth is probably the so-called "Great Rift Valley System," which stretches from the Middle East in the north to Mozambique in the south. The area is geologically active, and features volcanoes, hot springs, geysers, and frequent earthquakes.

Today, however, the Great Rift Valley exists as a cultural concept, not a scientific one. All of the rift valleys in the system are connected, but not part of a single unit.

Associated with the Jordan Rift Valley to the south is the Red Sea Rift. Millions of years ago, the Arabian Peninsula was connected to Africa. Seafloor spreading caused the Arabian and African plates to rift apart. The Indian Ocean flooded the rift valley between the continents, creating the Red Sea. Today, Africa and Asia are connected by the triangle of the Sinai Peninsula. Eventually, the Red Sea Rift will separate Africa and Asia entirely and connect the Mediterranean and Red Seas.

East African Rift
South of the Red Sea Rift lies the massive, complex East African Rift. Throughout the East African Rift, the continent of Africa is splitting in two. The African plate, sometimes called the Nubian plate, carries most of the continent, while the smaller Somali plate carries Horn of Africa.

The Gregory Rift stretches from the Red Sea and the Arabian Sea to as far south as Mount Kilimanjaro. One of the most important features of the Gregory Rift is the Afar Triple Junction, found where the Horn of Africa straddles the Red Sea and the Gulf of Aden in the Arabian Sea. At the Afar Triple Junction, the Arabian plate, Nubian plate and Somali plate are all tearing away from each other.

The Western Rift, also called the Albertine Rift, includes many of the African Great Lakes. The Western Rift is one of the most biodiverse regions in Africa, featuring a narrow corridor of highland forests, snow-capped mountains, savannas, and chains of lakes and wetlands.

Rift lakes, formed as freshwater floods rift valleys, often mark rift valley systems. More than one billion years ago, for instance, the North American plate began a rifting process. A triple junction formed in the middle of the young continent, and deep rift valley developed. Freshwater drained and collected in this rift valley, creating a lake. After millions of years, however, the rift failed. The continent remained intact and the rift's arms failed to open up a new ocean. Today, the remains of that ancient rift lake, Lake Superior, rest atop one of the oldest and deepest rift valleys in the world.

Lake Baikal, the rift lake over the Baikal Rift Valley in Siberia, is the deepest and oldest freshwater lake in the world. The deepest parts of Lake Baikal are 1,642 meters (5,387 feet), and are getting deeper every year. In addition, over the past 25 million years, layers of soft sediment have accumulated on the lakebed. The actual floor of the rift valley is more than five kilometers (three miles) deep. Lake Baikal also has the largest volume of liquid freshwater in the world-a staggering 23,615 cubic kilometers (5,700 cubic miles).

The Dead Sea is a rift lake in the Jordan Rift Valley. Although the Dead Sea is not the world's deepest lake, the deep Jordan Rift makes it the lowest land elevation on Earth. The surface of the Dead Sea is 429 meters (1,407 feet) below sea level, and the lake's depth is another 304 meters (997 feet). Unlike Lake Baikal, however, the Dead Sea is not a true rift lake as it was not formed entirely by the rift beneath it. The so-called Dead Sea Transform is a geologically complex area, where tectonic plates interact in many ways.

Lake Tanganyika is the world's second-deepest and second-biggest (by volume of freshwater) lake in the world. Only Lake Baikal is deeper and holds more water. Like many freshwater Rift Valley lakes, Lake Tanganyika is home to hundreds of endemic species of cichlid fish.

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A rift valley is a lowland region that forms where Earth's tectonic plates move apart, or rift.

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Over millions of years, the mantle cooled. Water trapped inside minerals erupted with lava, a process called "outgassing." As more water was outgassed, the mantle solidified.

The rocks that make up Earth's mantle are mostly silicates-a wide variety of compounds that share a silicon and oxygen structure. Common silicates found in the mantle include olivine, garnet, and pyroxene. The other major type of rock found in the mantle is magnesium oxide. Other mantle elements include iron, aluminum, calcium, sodium, and potassium. The temperature of the mantle varies greatly, from 1000°C (1832°F) near its boundary with the crust, to 3700°C (6692°F) near its boundary with the core. In the mantle, heat and pressure generally increase with depth. The geothermal gradient is a measurement of this increase. In most places, the geothermal gradient is about 25°C per kilometer of depth (1°Fper 70 feet of depth).

The viscosity of the mantle also varies greatly. It is mostly solid rock, but less viscous at tectonic plate boundaries and mantle plumes. Mantle rocks there are soft and able to move plastically (over the course of millions of years) at great depth and pressure. The transfer of heat and material in the mantle helps determine the landscape of Earth. Activity in the mantle drives plate tectonics, contributing to volcanoes, seafloor spreading, earthquakes, and orogeny (mountain-building).

Upper Mantle

The upper mantle extends from the crust to a depth of about 410 kilometers (255 miles). The upper mantle is mostly solid, but its more malleable regions contribute to tectonic activity.
Lithosphere
The lithosphere is the solid, outer part of Earth, extending to a depth of about 100 kilometers (62 miles). The lithosphere includes both the crust and the brittle upper portion of the mantle. The lithosphere is both the coolest and the most rigid of Earth's layers.

The most well-known feature associated with Earth's lithosphere is tectonic activity. Tectonic activity describes the interaction of the huge slabs of lithosphere called tectonic plates. The lithosphere is divided into 15 major tectonic plates: the North American, Caribbean, South American, Scotia, Antarctic, Eurasian, Arabian, African, Indian, Philippine, Australian, Pacific, Juan de Fuca, Cocos, and Nazca.
Asthenosphere
The asthenosphere is the denser, weaker layer beneath the lithospheric mantle. It lies between about 100 kilometers (62 miles) and 410 kilometers (255 miles) beneath Earth's surface. The temperature and pressure of the asthenosphere are so high that rocks soften and partly melt, becoming semi-molten.

Of course, tectonic plates are not really floating, because the asthenosphere is not liquid. Tectonic plates are only unstable at their boundaries and hot spots.

Transition Zone

From about 410 kilometers (255 miles) to 660 kilometers (410 miles) beneath Earth's surface, rocks undergo radical transformations. This is the mantle's transition zone.

In the transition zone, rocks do not melt or disintegrate. Instead, their crystalline structure changes in important ways. Rocks become much, much more dense.

The transition zone prevents large exchanges of material between the upper and lower mantle. Some geologists think the increased density of rocks in the transition zone prevents subducted slabs from the lithosphere from falling further into the mantle. These huge pieces of tectonic plates stall in the transition zone for millions of years before mixing with other mantle rock and eventually returning to the upper mantle as part of the asthenosphere, erupting as lava, becoming part of the lithosphere, or emerging as new oceanic crust at sites of seafloor spreading.

Some geologists and rheologists, however, think subducted slabs can slip beneath the transition zone to the lower mantle. Other evidence suggests that the transition layer is permeable, and the upper and lower mantle exchange some amount of material.

Perhaps the most important aspect of the mantle's transition zone is its abundance of water. Crystals in the transition zone hold as much water as all the oceans on Earth's surface.

Near the bottom of the transition zone, increasing temperature and pressure transform ringwoodite and wadsleyite. Their crystal structures are broken and hydroxide escapes as "melt." Melt particles flow upwards, toward minerals that can hold water. This allows the transition zone to maintain a consistent reservoir of water.

Lower Mantle

The lower mantle extends from about 660 kilometers (410 miles) to about 2,700 kilometers (1,678 miles) beneath Earth's surface. The lower mantle is hotter and denser than the upper mantle and transition zone.

The lower mantle is much less ductile than the upper mantle and transition zone. Although heat usually corresponds to softening rocks, intense pressure keeps the lower mantle solid.

Geologists do not agree about the structure of the lower mantle. Some geologists think that subducted slabs of lithosphere have settled there. Other geologists think that the lower mantle is entirely unmoving and does not even transfer heat by convection.

D Double-Prime (D'')

At the base of the mantle, about 2,900 kilometers (1,802 miles) below the surface, is the core-mantle boundary, or CMB. This point, called the Gutenberg discontinuity, marks the end of the mantle and the beginning of Earth's liquid outer core.

Mantle Convection

Mantle convection describes the movement of the mantle as it transfers heat from the white-hot core to the brittle lithosphere. The mantle is heated from below, cooled from above, and its overall temperature decreases over long periods of time. All these elements contribute to mantle convection.

Convection currents transfer hot, buoyant magma to the lithosphere at plate boundaries and hot spots. Convection currents also transfer denser, cooler material from the crust to Earth's interior through the process of subduction.

Geologists debate whether mantle convection is "whole" or "layered." Whole-mantle convection describes a long, long recycling process involving the upper mantle, transition zone, lower mantle, and even D''. In this model, the mantle convects in a single process. A subducted slab of lithosphere may slowly slip into the upper mantle and fall to the transition zone due to its relative density and coolness. Over millions of years, it may sink further into the lower mantle. Convection currents may then transport the hot, buoyant material in D'' back through the other layers of the mantle. Some of that material may even emerge as lithosphere again, as it is spilled onto the crust through volcanic eruptions or seafloor spreading.

Layered-mantle convection describes two processes. Plumes of superheated mantle material may bubble up from the lower mantle and heat a region in the transition zone before falling back. Above the transition zone, convection may be influenced by heat transferred from the lower mantle as well as discrete convection currents in the upper mantle driven by subduction and seafloor spreading. Mantle plumes emanating from the upper mantle may gush up through the lithosphere as hot spots.
Mantle Plumes
A mantle plume is an upwelling of superheated rock from the mantle. Mantle plumes are the likely cause of "hot spots," volcanic regions not created by plate tectonics. As a mantle plume reaches the upper mantle, it melts into a diapir. This molten material heats the asthenosphere and lithosphere, triggering volcanic eruptions. These volcanic eruptions make a minor contribution to heat loss from Earth's interior, although tectonic activity at plate boundaries is the leading cause of such heat loss.

The Hawaiian hot spot, in the middle of the North Pacific, sits above a likely mantle plume. As the Pacific plate moves in a generally northwestern motion, the Hawaiian hot spot remains relatively fixed. Geologists think this has allowed the Hawaiian hot spot to create a series of volcanoes, from the 85-million-year-old Meiji Seamount near Russia's Kamchatka Peninsula, to the Loihi Seamount, a submarine volcano southeast of the "Big Island" of Hawai'i. Loihi, a mere 400,000 years old, will eventually become the newest Hawaiian island.

Geologists have identified two so-called "superplumes." These superplumes, or large low shear velocity provinces (LLSVPs), have their origins in the melt material of D''. The Pacific LLSVP influences geology throughout most of the southern Pacific Ocean (including the Hawaiian hot spot). The African LLSVP influences the geology throughout most of southern and western Africa.

Geologists think mantle plumes may be influenced by many different factors. Some may pulse, while others may be heated continually. Some may have a single diapir, while others may have multiple "stems." Some mantle plumes may arise in the middle of a tectonic plate, while others may be "captured" by seafloor spreading zones.

Some geologists have identified more than a thousand mantle plumes. Some geologists think mantle plumes don't exist at all. Until tools and technology allow geologists to more thoroughly explore the mantle, the debate will continue.

Exploring the Mantle

The mantle has never been directly explored. Even the most sophisticated drilling equipment has not reached beyond the crust.

Most mantle studies are conducted by measuring the spread of shock waves from earthquakes, called seismic waves. The seismic waves measured in mantle studies are called body waves, because these waves travel through the body of Earth. The velocity of body waves differs with density, temperature, and type of rock.

Both body waves "reflect" off different types of rocks in different ways. This allows seismologists to identify different rocks present in Earth's crust and mantle far beneath the surface. Seismic reflections, for instance, are used to identify hidden oil deposits deep below the surface.

Sudden, predictable changes in the velocities of body waves are called "seismic discontinuities." The Moho is a discontinuity marking the boundary of the crust and upper mantle. The so-called "410-kilometer discontinuity" marks the boundary of the transition zone.

The Gutenberg discontinuity is more popularly known as the core-mantle boundary (CMB). At the CMB, S-waves, which can't continue in liquid, suddenly disappear, and P-waves are strongly refracted, or bent. This alerts seismologists that the solid and molten structure of the mantle has given way to the fiery liquid of the outer core.
Mantle Maps

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The mantle is the mostly solid bulk of Earth's interior. The mantle lies between Earth's dense, super-heated core and its thin outer layer, the crust. The mantle is about 2,900 kilometers (1,802 miles) thick, and makes up a whopping 84 percent of Earth's total volume.

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Seafloor spreading is a geologic process in which tectonic plates—large slabs of Earth’s lithosphere—split apart from each other.

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A volcano is a feature in Earth's crust where molten rock is squeezed out onto the Earth's surface. This molten rock is called magma when it is beneath the surface and lava when it erupts, or flows out, from a volcano. Along with lava, volcanoes also release gases, ash, and, solid rock.

Volcanoes are incredibly powerful agents of change. Eruptions can create new landforms, but can also destroy everything in their path. About 350 million people (or about one out of every 20 people in the world) live within the "danger range" of an active volcano. Volcanologists closely monitor volcanoes so they can better predict impending eruptions and prepare nearby populations for potential volcanic hazards that could endanger their safety.

Plate Tectonics

The two types of plate boundaries that are most likely to produce volcanic activity are divergent plate boundaries and convergent plate boundaries.

Divergent Plate Boundaries
At a divergent boundary, tectonic plates move apart from one another. They never really separate because magma continuously moves up from the mantle into this boundary, building new plate material on both sides of the plate boundary.

Another divergent plate boundary is the East Pacific Rise, which separates the massive Pacific plate from the Nazca, Cocos, and North American plates.

Of course, divergent plate boundaries also exist on land. The East African Rift is an example of a single tectonic plate being ripped in two. Along the Horn of Africa, the African plate is tearing itself into what is sometimes called the Nubian plate (to the west, including most of the current African plate) and the Somali plate (to the east, including the Horn of Africa and the western Indian Ocean). Along this divergent plate boundary are volcanoes such as Mount Nyiragongo, in the Democratic Republic of Congo, and Mount Kilimanjaro, in Kenya.
Convergent Plate Boundaries
At a convergent plate boundary, tectonic plates move toward one another and collide. Oftentimes, this collision forces the denser plate edge to subduct, or sink beneath the plate edge that is less dense. These subduction zones can create deep trenches. As the denser plate edge moves downward, the pressure and temperature surrounding it increases, which causes changes to the plate that melt the mantle above, and the melted rock rises through the plate, sometimes reaching its surface as part of a volcano. Over millions of years, the rising magma can create a series of volcanoes known as a volcanic arc.

The mighty Andes Mountains of South America run parallel to the Peru-Chile Trench. These mountains are continually built up as the Nazca plate subducts under the South American plate. The Andes Mountains include the world's highest active volcano, Nevados Ojos del Salado, which rises to 6,879 meters (over 22,500 feet) along the Chile-Argentina border.

For many years, scientists have been trying to explain why some volcanoes exist thousands of kilometers away from tectonic plate boundaries.

The dominant theory, framed by Canadian geophysicist J. Tuzo Wilson in 1963, states that these volcanoes are created by exceptionally hot areas fixed deep below Earth's mantle. These hot spots are able to independently melt the tectonic plate above them, creating magma that erupts onto the top of the plate.

In hot spots beneath the ocean, the tectonic activity creates a volcanic mound. Over millions of years, volcanic mounds can grow until they reach sea level and create a volcanic island. The volcanic island moves as part of its tectonic plate. The hot spot stays put, however. As the volcano moves farther from the hot spot, it goes extinct and eventually erodes back into the ocean. A new and active volcano develops over the hot spot, creating a continuous cycle of volcanism-and a string of volcanic islands tracing the tectonic plate's movement over time.

For Wilson and many scientists, the best example of hot spot volcanism is the Hawaiian Islands. Experts think this volcanic chain of islands has been forming for at least 70 million years over a hot spot underneath the Pacific plate. Of all the inhabited Hawaiian Islands, Kauai is located farthest from the presumed hot spot and has the most eroded and oldest volcanic rocks, dated at 5.5 million years. Meanwhile, on the "Big Island" of the U.S. state of Hawai'i-still fueled by the hot spot-the oldest rocks are less than 0.7 million years old and volcanic activity continues to create new land.

Hot spots can also create terrestrial volcanoes. The Yellowstone Supervolcano, for instance, sits over a hot spot in the middle of the North American plate, with a series of ancient calderas stretching across southern part of the U.S. state of Idaho. The Yellowstone hot spot fuels the geysers, hot springs, and other geologic activity at Yellowstone National Park, Wyoming, United States.

While some data seem to prove Wilson's hot spot theory, more recent scientific studies suggest that these hot spots may be found at more shallow depths in the planet's mantle and may migrate slowly over geologic time rather than stay fixed in the same spot.
Principal Types of Volcanoes
While volcanoes come in a variety of shapes and sizes, they all share a few key characteristics. All volcanoes are connected to a reservoir of molten rock, called a magma chamber, below the surface of Earth. When pressure inside the chamber builds up, the buoyant magma travels out a surface vent or series of vents, through a central interior pipe or series of pipes. These eruptions, which vary in size, material, and explosiveness, create different types of volcanoes.

Volcan de Fuego and Acatenango are a pair of stratovolcanoes that stand more than 3,700 meters (12,000 feet) above sea level near Antigua, Guatemala. While the volcanoes are considered twins because of their similar shape and size, they are made of different types of lava and have distinct eruption histories. While Acatenango erupts infrequently today, Fuego is considered to be the most active volcano in Central America, erupting more than 60 times since 1524.

Shield volcanoes make up the entirety of the Hawaiian Islands. The Kilauea and Mauna Loa shield volcanoes, located on the "Big Island" of Hawai'i, rise from the ocean floor more than 4,500 meters (15,000 feet) below sea level. The summit of Mauna Loa stands at 4,168 meters (13,677 feet) above sea level and more than 8,500 meters (28,000 feet) above the ocean floor, making it the world's largest active volcano-and, by some accounts, the world's tallest mountain. The smaller volcano, Kilauea, has been erupting continuously since 1983, making it one of the world's most active volcanoes.

The Galapagos Islands are also made up of a series of shield volcanoes. Isabela and Fernandina islands have flatter tops than other shield volcanoes because lava erupts from fissures around their tops and along ridges at their bases. As a result, the volcanoes rise at the top and grow outward at the bottom-but not in the middle, making them look like an "inverted soup bowl."

Parícutin, Mexico, is a unique pyroclastic cone. It was the first volcano to be studied for its entire life cycle. Emerging from a cornfield in 1943, Parícutin's explosive eruptions caused it to reach 80 percent of its height of 424 meters (1,391 feet) during its first year of activity. In that time, lava and ash buried the nearby town of San Juan. Over the next eight years, Parícutin built the remainder of its cone-and then went quiet. Geologists learned a great deal about the evolution of volcanoes in Parícutin's short, nine-year life.

Lava domes are like shield volcanoes in that they are built entirely of lava. This lava, however, is too thick and sticky to move great distances. It just piles up around the volcano vent. Lava domes are often found on the summit or flanks of a volcano, but they can also develop independently. Like pyroclastic cones, they only reach a few hundred meters, as they are formed during singular eruptions or slow lava releases.
Other Important Volcanic Features
Crater Lake, Oregon, United States, is in a caldera about 10 kilometers (six miles) wide. Crater Lake's caldera resulted from an eruption that occurred more than 7,000 years ago. The volcano's magma chamber collapsed, then filled with water from rain and snow, creating the lake. Crater Lake is the deepest lake in the United States.

Much like calderas, craters are depressions left after a volcano experiences a large eruption. While calderas are formed by the collapse of material inside a volcano, craters are formed as materials explode out from a volcano. Craters are usually much smaller than calderas, only extending to a maximum of about one kilometer (0.62 mile) in diameter.

Many volcanoes have multiple craters caused by different eruptions. The Maly Semiachik volcano, located on the Kamchatka Peninsula in far eastern Russia, has six craters at its summit. The youngest of these craters, Troitsky, filled in with water and snowmelt, creating a lake 140 meters (459 feet) deep. The lake is highly acidic, as volcanic gases continue to be released into the water from the active volcano below.

Lava lakes are also found in volcanic craters. Erta Ale, a volcano in Ethiopia, has a lava lake in its summit crater. Lava lakes are where magma has bubbled up to the surface and pooled in a crater. Volcanologists can fly over Erta Ale's summit crater to see how the lava lake is behaving and predict future behavior.

Types of Volcanic Eruptions

Volcanic eruptions are as diverse as volcanoes themselves-which is to say, very diverse! Some of the ways volcanologists have classified these eruptions are based on the heights they reach, the types of materials they eject, and the explosiveness of these ejections.

These eruptions are named after the Hawaiian Islands, where they most often occur. Kilauea, which has been erupting continuously since 1983, has produced lava flows covering more than 100 square kilometers (37 square miles) on the island of Hawai'i. These flows continuously destroy houses and communities in their path, while also adding new coastline to the island.
Strombolian
Strombolian eruptions are characterized by short-lived outbursts of lava rather than steady fountaining. The lava is thicker and has a higher gas content than that of Hawaiian eruptions. Large gas bubbles rise from the magma chamber, pushing the pasty lava upward until the bubbles explode at the summit vent. These explosions can reach heights up to 10 kilometers (6.2 miles) although most don't go higher than a few hundred meters into the air.

Strombolian eruptions are named after the Mediterranean island of Stromboli, Italy. Considered by many to be the most active volcano on Earth, Stromboli has been erupting almost continuously for 2,000 years. The island's eruptions are almost always Strombolian in nature: Small gas explosions eject blobs of lava into the air a couple of times per hour.

The 2013 vulcanian eruption of Sakurajima, on the island of Kyushu, Japan, covered the nearby city of Kagoshima in a thick coat of ash.

In 79 C.E., a series of Plinian eruptions from Mount Vesuvius buried the nearby Roman cities of Pompeii and Herculaneum (in what is today Italy). The cities and their 13,000 inhabitants were buried in volcanic ash and rock. Rainfall mixed with the ash and created a concrete-like substance that preserved the city for thousands of years.

Tonga's islands of Hunga Tonga and Hunga Ha'apai are actually the tops of a single, large underwater volcano. In 2009, the volcano erupted for several days, causing steam and ash to explode from the water to altitudes of five kilometers (3.1 miles). While the eruptions killed all signs of wildlife on and around the islands, it also added hundreds of square meters of land to Hunga Ha'apai.

Volcanic Hazards

Many volcanic materials and processes pose a threat to human, animal, and other ecological communities.
Volcanic Gas
In extreme cases, these "volcanic winters" can cause crop failures and drastically affect weather. The 1815 eruption of Mount Tambora, Indonesia, cooled the average global temperature by as much as 3° Celsius (5.4° Fahrenheit), causing the "year without a summer."

The enormous energy of volcanic eruptions can cause large landslides that move at speeds of more than 100 kilometers per hour (60 miles per hour). Mount St. Helens, Washington, is a stratovolcano that had an explosive Plinian eruption in 1980. The eruption produced the largest landslide in recorded history, covering a 36-kilometer (14-mile) area of land with ash and rocks. Reaching speeds of 50 to 80 meters (165 to 260 feet) per second, the landslide had enough power to surge over a ridge 400 meters (1,312 feet) high.
Pyroclastic Flows
Explosive eruptions sometimes produce pyroclastic flows, a mixture of hot rock fragments and toxic gases that move almost like a liquid out and away from the volcano. Reaching speeds greater than 80 kilometers per hour (50 miles per hour) and temperatures between 200-700° Celsius (392-1292° Fahrenheit), pyroclastic flows knock down, shatter, bury, or burn anything in their path.

Pyroclastic flows are responsible for the haunting figures from Pompeii and Herculaneum, Italy. While many scientists thought residents of Pompeii suffocated to death from volcanic gases released during Mount Vesuvius' eruption in 79 C.E., new studies suggest that they actually died from extreme heat produced by the volcano's pyroclastic flow.
Volcanic Ash
The 1994 double eruption of Vulcan and Tavurvur in Papua New Guinea covered the nearby city of Rabaul in a layer of ash up to 75 centimeters (about two feet) deep. Rains turned the ash into a cement-like substance that was heavy enough to collapse 80 percent of the buildings in the city.

Volcanic Monitoring and Research

Volcanic hazards can be incredibly dangerous to human life. In the United States alone, 54 volcanoes are a very high or high threat to public safety. By closely monitoring volcanic activity, volcanologists can warn people of impending eruptions. While these warnings are not exact predictions, they do provide communities with the valuable time they need to protect themselves against volcanic hazards and ensure their safety.

A number of international organizations lead the way in volcanic monitoring and research, providing invaluable information to scientists, volcanologists, and the public alike. The Smithsonian Institution's Global Volcanism Program documents current activity for all the volcanoes on the planet through publicly available data, reports, and images. The program also keeps the world's only archive of volcanic activity from the last 10,000 years.

As part of the UN International Decade for Natural Disaster Reduction, the International Association of Volcanology and Chemistry of the Earth's Interior (IAVCEI) created a list of 16 "Decade Volcanoes" to study because of the high risk they pose to public safety. Mount Nyiragongo in Democratic Republic of the Congo, for example, is dangerously close to the city of Goma. Its 2002 eruption killed 50 people and forced roughly 450,000 people to evacuate their communities. The Santa María Volcano, which sits right above the city of Quetzaltenango, Guatemala, has been continuously erupting since 2003. The Decade Volcanoes program has brought together geologists, volcanologists, and government officials to closely study these volcanoes and create risk-mitigation plans for potential eruptions.

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A volcano is a feature in Earth's crust where molten rock is squeezed out onto Earth's surface. Along with molten rock, volcanoes also release gases, ash, and solid rock.

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Photograph by Obliot

A caldera is a large depression formed when a volcano erupts and collapses. During a volcanic eruption, magma present in the magma chamber underneath the volcano is expelled, often forcefully. When the magma chamber empties, the support that the magma had provided inside the chamber disappears. As a result, the sides and top of the volcano collapse inward. Calderas vary in size from one to 100 kilometers (0.62 to 62 miles) in diameter.

Some calderas form a lake as the bowl-shaped depression fills with water. A famous example is Crater Lake, in Oregon. This caldera formed about 7,000 years ago when a stratovolcano, Mt. Mazama, violently erupted. For several thousand years after this eruption, smaller volcanic eruptions continued inside the caldera. One of these eruptions was so large it formed an island in Crater Lake named Wizard Island.

Calderas such as Crater Lake and those in Yellowstone National Park result from dramatic eruptions, but slower eruptions can also create calderas. This often occurs with shield volcanoes, which are typically flatter and more gradually sloped. Lava flows from shield volcanoes more slowly and often at regular intervals. Over time, this creates a series of nested depressions. The Kilauea caldera on Kilauea, one of the volcanoes that make up Hawai'i, is one example.

Another type of caldera is a resurgent caldera. These broad, vast calderas result when very large magma chambers empty quite forcefully, causing a series of pyroclastic flows. Over time, the refilling of the magma chamber pushes up the caldera floor. This upward movement is why the caldera is called resurgent, which means "risen again."

National Geographic Society

October 19, 2023

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A caldera is a large depression formed when a volcano erupts and collapses.

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A sleeping giant is nestled in the western part of the United States. Though it stirs occasionally, it has not risen from slumber in nearly 70,000 years. But when it finally awakes it may roar and heave with unprecedented force.

This giant is the "supervolcano" that lies beneath Yellowstone National Park, the wildlife and forest preserve positioned on a sprawling expanse that extends through the states of Wyoming, Idaho, and Montana. The volcano itself is actually located in northwestern Wyoming, which is where the bulk of Yellowstone is contained.

The ground above the Yellowstone supervolcano sits on a hot spot made of molten and semi-molten rock called . As magma feeds into a magma chamber, or reservoir situated about 6-10 kilometers (4-6 miles) beneath the park, the ground swells. When the magma begins to solidify and cool, the ground falls.

Volcanologists, who have been measuring this activity since 1923, say the ground rose about 25 centimeters (9.8 inches) between 2004 and 2009. However, in 2010 the land began to subside.

The period of slow, steady rise has many scientists wondering whether Yellowstone might erupt in the near future. And if it does, there is concern about how intense that eruption may be.

"The big question is if Yellowstone started shaking tomorrow, what is there to expect?" says Dr. Steve Anderson, a volcanologist and earth sciences professor at the University of Northern Colorado. "I don't think we know exactly what to expect."

While scientists may not know exactly what to expect, they have an idea-and most say it's unlikely to be doomsday.

In fact, Dr. Jacob Lowenstern, research geologist and Scientist-in-Charge at the Yellowstone Volcano Observatory, says that Yellowstone is currently a dormant volcano, with low levels of unrest.

"There is no current activity that is going on that would indicate anything is happening. If there was something coming, there is nothing to show at this point in time," he says.

Learning from the Past

Still, the level of recent underground activity fuels speculation about the intensity of an eruption. Within the past decade, the volcano has continued to rise at the fastest rate ever recorded.

Yellowstone also averages between 1,000 and 3,000 earthquakes a year. Most are virtually unnoticeable, with a magnitude of three or less. Still, these quakes give scientists insight into just how fast the magma chamber beneath the park is filling up. An increase in the shaking and rattling throughout the park might indicate a fresh batch of magma was recently fed into the reservoir.

Even with the increase in temblors, scientists don't think the rumblings in the magma chamber pose a threat anytime soon. However, since people haven't been around to analyze absolutely everything that happens in Yellowstone, it's hard to predict what exactly is going on, making it difficult for geologists to predict Yellowstone's next move.

Examinations of the volcano's distant past do provide something of a clue. Geologic evidence suggests that Yellowstone has produced three colossal eruptions within the past 2.1 million years. Volcanologists say the eruptions occurred at gaps of about 600,000 to 800,000 years. Evidence from the last big event, estimated to have to been about 640,000 years ago, is sprawled throughout the park and across thousands of kilometers of the surrounding landscape.

Each of the previous eruptions spewed enormous amounts of volcanic ash, gas, magma, and other volcanic debris that covered most of the continental U.S. Some material has been found as far away as Louisiana.

After each of these eruptions, the Yellowstone supervolcano collapsed on itself, sucking in trees, mountains and everything else in the landscape. The depression formed by this phenomenon is called a caldera. (In fact, the Yellowstone supervolcano is also called the Yellowstone caldera.) A caldera-forming eruption would create a massive natural hazard in Yellowstone.

Scientists say the last Yellowstone eruption was 1,000 times greater than the notorious 1980 Mt. Saint Helens eruption that killed 56 people and thousands of animals, and scorched hundreds of square kilometers of land in Washington and Oregon.

Thousands of years ago, the last blast from the Yellowstone supervolcano shot a fatal plume of hot ash, molten rock, and lethal gases thousands of meters into the air. A third of the continent was likely plunged into complete darkness. Pyroclastic flows (fast-moving currents of hot, dry rock fragments and gases) raced along the region at alarming speeds, burying or shattering anything in their path. Magma spewing out of the ground charred the once-charming landscape for kilometers.

Some evidence of the last eruption can be found in the Yellowstone caldera itself, 50 kilometers (30 miles) wide and 70 kilometers (45 miles) long. The thick volcanic debris that remained after the eruption can still be seen in an area referred to as the Lava Creek Tuff.

Unlikely to Erupt

Officials of the United States Geological Survey (USGS) say a massive eruption like the last one is an unlikely scenario. In fact, officials at the Yellowstone Volcano Observatory say the most likely activities that might take place in the future are hydrothermal explosions (eruptions of steam and hot water, rather than molten rock) or lava flows.

Although lava flows are a type of magmatic eruption, they are not as devastating as the caldera-forming explosions. Instead of instant destruction, lava flows slowly ooze out of the ground over a period of days, months, or even years.

They are also relatively rare. The last Yellowstone lava flows took place about 70,000 years ago. Yet even today, hikers can see evidence of those eruptions in the form of distinct rock layers along the park's trails. Some evidence of younger lava flows can be found near the cliffs surrounding the Upper Geyser Basin, near Old Faithful. (Old Faithful is a geyser and one of the park's most popular tourist attractions.)

Today, Yellowstone sleeps, with scientists checking its every hiccup or cough in an effort to predict its next move. While the brewing force beneath the park has been restrained for thousands of years, Yellowstone's dormancy does not mean it will not one day awaken. The question remains: When and with what force?

"We are getting into the time period where it is supposed to become more unstable," says Anderson, "but I am not holding my breath."

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Past volcanic eruptions that have taken place at Yellowstone National Park have been global disasters. Today, scientists are trying to predict how this ticking time bomb will explode-or fizzle out.

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Map: Path of eruptions of Yellowstone supervolcano.

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Chart and map of ancient eruptions of Yellowstone supervolcano.

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Yellowstone Volcano Observatory (Part 3)

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Yellowstone Volcano Observatory (Part 3)

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September 27, 2022

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Yellowstone Volcano Observatory (Part 3 of 3)

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Jake Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory, answers the following questions to explain volcanic eruptions at Yellowstone: When was the last supereruption at Yellowstone?", "Have any eruptions occurred since the last supereruption?", "Is Yellowstone overdue for an eruption?", "What does the magma below indicate about a possible eruption?", "What else is possible?", and "Why didn't you think the Yellowstone Lake earthquake swarm would lead to an eruption?"

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Yellowstone Volcano Observatory (Part 1)

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Yellowstone Volcano Observatory (Part 1)

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Yellowstone Volcano Observatory (Part 1 of 3)

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Jake Lowenstern, USGS Scientist-in-Charge of the Yellowstone Volcano Observatory, answers the following questions to explain volcanic features at Yellowstone: “How do we know Yellowstone is a volcano?”, “What is a Supervolcano?”, “What is a Caldera?”,“Why are there geysers at Yellowstone?”, and ”…

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A new 3-D model shows the 45-mile-wide (72-kilometer-wide), 410-mile-deep (660-kilometer-deep) plume of hot, molten rock rising under Yellowstone's supervolcano.

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A hot spot is fed by a region deep within the Earth's mantle from which heat rises through the process of convection. This heat facilitates the melting of rock at the base of the lithosphere, where the brittle, upper portion of the mantle meets Earth's crust. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.

Hot spot volcanism is unique because it does not occur at the boundaries of Earth's tectonic plates, where all other volcanism occurs. Instead it occurs at abnormally hot centers known as mantle plumes. Scientific models depict these plumes of molten rock almost like a lava lamp, with a rising bulbous head fed by a long, narrow tail that originates in the mantle. As the plume head reaches the lithosphere, it spreads into a mushroom shape that reaches roughly 500 to 1,000 kilometers (310 to 621 miles) in diameter. These features are called diapirs.

Scientists have different theories about where hot spots form. The dominant theory, framed by Canadian geophysicist J. Tuzo Wilson in 1963, states that hot spot volcanoes are created by exceptionally hot areas fixed deep below Earth's mantle. More recent scientific studies suggest that these hot spots may be found at more shallow depths in Earth's mantle and may migrate slowly over geologic time rather than stay fixed in the same spot. A volcano above a hot spot does not erupt forever. Attached to the tectonic plate below, the volcano moves and is eventually cut off from the hot spot. Without any source of heat, the volcano becomes extinct and cools. This cooling causes the rock of the volcano and the tectonic plate to become more dense. Over time, the dense rock sinks and erodes. A new and active volcano develops over the hot spot, creating a continuous cycle of volcanism.
Hot Spot Features
Most scientists think that 40 to 50 hot spots exist around the world, although this number varies widely because of differing definitions of what a hot spot is. Major hot spots include the Iceland hot spot, under the island of Iceland in the North Atlantic; the Réunion hot spot, under the island of Réunion in the Indian Ocean; and the Afar hot spot, located under northeastern Ethiopia. Volcanic activity at hot spots can create submarine mountains known as seamounts.

Some scientists estimate that seamounts make up 28.8 million square kilometers (17.9 million square miles) of Earth's surface, an area larger than any other habitat. Depending on the amount of volcanic activity, seamounts can rise hundreds or thousands of meters from the seafloor. The Louisville Seamount Chain, for example, comprises over 80 seamounts that extend in a 4,000-kilometer arc (2,485 miles) in the South Pacific Ocean, about 1,500 kilometers (932 miles) from Wellington, New Zealand. The seamounts originated from a single hot spot and have been slowly transported in a northwest direction by the Pacific plate.

Hot-spot seamounts that reach the surface of the water can create entire chains of islands, such as the U.S. state of Hawaii. Scientists think that this volcanic chain of islands has been forming for at least 70 million years over a hot spot underneath the Pacific plate. The Hawaiian Islands were created one right after the other as the plate moved northwest-almost like an island factory. Of all the inhabited Hawaiian Islands, Kauai is located farthest from the presumed hot spot and has the most eroded and oldest volcanic rocks, dated to be around 5.5 million years old. Meanwhile, on the "Big Island" of Hawaii, the oldest rocks are less than 0.7 million years old and volcanic activity continues to create new land.

Hot spots can also develop beneath continents. The Yellowstone hot spot, for example, has produced a series of volcanic features that extend in a northeastern direction. The features stretch from the U.S. states of Idaho and Oregon, some 650 kilometers (400 miles) to northwest Wyoming. Over 16.5 million years, the hot spot has generated 15 to 20 massive eruptions that left large volcanic depressions called calderas. The McDermitt Volcanic Field, located on the Nevada-Oregon border, is the hot spot's oldest large feature. It formed from an eruption roughly 16.1 million years ago. The active Yellowstone Caldera, in Yellowstone National Park in northwest Wyoming, is the hot spot's youngest large feature, having last erupted just 640,000 years ago.

Hot spots don't always create volcanoes that spew rivers of lava. Sometimes, the magma heats up groundwater under the Earth's surface, which causes water and steam to erupt like a volcano. These eruptions are called geysers. A famous geyser is Old Faithful in Yellowstone National Park. When it erupts, the water is 95.6 degrees Celsius (204 degrees Fahrenheit) and can reach more than 55 meters (180 feet) high.

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A hot spot is a region deep within Earth's mantle from which heat rises by convection.

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Resource

ENCYCLOPEDIC ENTRY

A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.

Subjects

Earth Science, Geology, Geography, Physical Geography

Image

hot spot

2018 eruption on Mount Kilauea.

Photograph by the USGS

A hot spot is an area on Earth that exists over a mantle plume. A mantle plume is an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. Heat from this extra hot magma causes melting and thinning of the rocky crust, which leads to widespread volcanic activity on Earth's surface above the plume.

While most volcanoes form along tectonic plate boundaries, mantle plumes and hot spots lead to their development as well. Hot spot volcanoes occur far from plate boundaries. Because the hot spot is caused by mantle plumes that exist below the tectonic plates, as the plates move, the hot spot does not, and may create a chain of volcanoes on the Earth's surface. Neither the Hawaiian Islands nor Yellowstone National Park are near plate boundaries. Rather, the volcanoes that form the Hawaiian Islands and the volcanic activity at Yellowstone National Park are due to their locations over hot spots.

Geologists estimate there are about 40 to 50 hot spots around the world.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Director

Tyson Brown, National Geographic Society

Author

National Geographic Society

Production Managers

Gina Borgia, National Geographic Society

Jeanna Sullivan, National Geographic Society

Program Specialists

Sarah Appleton, National Geographic Society, National Geographic Society

Margot Willis, National Geographic Society

other

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# data[].attributes.attachment_link.description
A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.

# data[].attributes.attachment_link.readable_text
A hot spot is fed by a region deep within the Earth's mantle from which heat rises through the process of convection. This heat facilitates the melting of rock at the base of the lithosphere, where the brittle, upper portion of the mantle meets Earth's crust. The melted rock, known as magma, often pushes through cracks in the crust to form volcanoes.

Hot spot volcanism is unique because it does not occur at the boundaries of Earth's tectonic plates, where all other volcanism occurs. Instead it occurs at abnormally hot centers known as mantle plumes. Scientific models depict these plumes of molten rock almost like a lava lamp, with a rising bulbous head fed by a long, narrow tail that originates in the mantle. As the plume head reaches the lithosphere, it spreads into a mushroom shape that reaches roughly 500 to 1,000 kilometers (310 to 621 miles) in diameter. These features are called diapirs.

Scientists have different theories about where hot spots form. The dominant theory, framed by Canadian geophysicist J. Tuzo Wilson in 1963, states that hot spot volcanoes are created by exceptionally hot areas fixed deep below Earth's mantle. More recent scientific studies suggest that these hot spots may be found at more shallow depths in Earth's mantle and may migrate slowly over geologic time rather than stay fixed in the same spot. A volcano above a hot spot does not erupt forever. Attached to the tectonic plate below, the volcano moves and is eventually cut off from the hot spot. Without any source of heat, the volcano becomes extinct and cools. This cooling causes the rock of the volcano and the tectonic plate to become more dense. Over time, the dense rock sinks and erodes. A new and active volcano develops over the hot spot, creating a continuous cycle of volcanism.
Hot Spot Features
Most scientists think that 40 to 50 hot spots exist around the world, although this number varies widely because of differing definitions of what a hot spot is. Major hot spots include the Iceland hot spot, under the island of Iceland in the North Atlantic; the Réunion hot spot, under the island of Réunion in the Indian Ocean; and the Afar hot spot, located under northeastern Ethiopia. Volcanic activity at hot spots can create submarine mountains known as seamounts.

Some scientists estimate that seamounts make up 28.8 million square kilometers (17.9 million square miles) of Earth's surface, an area larger than any other habitat. Depending on the amount of volcanic activity, seamounts can rise hundreds or thousands of meters from the seafloor. The Louisville Seamount Chain, for example, comprises over 80 seamounts that extend in a 4,000-kilometer arc (2,485 miles) in the South Pacific Ocean, about 1,500 kilometers (932 miles) from Wellington, New Zealand. The seamounts originated from a single hot spot and have been slowly transported in a northwest direction by the Pacific plate.

Hot-spot seamounts that reach the surface of the water can create entire chains of islands, such as the U.S. state of Hawaii. Scientists think that this volcanic chain of islands has been forming for at least 70 million years over a hot spot underneath the Pacific plate. The Hawaiian Islands were created one right after the other as the plate moved northwest-almost like an island factory. Of all the inhabited Hawaiian Islands, Kauai is located farthest from the presumed hot spot and has the most eroded and oldest volcanic rocks, dated to be around 5.5 million years old. Meanwhile, on the "Big Island" of Hawaii, the oldest rocks are less than 0.7 million years old and volcanic activity continues to create new land.

Hot spots can also develop beneath continents. The Yellowstone hot spot, for example, has produced a series of volcanic features that extend in a northeastern direction. The features stretch from the U.S. states of Idaho and Oregon, some 650 kilometers (400 miles) to northwest Wyoming. Over 16.5 million years, the hot spot has generated 15 to 20 massive eruptions that left large volcanic depressions called calderas. The McDermitt Volcanic Field, located on the Nevada-Oregon border, is the hot spot's oldest large feature. It formed from an eruption roughly 16.1 million years ago. The active Yellowstone Caldera, in Yellowstone National Park in northwest Wyoming, is the hot spot's youngest large feature, having last erupted just 640,000 years ago.

Hot spots don't always create volcanoes that spew rivers of lava. Sometimes, the magma heats up groundwater under the Earth's surface, which causes water and steam to erupt like a volcano. These eruptions are called geysers. A famous geyser is Old Faithful in Yellowstone National Park. When it erupts, the water is 95.6 degrees Celsius (204 degrees Fahrenheit) and can reach more than 55 meters (180 feet) high.

# data[].attributes.attachment_link.description
A hot spot is a region deep within Earth's mantle from which heat rises by convection.

# data[].attributes.attachment_link.readable_text
Resource

ENCYCLOPEDIC ENTRY

A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.

Subjects

Earth Science, Geology, Geography, Physical Geography

Image

hot spot

2018 eruption on Mount Kilauea.

Photograph by the USGS

A hot spot is an area on Earth that exists over a mantle plume. A mantle plume is an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. Heat from this extra hot magma causes melting and thinning of the rocky crust, which leads to widespread volcanic activity on Earth's surface above the plume.

While most volcanoes form along tectonic plate boundaries, mantle plumes and hot spots lead to their development as well. Hot spot volcanoes occur far from plate boundaries. Because the hot spot is caused by mantle plumes that exist below the tectonic plates, as the plates move, the hot spot does not, and may create a chain of volcanoes on the Earth's surface. Neither the Hawaiian Islands nor Yellowstone National Park are near plate boundaries. Rather, the volcanoes that form the Hawaiian Islands and the volcanic activity at Yellowstone National Park are due to their locations over hot spots.

Geologists estimate there are about 40 to 50 hot spots around the world.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Director

Tyson Brown, National Geographic Society

Author

National Geographic Society

Production Managers

Gina Borgia, National Geographic Society

Jeanna Sullivan, National Geographic Society

Program Specialists

Sarah Appleton, National Geographic Society, National Geographic Society

Margot Willis, National Geographic Society

other

For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

Media

If a media asset is downloadable, a download button appears in the corner of the media viewer. If no button appears, you cannot download or save the media.

Text

Text on this page is printable and can be used according to our Terms of Service.

Interactives

Any interactives on this page can only be played while you are visiting our website. You cannot download interactives.

# data[].attributes.attachment_link.description
A hot spot is an area on Earth over a mantle plume or an area under the rocky outer layer of Earth, called the crust, where magma is hotter than surrounding magma. The magma plume causes melting and thinning of the rocky crust and widespread volcanic activity.

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Earth's rocky outer shell, its crust, is actually made of dozens of huge pieces of rock known as tectonic plates. These plates ride on currents of molten rock in the upper mantle, which lies just below the crust. Activity in the mantle and crustal plates results in earthquakes and volcanic eruptions. Most of these seismic events take place where two plates come together or tear apart.

The Hawaiian Islands, however, sit in the middle of the Pacific plate. They lie over a hot spot, where magma from the mantle pushes to the surface. The Hawai'i hot spot remains in one place while the Pacific plate moves steadily northwest. Hawai'i's "Big Island" is still being formed by Mauna Loa and Kilauea, two volcanoes currently sitting over the hot spot. Loihi, an undersea volcano, also sits above the hot spot and will likely become the next Hawaiian island.

Fast Fact

The Loihi seamount is an active volcano on the seafloor about 35 kilometers (22 miles) southeast of the Big Island of Hawaii.

Fast Fact

Mauna Kea sits 4,205 meters (13,796 feet) above sea level, but its total height from the seafloor to its summit is 10,200 meters (33,500 feet).

Fast Fact

Hydrothermal vents on the seafloor were first discovered, sampled, and photographed in 1977. Scientists had long suspected that these undersea geysers existed but were shocked to find the thriving community of organisms living around them without access to sunlight.

Media Credits

The audio, illustrations, photos, and videos are credited beneath the media asset, except for promotional images, which generally link to another page that contains the media credit. The Rights Holder for media is the person or group credited.

Editor

Caryl-Sue Micalizio, National Geographic Society

Educator Reviewer

Julie Brown, National Geographic Society

Producers

Julie Brown, National Geographic Society

other

Last Updated

September 27, 2022

For information on user permissions, please read our Terms of Service. If you have questions about licensing content on this page, please contact ngimagecollection@natgeo.com for more information and to obtain a license. If you have questions about how to cite anything on our website in your project or classroom presentation, please contact your teacher. She or he will best know the preferred format. When you reach out to him or her, you will need the page title, URL, and the date you accessed the resource.

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Bob Ballard travels to Hawai'i to explore the terrestrial and deep sea geology of the Mauna Kea, the tallest mountain in the world.

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This story map requires JavaScript, but running JavaScript is not currently allowed by your web browser. If you wish to view this story, please enable JavaScript in this browser or try a different browser.

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This story map was created with the Story Map Journal application in ArcGIS Online.

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THE RED SEA CONNECTS the MEDITERRANEAN SEA to the INDIAN OCEAN via the Suez Canal. It lies in the Great Rift Valley between Africa and the Arabian Peninsula.

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What Is A Volcanic 'Hot Spot' And What Does That Have To Do With Hawaiian Island Formation? A volcanic hot spot is an upwelling in the earth's mantle. Magma rises up through the earth and as magma escapes, it forms a volcano. Imagine a nail in a tire, the air that escapes through the puncture is essentially like magma escaping to form a volcano.

The hot spot is stationary, but there is a moving tectonic plate above the hot spot. The hot spot forms a volcano, which becomes a Hawaiian Island, and that island moves NW 2-4″ per year. Eventually, that hot spot forms Kauai, Oahu, Molokai, Lanai, Maui and the Big Island of Hawaii.

Why Is The Big Island The Youngest Island? Because it is currently over the 'hot spot.' The Hawaiian hot spot has been active at least 70 million years, producing a volcanic chain that extends 3,750 miles (6,000 km) across the northwest Pacific Ocean

A cutaway view along the Hawaiian island chain showing the inferred mantle plume that has fed the Hawaiian hot spot on the overriding Pacific Plate. The reason for the Hawaiian Island chain's correspondence in location and age is the Hawaiian hot spot, the place where magma rises from deep within the Earth and forms underwater volcanoes that grow to rise above sea level and create islands. The movement carries the volcanic islands away from the hot spot, making them dormant. Meanwhile, new, active volcanoes form at the hot spot, which today is underneath the Big Island (see image below).

Hot Spot Videos: Here are educational videos about the Hawaiian Islands 'hot spot.'

The Hawaiian Islands: There are six major islands of Hawaii - Kauai, Oahu, Molokai, Lanai, Maui and the Big Island of Hawaii. Each Hawaiian Island offers a distinctive landscape and appearance that plays a major part in its appeal to locals and visitors alike. You can find a lush, rainforest-covered island (Kauai, the oldest of the main islands), to the active lava flows of the Big Island (the youngest).

The Hawaiian Islands, By Age: The ages of the Hawaiian Islands correspond directly with their current geographical positions. The main islands are positioned in order of age, from oldest to youngest. The oldest Hawaiian Islands are in the northwest and youngest islands are to the southeast:

Kauai is approximately 5.1 million years old

Oahu is approximately 2.2 to 3.4 million years old

Molokai is approximately 1.3 to 1.9 million years old

Lanai, at approximately 1.3 million years

Maui, at 0.8 to 1.3 million years old. T

The Big Island is less than 0.7 million years old

Big Island Volcanoes: Of the Big Island's five volcanoes, Kohala and Mauna Kea are considered dormant, last erupting 60,000 and 4,500 years ago, respectively. For Kona area residents, note that Hualalai hasn't erupted since 1801; Mauna Loa is considered active but has not erupted since 1984. Kilauea has been very active.

Why The Big Island Is The 'Youngest' Island: Pay a visit to Hawaii Volcanoes National Park and you can see fresh lava, days, hours and even minutes old. The Big Island is the newest of all the Hawaiian Islands due to a geologic 'hot spot' combined with tectonic plate movement. As the tectonic plates move, they slide over a fixed 'geologic hot spot.' This hot spot erupts into a volcano as the tectonic plate moves northwest. The hot spot remains stationary, while the Pacific plate moves in a northwesterly direction at a rate of approximately 2 to 4 inches per year.

Hualalai Eruption Pattern Mimics Hawaiian Islands Pattern: Now compare this Google Earth image of Hualalai

The relative age of an island or atoll can be determined based on its state of growth or erosion. The Hawaiian archipelago rides on the Pacific Plate that is moving in a northwesterly direction. The oldest islands in the archipelago are located far to the northwest of the main Hawaiian Islands. The youngest island (Lō'ihi) is forming under the ocean off the eastern coast of the Big Island of Hawai'i.

Volcanoes National Park: Pay a visit to Hawaii Volcanoes National Park and you can see fresh, Kilauea Volcano lava, days, hours and even minutes old.

The Eight Stages Of Hawaiian Island Formation: Hawaiian volcanic islands have been forming over a hot spot on the ocean floor for millions of years. There are eight stages in the development of the Hawaiian islands (and eventual erosion). The stages are:

1. Initial - deep submarine stage - earliest formation of building from the ocean floor

2. Submarine - shield-building stage - growing larger nearing surface but still underwater

3. Sea level - shield-building stage - emerging at the surface of the water

4. Subaerial - shield-building stage - above water growth period, the mountain is growing

5. Capping stage - activity stops temporarily

6. Erosional stage - reef growth - weathering and erosion happen and reefs begin to form

7. Renewed volcanism stage - cinder cones and ash cones form from smaller eruptions

8. Atoll stage - weathering and erosion have reduced volcano back to near sea level

Examples Of The Island Formation Stages: The island of Hawai'i is approaching mid-life, while Lō'ihi (still submerged) is still in the deep submarine stage. By contrast, Kure and Midway atolls are in the final stages of the life cycle of an island.

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How The Hawaii Volcanic 'Hot Spot' Created The Hawaiian Islands

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What Is A Volcanic 'Hot Spot' And What Does That Have To Do With Hawaiian Island Formation? A volcanic hot spot is an upwelling in the earth's mantle. Magma rises up through the earth and as magma escapes, it forms a volcano.