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Weathering for Kids | What Is Weathering? Fun Introduction to Weathering for Kids

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Weathering is the breaking down of Rock (geology) rocks, soil and their minerals through direct contact with the Earth's atmosphere, waters, or living things. It is a natural process.

Weathering occurs in one place with little or no movement, and should not be confused with erosion which is when rocks and minerals are moved to another place by ice, water, wind or gravity.

Mechanical weathering

Mechanical or physical weathering is when the rocks and minerals are broken down but the Chemical composition remains the same. Mechanical weathering physically breaks up rock.

Wind can blow water or small particles such as sand against the rock thus breaking it down. The wind blowing over your skin removes body heat.local winds are the winds that blow over short distances.

Rain is another force that works slowly. The force of raindrops on some rocks make them wear down. Rain also can make a chemical change in some rocks, because it is usually slightly acidic. The water mixes with the minerals in the rock to break it down.

Temperature

Changing temperature can make a rock crack. Every day when the sun shines on the rock, its surface is heated. Heat causes the surface to expand (get bigger) a little. The inside of the rock, though, does not heat up as fast as the outside of the rock. The inside of the rock stays cooler. At night, the surface cools down and contracts. The expanding and contracting makes some places on the surface weak, and a crack is made.

Also, if water gets into a crack in a rock and the temperature goes below the freezing point, the water will freeze and expand. After some time, the rock may be weak enough to break into pieces.

Ice, which can be miles thick, grinds the surface of the rock below it. The particles are carried with the ice, and if a glacier ends up in the sea, so does all the material carried with it.

Lava or magma

Lava or magma can cause weathering when molten rock touches older rock. It causes the older rock to change form to a different crystal structure.

Chemical weathering

Chemical weathering is the breaking down of rock which changes the chemical composition.

Carbon dioxide cycle

The carbon dioxide cycle is the most important for weathering. CO ₂ is put into the atmosphere mostly by volcanoes, and it is taken out of the atmosphere by photosynthesis, and by one other process.

While it is in the air, CO ₂ can dissolve in water droplets to form weak carbonic acid.

When rain hits rock it does so with mechanical energy and dilute acid. The acid dissolves many types of minerals and rocks though, of course, very slowly. When a mineral like feldspar is dissolved, it lets sodium ions into the sea; chlorine ions come from other minerals. The sea tastes salty because of the elements which have been dissolved out of rocks.

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Images for kids

Wave action and water chemistry lead to structural failure in exposed rocks.

Pressure release could have caused the exfoliated granite sheets shown in the picture.

Weathering effect on a sandstone statue in Dresden, Germany.

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Weathering is the breaking down of Rock (geology) rocks, soil and their minerals through direct contact with the Earth's atmosphere, waters, or living things. It is a natural process. Weathering occurs in one place with little or no movement, and should not be confused with erosion which is when rocks and minerals are moved to another place by ice, water, wind or gravity.

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The forces that cause weathering may be physical, chemical, or biological. Often, weathering results from a combination of forces.

Physical forces include changes in temperature or pressure, freezing or moving water, and wind. An increase in temperature may cause rock to expand. As the rock cools, it contracts, or shrinks. The expanding and contracting may cause the rock to crack and break apart. If heavy material on top of a rock is removed (by a glacier, for example), the pressure on the rock decreases. The release of pressure may cause the rock to split. Water that freezes inside cracks in a rock may widen the cracks. Particles carried by water or wind may slowly scrape away a rock's surface.

In chemical weathering, the minerals that make up the rock are changed. Water usually is involved in chemical weathering. Elements in the water may react with the minerals in the rock. The minerals may break down or form different minerals.

Biological weathering results from the actions of living things. The roots of plants may reach inside rock openings. Over time, they may push apart sections of rock. Lichens grow on rock surfaces or within cracks. They may wear down rock or etch patterns on its surface.

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Weathering is a natural process that slowly breaks apart or changes rock. Heat, water, wind, living things, and other natural forces cause weathering. Over many years,...

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What Is Pangaea & Plate Tectonic? | CONTINENTAL DRIFT | The Dr Binocs Show | Peekaboo Kidz

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Volcano | The Dr. Binocs Show | Learn Videos For Kids

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Earthquakes for Kids STEM | Learn why earthquakes happen and how to measure them

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Erosion is a process where natural forces like water, wind, ice, and gravity wear away rocks and soil. It is a geological process, and part of the rock cycle. Erosion occurs at the Earth's surface, and has no effect on the Earth's mantle and core.

Most of the energy that makes erosion happen is provided by the Sun. The Sun's energy causes the movement of water and ice in the water cycle and the movement of air to create wind.

Erosion can cause problems that affect humans. Soil erosion, for example, can create problems for farmers. Soil erosion can remove soil, leaving a thin layer or rocky soil behind. Erosion can also cause problems for humans by removing rocks or soil that support buildings.

Erosion by water

Temperature changes cause pieces of rock to flake away from the surface. Also, the acid in rainwater dissolves rocks containing calcium carbonate. These processes are called weathering.

Water erosion happens when water moves the pieces of rock or soil downhill. Waves also carry away small pieces of material. A wave can wash up onto the surface of rock or soil and then carry away pieces of material as it flows back into the ocean or lake.

The size of earth materials that can be moved by water depends on how fast the water is moving. A fast-flowing stream can carry large rocks while a slow moving stream might only be able to carry very small things like clay. Canyons, like the Grand Canyon, are among the most obvious features made by erosion. Where a river meets the sea, it drops the solids, sometimes making a river delta.

Tropical rivers

Large tropical rivers like the Paraná, Indus, Brahmaputra, Ganges, Zambezi, Mississippi and the Amazon carry huge amounts of sediment down to the sea. The Nile, perhaps the world's longest river, carries much less sediment than the others because, part of the way, it runs through less fertile regions than the other great rivers.

The Amazon has by far the largest waterflow, with an average discharge greater than the next seven largest rivers combined. It has the largest drainage basin in the world, about 7,050,000 square kilometres (2,720,000 sq mi). The Amazon accounts for about one-fifth of the world's total river flow.

The sediment discharged by the gigantic mouth of the Amazon stains the sea brown for hundreds of miles out to sea.

Erosion by ice

Ice erosion happens when a glacier moves downhill. As the ice of the glacier moves downhill, it pushes and pulls earth materials along with it. Glaciers can move very large rocks. Ice erosion can happen in another way. Cold weather causes water inside tiny cracks in rocks to freeze. As it freezes, the ice gets bigger, and pushes hard against the rock. This can break the rock.

Erosion by wind

Wind erosion occurs when wind moves pieces of earth materials. Wind erosion is one of the weakest kinds of erosion. Small pieces of earth material can be rolled along the ground surface by wind. Very small pieces can be picked up and carried by the wind. Sometimes, wind can carry small pieces of earth materials over large distances. Some sediment from the Sahara Desert is carried across the Atlantic Ocean by wind.

One of the most famous examples of wind erosion occurred in the Dust Bowl, when wind erosion severely damaged farming communities.

Erosion by gravity

Gravity erosion is the simplest kind of erosion. Gravity simply pulls loose earth materials downhill. Landslides are dramatic examples of gravity erosion.

Erosion and tectonics

Tectonic effects on erosion has long been recognized. For example, rivers form as a result of tectonic uplift (as Himalayas and Tibetan Plateau). All of the Earth's mountain ranges were created by the upward movement of the land by changes beneath the Earth's surface. When the ground rises the whole weather system can also be changed including local sea levels, wind strength and direction, rainfall and more.

The Earth's landscape is a product of two factors. Tectonics builds up height by surface and rock uplift, and climate controls the erosion. Erosion wears away upland areas over time. The interaction of these processes can form, modify, or destroy features of the Earth's surface.

Images for kids

Wave cut platform caused by erosion of cliffs by the sea, at Southerndown in South Wales

In Spanish: Erosión para niños

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Continental drift is a historical, scientific theory. The theory was first proposed by Abraham Ortelius in 1596. It was fully developed by the German geologist and meteorologist Alfred Wegener in 1915.

The theory said that parts of the Earth's crust move slowly on top of a liquid mantle of higher density. The theory has now been included in the wider theory of plate tectonics.

The theory was supported by finding the same minerals and fossils in western Europe and eastern North America. There are also similar fossils on the western coast of Africa and the eastern South America. The shapes of these continents nearly fit together. The theory was plausible (believable), but there was no known mechanism to drive these great movements. This problem was later solved by plate tectonics.

The pattern of volcanic activity, mountain building ( orogeny) and earthquakes is explained by continental drift. The existence of identical rocks widely apart supports the theory.

Examples (there are hundreds):

1. Fossils of the fern Glossopteris are found in rocks from Australia, South America, Antarctica, India, Africa and Madagascar. These were all together in the supercontinent Gondwana, after the global continent Pangaea broke up.

2. Table Mountain at the Cape of Good Hope, South Africa, and mountains south of Rio de Janeiro are made of identical rocks. This corresponds to the fit of Africa with South America in Pangaea.

3. The Giant's Causeway in Northern Ireland, and Fingal's Cave on Staffa, Inner Hebrides, Scotland is the same rock formation.

The basic machine driving continental movement is heat moving from the Earth's mantle through the crust and out of the planet. The effect of this it to cause convection, and plate movement.

Two events in particular are of huge importance:

1. The production of new crust at places such as the Mid-Atlantic Ridge.

2. The removal of crust by subduction (moving under) at the points where plates collide.

Images for kids

In Spanish: Deriva continental para niños

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A volcanic eruption occurs when hot materials from the Earth's interior are thrown out of a volcano. Lava, rocks, dust, and gas compounds are some of these "ejecta".

Eruptions can come from side branches or from the top of the volcano. Some eruptions are terrible explosions that throw out huge amounts of rock and volcanic ash and can kill many people. Some are quiet outflows of hot lava. Several more complex types of volcanic eruptions have been described by volcanologists. These are often named after famous volcanoes where that type of eruption has been seen. Some volcanoes may show only one type of eruption during a period of activity, while others may show a range of types in a series.

Volcanic explosivity index

The volcanic explosivity index (commonly shortened VEI) is a scale, from 0 to 8, for measuring the strength of eruptions. It is used by the Smithsonian Institution's Global Volcanism Program to assess historic and prehistoric lava flows. It works in a way similar to the Richter scale for earthquakes: each interval in value is a tenfold increase in magnitude (it is logarithmic). Most volcanic eruptions are of VEIs between 0 and 2.

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An example of the lava arcs formed during Strombolian activity. This image is of Stromboli itself.

The lava spine that developed after the 1902 eruption of Mount Pelée

Mount Lamington following the devastating 1951 eruption

Surtsey, erupting 13 days after breaching the water. A tuff ring surrounds the vent.

The fissure formed by the 1886 eruption of Mount Tarawera, an example of a fracture zone eruption

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A volcanic eruption occurs when hot materials from the Earth's interior are thrown out of a volcano. Lava, rocks, dust, and gas compounds are some of these "ejecta". Eruptions can come from side branches or from the top of the volcano.

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An earthquake (or quakes, tremors) is shaking of the surface of earth, caused by sudden movement in the Earth's crust. They can be extremely violent.

Earthquakes are usually quite brief, but may repeat. They are the result of a sudden release of energy in the Earth's crust. This creates seismic waves, which are waves of energy that travel through the Earth. The study of earthquakes is called seismology. Seismology studies the frequency, type and size of earthquakes over a period of time.

There are large earthquakes and small earthquakes. Large earthquakes can take down buildings and cause death and injury. Earthquakes are measured using observations from seismometers. The magnitude of an earthquake, and the intensity of shaking, is usually reported on the Richter scale. On the scale, 3 or less is scarcely noticeable, and magnitude 7 (or more) causes damage over a wide area.

An earthquake under the ocean can cause a tsunami. This can cause just as much death and destruction as the earthquake itself. Landslides can happen, too. Earthquakes are part of the Earth's rock cycle.

The ancient Chinese used a device that looked like a jar with dragons on the top surrounded by frogs with their mouths open. When an earthquake occurred, a ball fitted into each dragon's mouth would drop out of the dragon's mouth into the frog's. The position of the frog which received a ball indicated the direction of the earthquake. This was one of the first tools to help figure out where an earthquake originated from.

Causes of an earthquake

Earthquakes are caused by tectonic movements in the Earth's crust. The main cause is that when tectonic plates collide, one rides over the other, causing orogeny (mountain building), earthquakes and volcanoes.

The boundaries between moving plates form the largest fault surfaces on Earth. When they stick, relative motion between the plates leads to increasing stress. This continues until the stress rises and breaks, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy.

Earthquake fault types

There are three main types of geological fault that may cause an earthquake: normal, reverse (thrust) and strike-slip. Normal faults occur mainly in areas where the crust is being extended. Reverse faults occur in areas where the crust is being shortened. Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other.

Earthquake clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time. Most earthquake clusters consist of small tremors which cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern.

A foreshock is an earthquake that occurs before a larger earthquake, called the mainshock. A foreshock is in the same area of the main shock but always of a smaller magnitude.

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. Aftershocks are formed as the crust adjusts to the effects of the main shock.

Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notably higher magnitudes than the other. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.

Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and with some of the later earthquakes as damaging as the early ones. Such a pattern occurred in the North Anatolian fault in Turkey in the 20th century.

Tsunami or a chain of fast moving waves in the ocean caused by powerful earthquakes is a very serious challenge for people's safety and for earthquake engineering. Those waves can inundate coastal areas, destroy houses and even swipe away whole towns.

Unfortunately, tsunamis can not be prevented. However, there are warning systems which may warn the population before the big waves reach the land to let them enough time to rush to safety.

Earthquake-proofing

Some places, such as Japan or California, have many earthquakes and many inhabitants. There, it is good practice to construct houses and other buildings which will resist collapse in an earthquake. This is called seismic design or " earthquake-proofing".

Earthquake-proof buildings are constructed to withstand the destructive force of an earthquake. This depends upon its type of construction, shape, mass distribution, and rigidity. Different combinations are used. Square, rectangular, and shell-shaped buildings can withstand earthquakes better than skyscrapers. To reduce stress, a building's ground floor can be supported by extremely rigid, hollow columns, while the rest of the building is supported by flexible columns inside the hollow columns. Another method is to use rollers or rubber pads to separate the base columns from the ground, allowing the columns to shake parallel to each other during an earthquake.

To help prevent a roof from collapsing, builders make the roof out of light-weight materials. Outdoor walls are made with stronger and more reinforced materials such as steel or reinforced concrete. During an earthquake flexible windows may help hold the windows together so they don't break.

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Images for kids

Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.

Comparison of the 1985 and 2017 earthquakes on Mexico City, Puebla and Michoacán/Guerrero

Ruins of the Għajn Ħadid Tower, which collapsed during the 1856 Heraklion earthquake

An image from a 1557 book depicting an earthquake in Italy in the 4th century BCE

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An earthquake (or quakes, tremors) is shaking of the surface of earth, caused by sudden movement in the Earth's crust. They can be extremely violent. Earthquakes are usually quite brief, but may repeat. They are the result of a sudden release of energy in the Earth's crust.

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A tsunami is a natural disaster which is a series of fast-moving waves in the ocean caused by powerful earthquakes, volcanic eruptions, landslides, or simply an asteroid or a meteor crash inside the ocean. A tsunami has a very long wavelength. It can be hundreds of kilometers long. Usually, a tsunami starts suddenly. The waves travel at a great speed across an ocean with little energy loss. They can remove sand from beaches, destroy trees, toss and drag vehicles, houses and even destroy whole towns. Tsunamis can even be caused when a meteorite strikes the earth's surface, though it is very rare. A tsunami normally occurs in the Pacific Ocean, especially in what is called the ring of fire, but can occur in any large body of water.

The water often draws back from the seacoast half of the wave period prior to the wave getting to the coast. If the slope of the coast is not steep, the water may pull back for hundreds of meters. People who do not know of the danger often remain at the shore.

Tsunamis cannot be prevented. However, there are ways to help stop people dying from a tsunami. International and regional warning systems, especially for the Pacific Ocean, issue alerts before the big waves reach the shore. Because the earthquake that caused the tsunami can be felt before the wave gets to the shore, people can be warned to go somewhere safe.

Tsunamis are often called tidal waves because they usually rise and fall more slowly than ordinary ocean surface waves. This name is misleading, because tsunamis are not related to tides; they merely rise slowly as a series of fast-moving waves in the ocean caused by powerful earthquakes or volcanic eruptions.

The deadliest tsunami recorded in documented history was on 26 December 2004, and is known as the 2004 Indian Ocean Tsunami. It was caused by an earthquake. The earthquake was said to have a magnitude of 9.3 on the Moment magnitude scale. It was centered in the ocean near the coast of Sumatra, Indonesia. Over 215,000 people, mainly on the shores of the Indian Ocean, died from this disaster. The giant wave moved very quickly. Thousands of people in Indonesia, Sri Lanka, Thailand, India, Somalia, and other nations, were killed or injured by it.

Yet, the most expensive tsunami ever was the 2011 Tōhoku earthquake and tsunami. It is said to have cost the Japanese government around $150 billion, which is equivalent to about 12 trillion yen. It went a huge distance in inland, and is also the 4th largest tsunami in history.

There is another type of tsunami known as a megatsunami, which is mainly due to external impact on the ocean, like an asteroid or meteor crash, a landslide, a rockslide etc.

While Japan may have the longest recorded history of tsunamis, the sheer destruction caused by the 2004 Indian Ocean earthquake and tsunami event mark it as the most devastating of its kind in modern times, killing around 230,000 people. The Sumatran region is also accustomed to tsunamis, with earthquakes of varying magnitudes regularly occurring off the coast of the island.

Of historical and current importance are the 1755 Lisbon earthquake and tsunami (which was caused by the Azores-Gibraltar Transform Fault), the 1783 Calabrian earthquakes, each causing several tens of thousands of deaths and the 1908 Messina earthquake and tsunami. The tsunami claimed more than 123,000 lives in Sicily and Calabria and is among the most deadly natural disasters in modern Europe. The Storegga Slide in the Norwegian Sea and some examples of tsunamis affecting the British Isles refer to landslide and meteotsunamis predominantly and less to earthquake-induced waves.

As early as 426 BC the Greek historian Thucydides inquired in his book History of the Peloponnesian War about the causes of tsunami, and was the first to argue that ocean earthquakes must be the cause.

The Roman historian Ammianus Marcellinus ( Res Gestae 26.10.15-19) described the typical sequence of a tsunami, including an earthquake, the sudden retreat of the sea and a following gigantic wave, after the 365 AD tsunami devastated Alexandria.

The principal generation mechanism of a tsunami is the displacement of a substantial volume of water. This displacement of water is usually attributed to either earthquakes, landslides, volcanic eruptions, glacier calvings or more rarely by meteorites and nuclear tests.

Earthquakes

Tsunamis can be generated when the sea floor abruptly deforms and vertically displaces the overlying water.

Tectonic earthquakes are a particular kind of earthquake that are associated with the Earth's crust deforming; when these earthquakes occur beneath the sea, the water above the deformed area is displaced. Movement on normal faults can also cause displacement of the seabed, but only the largest of such events cause enough displacement to cause a significant tsunami, such as the 1977 Sumba and 1933 Sanriku events.

Tsunamis have a small wave height offshore, and a very long wavelength (often hundreds of kilometres long, whereas normal ocean waves have a wavelength of only 30 or 40 metres), which is why they generally pass unnoticed at sea, forming only a slight swell usually about 300 millimetres (12 in) above the normal sea surface. They grow in height when they reach shallower water. A tsunami can occur in any tidal state and even at low tide can still inundate coastal areas.

Landslides

In the 1950s, it was discovered that tsunamis larger than had previously been believed possible can be caused by giant submarine landslides.

These rapidly displace large water volumes, as energy transfers to the water at a rate faster than the water can absorb.

Scientists named these waves megatsunamis.

Meteorological

Some meteorological conditions, especially rapid changes in barometric pressure, as seen with the passing of a front, can displace bodies of water enough to cause trains of waves with wavelengths like seismic tsunamis, but usually with lower energies.

Man-made or triggered tsunamis

There have been studies and one actual attempt to create tsunami waves as a tectonic weapon.

In World War II, the New Zealand Military Forces initiated Project Seal, which attempted to create small tsunamis with explosives in the area of today's Shakespear Regional Park; the attempt failed.

Tsunamis are made by permanent large vertical displacements of very large volumes of water which do not occur in explosions.

Surviving tsunamis

Tsunamis are very strong and can go many kilometers inland. Around 5 to 10 minutes before a tsunami hits, the sea seems to go back by an unusual distance. This is a warning that a tsunami can occur.

The best way to evacuate is to climb to an elevated area. If a person notices strange or unusual behavior in animals, he/she can also take that as a warning and go inland. However, if it still looks like the wave can absorb the person, the most suitable alternative will be to hold on to something sturdy, like a tree, so he/she does not totally get carried away and injured.

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In Spanish: Tsunami para niños

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River water picks up and moves mud, pebbles, and larger rocks as it flows downstream. These particles rub against the riverbed and wear away more rock and soil. This kind of erosion helped to carve the Grand Canyon in the southwestern United States. Over millions of years the swiftly moving waters of the Colorado River carried away bits of earth and rock from the land. Little by little the constant rush of water dug a canyon out of a flat stretch of ground.

The pounding of ocean waves against land also causes erosion. The waves constantly move pebbles and sand on beaches. The particles rub against each other and against the rock along the coast. Over time the water and the particles wear down rock into more sand. The water then carries the new sand away.

Like waves, wind constantly carries sand and other small bits of earth from one place to another. Wind forms sand dunes and changes their shape. It also blows soil off dry farmland. As wind throws sand and soil at rock, the shape of the rock slowly changes.

The huge masses of ice called glaciers also cause erosion. Glaciers scrape away parts of the rocks and the earth below as they creep down mountain valleys. They carry this material along with them. Glaciers can even move boulders as big as houses. When the glaciers melt, the moved rocks and earth stay behind.

A landslide shows how gravity helps erosion. Wind and rain can weaken the sides of mountains and hills. Gravity then causes soil, mud, and rocks to tumble down.

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Water, wind, and other natural forces cause rocks and earth to wear away. These forces also move bits of rock and earth to new places. This movement changes the shape of the...

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Kids learn about the Earth science subject of plate tectonics including major and minor plates, convergent, divergent, and transform boundaries.

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How Volcanoes Form

In 1980 in Washington, after 123 years of hibernation, Mount St. Helens erupted. The blast destroyed and scorched 230 square miles (370 square kilometers) of forest within minutes. The eruption released an avalanche of hot ash, gas, steam, and rocks that mowed down giant trees up to 15 miles (24 kilometers) away.

When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

Volcanoes erupt in different ways. Some, like Mount St. Helens, explode. Explosive eruptions are so powerful, they can shoot particles 20 miles up (32 kilometers), hurl 8-ton boulders more than a half mile (0.8 kilometers) away, and cause massive landslides. Explosive eruptions also create an avalanche of hot volcanic debris, ash, and gas that bulldozes everything in its path. Explosive volcanoes cause most of the volcano-related fatalities.

Volcanoes, like Mauna Loa in Hawaii, are effusive. Rather than a violent explosion, lava pours or flows out. Fatalities from effusive volcanoes are rare because people can usually outrun the lava. However, some people get too close or become trapped with no escape. The flowing lava burns, melts, and destroys everything it touches including farms, houses, and roads.

A volcanic eruption forever changes the landscape. Though volcanoes destroy, they also create mountains, islands, and, eventually, incredibly fertile land.

Carpet of Ash

Volcanic eruptions can cause damage hundreds of miles away. Volcanic ash causes airplane engines to fail, destroys crops, contaminates water, and damages electronics and machinery. The ash carpets the ground, burying everything, sometimes even causing buildings to collapse. Mount St. Helens produced more than 490 tons of ash that fell over a 22,000 square mile (56,980 square kilometer) area and caused problems in cities 370 miles (600 kilometers) away.

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When magma finds a way to escape from beneath the earth's surface, it creates a volcano.

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You feel the ground suddenly shake, and nearby objects are trembling. An earthquake is happening.

Also called a temblor, an earthquake is caused by the movement of parts of the Earth's crust, its outermost layer. They happen millions of times a year, but most are so small people don't even feel them.

But powerful earthquakes can cause landslides, tsunamis, flooding, and other dangerous events. Most damage and deaths happen in places where a lot of people live, because the shaking causes windows to break, structures to collapse, fire to break out, and other dangers.

Learn more about these unpredictable Earth tremors-and what to do if one rattles near you.

How earthquakes develop

The action all starts thousands of miles below your feet.

Picture Earth as a hard-boiled egg: Earth's core is the yolk, and the mantle is the white part. The outer crust is the eggshell.

People live on the surface of the crust. Below the surface-but still within the crust-are tectonic plates. Like gigantic puzzle pieces, these huge slabs of rock encircle the Earth. The seven major plates are named for the regions they rest under: the African, Antarctic, Eurasian, Indo-Australian, North American, Pacific, and South American tectonic plates

Tectonic plates aren't connected but are close together. Where they meet along their edges is called a fault. When heat from the Earth's core creates currents in the crust, the tectonic plates can scrape, bump, or drag along each other. This is what causes an earthquake-and why the surface sometimes cracks like an eggshell.

How to measure earthquakes

About a half-million quakes rock the Earth every day. Usually the quake is too small, too far below the surface, or too deep in the seafloor to be felt. Some, however, are so powerful they can be felt thousands of miles away.

The spot on the surface just above where an earthquake starts is called the epicenter. Ripples called seismic waves travel out from the epicenter. This causes vibrations that people can feel, sometimes very far from the epicenter.

How far away people can feel an earthquake's vibrations depends on its size, or magnitude. Scientists base the magnitude on the strength and duration of the quake's seismic waves. The higher the number, the more powerful the earthquake: A magnitude 3 to 4.9 earthquake is considered minor; 5 to 6.9 is moderate to strong; 7 to 7.9 is major; and 8 or more is an extremely powerful temblor.

As the crust settles after an earthquake, another temblor called an aftershock can happen. Usually, aftershocks are not as powerful as the first quake but can still be very strong.

Geologists can't predict earthquakes. But they're working to change that with new research and technology.

Where earthquakes happen

Earthquakes occur along faults, the areas where tectonic plates meet. About 80 percent of earthquakes occur along the rim of the Pacific Ocean. Called the Ring of Fire because of the large number of volcanoes there, the area is a meeting point for many tectonic plates.

Earthquakes are also common in California because the region sits on top of the Pacific and North American tectonic plates. Temblors happen when these two plates grind against each other. About two-thirds of this movement happens along the San Andreas Fault.

Another major earthquake area in the United States is the New Madrid Seismic Zone, which affects Missouri, Arkansas, Tennessee, Kentucky, and Illinois.

How to survive an earthquake

Earthquakes can happen anytime or anywhere-even if you don't live near a fault. So it's a good idea to prepare.

* Talk with your family about the safest places in your home in case an earthquake hits. This could be under a sturdy table or next to an interior wall (one that is not connected to the outside).

* Look for heavy items that could fall or break during a quake, and move them to safer spots.

* Ask your parents to make sure you have an emergency kit containing things like first-aid supplies, a flashlight, a cell phone charger, and a battery-operated radio. Your family should also have enough food and water for at least 72 hours

DURING AN EARTHQUAKE: Most earthquakes last only 10 to 30 seconds, so it's important to get to a safe place fast. Remember three things during an earthquake: drop, cover, and hold on.

Drop: Get down on your hands and knees and crawl to your shelter.

Cover: Underneath a sturdy table, desk, or bed, cover your head and neck with your arms. If furniture isn't nearby, crouch down on your knees with your arms over your head and neck next to an interior wall. (Don't stand under a doorway-they can easily collapse.)

Hold on: If you're under a piece of furniture, hold on with one hand and move with the furniture if it starts sliding. Stay where you are until the shaking stops.

AFTER AN EARTHQUAKE: Once the earthquake ends, check for injuries. Listen to a radio for any warnings and instructions from official organizations like the United States Geological Survey. Be prepared for any aftershocks.

Text and images adapted from Everything Volcanoes and Earthquakes: Earthshaking photos, facts, and fun!

(Learn more about earthquakes at National Geographic.)

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Learn the science behind how earthquakes happen-and how you can stay safe if one hits.

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What is a tsunami?
A tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it moves over the water. With typical waves, water flows in circles, but with a tsunami, water flows straight. This is why tsunamis cause so much damage!

How are tsunamis generated?
Tsunamis are generated by any large, impulsive displacement of the sea level. The most common cause of a tsunami is sea floor uplift associated with an earthquake. Tsunamis are also triggered by landslides into or under the water surface, and can be generated by volcanic activity and meteorite impacts.

How often do tsunamis occur?
On the average, two tsunamis occur per year throughout the world which inflict damage near the source. Approximately every 15 years a destructive, ocean-wide tsunami occurs.

Can strike-slip (horizontal motion) earthquakes trigger tsunamis?
Yes, approximately 10-15% of damaging tsunamis are triggered by strike-slip earthquakes. This type of earthquake is less likely to trigger a tsunami than one with vertical motion. The waves are likely generated by associated landslides or motion of a sloping bathymetric feature. Tsunamis generated by strike-slip earthquakes normally affect regions near the source only.

What does the word "tsunami" mean?
Tsunami (soo-NAH-mee) is a Japanese word meaning harbor wave.

How fast do tsunamis travel?
Tsunami velocity depends on the depth of water through which it travels. Velocity equals the square root of the product of the water depth times the acceleration of gravity. Tsunamis travel approximately 475 mph in 15,000 feet of water. In 100 feet of water the velocity drops to about 40 mph.

Did you know...A tsunami travels from the central Aleutian Islands to Hawaii in about 5 hours and to California in about 6 hours, or from the Portugal coast to North Carolina in about 8.5 hours.

How big is a tsunami?
Tsunamis range in size from inches to over a hundred feet. In deep water (greater than 600 feet), tsunamis are rarely over 3 feet and are not normally noticed by ships due to their long period or time between crests. As tsunamis propagate into shallow water, the wave height can increase by over 10 times. Tsunami heights vary greatly along a coast. The waves can be amplified by shoreline and sea floor features. A large tsunami can flood low-lying coastal land over a mile from the coast.

What does a tsunami look like when it reaches shore?
Normally, a tsunami appears as a rapidly advancing or receding tide. In some cases, a wall of water or series of breaking waves may form.

How is a tsunami different from a wind-generated wave?
Wind-generated waves usually have periods or time between crests between 5 and 15 seconds. Tsunami periods normally range from 5 to 60 minutes. Also, wind-generated waves break as they shoal and lose energy offshore. Tsunamis act more like a flooding wave. A twenty foot tsunami is a twenty foot rise in sea level.

What are nature's signs that a tsunami may be imminent?
There are a few signs like hard ground shaking for 20+ seconds near the coast or a sudden sea level withdrawal. Tsunamis may be accompanied by loud, booming noises.

Can earthquakes and tsunamis be predicted?
No, earthquakes cannot be predicted. Once an earthquake has occurred, the arrival time of a tsunami, if generated, can be determined accurately. There is not normally enough time to accurately predict tsunami heights near the source. Away from the source, tsunami wave heights can be estimated based on mathematical tsunami models and observed wave heights.

Aerial video of the tsunami that devastated Japan on March 11, 2011.

Click Here to see an animation of an earthquake and the resulting tsunami. It's great for kids, because they get to see how it actually happens!
What are some of the most damaging tsunamis?

Japan: Major tsunami in 2011 generated in the Pacific Ocean.

Asia: Asian tsunami in 2004 generated in the Indian Ocean.

Alaska: Major tsunamis were generated along the Alaskan coast in 1946, 1957, 1958, 1964, and 1965. Many other locally generated tsunamis occurred prior to those dates.

US/Canada West Coast: Tsunamis were generated locally in 1812, 1873, 1878, 1927, 1930, 1946 and 1949. The west coast was also impacted by tsunamis generated in other regions in 1877, 1946, 1952, 1957, 1960, 1964, 1975, 2006, and 2010.

US/Canada Atlantic Coast: Tsunamis were recorded in 1755, 1884, 1886, and 1929.

Puerto Rico and the Virgin Islands experienced damaging tsunamis in 1867 and 1918.

Click Here for the NOAA/National Geophysical Data Center tsunami catalog.

TSUNAMI WARNING- A tsunami warning indicates that a tsunami may be imminent and that coastal locations in the warned area should prepare for flooding. The initial warning is typically based solely on seismic information. After the tsunami is recorded on sea level gages, the warning will be cancelled, restricted, expanded, or downgraded to an advisory. Warnings indicate that flooding up to the maximum expected limit is possible and residents should follow their local emergency management instructions. Warnings are issued when the earthquake information or tsunami forecasts indicate that a wave over 1 meter in amplitude is expected, possible, or ongoing.

TSUNAMI ADVISORY- A tsunami advisory indicates a tsunami which may produce strong currents and is dangerous to those in or very near the water is expected. Large inundations are not expected in areas under advisory status. Advisories will be cancelled, extended, or upgraded to a warning depending on the event severity. Advisories are issued when the tsunami forecast is in the range of 0.3 to 1 meter, or an observed tsunami is in the range of 0.5 to 1.0 meters.

TSUNAMI WATCH- A tsunami watch is an early alert issued to areas which may later be impacted by a tsunami. Tsunami impact is normally at least three hours away for regions within a tsunami watch. The watch will either be upgraded to a warning or advisory in subsequent messages or cancelled depending on the severity of the tsunami. People within a watch area should stay alert for further information regarding tsunami threat.

CREST - The top of a wave.

FJORD - A narrow sea inlet between cliffs or steep slopes.

SURGE - A large wave or billow.

TROUGH - The lowest point between waves.

Click Here to get the latest tsunami warning information from the NWS.

PLAN FOR A TSUNAMI: Have a disaster plan. Know whether you're at risk for danger. Plan an evacuation route. Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water.

DURING A TSUNAMI: Follow the instructions issued by local authorities. You will probably want to evacuate immediately. Get to higher ground and as far inland as you can.

AFTER A TSUNAMI: Help injured or trapped people. Stay out of a building if water remains around it. Tsunami waters can cause buildings to sink, floors to crack, or walls to collapse. When re-entering homes, use extreme caution. Check for gas leaks. Open windows and doors to help dry things out. Look for fire hazards.

Lesson Plan: Here is a great lesson plan on learning about tsunamis. Note: This is a PDF file, so you need to have Adobe Acrobat Reader.

Lesson Plan: Here is a great lesson plan on tracking a tsunami.

Lesson Plan: Here is a great lesson plan on tsunamis and how they devastating effects they may cause in the world.

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What is a tsunami? A tsunami is a large ocean wave usually caused by an underwater earthquake or a volcanic explosion. Tsunamis are NOT tidal waves. Tidal waves are caused by the forces of the moon, sun, and planets upon the tides, as well as the wind as it moves over the water.

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