Volcanoes, Earthquakes and Our Changing Earth

You live on Earth's outermost layer. Under it lie thousands of kilometers of hot rock and metal. From the surface to the center is about 6,371 km (3,960 miles).

Travel from the outside in

The crust varies in thickness. Beneath oceans it is about 5–10 km (3–6 miles) thick. Beneath continents it is usually 30–50 km (20–30 miles). Under the highest mountains, it can reach about 70 km (over 40 miles).

The mantle is Earth's thickest layer. Its bottom lies about 2,900 km (1,800 miles) below the surface. Its rock can slowly bend and flow over millions of years. Think of extremely thick putty, but remember that this is solid rock.

Hotter does not always mean liquid

The core has two parts. The liquid outer core surrounds the solid inner core. Near the center, temperatures reach about 5,000–6,000 °C (9,000–11,000 °F), roughly the Sun's surface temperature.

Why is the hottest part solid? All the layers above squeeze it with enormous pressure. This pressure keeps the inner core solid. Even a few kilometers down in deep mines, rock can be hotter than 50 °C (120 °F).

Find a layer from its depth

Imagine three dots on a cut-away drawing beneath a continent.

1. A dot 100 km down is below the crust. It sits in the mantle.
2. A dot 3,000 km down is just beyond the mantle's bottom. It sits in the liquid outer core.
3. A dot 6,000 km down is close to Earth's center. It sits in the solid inner core.

Depth means distance down from the surface. It is different from a layer's thickness.

Where melted rock comes from

Some rock partly melts near the mantle's top or deep in the crust. Melted rock underground is magma. It rises because it is less dense than the surrounding solid rock. Less dense means lighter for the same amount of space.

Magma that reaches the surface becomes lava. It comes from rock, not the metal core. Earth's inside is mostly solid; a red or orange mantle in a drawing shows heat, not a planet full of liquid lava.

A model helps you picture something hard to see. You can use a peach, an egg, clay, or a drawing to show Earth's layers. Each model leaves some things out.

Choose what your model shows

A peach has thin skin, thick fruit, and a pit. These can stand for the crust, mantle, and core. But the pit is solid throughout. It cannot show the liquid outer core correctly.

A hard-boiled egg shows a thin shell around thicker layers. Cracks in its shell help you picture Earth's broken outer shell. Its yolk does not show the core's two different states. Colored clay lets you add both core layers and label them.

In a cut-away diagram, a slice appears removed so you can see inside. Artists often make the crust too thick to keep it visible. Check the labels and scale before using a drawing to compare sizes.

Shrink Earth to a ball

Picture a ball 1 m (100 cm) across. Its radius, from the surface to the center, is 50 cm. That stands for Earth's real radius of 6,371 km.

Each centimeter in the model stands for about 127 km. A continent's crust, about 35 km thick, becomes only about 3 mm thick. That is thinner than many pencil erasers.

The mantle's bottom lies about 23 cm below the model's surface. The whole core has a radius of about 27 cm. The inner core has a radius of about 10 cm. These are distances in different directions: depth starts at the surface; radius ends at the center.

A real 35 km crust is less than one hundredth of Earth's radius. Equal-width rings would give a very misleading picture.

Learn about places no one can visit

The Kola Superdeep Borehole in Russia reached about 12 km (7.6 miles) down. It stayed within the crust. Heat and pressure make deeper drilling extremely difficult.

Scientists use evidence, meaning observations that help answer a question. Earthquakes send waves through Earth. The waves change speed and bend as they enter different materials. Their arrival times at stations around the world help reveal the layers.

One kind of earthquake wave cannot pass through liquid. Its path is blocked by the outer core, supporting the model of a liquid layer there. Lava supplies evidence of melted rock underground. Iron meteorites, which reach Earth from space, give clues about the material inside planets. Scientists combine these clues; they do not need to travel to the core.

A tree can split a rock without moving it away. Ice and water can do this too. Weathering means rock breaks down or dissolves where it is. Its pieces help form soil.

Water freezes inside a crack

Freeze-thaw weathering is also called ice wedging.

1. Water enters a crack in a rock.
2. The temperature falls below freezing: 0 °C (32 °F).
3. Water freezes and takes up about one-tenth more space.
4. The growing ice pushes the crack wider.
5. The ice melts, and water can enter farther.

Many freezing and thawing cycles can split the rock. Places that repeatedly cross freezing temperature are good settings for this process. Ice also helps potholes grow in roads.

Living things and changing temperatures

Roots grow into cracks and push them wider, much like tree roots lifting a sidewalk. Burrowing animals loosen rock and soil. Lichens growing on bare rock slowly wear its surface.

Heating and cooling can also crack rock. A desert rock's surface warms and expands during the day. At night it cools and shrinks. Repeated changes can make thin outer layers flake away.

Water can change the rock itself

Rainwater mixes with carbon dioxide in the air and becomes slightly acidic. Over many years it dissolves limestone and marble. This can blur carvings on marble and help form limestone caves. Iron in some rocks reacts with oxygen and water: it rusts, turning reddish brown and weakening the rock.

Weathering often takes hundreds or thousands of years to show a large change. Softer rocks, such as chalk and some sandstones, wear away more easily than hard granite. Wet conditions, freezing and thawing, and growing plants can speed it up.

Model two kinds of weathering

With an adult, use a plastic tub with a loose lid. Fill it to the brim with water and freeze it. Ice bulging above the rim shows that freezing water needs more room. Never freeze water in a sealed glass container: expanding ice can break it.

For dissolving, put similar small limestone pieces in water and vinegar. The vinegar piece fizzes and shrinks faster. Vinegar models acidic rain, but acts much faster. Natural chalk can work too; classroom chalk made from gypsum may barely fizz.

A cracked rock that stays in place has been weathered. When water carries its pieces away, erosion has begun. The memory phrase "Weathering breaks, erosion takes" helps with this difference, though weathering also includes dissolving.

A brown river carries tiny bits of land. These bits, along with sand, gravel, and mud, are sediment. Erosion removes material; transportation carries it; deposition drops it.

Rivers wear down and build up

Running water does more erosion on land than any other agent. A river carries mud and sand and cuts into its bed. Larger, faster flows can move bigger pieces. Pebbles knock together as they travel, becoming smaller and rounder.

The Colorado River carved most of the Grand Canyon over about 5–6 million years. The canyon is about 1.6 km (1 mile) deep and 446 km (277 miles) long. Cutting 1.6 km down in about 5.5 million years averages only about 0.3 mm a year. A tiny yearly change can make a huge landform.

When water slows, it often drops sediment. Rivers deposit it inside bends, beside their channels during floods, and at river mouths. A delta grows where a river drops sediment as it enters a lake or sea. The Mississippi River Delta is one example. Bigger, heavier pieces settle before fine mud.

Waves and wind move sediment too

Waves pound the foot of a cliff. Unsupported rock above can fall. Over time, waves can enlarge a cave through a headland, making an arch. If its roof collapses, a tall pillar called a sea stack can remain. Waves also move sand alongshore and deposit it on beaches.

Wind picks up loose sand and dust where land is dry and plants are scarce. Blowing sand rubs against rock like sandpaper. Sand dropped by slowing wind builds dunes. During the 1930s Dust Bowl, wind carried huge amounts of dry farm soil from the US Great Plains.

Moving ice and gravity

A glacier is a large mass of ice that slowly moves downhill. It scrapes and plucks rock, carries boulders, and carves wide U-shaped valleys. Yosemite Valley is an example. Glaciers leave sediment behind where their ice melts.

Gravity pulls material downhill. A rockfall or landslide happens quickly. Creep moves soil a little each year and can tilt fences or tree trunks.

Trace one pebble's journey

Ice widens a crack until a mountain rock breaks: weathering. Gravity carries the piece into a stream: erosion. The stream transports it, and collisions round its edges. When the water slows near the sea, it drops the pebble: deposition.

Erosion changes one place while supplying material to another. The same moving water can cut away a riverbank upstream and build a sandbar downstream.

You can watch a model river change a tray of sand. A stream table has one end raised so water flows downhill. Channels appear, sediment travels, and piles build at the bottom.

Ask one clear question

Suppose you ask, "Does a steeper slope carry sand farther?" Change the tray's slope. Keep the sand, water amount, pouring place, and pouring method the same. Measure the distance the sand travels.

The thing you change is your test variable. A fair test changes one thing so you can connect it to the result. Making the slope steeper and adding extra water together would muddle that connection.

You could also test plant cover, soil type, or water amount. To test plants, compare bare soil with grass-covered soil under matching conditions. Roots hold soil together, and leaves soften falling raindrops.

Work through some results

A class pours 500 mL of water for each test.

The steeper tray carried sand farther in these trials. The class did not time the water, so these results do not show its speed. To measure speed too, time the water over a fixed distance, such as 20 cm.

Repeat each slope test using freshly prepared sand. Three trials at two books give 10 cm, 12 cm, and 11 cm. Find the mean by adding the distances and dividing by three:

The mean distance is 11 cm. A very different result calls for checking the setup and testing again.

Record what you actually measure

Use a ruler for distance, a measuring cup for water, and a kitchen scale for soil lost. Give table headings their units. A bar chart helps you compare results at a glance.

A stream table speeds up change and uses loose sand. A real river is much larger and may cut solid rock.

Read clues outdoors

Rounded pebbles suggest transport by water. A V-shaped valley points to river erosion; a broad U-shaped valley points to a glacier. Deltas show deposition. Exposed roots can show that surrounding soil washed away. Old photographs and maps help you check changes over time.

Rates help with planning too. Suppose a cliff retreats 0.5 m each year at a steady rate. In 20 years it retreats 10 m. A path 15 m from the edge would reach the edge after 30 years at that rate. Real rates can change, so planners also need recent measurements.

Melted rock below ground is magma. At the surface, it is lava. A volcano is an opening where lava, gas, and ash escape, and the hill or mountain built around it.

Trace the route upward

Magma collects in a magma chamber below ground. It can rise through the main vent, a passage through the rock. A bowl-shaped opening at the top is the crater. Some volcanoes also have side vents. Old lava and ash build layers around the openings, making the cone.

Magma rises because it is less dense than nearby solid rock. It contains dissolved gas. As it rises, the rock pressing down on it becomes less. Gas comes out of the magma as bubbles, and those bubbles grow.

Think of opening a bottle of fizzy soda. Gas bubbles expand and push liquid upward. A bottle helps model gas expansion; it does not model the heat of real magma.

Why eruptions differ

Mauna Loa and Kīlauea in Hawaii are shield volcanoes. Mount Fuji, Mount Vesuvius, and Mount St. Helens are steep examples. Many volcanoes are hidden underwater.

Lava is about 700–1,200 °C (1,300–2,200 °F). It cools and hardens into new rock. Volcanic ash is made of tiny, sharp rock and glass fragments. It is different from soft campfire ash. Volcanic bombs are blobs of partly or fully melted rock thrown out; blocks are solid when thrown out. Gases include water vapor, carbon dioxide, and sulfur gases. Pumice has so many gas holes that it can float.

Quiet does not always mean finished

An active volcano is erupting or has erupted in recent history and is likely to erupt again. A dormant volcano has been quiet a long time but could erupt again. An extinct volcano is not expected to erupt again. Pinatubo was quiet for about 500 years before its 1991 eruption.

Build land or reshape a mountain

Eruptions built the Hawaiian Islands from the seafloor. Surtsey appeared off Iceland after an eruption began in 1963.

At Mount St. Helens, magma made the north side bulge before May 18, 1980. An earthquake triggered a huge landslide. Removing that side released pressure on gas-filled magma, which blasted outward. The mountain lost about 400 m (1,314 feet) of height in minutes.

A cloud above a volcano contains gases and sometimes ash. It is not smoke from a mountain burning.

An earthquake begins when rock suddenly breaks or slips underground. The shaking releases energy that built up while the rock was stuck.

Stuck rock suddenly slips

A fault is a crack where rocks on either side move. Slow movements in Earth's crust push or pull those rocks. For a time, they catch against each other and strain builds. Eventually they slip. Energy spreads outward as seismic waves, like ripples spreading across a pond.

The underground starting point is the focus, also called the hypocenter. The epicenter is directly above it on the surface. They line up vertically, but they are not the same place. Shaking often weakens with distance from the epicenter.

A seismometer detects earthquake waves. Its record, a seismogram, shows a wavy or zigzag line. Bigger waves on a comparable record mean larger measured ground movement.

Compare earthquake size

An earthquake's magnitude describes its size. Scientists use recordings to work it out. Modern reports commonly use moment magnitude; the Richter scale is an older scale.

Each whole step represents about 10 times the measured wave size on a seismogram and about 32 times the energy released. These are different quantities.

Compare magnitude 6 with magnitude 4:

1. The gap is two whole steps.
2. Recorded wave size grows by about $10\times 10=100$ times.
3. Energy grows by about $32\times 32=1,024$ times, roughly 1,000.

Shaking differs from place to place. Distance, depth, local ground, and building strength affect damage. Most earthquakes are small; those below about magnitude 2.5 are usually not felt.

Changes after the first shaking

Smaller earthquakes called aftershocks can follow in the same area for days, weeks, or longer. They can damage buildings already weakened by the first quake.

Earthquakes can lift or lower land, trigger landslides, and soften wet, sandy ground so buildings tilt. Most harm comes from falling objects and damaged structures, not giant holes swallowing towns.

When the seafloor moves water

An undersea earthquake can suddenly lift or lower the seafloor. This pushes a large amount of water and may start a tsunami, a series of waves. Underwater landslides and eruptions can also start one.

In deep ocean, tsunami waves travel very fast but can be low. Near shore they slow down and grow taller. Tides and wind do not cause tsunamis, and not every undersea earthquake produces one.

A landform is a natural shape of Earth's surface. A beach, valley, mountain, cliff, or island has a history. The time needed to change it is part of that history.

Compare the time taken

Surtsey grew from eruptions beginning in 1963. Forming an island over a few years is fast beside carving a giant canyon. A fast change does not have to finish in a single second.

Some mountains grow through eruptions, like Mount Fuji. Others rise where huge pieces of crust push together. Parts of the Himalayas and Andes rise only a few millimeters each year. Weathering and erosion wear them down at the same time. The older Appalachians have had much longer to be worn into lower, rounder shapes.

Small amounts become large totals

Suppose a river cuts down about 0.3 mm each year. Over an 80-year lifetime:

That is 24 mm, or 2.4 cm. You might barely notice it. Continue the process for millions of years, and it can carve a deep canyon. The Grand Canyon shows why a slow process can make a huge landform.

One process can work at different speeds

A river may erode slowly most days. During a flood, it can cut a new channel in a day. Gravity causes slow soil creep and sudden landslides.

Processes also work together. Years of weathering can weaken a hillside. Heavy rain or an earthquake then triggers a quick collapse. After an eruption builds fresh rock, weathering begins to break it down and erosion carries pieces away.

Use clues to rebuild the story

Compare a recent photograph with an old one taken from the same spot. Look for a new landslide scar, a changed river channel, or a cliff farther inland. Maps can show an old coastline. Old lava flows and ash layers give clues to eruptions.

A broad valley and a fresh landslide scar may tell two different parts of one landscape's story. Match each feature to a process and its likely timescale.

A world map can show thousands of events at once. Start with its title: does it show volcanoes, earthquakes, or land height? Check the time period too. One year's earthquake map is a record of that year.

Read symbols before counting them

A map's key, or legend, tells you what each symbol means. Triangles often mark volcanoes; dots often mark earthquakes. Colors and sizes may show different magnitudes. The key decides their meaning, not the symbol alone.

Find north, south, east, and west. Use continents and oceans to describe locations. A crowd of earthquake dots means many events in that area during the mapped period.

Follow the main belts

Most volcanoes and earthquakes lie in long, narrow belts. The largest is the Ring of Fire, a horseshoe-shaped belt around the Pacific Ocean. It is about 40,000 km (25,000 miles) long. About 90% of Earth's earthquakes occur along it, together with most active volcanoes.

Follow it past New Zealand, Indonesia, the Philippines, Japan, and Alaska. Then trace the west coasts of North and South America. Japan and Chile lie on this belt.

Other belts run through the middle of the Atlantic, including Iceland; from the Mediterranean through Türkiye (also called Turkey) and Iran toward the Himalayas; and through East Africa. Kilimanjaro and Nyiragongo are African volcanoes.

Compare mountains and deep ocean valleys

Many mountains and ocean trenches lie near the earthquake belts. The Andes follow western South America. Deep trenches lie near Japan and the Mariana Islands. The Mariana Trench is about 11 km (almost 7 miles) deep.

The patterns overlap without matching everywhere. The Himalayas have many earthquakes but almost no volcanoes. Central Australia, Brazil, central Canada, and Scandinavia have few active volcanoes and fewer strong earthquakes. Small quakes can still happen there.

Describe what the map shows

Build a description from shape, location, and an exception:

"Many volcano symbols form a horseshoe around the Pacific. A second line crosses the Atlantic through Iceland. Central Australia has very few."

Then support a comparison with a map clue: "Japan has many earthquake dots close together; central Brazil has far fewer."

Cold Iceland and Alaska have volcanoes. Warm weather is not what makes them form. A coastline alone is not enough either: the belts matter, and many Atlantic coasts lie away from them.

The map's long belts have a cause. Earth's crust and the very top of the mantle form huge pieces called plates. Their edges do not simply trace the edges of continents.

Pieces move slowly; rocks can slip quickly

There are seven or eight very large plates and many smaller ones. One can carry both land and ocean floor. Plates move a few centimeters each year, roughly as fast as fingernails grow. You cannot feel this steady movement.

Where plates meet, their edges push together, pull apart, or slide past. Rocks become strained and can slip suddenly, causing earthquakes. In many edge regions, cracks also let magma reach the surface. This explains the belts on the map.

The mantle underneath is mostly solid rock. It can flow very slowly over long times. The plates do not float on a worldwide sea of lava.

Compare three places

Around much of the Pacific, including Japan and Chile, pieces push together. Earthquakes and volcanoes are common there. The Ring of Fire follows the edges around that ocean.

In the middle of the Atlantic, pieces pull apart. Magma rises in the gap, cools, and builds new ocean floor. Iceland is a place where this volcanic belt reaches above the sea.

In California, pieces slide past each other along the San Andreas Fault. This produces many earthquakes but few volcanoes along that fault. A line of earthquakes does not guarantee a line of volcanoes.

Mountains and an island exception

Pushing together can crumple and lift crust over millions of years. This helps build ranges such as the Himalayas and Andes. That is why many mountain ranges share belts with earthquakes.

Hawaii sits far from a plate edge. Very hot rock rises beneath it at a hot spot. As the plate moves across this area, new volcanoes form in different places, building an island chain.

Picture a slowly moving sheet passing over one small opening below. Marks made through that opening appear in a line on the sheet. The moving sheet helps you picture why the volcanoes form a chain, though real islands grow from erupting rock.

Use the explanation

Suppose a map shows earthquakes in a line through an ocean's middle. An edge between moving pieces can lie there, even far from land. A continent outline cannot show all the plate edges. Crowded event belts help you locate them.

A natural hazard is an event that could harm people or property. An earthquake far from people may do little damage. A hazard becomes a disaster when it causes great harm to a community.

Different hazards cause different harm

Pyroclastic flows can exceed 100 km/h (60 mph). Lava often travels more slowly, but its speed varies. Lava is only one volcanic danger. Falling ash can also reach places far from the volcano.

Eyjafjallajökull erupted in Iceland in 2010. Its ash threatened airplane engines, disrupting European air travel for about a week. About 100,000 flights were canceled. The affected travelers did not have to be near the eruption.

Immediate effects and long recovery

Injuries, closed schools, damaged homes, and broken water supplies happen right away. Rebuilding, replacing lost jobs, and finding new homes can take months or years. These are long-term effects.

In AD 79, Vesuvius erupted in Italy. Ash and pyroclastic flows buried Pompeii. Archaeologists later uncovered streets, houses, and paintings preserved under the ash. Vesuvius remains active; it last erupted in 1944, and hundreds of thousands of people live nearby.

In 2011, a magnitude 9.1 earthquake struck off northeastern Japan. Many strong buildings survived the shaking, but a tsunami flooded the coast. Waves exceeded 10 m (30 feet) in places and caused most deaths.

In Türkiye and Syria in 2023, a magnitude 7.8 earthquake and another strong quake hours later caused many buildings to collapse. Tens of thousands of people died. Building quality matters, alongside earthquake size, depth, distance, ground conditions, and the number of people exposed. These disasters cannot be compared by magnitude alone.

Why people stay

Weathered volcanic ash makes fertile soil. Underground heat supplies energy and hot water. In Iceland, about nine in ten homes use underground heat, which also supplies about a quarter to a third of the country's electricity. Tourism, hot springs, rocks, and minerals bring jobs.

Families also have homes, friends, and work in these places. Moving can be expensive. Cities such as Tokyo, Los Angeles, and San Francisco grew around harbors and jobs despite earthquake risk. People can reduce harm through preparation and stronger buildings even when they cannot stop the natural process.

Warnings give people time to act. Different hazards offer different clues. A volcano can show changes before an eruption; an earthquake alert begins after the earthquake has started.

Watch a volcano

Scientists called volcanologists monitor small earthquakes, swelling ground, gas, and temperature. GPS and tiltmeters detect changes in the ground's position or tilt. Several growing signs can show magma moving upward.

Before Pinatubo erupted in 1991, scientists watched earthquakes, ground swelling, and gas. Their forecast helped authorities move tens of thousands of people away. It saved many thousands of lives.

A volcano that has been quiet for centuries can erupt again. Monitoring remains useful at dormant volcanoes.

Separate prediction from early warning

Scientists cannot predict an earthquake's exact day, time, place, and size. They can identify areas likely to face strong earthquakes and plan for them.

An early warning system detects the first fast earthquake waves. It sends an alert that may arrive before stronger shaking. ShakeAlert on the US West Coast and Japan's system work this way. Some places get only seconds; places very near the starting point may get no advance notice. Alerts can help people shelter and allow trains to stop.

Tsunami warnings need quick action

Warning centers combine earthquake readings with ocean sensors. Towns use sirens, evacuation signs, and routes to high ground. Strong or long coastal shaking, a sudden sea retreat, or an ocean roar can also warn of a tsunami.

Imagine a tsunami 600 km away, traveling at 800 km/h across deep ocean. Its travel time is:

That is 0.75 hours, or 45 minutes. Detection and messages take some of that time. Walking to high ground takes more. Forty-five minutes of travel does not mean 45 minutes of warning. A nearby tsunami may arrive within minutes.

Plan the route before it is needed

A hazard map shows areas threatened by shaking, lava, lahars, floods, or tsunamis. Towns can place schools and hospitals away from the most dangerous zones. They plan routes, meeting places, and shelters, then practice drills.

River gauges measure water levels. Combined with weather forecasts, they help give flood warnings hours or days ahead. A plan must match the hazard: a tsunami route goes uphill or inland, while an ash plan may involve sheltering indoors or leaving an evacuation zone.

Tsunamis arrive as a series of waves. A small first wave does not show that later waves will be small.

An engineer starts with a problem: "How can we keep this building standing during shaking?" A good solution must meet its criteria, the things it needs to do, within its constraints, such as cost, time, and materials.

Make, test, improve

Engineers consider several ideas, build models, test them, and improve the designs. For an earthquake tower test, build two straw towers of equal height. Add diagonal X-shaped cross-braces to one. Shake both trays the same way for 10 seconds, and repeat three times.

Measure whether each tower stays up and how far its top sways. If the braced tower stays up every time and the plain tower falls, the evidence supports cross-braces. A much gentler shake for one tower would spoil the comparison.

Help buildings move safely

Steel frames, concrete strengthened with steel, strong foundations, and cross-braces help buildings survive. Some use base isolators, rubber-and-steel pads that reduce shaking passed from the ground. Buildings need to bend a little without breaking. Light roofs, fastened furniture, and houses bolted to foundations also reduce harm. Building codes require safer designs.

Match a solution to a hazard

Lava barriers can steer some flows away from important places. Iceland built barriers near Grindavík and a power plant in 2023 and 2024. On Heimaey in 1973, pumping seawater onto lava helped cool it and protect the harbor. Strong, steep roofs help shed volcanic ash.

Sea walls, evacuation towers, higher building sites, sirens, and marked routes help coastal communities. Mangroves can slow smaller waves. Flood walls and levees keep some river water back. Wetlands store extra water, and raised houses reduce flood damage. Grass, trees, terraces, and retaining walls slow erosion; rocks, added beach sand, and sea walls protect coasts.

Compare benefits and costs

A town gives each idea a score from 1 (poor) to 3 (good). A higher cost score means more affordable.

Warnings score highest overall, but score only 1 for protecting buildings. The town could combine warnings with another measure. Scores show the town's priorities; the highest total does not fix every problem.

Every design has trade-offs. A sea wall is expensive, can worsen erosion elsewhere, and can be overtopped. Levees can break. Several layers of protection usually work better than relying on one barrier.

Practice makes emergency actions easier to remember. Your family plan should name a meeting place, ways out of home, and someone to call if you are separated. Include a contact who lives far away. Practice school and family drills.

Get supplies ready

An emergency kit needs drinking water and food that keeps, plus a flashlight, spare batteries, radio, first aid kit, medicines, whistle, and dust masks. Plan for at least three days. Allow about 4 liters (1 gallon) of water per person each day. An adult can check the kit with you.

When the ground shakes

Use Drop, Cover and Hold On.

1. Drop onto your hands and knees so shaking is less likely to knock you down.
2. Cover your head and neck. Crawl under a sturdy nearby desk or table. If none is nearby, stay low next to an inside wall away from windows and tall furniture, and protect your head with your arms.
3. Hold on to the shelter until shaking stops. If you have no shelter, keep both arms over your head and neck.

Stay inside during shaking. Running outside takes you past falling objects and glass. A doorway in most modern homes is no stronger than other areas, and its door can swing.

Outside, move to an open space away from buildings, trees, and power lines, then drop. In bed, stay there and cover your head with a pillow.

After shaking, follow your teacher or trusted adult. Expect aftershocks and be ready to shelter again. Leave a damaged building when shaking has stopped and tell an adult about injuries or a gas smell.

Near the coast

After strong or long shaking, move to high ground or inland as soon as the shaking stops. A sudden sea retreat is another reason to move at once. Walk if you can, following evacuation signs. Do not wait for a siren or go closer to watch. Stay away until officials say it is safe; waves can continue for hours.

Ash, eruptions, and floodwater

Follow eruption evacuation orders. During ash fall, stay indoors with windows and doors closed. If you must go outside, protect your eyes and cover your nose and mouth with a well-fitting mask made to filter fine dust. Keep out of valleys below a volcano because lahars can race through them.

Never walk, swim, or ride a bike through floodwater. Only 15 cm (6 inches) of fast-moving water can knock an adult down. It can also hide holes and sharp objects. Move to higher ground. Remember, "Turn around, don't drown."