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Article of Mt. St. Helens (Washington State)

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Article of Mt. St. Helens (Washington State)

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Forty years ago, after two months of earthquakes and small explosions, Mount St. Helens cataclysmically erupted. A high-speed blast leveled millions of trees and ripped soil from bedrock. The eruption fed a towering plume of ash for more than nine hours, and winds carried the ash hundreds of miles away. Lahars (volcanic mudflows) carried large boulders and logs, which destroyed forests, bridges, roads and buildings. These catastrophic events led to 57 deaths, including that of David Johnston, a dedicated USGS scientist, and caused the worst volcanic disaster in the recorded history of the conterminous United States.

Had we known then what we know today about volcanoes, could the loss of life and economic damage caused by the Mount St. Helens eruption have been prevented or mitigated?

For the answer, let's travel forward to the present. Over the past 40 years, technology and the scientific study of volcanoes have made significant advances. Better cooperation, monitoring and forecasting possibly could have allowed for earlier evacuations, hazard mitigation and reduced risk. But the truth is the eruption of Mount St. Helens sparked the advances in cutting-edge volcano science and monitoring that exist today.

Mount St. Helens turned out to be the ideal laboratory to study volcanic activity. The 1980 eruption was the first large explosive eruption studied by scientists and observers using modern volcanology. The volcano was also easily viewed and accessible. As a result, the eruption and its effects were heavily photographed from numerous vantage points. The debris avalanche opened the cone, and scientists were able to inspect its interior in a new and novel way. The eruption jump-started interest in the study of explosive eruptions and monitoring efforts to improve warning systems that help mitigate hazards. The eruption underscored the importance of using as many monitoring tools as possible to track unrest and eruption activity.

The north flank collapse and eruption at Mount St. Helens also informed volcano scientists on how to interpret the hummocky terrain near other Cascades volcanoes, such as California's Mt. Shasta. We now know that type of terrain is evidence of a past flank collapse at that volcano about between 300,000 and 380,000 years ago that occurred without an eruption.

Before 1980, scientists saw sharp divisions among volcano hazard studies, volcano monitoring and basic volcanology research. The 1980 eruption, however, required scientists to work together in a more integrated manner. Mount St. Helens changed the way that scientists do business by linking specialists from many disciplines. Now, 40 years later, it is routine for geologists, seismologists, geophysicists, hydrologists, geochemists and biologists to cooperate in studies of natural science processes resulting in well-integrated research, monitoring and communication.

The eruption also led to a new era of volcanic monitoring. During studies at Mount St. Helens, scientists refined their interpretations of monitoring data in order to better forecast future eruptions. Earthquakes, ground deformation and gas measurements took on new meaning as the volcano demonstrated that patterns of change could help scientists forecast lava-dome building eruptions. Scientists now use similar patterns of change to forecast future activity at volcanoes around the world.

Since the eruption of Mount St. Helens, volcano monitoring has evolved from placing a few scientific instruments on a volcano's flanks to a broader integrated network of monitoring devices that measure earthquakes, deformation and volcanic gases, and can detect eruptions or changes on the Earth's surface from space. The evolution of tools like photogrammetry, Geographic Information Systems (GIS), and Light Detection and Ranging (lidar) enable scientists to make precise measurements and illustrations of changes to Earth's surface, including inflation and deflation at volcanoes. Technological revolutions in telemetry, broad-band seismometer technology, and low-power instrumentation are fueling a new era of volcano monitoring equipment capable of collecting and transmitting real-time data remotely with increased precision, efficiency, portability and value, and with reduced risk to scientists.

The explosive eruption of May 18, 1980, illustrates the importance of developing new tools for measuring ground deformation at explosive volcanoes. Tiltmeters and surveying instruments were the only instruments available for monitoring the large .9- to 1.2-mile bulge (1.5 by 2 km) in the north face of Mount St. Helens in 1980. Today, scientists can remotely use high-precision Global Positioning System receivers, sophisticated borehole tiltmeters and strainmeters, and other sensors to measure and report even small amounts of deformation at the centimeter scale continuously and in real time. In addition, using a remote sensing technique called InSAR (interferometric synthetic aperture radar), they combine satellite radar images to map ground deformation in remarkable detail over large areas. With the experience gained at Mount St. Helens, new deformation monitoring tools have enabled scientists to reduce risks to lives and property globally.

The Mount St. Helens eruption also gave credibility to U.S. volcanologists who were subsequently invited to participate in the response to volcanic crises in other countries. Scientists at the U.S. Geological Survey (USGS) Cascades Volcano Observatory, for example, developed a mobile observatory to help respond to quickly developing volcanic situations. This rapid-deployment capability led to the formation of the Volcano Disaster Assistance Program, which is co-funded by the U.S. Agency for International Development (USAID) and the USGS. VDAP scientists have traveled to volcanoes world-wide to share their experience at Mount St. Helens and to learn from other volcanic events. Since 1986, VDAP has responded to more than two dozen major volcanic crises in a dozen countries.

Now, let's step into to the future. The eruption of Mount St. Helens has influenced volcanology in many ways, and the next step in this evolution is the National Volcano Early Warning System, or NVEWS. In March 2019, USGS was authorized by Congress to develop and implement NVEWS to more fully monitor volcanoes and to warn and protect citizens of the United States from danger caused by volcanic activity. When NVEWS is fully implemented, all hazardous U.S. volcanoes will be monitored at levels consistent with the threat they pose to communities, infrastructure and aviation. Pro-active early warning of a potential eruption is key to minimizing loss of life and economic disruption by increasing the time that emergency managers can initiate mitigation measures, improve evacuation alerts and better position resources for recovery. Earliest detection of eruption precursors with multiple instrument types allows for more accurate forecasts of hazardous eruptive activity needed by land managers and the aviation sector.

As we reflect on the influences of the Mount St. Helens eruption over the last 40 years, we should remember that many volcanoes are basically unstable mountains. They grow by piling up lava and ash into cones with steep-sided slopes that are prone to collapse causing massive landslides known as debris avalanches. The debris avalanche caused by the 1980 eruption was the third large debris avalanche known to have happened there in the last 20,000 years. By understanding its history, scientists know that over time Mount St. Helens will be rebuilt again, a process already evident in the volcano's 2004 eruptive events.

To learn more about how the eruption influenced Volcanology please read, " Ten Ways Mount St. Helens Changed Our World-The Enduring Legacy of the 1980 Eruption."

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Mount St. Helens' 1980 Eruption Changed the Future of Volcanology

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Forty years ago, after two months of earthquakes and small explosions, Mount St. Helens cataclysmically erupted. A high-speed blast leveled millions of trees and ripped soil from bedrock. The eruption fed a towering plume of ash for more than nine hours, and winds carried the ash hundreds of miles away.

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Get more information about volcanoes from National Geographic.

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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 come in many different shapes and sizes but are most commonly cone-shaped hills or mountains. They are found throughout the world, forming ridges deep below the sea surface and mountains that are thousands of meters high. About 1,900 volcanoes on Earth are considered active, meaning they show some level of occasional activity and are likely to erupt again. Many others are dormant volcanoes, showing no current signs of exploding but likely to become active at some point in the future. Others are considered extinct. 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 Most volcanoes form at the boundaries of Earth's tectonic plates. These plates are huge slabs of the Earth's crust and upper mantle, which fit together like pieces of a puzzle. These plates are not fixed, but are constantly moving at a very slow rate. They move only a few centimeters per year. Sometimes, the plates collide with one another or move apart. Volcanoes are most common in these geologically active boundaries. 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. The Atlantic Ocean is home to a divergent plate boundary, a place called the Mid-Atlantic Ridge. Here, the North American and Eurasian tectonic plates are moving in opposite directions. Along the Mid-Atlantic Ridge, hot magma swells upward and becomes part of the North American and Eurasian plates. The upward movement and eventual cooling of this buoyant magma creates high ridges on the ocean floor. These ridges are interconnected, forming a continuous volcanic mountain range nearly 60,000 kilometers (37,000 miles)-the longest in the world. Another divergent plate boundary is the East Pacific Rise, which separates the massive Pacific plate from the Nazca, Cocos, and North American plates. Vents and fractures (also called fissures) in these mid-ocean ridges allow magma and gases to escape into the ocean. This submarine volcanic activity accounts for roughly 75% of the average annual volume of magma that reaches the Earth's crust. Most submarine volcanoes are found on ridges thousands of meters below the ocean surface. Some ocean ridges reach the ocean surface and create landforms. The island of Iceland is a part of the Mid-Atlantic Ridge. The diverging Eurasian and North American plates caused the eruptions of Eyjafjallajökull (in 2010) and Bardarbunga (in 2014). These eruptions were preceded by significant rifting and cracking on the ground surface, which are also emblematic of diverging plate movement. 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 BoundariesAt 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 majority of volcanic arcs can be found in the Ring of Fire, a horseshoe-shaped string of about 425 volcanoes that edges the Pacific Ocean. If you were to drain the water out of the Pacific Ocean, you would see a series of deep canyons (trenches) running parallel to corresponding volcanic islands and mountain ranges. The Aleutian Islands, stretching from Alaska to Russia in the Bering Sea, for instance, run parallel to the Aleutian Trench, formed as the Pacific plate subducts under the North American plate. The Aleutian Islands have 27 of the United States' 65 historically active volcanoes. 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 Hawaii-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 Idaho. The Yellowstone hot spot fuels the geysers, hot springs, and other geologic activity at Yellowstone National Park, Wyoming. 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 Earth'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 the 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. Stratovolcanoes Stratovolcanoes are some of the most easily recognizable and imposing volcanoes, with steep, conic peaks rising up to several thousand meters above the landscape. Also known as composite volcanoes, they are made up of layers of lava, volcanic ash, and fragmented rocks. These layers are built up over time as the volcano erupts through a vent or group of vents at the summit's crater. Mount Rainier is an impressive stratovolcano that rises 4,392 meters (14,410 feet) above sea level just south of Seattle, Washington. Over the past half million years, Mount Rainier has produced a series of alternating lava eruptions and debris eruptions. These eruptions have given Mount Rainier the classic layered structure and conic shape of a composite volcano. The volcano's peak has also been carved down by a series of glaciers, giving it a craggy and rugged shape. 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 Shield volcanoes are built almost exclusively of lava, which flows out in all directions during an eruption. These flows, made of highly fluid basalt lava, spread over great distances and cool in thin layers. Over time, the layers build up and create a gently sloping dome that looks like a warrior's shield. While they are not as eye-catching as their steep stratovolcano cousins, shield volcanoes are often much larger in volume because of their broad, expansive structure. Shield volcanoes make up the entirety of the Hawaiian Islands. The Kilauea and Mauna Loa shield volcanoes, located on the "Big Island" of Hawaii, 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." prolific type of volcano on Earth. They can develop as part of stratovolcanoes, shield volcanoes, or independently. Also known as cinder cones, they form after violent eruptions blow lava into the air. In the atmosphere, the lava fragments solidify and fall as "cinders" around a singular vent. Often formed from a single eruption or short series of eruptions, pyroclastic cones only stand at heights of tens of meters to hundreds of meters. 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% 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. One of the most iconic lava domes developed after the devastating 1902 eruption of Mount Pelée on the island of Martinique. For almost a year, a lava dome grew out of a summit crater created from the eruption, reaching a height of more than 300 meters (1,000 feet). Known as the Tower of Pelée, the obelisk-shaped structure was twice the height of the Washington Monument. It ultimately collapsed into a pile of rubble after 11 months of growth. Other Important Volcanic Features CalderasSome volcanoes experience such large, explosive eruptions that they release most of the material in their magma chamber. This causes the land around the erupting vent or vents to collapse inwardly, creating circular depressions called calderas. Depending on their intensity and duration, volcanic eruptions can create calderas as much as 100 kilometers wide. Crater Lake, Oregon, is in a caldera about 10 kilometers (6 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. Deception Island, located off the coast of Antarctica, experienced a violent eruption roughly 10,000 years ago. The volcano summit collapsed, forming a caldera 7 kilometers (4.4 miles) wide and flooded with seawater. The caldera gives Deception Island its horseshoe shape, which opens to the sea through a narrow channel. Deception Island's unique geologic structure makes it one of the only places in the world where ocean vessels can sail directly into an active volcano. CratersMuch 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 (.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. Hawaiian Hawaiian eruptions are the calmest eruption type. They are characterized by steady lava eruptions known as lava fountains or fire fountains. Lava fountains are able to reach heights of up to 2 kilometers (1.2 miles). The highly fluid lava associated with Hawaiian eruptions flows easily away from the volcano summit, often creating fiery rivers and lakes of lava within depressions on the surrounding landscape. 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 Hawaii. 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. VulcanianVulcanian eruptions are short-lived but much more explosive than Strombolian eruptions. Very thick lava causes gas pressure to build up in the magma chamber. When this pressure is finally released it creates canon-like explosions that can travel faster than 350 meters per second (800 miles per hour). Lava, rock, and ash are propelled up to 20 kilometers (12.4 miles) in the air, although most eruption columns are between 5 and 10 kilometers high. These plumes of material have the ability to drift moderate distances away from the eruption site. The 2013 vulcanian eruption of Sakurajima, on the island of Kyushu, Japan, covered the nearby city of Kagoshima in a thick coat of ash. Plinian Reaching as high as 50 kilometers (35 miles) in the atmosphere, Plinian eruptions are the largest of all eruption types. Much like vulcanian eruptions, they eject materials at speeds of hundreds of meters per second. Plinian eruptions, however, are more sustained than the coughing fits of vulcanian eruptions. These consistent eruptions result from the volcano's magma and growing gas bubbles rising at a similar velocity. Plinian eruptions are the most destructive type of eruption. They release a deadly mixture of lava, ash, and volcanic rocks such as scoria and pumice, which can fall kilometers away from the eruption site. They are also characterized by pyroclastic flow, a fluid mixture of fragmented materials and extremely hot, toxic gases. In 79 CE, 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. SurtseyanSurtseyan eruptions occur where magma or lava interacts with water, most often when an undersea volcano reaches the ocean surface. Another term for this sort of interaction is a phreatomagmatic eruption. When heated rapidly by lava, water flashes to steam and expands violently, creating the most explosive of all eruption types. This aggressive interaction between water and heat is able to fragment lava into very fine grains of ash that can reach heights of 20 kilometers (12.4 miles). 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 5 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 Volcanoes are some of Earth's most potent natural hazards and agents of change. They release enormous amounts of energy and material, engaging natural processes that can modify landscapes at a local, regional, and even global scale. Many volcanic materials and processes pose a threat to human, animal, and other ecological communities. Volcanic GasVolcanoes regularly release volcanic gases that can be dangerous at concentrated levels. Carbon dioxide and fluorine can collect in soil or volcanic ash, causing crop failure, animal death and deformity, and human illness. Volcanic eruptions can also release massive amounts of sulfur dioxide, which rises into the stratosphere. There, it reflects incoming solar radiation while absorbing outgoing land radiation, leading to a cooling of the Earth's temperature. 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. Landslides can mix with surrounding rivers, ice, snow, or rain to produce watery mixtures called lahars. This mixture of water, rock, and debris creates a sludge that can obliterate almost anything in its path. The 1985 eruption of Nevado del Ruiz, Colombia, caused small lahars of rock, ash, and melted snow to flow down into the surrounding river valleys. The lahars gained momentum and size as they traveled the riverbeds, ultimately destroying more than 5,000 homes and killing more than 23,000 people. Pyroclastic FlowsExplosive 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 CE, new studies suggest that they actually died from extreme heat produced by the volcano's pyroclastic flow. Volcanologist Giuseppe Mastrolorenzo and the Italian National Institute for Geophysics and Volcanology recently discovered that the pyroclastic flow that reached Pompeii produced temperatures of up to 300° Celsius (570° Fahrenheit). These extreme temperatures are able to kill people in a fraction of a second, causing them to spasm in contorted postures like those found amongst the plaster Pyroclastic ConesPyroclastic cones are the most casts of Vesuvius' victims. Volcanic Ash Huge plumes of volcanic ash can spread over large areas of the sky, turning daylight into complete darkness and inhibiting air traffic. (During the eruption of Iceland's Eyjafjallajökull in 2011, flights to and from northern Europe were suspended for more than a week.) Volcanic ash conducts electricity when wet and can contain concentrated levels of toxic materials, posing threats to humans that come in close contact with it on land. 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 2 feet) deep. Rains turned the ash into a cement-like substance that was heavy enough to collapse 80% 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. Volcanologists predict volcanic activity by taking real-time measurements and comparing them against what happened in the past. They use a variety of instruments and technologies to monitor temperatures, gas emissions, water levels, ground movements, and changes in the landscape. These measurements paint a clear portrait of a volcano's current state, which volcanologists then interpret against historical data. Volcanologists issue eruption warnings when these measurements stray far from the norm or mirror those that preceded a historic eruption. Different countries use different systems to issue eruption warnings to the public. All of these systems categorize their alerts based on the probability and severity of an impending eruption. Typical volcanic behavior is often represented by the number 1 or the color green, while an imminent and potentially destructive eruption is typically represented by the number 4 or the color red. 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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Plate Tectonics and Volcanic Activity | National Geographic Society

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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.

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https://oceanexplorer.noaa.gov/facts/plate-boundaries.html

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The Earth's lithosphere, which includes the crust and upper mantle, is made up of a series of pieces, or tectonic plates, that move slowly over time.

A divergent boundary occurs when two tectonic plates move away from each other. Along these boundaries, earthquakes are common and magma (molten rock) rises from the Earth's mantle to the surface, solidifying to create new oceanic crust. The Mid-Atlantic Ridge is an example of divergent plate boundaries.

When two plates come together, it is known as a convergent boundary. The impact of the colliding plates can cause the edges of one or both plates to buckle up into a mountain ranges or one of the plates may bend down into a deep seafloor trench. A chain of volcanoes often forms parallel to convergent plate boundaries and powerful earthquakes are common along these boundaries. The Pacific Ring of Fire is an example of a convergent plate boundary.

At convergent plate boundaries, oceanic crust is often forced down into the mantle where it begins to melt. Magma rises into and through the other plate, solidifying into granite, the rock that makes up the continents. Thus, at convergent boundaries, continental crust is created and oceanic crust is destroyed.

Two plates sliding past each other forms a transform plate boundary. One of the most famous transform plate boundaries occurs at the San Andreas fault zone, which extends underwater. Natural or human-made structures that cross a transform boundary are offset - split into pieces and carried in opposite directions. Rocks that line the boundary are pulverized as the plates grind along, creating a linear fault valley or undersea canyon. Earthquakes are common along these faults. In contrast to convergent and divergent boundaries, crust is cracked and broken at transform margins, but is not created or destroyed.

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What are the different types of plate tectonic boundaries?

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The Earth's lithosphere, which includes the crust and upper mantle, is made up of a series of pieces, or tectonic plates, that move slowly over time. A divergent boundary occurs when two tectonic plates move away from each other.

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The most destructive explosion on earth in the past 10,000 years was the eruption of an obscure volcano in Indonesia called MountTambora. More than 13,000 feet high, Tambora blew up in 1815 and blasted 12 cubic miles of gases, dust and rock into the atmosphere and onto the island of Sumbawa and the surrounding area. Rivers of incandescent ash poured down the mountain's flanks and burned grasslands and forests. The ground shook, sending tsunamis racing across the JavaSea. An estimated 10,000 of the island's inhabitants died instantly.

It's the eruption's far-flung consequences, however, that have most intrigued scholars and scientists. They have studied how debris from the volcano shrouded and chilled parts of the planet for many months, contributing to crop failure and famine in North America and epidemics in Europe. Climate experts believe that Tambora was partly responsible for the unseasonable chill that afflicted much of the Northern Hemisphere in 1816, known as the "year without a summer." Tamboran gloom may have even played a part in the creation of one of the 19th century's most enduring fictional characters, Dr. Frankenstein's monster.

The eruption of Tambora was ten times more powerful than that of Krakatau, which is 900 miles away. But Krakatau is more widely known, partly because it erupted in 1883, after the invention of the telegraph, which spread the news quickly. Word of Tambora traveled no faster than a sailing ship, limiting its notoriety. In my 40 years of geological work I had never heard of Tambora until a couple of years ago when I started researching a book on enormous natural disasters.

The more I learned about the eruption of Tambora, the more intrigued I became, convinced that few events in history show more dramatically how earth, its atmosphere and its inhabitants are interdependent-an important matter given concerns such as global warming and destruction of the atmosphere's protective ozone layer. So when the chance arose to visit the volcano while on a trip last fall to Bali and other Spice Islands, I took it.

Indonesia's Directorate of Volcanology and Geologic Hazard Mitigation said that I should not attempt to climb Tambora-too dangerous. As my guide would later tell me, the name of the mountain means "gone" in a local language, as in people who have vanished on its slopes. But researchers who have studied the volcano encouraged me. "Is it worth it?" I asked Steve Carey, a volcanologist at the University of Rhode Island, who has made the climb. "Oh, my!" he said. That was all I needed to hear.

Through a travel agent in Bima, a city on Sumbawa, a friend and I hired a guide, a translator, a driver, a driver's mate, a cook and six porters. We filled a van and traveled for hours, weaving among horse-drawn carriages (known locally as Ben-Hurs, after the chariots in the movie) as we headed for Tambora's southern slope. The parched terrain was like savanna, covered with tall grasses and only a few trees. A few hours west of Bima, the huge bulk of Tambora begins to dominate the horizon. Formerly a cone or double-cone, it's now shaped like a turtle's shell: the eruption reduced the mountain's height by more than 4,000 feet.

We camped a third of the way up the mountain, and set out at dawn for the summit, wending around boulders the size of small cars that were tossed like pebbles from the erupting volcano nearly two centuries ago. Our guide, Rahim, chose a trail that switched back and forth for about four miles. The day was warm and humid, the temperature in the 70s. Grasses in places were charred black, burned by hunters in pursuit of deer.

I was excited to approach the site of one of the most important geological events since human beings first walked the planet. Yet as I looked up at the mountain, I realized I had another purpose in mind. The climb was a chance to reassure myself that after treatment for two kinds of cancer in the past decade, I could still master such a challenge. For me, then, it was a test. For the two porters, striding along in flip-flops, it was a pleasant stroll in the country.

In repose for thousands of years, the volcano began rumbling in early April of 1815. Soldiers hundreds of miles away on Java, thinking they heard cannon fire, went looking for a battle. Then, on April 10, came the volcano's terrible finale: three columns of fire shot from the mountain, and a plume of smoke and gas reached 25 miles into the atmosphere. Fire-generated winds uprooted trees. Pyroclastic flows, or incandescent ash, poured down the slopes at more than 100 miles an hour, destroying everything in their paths and boiling and hissing into the sea 25 miles away. Huge floating rafts of pumice trapped ships at harbor.

Throughout the region, ash rained down for weeks. Houses hundreds of miles from the mountain collapsed under the debris. Sources of fresh water, always scarce, became contaminated. Crops and forests died. All told, it was the deadliest eruption in history, killing an estimated 90,000 people on Sumbawa and neighboring Lombok, most of them by starvation. The major eruptions ended in mid-July, but Tambora's ejecta would have profound, enduring effects. Great quantities of sulfurous gas from the volcano mixed with water vapor in the air. Propelled by stratospheric winds, a haze of sulfuric acid aerosol, ash and dust circled the earth and blocked sunlight.

In China and Tibet, unseasonably cold weather killed trees, rice, and even water buffalo. Floods ruined surviving crops. In the northeastern United States, the weather in mid-May of 1816 turned "backward," as locals put it, with summer frost striking New England and as far south as Virginia. "In June . . . another snowfall came and folk went sleighing," Pharaoh Chesney, of Virginia, would later recall. "On July 4, water froze in cisterns and snow fell again, with Independence Day celebrants moving inside churches where hearth fires warmed things a mite." Thomas Jefferson, having retired to Monticello after completing his second term as President, had such a poor corn crop that year that he applied for a $1,000 loan.

Failing crops and rising prices in 1815 and 1816 threatened American farmers. Odd as it may seem, the settling of the American heartland was apparently shaped by the eruption of a volcano 10,000 miles away. Thousands left New England for what they hoped would be a more hospitable climate west of the Ohio River. Partly as a result of such migration, Indiana became a state in 1816 and Illinois in 1818.

Climate experts say that 1816 wasn't the coldest year on record, but the long cold snap that coincided with the June-to-September growing season was a hardship. "The summer of 1816 marked the point at which many New England farmers who had weighed the advantages of going west made up their minds to do so," the oceanographer Henry Stommel and his wife, Elizabeth, wrote in their 1983 book about Tambora's global effects, Volcano Weather. If the ruinous weather wasn't the only reason for the emigration, they note, it played a major part. They cite historian L. D. Stillwell, who estimated that twice the usual number of people left Vermont in 1816 and 1817-a loss of some 10,000 to 15,000 people, erasing seven years of growth in the Green Mountain State.

In Europe and Great Britain, far more than the usual amount of rain fell in the summer of 1816. It rained nonstop in Ireland for eight weeks. The potato crop failed. Famine ensued. The widespread failure of corn and wheat crops in Europe and Great Britain led to what historian John D. Post has called "the last great subsistence crisis in the western world." After hunger came disease. Typhus broke out in Ireland late in 1816, killing thousands, and over the next couple of years spread through the British Isles.

Researchers today are careful not to blame every misery of those years on the Tambora eruption, because by 1815 a cooling trend was already under way. Also, there's little evidence that the eruption affected climate in the Southern Hemisphere. In much of the Northern Hemisphere, though, there prevailed "rather sudden and often extreme changes in surface weather after the eruption of Tambora, lasting from one to three years," according to a 1992 collection of scientific studies titled The Year Without a Summer?: World Climate in 1816.

In Switzerland, the damp and dark year of 1816 stimulated Gothic imaginings that still entertain us. Vacationing near Lake Geneva that summer, Lord Byron, Percy Bysshe Shelley and his soon-to-be wife, Mary Wollstonecraft, and some friends sat out a June storm reading a collection of German ghost stories. The mood was captured in Byron's "Darkness," a narrative poem set when the "bright sun was extinguish'd" and "Morn came and went-and came, and brought no day." He challenged his companions to write their own macabre stories. John Polidori wrote The Vampyre, and the future Mary Shelley, who would later recall that inspirational season as "cold and rainy," began work on her novel, Frankenstein, about a well-meaning scientist who creates a nameless monster from body parts and brings it to life by a jolt of laboratory-harnessed lightning.

For Mary Shelley, Frankenstein was primarily an entertainment to "quicken the beatings of the heart," she wrote, but it has also long served as a warning not to overlook the consequences of humanity's tampering with nature. Fittingly, perhaps, the eruption that probably influenced the invention of that morality tale has, nearly two centuries later, taught me a similar lesson about the dangers of humanity's fouling our own atmosphere.

After several hours of hard, slow climbing, during which I stopped frequently to drink water and catch my breath, we reached the precipice that is the southern rim of Tambora. I stared in silent awe down the volcano's throat. Clouds on the far side of the great crater formed and reformed in the light breeze. A solitary raptor sailed the currents and updrafts.

Three thousand feet deep and more than three miles across, the crater was as barren as it was vast, with not a single blade of grass in its bowl. Enormous piles of rubble, or scree, lay at the base of the steep crater walls. The floor was brown, flat and dry, with no trace of the lake that is said to collect there sometimes. Occasional whiffs of sulfurous gases warned us that Tambora is still active.

We lingered at the rim for a couple of hours, talking quietly and shaking our heads at the immensity before us. I tried to conceive of the unimaginable noise and power of the eruption, which volcanologists have classified as "super-colossal." I would have liked to stay there much longer. When it was time to go, Rahim, knowing that I would probably never return, suggested I say good-bye to Tambora, and I did. He stood at the rim, whispering a prayer to the spirits of the mountain upon whose flanks he has lived most of his life. Then we made our descent.

Looking into that crater, and having familiarized myself with others' research on the consequences of the eruption, I saw as if for the first time how the planet and its life-forms are linked. The material that it ejected into the atmosphere perturbed climate, destroyed crops, spurred disease, made some people go hungry and others migrate. Tambora also opened my eyes to the idea that what human beings put into the atmosphere may have profound impacts. Interestingly, scientists who study global climate trends use Tambora as a benchmark, identifying the period 1815 to 1816 in ice cores from Greenland and Antarctica by their unusually high sulfur content-signature of a great upheaval long ago and a world away.

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The most destructive explosion on earth in the past 10,000 years was the eruption of an obscure volcano in Indonesia called MountTambora. More than 13,000 feet high, Tambora blew up in 1815 and blasted 12 cubic miles of gases, dust and rock into the atmosphere and onto the island of Sumbawa and the surrounding area.

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On August 24, after centuries of dormancy, Mount Vesuvius erupts in southern Italy, devastating the prosperous Roman cities of Pompeii and Herculaneum and