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Written by Elizabeth Austin

Earthquakes,Volcanoes,

and TsunamisA Reading A–Z Level Q Leveled Reader

Word Count: 1,462

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Earthquakes,Volcanoes,

and Tsunamis

Earthquakes,Volcanoes,

and Tsunamis

Earhquakes, Volcanoes, and TsunamisLevel Q Leveled Reader© 2004 Learning Page, Inc.Written by Elizabeth AustinIllustrations by Craig Frederick

ReadingA–ZTM

© Learning Page, Inc.

All rights reserved.

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www.readinga-z.com

Earthquakes,Volcanoes,

and Tsunamis

www.readinga-z.com

Written by Elizabeth AustinCorrelation

LEVEL QFountas & Pinnell NReading Recovery 21

DRA 30

Photo Credits:Front cover: © PhotoDisc; back cover, title page, pages4, 7, 11, 13, 14, 16, 17, 20, 21 : clipart.com; page 8:© Tom Fumal/USGS; page 9: Tony Freeman/PhotoEdit;page 15: © AFP/CORBIS; page 19: Courtesy of Dr. Harry Yeh (http://nees.orst.edu).

43

Table of Contents

Introduction . . . . . . . . . . . . . . . . . . . . . . . . 4

Deep Within the Earth . . . . . . . . . . . . . . . . 5

Earthquakes: Terrible Trembling . . . . . . . 7

The Richter Scale . . . . . . . . . . . . . . . . . 10

Volcanoes: Enormous Explosions . . . . . . 11

Tsunamis: Wild Waves . . . . . . . . . . . . . . . 16

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . 21

Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . 22

Introduction

We usually think of the ground and theocean as peaceful things. The ground liesquietly beneath our feet, and the ocean lapsgently against the shore. But forces deepwithin the earth can suddenly come to life,destroying that peacefulness. These forcescause violent shakings called earthquakes,explosions of ash, gasses, and hot rocks calledvolcanoes, and huge waves called tsunamis(tsoo-NAM-ees). In this book, you will readabout these amazing events and the forcesthat cause them.

Smoke rises from what seems to be a peaceful volcano.

65

Underneath the plates,the earth is very hot. It is so hot that rock meltsinto a liquid calledmagma. The plates floaton top of this liquidmagma. The magma isalways moving, draggingthe plates around with it.

At the edges of themoving plates, threedifferent things canhappen. If the plates aremoving against eachother, one plate slidesover or under the otherplate (Fig. 1). If the plates are moving pasteach other, the edges ofthe plates grind together(Fig. 2). And if the plates are moving apart,they make a gap wheremagma seeps out (Fig. 3).

Deep Within the Earth

Beneath the soil, rock, and water on thesurface of our planet, the earth is constantlychanging. The top layer of Earth is made of giant pieces of rock, like the pieces of a puzzle. The pieces of rock, called plates,make up continents and ocean floors. Wherethe edges of the plates come together, thereare often cracks and gaps, called faults.

The dotted lines show the edges of the plates.

MAGMA

Mountains

MAGMA

MAGMA

PacificPlate

AustralianPlate

IndianPlate

EurasianPlate

NazcaPlate

SouthAmerican

Plate

NorthAmerican

PlateAfricanPlate

AntarticPlate

PacificPlate

Scotia Plate

EQUATOR

Fig. 1

Fig. 2

Fig. 3

87

Some earthquakes are small and harmless.In a small earthquake, the ground shakes alittle, causing some hanging objects to swing. Tree branches sway, as if there were a gentlebreeze. Some earthquakes are so small thatwe do not notice them. But sometimes theshaking is so strong that buildings crumble,bridges collapse, and large cracks open in the ground.

Earthquakes: Terrible Trembling

A lot of things can happen along the edgesof the plates. The plates usually move veryslowly. But sometimes large pieces of theplates get caught. The plates keep trying to move, but these large blocks of rock holdthem back. The pressure and energy buildsup. Then, suddenly, the rocks give way,releasing all that pressure and energy. The plates jerk forward, and the groundshakes. Far above, people feel an earthquake. The ground here was ripped open by an earthquake.

Earthquakes can damage or even destroy buildings.

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The Richter Scale1 People cannot feel it—only sensitive

instruments can detect it.2 People usually do not feel it; some people

in tall buildings may sense a slight swaying. 3 Many people near the origin of the

earthquake notice the shaking. No damageoccurs.

4 People at the origin of the quake definitely feelit. Hanging objects sway. Water sloshes inswimming pools. Some weak buildings maybe damaged.

5 Felt over a wider area. Usually lots of damageto weak buildings at and around center. Some damage to strong buildings.

6 Lots of damage to weak buildings; somedamage to strong buildings. Damage canspread over 160 kilometers (100 mi.).

7 A very major earthquake. Most buildings atthe center are destroyed. Cracks form in theearth. Underground pipes break. Largelandslides can occur.

8 Buildings and bridges destroyed. Large cracksappear in the ground. Large landslides.

9 The ground appears to move in “waves.” Entire rivers may move. Objects can bethrown into the air. Total destruction ofbuildings and other structures.

We measure the strength ofearthquakes on aninstrument called a seismograph(SIZE-moh-graf).Each earthquake is given a numberdepending on its strength. Thenumbers are fromthe Richter (RICK-ter) scale. You can look atthe chart on the next page to learn what thedifferent strengths of earthquakes feel like.For each number on the Richter scale, anearthquake is ten times as strong as theprevious number. A 6.0 earthquake is tentimes as strong as a 5.0 earthquake. It is 100 times as strong as a 4.0 earthquake! Thelargest earthquake ever recorded measured9.5 on the Richter scale. It occurred on thecoast of the South American country of Chile. Scientists are still learning about thesedangerous events. One day, they may be ableto warn people before earthquakes occur. There is no top to the Richter scale, but the strongest earthquake

ever recorded was a 9.5.

A seismograph

But sometimes, in very powerful volcanoes,the hot magma cools before it gets to thesurface. It hardens into a solid piece of rock,plugging up the crack or hole where it hadbeen seeping out. It acts like a plug in a bottleof soda pop. The magma continues to pushupward. Hot gasses in the magma pressagainst the plug. The pressure gets greaterand greater. Suddenly, the volcano explodes.Huge chunks of rock burst from the volcano.Entire mountainsides can be ripped away.Hot, poisonous gas, ash, and melted rockshoot into the sky. The volcano erupts withunbelievable power.

Volcanoes: Enormous Explosions

A volcano occurs wherever magma fromdeep inside the earth comes out through a crack in the surface. Volcanoes usuallyhappen near the edges of the plates, wherethere are many cracks and thin spots wherethe magma can leak out. When the magmapours onto the surface, it hardens, oftenpiling up into a mountain. Sometimes, theliquid rock flows peacefully out across theland. Many volcanoes on the islands ofHawaii act like this.

1211

Some volcanoes become plugged (left), and then they explodeviolently (right).

MAGMA

Plug

dust, ash, and gas

Lava flow

Runny liquid rock on this Hawaiian volcano flows smoothly, like a peaceful river.

A volcano can cause an explosion ofextremely hot, poisonous gasses. Theexplosion can be so powerful that it knocksover entire forests, and so hot that it startsdestructive fires. Some large volcanoes havesnow and ice on top. The hot gasses melt all the snow and ice at once, and the waterrushes down the mountain. This large, dirt-filled flood is called a mudslide. Amudslide is like a liquid landslide.

Many dangerous and destructive thingshappen during volcanic eruptions. Whenmountains explode, they send tons of rockrolling downtheir sides. Thesefalling rocks arecalled landslides.Landslides canbury whole cities.They can blockrivers, causingfloods. Clouds ofash and dust rise into the air during volcaniceruptions. The ash falls to the ground like

snow. The ash is soheavy that the roofsof houses cancollapse under itsweight. An ashcloud can spread allaround the world.Large ash cloudscan even block out

sunlight. The temperature of the entire earthcan cool down after a large volcanic eruption.

1413

Mount St. Helens after it erupted

These trees were blown over by the explosion of Mount St. Helens.

Mount St. Helens, in Washington State, before it erupted in 1980

Tsunamis: Wild Waves

Tsunamis are huge waves caused byearthquakes or volcanoes. They used to becalled “tidal waves.” But the word “tidal”means something to do with the ocean’snormal tides. But tsunamis have nothing todo with the tides. Tsunamis can be as high as a football field is long. They are the largestwaves in the world.

Scientists are not yet able to predict whenearthquakes will happen. But fortunately theyhave gotten very good at predicting when a large volcano is about to erupt. In 1991,scientists warned the people living around avolcano in the country of the Philippines thatthe volcano was about to erupt. Many peopleleft the area and found safety before the hugevolcano erupted.

1615

Scientists gather information from a volcanic crater.

Tsunamis are the largest waves in the world.

Tsunamis speed outward away from theirsource in all directions. A tsunami can cross anentire ocean. Tsunamis travel extremely fast—up to 320 kilometers per hour (200 mph).

In the open ocean, tsunamis may not bevery high above the surface of the water, but they are very deep. As tsunamis approachland and move into shallow water, theelevated ocean floor pushes the wave upward.The wave slows to about 70 kilometers perhour (45 mph), but the ocean floor lifts ithigher and higher. By the time a tsunamireaches land, it is tall enough to destroyalmost anything in its path.

The edges of the plates, where earthquakesand volcanoes often occur, usually lie near the edges of the oceans. The shaking of anearthquake or the explosion of a volcano can cause large landslides. Entire hills cancollapse, and sometimes, they fall into the sea and make huge waves. Earthquakes andvolcanoes can also be found under the sea.Underwater earthquakes cause the sea floorto move violently. Undersea volcanoes causeexplosions under the water. Both of theseevents create huge waves that spread across the surface of the ocean.

17

Steam rises from a volcano near the sea. When tsunamis approach the shore, they break as giant waves.

Tsunamiin openocean

Tsunaminearshore

Shore

18

Like volcanoes, tsunamis are becomingeasier to predict. They usually do not hit the shore until a few minutes to a few hours after the earthquake or volcano that causesthem. Scientists have instruments that detectvolcanoes and earthquakes. When a large onehappens, scientists have time to warn peoplethat a tsunami may be coming. Unfortunately,the system cannot warn people in time tosave their homes or belongings. But they dohave time to save their lives, which is themost important thing.

The largest tsunami ever recorded cameashore along the coast of Alaska. It was tallerthan the world’s tallest building. But thiswave was in a very small bay, only a shortdistance from the landslide that caused it.Most tsunamis are not that high when theyreach shore. They are usually between 1 to 10 stories high. That might not sound veryhigh, but it is hard to imagine the power ofthis much moving water. Most coastal townsand villages are much less than 30 meters(100 ft.) above the sea. Even a small tsunamican destroy houses, streets, and entire towns. A tsunami caused by a volcano in Indonesiakilled 36,000 people in 1883.

2019

Many people describe tsunamis as “walls of water.”

Damage from a tsunami

Glossary

earthquake a shaking of the groundcaused by rocks moving underthe surface of the earth (p. 4)

faults cracks in the surface of theearth, usually around theedges of plates (p. 5)

landslides when soil and rock collapseand fall down a hill ormountainside (p. 13)

magma hot, liquid rock from deepinside the earth (p. 6)

mudslide a dirt- and debris-filled floodof water (p. 14)

plates the giant pieces of rock andsoil that make up the surfaceof the earth (p. 5)

Richter scale the scale that measures thestrength of earthquakes (p. 9)

tsunamis enormous ocean waves causedby earthquakes or volcanos (p. 4)

volcanoes places on the earth’s surfacewhere hot, liquid rock seeps or explodes out (p. 4)

Conclusion

Our quiet planet occasionally turns violent.During a large earthquake, the ground shakes, destroying homes and property. In an explosive volcanic eruption, liquid rock,poisonous gasses, ash, and landslides canbury cities. And tsunamis can cost billions ofdollars in damage along coastlines. Scientistsare trying to learn as much as they can aboutthese violent events. As they learn more,scientists can predict volcanoes, earthquakes,and tsunamis, saving thousands of lives.

2221

An earthquake destroyed this building.