原版英语RAZ 教案(Z) Volcanoes.pdf

Visit www.readinga- for thousands of books and materials.VolcanoesA Reading AZ Level Z Leveled BookWord Count:2,415www.readinga-VolcanoesLEVELED BOOK ZWritten by Chuck GarofanoSVZWritten by Chuck Garofanowww.readinga-VolcanoesLevel Z Leveled Book Learning AZISBN 1-59827-752-9Written by Chuck GarofanoAll rights reserved.www.readinga-CorrelationLEVEL ZUVN/A50Fountas&PinnellReading RecoveryDRAVolcanoesPhoto Credits:Front cover:iS Grodin;back cover:iS Albiez;title page:courtesy of Robert Krimmel/U.S.Geological Survey;page 3:Windwardskies/D;page 4:ArtToday;page 5:iS Huss;page 6:InterNetworkMedia/PhotoDisc/Getty Images;page 7:Peter Horree/Alamy;page 8:courtesy of James St.John;page 9:Jill Battaglia/D;page 10:Andrea Danti/D;page 13(inset):courtesy of Jacques Descloitres/MODIS Land Rapid Response Team/NASA/GSFC;page 14:iS 15(left):courtesy of Jim Nieland,U.S.Forest Service,Mount St.Helens National Volcanic Monument;page 15(right):courtesy of Lyn Topinka/USGS;page 16:courtesy of Tom Casadevall/USGS;page 17:Pierrette Guertin/123RF;page 18:Keoni Debelka/D;page 19:iS Moments;page 20:iS Fortelny;page 21(top):courtesy of T.P.Miller/USGS;page 21(bottom):courtesy of Lyn Topinka/USGS;page 22:Hiroshi Ichikawa/DArt Credits:page 11:Signe Nordin/Learning AZ;pages 12,13(main):Craig Frederick/Learning AZVolcanoes Level Z 34Table of ContentsThe Eruption of Vesuvius.4People and Volcanoes .8Where and Why Volcanoes Form .10Composite Volcanoes.14Shield Volcanoes.18Cinder Cones and Lava Domes.20Conclusion.22Glossary.23The Eruption of VesuviusFew people in the Roman city of Pompeii were alarmed by the earthquakes that began shaking the region in ad 79.They had endured seismic activity in the past and had rebuilt their city whenever any significant damage occurred.Usually,though,the earthquakes were minor,and people had grown accustomed to them.The residents of Pompeii loved their beautiful city and would not leave just because the ground occasionally shook or a building fell down.No one connected the trembling ground with the plume of smoke that steadily hissed from nearby Mount Vesuvius.After all,people had lived in Pompeii for centuries without ever witnessing a volcanic eruption,and the slopes of Mount Vesuvius were teeming with life and were covered with trees,flowers,and grass.It had been a thousand years since the volcano had erupted,so most people assumed that it was dormant,or even extinct.This volcano shows signs of activity.Volcanoes Level Z 56People in the cities surrounding Mount Vesuvius tried to evacuate the area as the volcano demolished their homes and farms.They gathered their valuables and most portable treasures and hurried their families away from the disaster.Some people tried to traverse the thick layers of ash that covered the ground,but the ash was so deep and so hot that many people died.Others were struck and killed by stones falling from the dark sky,and some choked and suffocated on the ash-and dust-clogged air.Around midnight,the crisis grew even worse.The massive cloud of ash,poisonous gases,glowing-hot dust,and smoke had become so dense and heavy that it could no longer remain airborne.The cloud collapsed into a pyroclastic flow,racing down the mountain at speeds of up to 500 kilometers per hour(310 mph).But everything changed on August 24 around one oclock in the afternoon.Suddenly,a tremendous explosion shook the area around the mountain,sending molten rock,ash,and dust spewing from the summit of the volcano and darkening the sky.This dust,ash,and stone(collectively known as tephra)rained down on the city,covering the ground as far away as 16 kilometers(10 mi)from the mountain.By three oclock,lava gushed from the mouth of the volcano at an alarming rate,destroying everything in its path.By six oclock,the cloud of dust and ash had ascended to 32 kilometers (20 mi)in height,and the swirling energy inside it generated lightning bolts.The ash continued to blanket the area,covering the ground to a depth of 1 meter(3.3 ft)and causing buildings to collapse under the weight of the falling debris.Glowing-hot lava bubbles up inside a volcano.Mount Vesuvius overlooks the excavated ruins of Pompeii.Volcanoes Level Z This was Mount Vesuviuss first surge cloud,which within a few moments scorched and buried the people in the cities of Pompeii and Herculaneum as it swept over them like a wave.As more dust and ash billowed from the volcano,more surge clouds followed.When the eruption was over,two cities of the Roman Empire were completely buried and wiped off the face of the Earth.They would not be rediscovered for over a thousand years.78What you just read is an account of a real event,but how did it happen,and what could cause such a catastrophic explosion?And if volcanoes are so dangerous,why do people choose to live near them?People and VolcanoesPeople live near volcanoes for a variety of reasons.They often find nutrient-rich soil for farming in these regions or wonderful hot springs where they can take relaxing baths.Still,people have learned over time to respect volcanoes.Long ago,people had no way to predict or understand volcanoes;they told stories to explain the dangerous and sporadic eruptions.For instance,people in Hawaii believed the goddess Pele(PAY-lay)caused the volcanoes to erupt when she was angry.Some types of volcanic glass,such as Peles hair and Peles tears,are named in honor of this goddess.Peles tears are small drops of lava that cool and become solid while flying through the air.A plaster cast of the body of an inhabitant of Pompeii killed by the eruption of Mount VesuviusDo You Know?Pompeii,a city not far from Mount Vesuvius,was completely buried by a surge cloud.As the bodies of victims decayed over time,they left pockets of air in the hardened ash and mud that surrounded them.These air pockets preserved the exact shapes of the bodies they once contained.Archaeologists filled the holes with plaster to make casts showing how the people looked when they died.Volcanoes Level Z 910Native Americans told stories to explain the origin of an extinct volcano in Wyoming known as Devils Tower.They told how this towering column of rock,so striking in appearance,was created by magic and how its deeply gouged sides were shaped by the claws of an angry bear.In ancient Rome,people believed that the Roman god Vulcan worked in a blacksmiths forge beneath Earths surface.They saw volcanoes as the chimneys of the underground forge where Vulcan fashioned lightning bolts for use by Jupiter,the king of the gods,and made weapons and armor for Mars,the god of war.The word volcano comes from the name Vulcan.Even today,volcanologists say that volcanoes smell like a blacksmiths forge.In Japan,people still climb Mt.Fuji,a volcano that last erupted in 1707,as a form of spiritual practice in both the Shinto and Buddhist traditions.Today,scientists use a variety of tools and instruments to help them gather information about volcanoes.They understand the forces that create mountains and have equipment that can help them predict when a volcano will next erupt.Where and Why Volcanoes FormThe first volcanoes appeared about 3.5 billion years ago,covering vast areas with hot lava that spewed from deep within Earth.Earths hard surface,or crust,is made of many continent-sized sheets of rock called tectonic plates.Some plates make up the continents themselves,while others make up the ocean floors.Just under the surface of the plates,the Earth is extremely hot(about 1,200o Celsius or 2,192o Fahrenheit)so hot that rock melts into a liquid called magma.Sometimes,the magma forces its way up to the surface and seeps out through cracks in the crust,causing volcanoes to form.Devils Tower,an extinct volcano in Wyomingmagma chamberventsVolcanoes Level Z When an ocean plate crashes into a continental plate,the ocean plate moves down,creating an active volcanic region.12Scientists estimate that more than fifteen hundred different volcanoes have erupted in the last ten thousand years,and every year about thirty-five or forty volcanoes erupt at various places around the world.Sometimes the only sign of volcanic activity is a small amount of smoke or steam emerging from an erupting volcano.Some volcanoes are always erupting slowly,while others,like Vesuvius,can remain quiet for hundreds or even thousands of years between explosive eruptions.Volcanoes usually form at the edges of tectonic plates,which are slowly floating on the thick,liquid magma underneath them.But the various plates are moving in different directions,and as they move,they can crash into,pull away from,or grind past other plates.As the huge plates slide and rub against each other,their movements create large cracks in the crust where magma can break through to form volcanoes.There are at least five hundred active volcanoes in the world,most of which are located near the edges of tectonic plates.The edge of the Pacific Ocean plate is a particularly dense volcanic region known as the Ring of Fire.Another notably active volcanic region runs along the Mid-Atlantic Ridge,which is a mountain chain in the Atlantic Ocean.Two plates are drifting apart in the Atlantic Ocean,allowing magma to seep up through the ocean floor,where it accumulates.Over time,the magma can build up and create mountains so tall that they emerge from the water.The country of Iceland sits atop the summits of large volcanoes in the Mid-Atlantic Ridge.11Continental crustTrenchVolcanic arcMantleMantleOceanic crustPlate MovementPacific OceanRing of FireMore than half the active volcanoes in the world occur along the Ring of Fire.EQUATORVolcanoes Level Z 1314Other volcanoes are located in areas far away from the edges of the plates.For example,the islands of Hawaii are in the center of the Pacific Ocean plate.They are located above a“hot spot,”a place where hot magma sits very close to the surface of Earths crust.Sometimes the magma creates a new island,but the process is gradual,taking tens or even hundreds of thousands of years.In Yellowstone National Park,in the middle of the North American plate,an underground hot spot sits directly beneath underground lakes and waterways.The magma heats up the ground and the water in this area like a giant teapot,creating geysers and hot springs.You can visit Yellowstone in Wyoming and see water erupting from the ground at geysers such as Old Faithful.Different volcanoes erupt in different ways,depending on where and why the volcano forms.Some volcanoes erupt gently and gradually,while others suddenly explode with the force of many atomic bombs.Lets examine different kinds of volcanoes and learn how they erupt.Composite VolcanoesMount Vesuvius,which you read about earlier,is a composite volcano on the west coast of southern Italy.Composite volcanoes are explosive volcanoestheir eruptions can be extremely violent and destructive.Also called stratovolcanoes,they are the most common type of volcano.They are usually very large mountains with steep sides and evenly shaped peaks,often with a bowl-shaped crater at the top.The crater is a hollow area where the magma,hot gases,and ash come out.HawaiiKauaihot spotplate movementThe impressive shape of a composite volcanoHawaiiKauaiplate movementVolcanoes Level Z 15Most composite volcanoes occur where the magma near the surface is viscousthick and slow moving like syrup.Magma moves toward the surface in tubes called vents.When the magma is unusually thick,it can cool and harden inside the vent,plugging the vent and trapping the magma below.Because the heat and gases beneath the plugged vent have nowhere to go,the pressure slowly begins to increase.Eventually the pressure becomes so great that it reaches a critical threshold,and the volcano explodes.Sometimes the explosion is so violent that the whole mountain is destroyed in the blast.When Washington States Mount St.Helens erupted in 1980,the entire northern side of the mountain was obliterated.16When composite volcanoes erupt,they send massive clouds of ash,dust,smoke,hot gas,and rock into the air.These clouds rise for many kilometers,turning the sky black and raining ash onto the ground.When a cloud of debris becomes too dense to remain in the air,it collapses in a violent surge cloud.Many composite volcanoes are very tall,and they are often capped with ice and snow.In an instant,an explosion can melt all of the ice and snow on the top of the volcano,sending a flood of water,mud,and rock racing down the mountain at up to 100 kilometers per hour (62 mph).Such a mudslide triggered by volcanic activity is known as a lahar.Mount St.Helens before 1980 eruptionMount St.Helens after 1980 eruptionDo You Know?When Mount St.Helens,in Washington State,erupted on May 18,1980,63 people died and 311 square kilometers(193 sq mi)of forest were flattened by hot winds that blew down the mountainside.Melting ice and snow sent a massive lahar racing down the side of this volcano.Volcanoes Level Z 1718Some volcanic ash clouds are so gigantic that the ash and dust can travel around the world,blocking out sunlight and cooling down the entire planet.After the 1815 eruption of Tambora,a volcano in Indonesia,people living as far away as North America experienced a cold,snowy summer.Sometimes an entire underground lake of magma can pour out of a composite volcano,leaving a huge empty space below.With nothing to support it,the surface collapses into the empty chamber,leaving a large bowl-shaped basin called a caldera.Calderas can measure as much as 100 kilometers(62 mi)from side to side.Over time,they often fill with water,creating large lakes such as Crater Lake in Oregon.Composite volcanoes can destroy huge forests,bury entire cities,and kill thousands of people.These volcanoes are very dangerous because they often remain quiet for hundreds of years between eruptions.People forget that the volcano might erupt,and they build their homes dangerously close to the mountain.Shield VolcanoesYou may have seen a video of bright orange lava flowing or spraying from the top of a volcano.The lava,which is very runny,flows smoothly and quickly,moving like water in a stream.The lava spreads out over the land before slowly hardening and building up.This type of lava comes from a shield volcano.Shield volcanoes usually have gentle,smooth mountain slopes in the shape of shields.Do You Know?The Klamath Indians in southern Oregon used to tell a story about the origin of Crater Lake.In the story,the first coyote fell in love with a star and found a way to join her in the sky.When he fell back to Earth,his impact made a hole that became Crater Lake.Crater Lake is a well-known caldera in Oregon.This huge caldera was formed when the volcano collapsed in on itself.Mauna Loa,a shield volcano in HawaiiVolcanoes Level Z 1920Eruptions of shield volcanoes are usually gentle rather than explosive,although the lava flows can still destroy roads,homes,and forests.Sometimes a shield volcano contains hot gases or steam that sprays from the crater,creating a