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    VOLCANOES

    AND EARTHQUAKES

    VOLCANOES

    AND EARTHQUAKES? 2008 Editorial Sol 90

    All rights reserved.

    Idea and Concept of This Work: Editorial Sol 90

    Project Management: Fabián Cassan

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    Farías, Joana Garrido, Celina Hilbert, Isidro López, Diego

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    Composition and Pre-press Services: Editorial Sol 90

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    Britannica Illustrated Science Library Staff

    Editorial

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    International Standard Book Number (set):

    978-1-59339-797-5

    International Standard Book Number (volume):

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    Britannica Illustrated Science Library:

    Volcanoes and Earthquakes 2008

    Printed in China

    www.britannica.comVolcanoes and

    EarthquakesContents

    Continuous

    Movement

    Page 6

    Continuous

    Movement

    Page 6

    Study and

    Prevention

    Page 44

    Study and

    Prevention

    Page 74

    Volcanoes

    Page 24

    Earthquakes

    Page 58S

    ome photos speak for themselves.

    Some gestures communicate more

    than words ever could, like these

    clasped hands, which seek comfort in the

    face of fear of the unknown. The picture was

    taken Oct. 8, 2005, when aftershocks were

    still being felt from the strongest earthquake

    ever to strike Kashmir, in northern India.

    Those clasped hands symbolize terror and

    panic; they speak of fragility and

    helplessness, of endurance in the face of

    chaos. Unlike storms and volcanic eruptions,earthquakes are unpredictable, unleashed

    within seconds, and without warning. They

    spread destruction and death, forcing

    millions to flee from their homes. The day

    after the catastrophe revealed a terrifying

    scene: debris everywhere, a number of

    people injured and dead, others wandering

    desperately, children crying, and over three

    million survivors seeking help after losing

    everything. Throughout history Earth has

    been shaken by earthquakes of greater or

    lesser violence. These earthquakes have

    caused great harm. One of the most famous

    is the earthquake that rocked San Francisco

    in 1906. Registering 8.3 on the Richter scale,the temblor left nearly three thousand dead

    and was felt as far away as Oregon to the

    north, and Los Angeles in southern

    California.

    T

    he purpose of this book is to help you

    better understand the causes of

    fractures and the magnitude and

    violence of the forces deep within the earth.

    The full-color, illustrated book you hold in

    your hands contains shocking scenes of

    cities convulsed by earthquakes and

    volcanoes, natural phenomena that, in mere

    seconds, unleash rivers of fire, destroy

    buildings, highways and bridges, and gas and

    water lines and leave entire cities without

    electricity or phone service. If fires cannot

    be put out quickly, the results are even more

    devastating. Earthquakes near coastlands

    can cause tsunamis, waves that spread

    across the ocean with the speed of an

    airplane. A tsunami that reaches a coast can

    be more destructive than the earthquake

    itself. On Dec. 26, 2004, the world

    witnessed one of the most impressive

    natural disasters ever. An undersea quake

    with a magnitude of 9 on the Richter scale

    shook the eastern Indian Ocean, causing

    tsunamis that reached the coastal areas of

    eight Asian nations, causing about 230,000

    deaths. The earthquake was the fifth

    strongest since the invention of the

    seismograph. Satellite images show the

    region before and after the catastrophe.

    T

    hroughout history, nearly all ancient

    peoples and large societies have

    thought of volcanoes as dwelling

    places of gods or other supernatural beings

    to explain the mountains' fury. Hawaiian

    mythology, for instance, spoke of Pele, the

    goddess of volcanoes, who threw out fire to

    cleanse the earth and fertilize the soil. She

    was believed to be a creative force.

    Nowadays, specialists try to find out when a

    volcano might start to erupt, because within

    hours after an eruption begins, lava flows

    can change a lush landscape into a barren

    wilderness. Not only does hot lava destroy

    everything in its path, but gas and ash

    expelled in the explosion also replace oxygen

    in the air, poisoning people, animals, and

    plants. Amazingly, life reemerges once again

    from such scenes of destruction. After a

    time, lava and ash break down, making the

    soil unusually fertile. For this reason many

    farmers and others continue to live near

    these “smoking mountains,” in spite of the

    latent danger. Perhaps by living so close to

    the danger zone, they have learned that no

    one can control the forces of nature, and the

    only thing left to do is to simply live.

    The Power

    of Nature

    Kashmir, 2005

    Farmer Farid Hussain, 50, grasps

    the hand of his wife, Akthar Fatma,after the earthquake that rocked

    the Himalayas on the Indian

    subcontinent. Eighty thousand

    people were killed, and thousands

    of families were left homeless.OCEAN TRENCHES 16-17

    WRINKLES IN THE EARTH 18-19

    FOLDS 20-21

    WHEN FAULTS RESOUND 22-23

    Continuous Movement

    I

    n the volatile landscape of

    Volcano National Park in Hawaii,the beginning and end of life

    seem to go hand in hand.

    Outpourings of lava often reach

    the sea. When the molten rock enters

    the water, the lava quickly cools and

    hardens into rock that becomes part

    of the coastline. By this process,volcanic islands grow constantly, and

    nothing stays the same from one

    moment to another. One day rivers of

    lava blaze down the volcano's slopes,and the next day there are new, silver-

    colored rocks. The ongoing

    investigation of lava samples under the

    microscope helps volcanologists

    discover the rock's mineral

    composition and offers clues about

    how the volcano may behave.

    SCORCHING FLOW 8-9

    THE LONG HISTORY OF THE EARTH 10-11

    STACKED LAYERS 12-13

    THE JOURNEY OF THE PLATES 14-15

    PAHOEHOE LAVA

    A type of Hawaiian lava

    that flows down the slopes

    of Mt. Kilauea to the sea.VOLCANOES AND EARTHQUAKES 9 8 CONTINUOUS MOVEMENT

    Scorching Flow

    Most of the Earth's interior is in a liquid and incandescent state at extremely high

    temperatures. This vast mass of molten rock contains dissolved crystals and

    water vapor, among other gases, and it is known as magma. When part of the

    magma rises toward the Earth's surface, mainly through volcanic activity, it is called lava.

    As soon as it reaches the surface of the Earth or the ocean floor, the lava starts to cool

    and solidify into different types of rock, according to its original chemical composition.

    This is the basic process that formed the surface of our planet, and it is the reason the

    Earth's surface is in constant flux. Scientists study lava to understand our planet better.

    is the average temperature

    of liquid lava.

    1,800o F

    (1,000o C)

    TYPES OF LAVA

    Basaltic lava is found mainly in islands and in mid-ocean ridges; it is so fluid that it tends to spread as

    it flows. Andesitic lava forms layers that can be up to 130 feet (40 m) thick and that flow very slowly,whereas rhyolitic lava is so viscous that it forms solid fragments before reaching the surface.

    Streams of Fire

    Lava is at the heart of every volcanic eruption. The characteristics of lava vary, depending on

    the gases it contains and its chemical composition. Lava from an eruption is loaded with water

    vapor and gases such as carbon dioxide, hydrogen, carbon monoxide, and sulfur dioxide. As these

    gases are expelled, they burst into the atmosphere, where they create a turbulent cloud that

    sometimes discharges heavy rains. Fragments of lava expelled and scattered by the volcano are

    classified as bombs, cinders, and ash. Some large fragments fall back into the crater. The speed at

    which lava travels depends to a great extent on the steepness of the sides of the volcano. Some lava

    flows can reach 90 miles (145 km) in length and attain speeds of up to 30 miles per hour (50 kmhr).

    Rock Cycle

    Once it cools, lava forms igneous rock.

    This rock, subjected to weathering and

    natural processes such as metamorphism

    and sedimentation, will form other types of

    rocks that, when they sink back into the

    Earth's interior, again become molten rock.

    This process takes millions of years and is

    known as the rock cycle.

    Mineral Composition

    Lava contains a high level of silicates, light rocky minerals

    that make up 95 percent of the Earth's crust. The second

    most abundant substance in lava is water vapor. Silicates

    determine lava's viscosity, that is, its capacity to flow. Variations

    in viscosity have resulted in one of the most commonly used

    classification systems of lava: basaltic, andesitic, and rhyolitic,in order from least to greatest silicate content. Basaltic lava

    forms long rivers, such as those that occur in typical Hawaiian

    volcanic eruptions, whereas rhyolitic lava tends to erupt

    explosively because of its poor fluidity. Andesitic lava, named

    after the Andes mountains, where it is commonly found, is an

    intermediate type of lava of medium viscosity.

    INTENSE HEAT

    Lava can reach temperatures

    above 2,200o F (1,200o C). The

    hotter the lava, the more fluid it is.

    When lava is released in great

    quantities, it forms rivers of fire.

    The lava's advance is slowed down

    as the lava cools and hardens.

    SOLID LAVA

    Lava solidifies at temperatures below

    1,700o F (900o C). The most viscous

    type of lava forms a rough landscape,littered with sharp rocks; more fluid

    lava, however, tends to form flatter and

    smoother rocks.

    LAVA

    The state in which magma

    flows to the Earth's outer

    crust, either reaching the

    surface or getting trapped

    within the crust.

    Silicates

    1.

    IGNEOUS ROCK

    Rock formed when lava

    solidifies. Basalt and

    granite are good examples

    of igneous rocks.

    TURNS

    BACK INTO

    LAVA

    TURNS

    BACK INTO

    LAVA

    2.

    SEDIMENTARY

    ROCK

    Rock formed by

    eroded and

    compacted materials.

    METAMORPHIC

    ROCKS

    Their original

    structure is changed

    by heat and pressure.

    Andesitic Lava

    Silicates 63%

    Other

    Content 37%

    Rhyolitic Lava

    Silicates 68%

    Other

    Content 32% 52% Other Content

    48%VOLCANOES AND EARTHQUAKES 11 10 CONTINUOUS MOVEMENT

    FORMATION

    4.5 BILLION YEARS AGO

    4 BILLION YEARS AGO

    The accumulation of matter into solid

    bodies, a process called accretion, ended,and the Earth stopped increasing in volume.

    COOLING

    The first crust formed as it

    was exposed to space and

    cooled. Earth's layers became

    differentiated by their density.

    WARMING

    Earth warmed again, and the

    glaciers retreated, giving way to

    the oceans, in which new

    organisms would be born. The

    ozone layer began to form.

    METEORITE COLLISION

    Meteorite collisions, at a rate

    150 times as great as that of

    today, evaporated the primitive

    ocean and resulted in the rise of

    all known forms of life.

    The oldest rocks

    appeared.

    CONTINENTS

    The first continents, made of light

    rocks, appeared. In Laurentia (now

    North America) and in the Baltic,there are large rocky areas that

    date back to that time.

    Hypothesis of a first,great glaciation.

    1.8 BILLION YEARS AGO

    FOLDING IN THE

    TERTIARY PERIOD

    The folding began that would produce

    the highest mountains that we now

    have (the Alps, the Andes, and the

    Himalayas) and that continues to

    generate earthquakes even today.

    60 MILLION YEARS AGO

    The Long History of the Earth

    T

    he nebular hypothesis developed by astronomers suggests that the Earth was formed

    in the same way and at the same time as the rest of the planets and the Sun. It all

    began with an immense cloud of helium and hydrogen and a small portion of heavier

    materials 4.6 billion years ago. Earth emerged from one of these “small” revolving clouds,where the particles constantly collided with one another, producing very high temperatures.

    Later, a series of processes took place that gave the planet its present shape.

    Earth was formed 4.6 billion years ago. In the beginning it was a body of

    incandescent rock in the solar system. The first clear signs of life appeared in

    the oceans 3.6 billion years ago, and since then life has expanded and diversified.

    The changes have been unceasing, and,according to experts, there will be

    many more changes in the future.

    From Chaos to Today's Earth

    When the first crust

    cooled, intense volcanic

    activity freed gases

    from the interior of the

    planet, and those gases

    formed the atmosphere

    and the oceans.

    3.8 BILLION YEARS AGO

    2.3 BILLION YEARS AGO

    THE AGE OF THE

    SUPER VOLCANOES

    STABILIZATION

    The processes that formed

    the atmosphere, the oceans,and protolife intensified.

    At the same time, the crust

    stabilized, and the first

    plates of Earth's crust

    appeared. Because of their

    weight, they sank into

    Earth's mantle, making way

    for new plates, a process

    that continues today.

    “SNOWBALL” EARTH

    ARCHEAN EON

    PROTEROZOIC EON

    FRAGMENTATION

    The great landmass formed that would

    later fragment to provide the origin of the

    continents we have today. The oceans

    reached their greatest rate of expansion.

    540 MILLION YEARS AGO

    PALEOZOIC ERA

    2.2 BILLION YEARS AGO

    Indications of komatite,a type of igneous

    rock that no longer

    exists.

    SUPERCONTINENTS

    Rodinia, the first

    supercontinent, formed, but it

    completely disappeared about

    650 million years ago.

    1.0 BILLION YEARS AGO

    4.6

    BILLION

    YEARS

    AGOVOLCANOES AND EARTHQUAKES 13 12 CONTINUOUS MOVEMENT

    Earth's crust is its solid outer layer, with a thickness

    of 3 to 9 miles (4 to 15 km) under the oceans and up

    to 44 miles (70 km) under mountain ranges. Volcanoes on

    land and volcanic activity in the mid-ocean ridges generate

    new rock, which becomes part of the crust. The rocks at the

    bottom of the crust tend to melt back into the rocky mantle.

    Earth's crust

    The air and most of the weather events that affect our lives occur only in

    the lower layer of the Earth's atmosphere. This relatively thin layer, called

    the troposphere, is up to 10 miles (16 km) thick at the equator but only 4 miles

    (7 km) thick at the poles. Each layer of the atmosphere has a distinct composition.

    The Gaseous Envelope

    Composed mainly of

    molten iron and nickel

    among other metals at

    temperatures above

    8,500o F (4,700° C).

    The inner core behaves

    as a solid because it is

    under enormous pressure.

    Composition similar to that

    of the crust, but in a liquid

    state and under great pressure,between 1,830° and 8,130° F

    (1,000° and 4,500° C).

    THE MID-OCEAN RIDGES

    The ocean floor is regenerated with new

    basaltic rock formed by magma that solidifies

    in the rifts that run along mid-ocean ridges.

    THE CONTINENTAL

    SHELF

    In the area where

    the oceanic crust

    comes in contact with

    a continent, igneous

    rock is transformed

    into metamorphic rock

    by heat and pressure.

    KEY Sedimentary Rock

    PLUTONS

    Masses of rising

    magma trapped

    within the Earth's

    crust. Their name is

    derived from Pluto,the Roman god of

    the underworld.

    INTERNAL ROCK

    The inside of a

    mountain range

    consists of igneous

    rock (mostly

    granite) and

    metamorphic rock.

    GRANITIC

    BATHOLITHS

    Plutons can solidify

    underground as

    masses of granite.

    COASTAL ROCK

    Lithified layers of

    sediments, usually

    clay and pebbles,that come from the

    erosion of high

    mountains.

    OCEANIC ISLANDS

    Some sedimentary rocks are

    added to the predominantly

    igneous rock composition. MOUNTAIN RANGES

    Made up of the three

    types of rock in about

    equal parts.

    Contains 75 percent

    of the gas and almost

    all of the water vapor

    in the atmosphere.

    1,410 miles

    756 miles

    E

    very 110 feet (33 m) below the Earth's surface, the temperature increases by 1.8 degrees

    Fahrenheit (1 degree Celsius). To reach the Earth's center—which, in spite of temperatures

    above 12,000° F (6,700° C), is assumed to be solid because of the enormous pressure

    exerted on it—a person would have to burrow through four well-defined layers. The gases that

    cover the Earth's surface are also divided into layers with different compositions. Forces act on

    the Earth's crust from above and below to sculpt and permanently alter it.

    Stacked Layers

    (600 km)

    (2,300 km)

    (2,270 km)

    (1,216 km)

    370 miles

    3-44

    miles

    (5-70 km)

    CRUST

    LOWER MANTLE

    LITHOSPHERE 93 miles

    (150 km)

    (450 km)

    280 miles ASTHENOSPHERE

    UPPER MANTLE

    OUTER CORE

    INNER CORE

    1,430 miles

    Very dry; water vapor

    freezes and falls out

    of this layer, which

    contains the ozone layer.

    The temperature is

    -130o F (-90° C), but

    it increases gradually

    above this layer.

    THE SOLID EXTERIOR

    The crust is made up of

    igneous, sedimentary, and

    metamorphic rock, of

    various typical compositions,according to the terrain.

    Includes the solid

    outer part of the

    upper mantle, as

    well as the crust.

    Underneath is the

    asthenosphere,made up of partially

    molten rock.

    Metamorphic Rock Igneous Rock

    TROPOSPHERE

    6 miles

    Less than

    (10 km)

    STRATOSPHERE

    31 miles

    Less than

    (50 km)

    MESOSPHERE

    62 miles

    Less than

    (100 km)

    Very low density. Below

    155 miles (250 km) it

    is made up mostly of

    nitrogen; above that

    level it is mostly oxygen.

    THERMOSPHERE

    310 miles

    Less than

    (500 km)

    No fixed outer limit. It

    contains lighter gases

    such as hydrogen and

    helium, mostly ionized.

    EXOSPHERE

    310 miles

    Greater than

    (500 km)Continental Drift

    VOLCANOES AND EARTHQUAKES 15 14 CONTINUOUS MOVEMENT

    CONVECTION CURRENTS

    The hottest molten rock rises; once it rises,it cools and sinks again. This process causes

    continuous currents in the mantle.

    CONVERGENT BOUNDARY

    When two plates collide, one sinks

    below the other, forming a subduction

    zone. This causes folding in the crust

    and volcanic activity.

    Indo-Australian

    Plate

    Tongan

    Trench Eastern

    Pacific Ridge

    Nazca

    Plate

    South

    American Plate

    Mid-Atlantic

    Ridge

    Continental

    crust

    Subduction zone

    East

    African

    Rift

    Valley

    Somalian

    Subplate

    Peru-Chile

    Trench

    OUTWARD MOVEMENT

    The action of the magma causes

    the tectonic plate to move toward

    a subduction zone at its far end.

    WIDENING

    At divergent plate boundaries the magma

    rises, forming new oceanic crust. Folding

    occurs where plates converge.

    250

    DIVERGENT BOUNDARY

    When two plates separate, a

    rift is formed between them.

    Magma exerts great pressure,and it renews the ocean floor

    as it solidifies. The Atlantic

    Ocean was formed in this way.

    Continental

    granite

    The number of years it will take for

    the continents to drift together again.

    2 inches

    (5 cm)

    Typical distance the plates

    travel in a year.

    The Journey of the Plates

    When geophysicist Alfred Wegener suggested in 1910 that

    the continents were moving, the idea seemed fantastic.

    There was no way to explain the idea. Only a half-century

    later, plate tectonic theory was able to offer an explanation of the

    phenomenon. Volcanic activity on the ocean floor, convection

    currents, and the melting of rock in the mantle power the

    continental drift that is still molding the planet's surface today.

    Convection currents of molten rock

    propel the crust. Rising magma

    forms new sections of crust at divergent

    boundaries. At convergent boundaries,the crust melts into the mantle.

    Thus, the tectonic plates act like

    a conveyor belt on which

    the continents travel.

    The Hidden Motor

    The landmass today's continents come from was

    a single block (Pangea) surrounded by the ocean....180 MILLION YEARS AGO

    The North American Plate has separated, as has

    the Antarctic Plate. The supercontinent Gondwana

    (South America and Africa) has started to divide

    and form the South Atlantic. India is separating

    from Africa.…100 MILLION YEARS AGO

    The Atlantic Ocean has formed. India is headed

    toward Asia, and when the two masses collide,the Himalayas will rise. Australia is separating

    from Antarctica.... 60 MILLION YEARS AGO MILLION

    YEARS The continents are near their current location. India

    is beginning to collide with Asia. The Mediterranean

    is opening, and the folding is already taking place that

    will give rise to the highest mountain ranges of today.

    250 MILLION YEARS AGO

    GONDWANA

    LAURASIA

    ANTARCTICA

    AFRICA

    INDIA

    AFRICA

    ATLANTIC

    OCEAN

    ATLANTIC

    OCEAN

    ANTARCTICA

    NORTH

    AMERICA

    AUSTRALIA

    NORTH

    AMERICA

    SOUTH

    AMERICA

    SOUTH

    AMERICA

    ASIA

    EURASIA

    The first ideas on continental drift proposed

    that the continents floated on the ocean.

    That idea proved inaccurate. The seven tectonic

    plates contain portions of ocean beds and continents.

    They drift atop the molten mantle like sections of a

    giant shell. Depending on the direction in which

    they move, their boundaries can converge (when

    they tend to come together), diverge (when they

    tend to separate), or slide horizontally past each

    other (along a transform fault).

    PANGEA

    African

    PlateInside and Outside the Ridge

    The abyssal (deep-ocean) plains of the Atlantic are the

    flattest surfaces on Earth; for thousands of miles, the

    elevation varies by only about 10 feet (3 m). The plains are

    made mostly of sediment. Variations in the ocean's depth are

    mainly the result of volcanic activity, not just within the mid-

    Atlantic Ridge but elsewhere as well.

    A spongy layer of rock several

    dozen miles wide rises above the

    rift. As the layer fractures and moves

    away from the fissure, it solidifies into

    angled blocks that are parallel to the

    fissure and separated by dikes. Thus the

    ocean widens as the ridge spreads. The

    magma exists in a fluid form 2 miles

    (3.5 km) below the crest of the ridge.

    Magnetic Reversals

    The Earth's magnetic field changes direction

    periodically. The magnetic north pole changes

    places with the magnetic south pole. Rock that solidified

    during a period of magnetic polarity reversal was

    magnetized with a polarity opposite that of newly forming

    rocks. Rocks whose magnetism corresponds to the present

    direction of the Earth's magnetic field are said to have

    normal polarity, whereas those with the opposite magnetic

    polarity are said to have reversed polarity.

    The constant generation of new

    ocean crust along rift zones

    powers a seemingly endless process that

    generates new lithosphere that is carried

    from the crest of the ridges, as if on a

    conveyor belt. Because of this, scientists

    have calculated that in about 250 million

    years, the continents will again join and

    form a new Pangea as they are pushed

    by the continually expanding ocean floor.

    Ocean plates are in contact with land

    plates at the active boundaries of

    subduction zones or at passive

    continental boundaries (continental

    shelves and slopes). Undersea

    subduction zones, called ocean trenches,also occur between oceanic plates: these

    are the deepest places on the planet.

    AFRICA

    EUROPE

    SOUTH AMERICA

    OCEAN MOUNTS

    Isolated volcanic cones. Some rise

    above the ocean's surface to

    become islands, such as the Azores.

    ATOLLS

    Also called coral reefs, atolls are

    formations of coral deposited

    around a volcanic cone in warm

    seas. They form ring-shaped islands.

    29,035 feet (8,850 m)

    Highest point

    (Mount Everest)

    2,900 feet (870 m)

    Average land elevation

    7,900 feet (2,400 m)

    Earth's average elevation

    12,240 feet (3,730 m)

    Average depth

    Greatest depth

    (Mariana Trench)

    About 36,000 feet

    (11,000 m)

    0 feet (0 m)

    Sea level

    1

    2

    Rising

    magma

    Oceanic

    lithosphere

    Asthenosphere

    Dikes within

    host rock

    Pillow

    lava

    Fumarole

    Volcanic

    smoke

    HEIGHTS

    AND DEPTHS

    Deep-ocean basins cover

    30 percent of the Earth's

    surface. The depth of the

    ocean trenches is greater than

    the height of the greatest

    mountain ranges, as shown in

    the graphic below at left.

    ENLARGED AREA

    Cracks in the Ocean Floor

    16 CONTINUOUS MOVEMENT VOLCANOES AND EARTHQUAKES 17

    T

    he concept that the ocean floor is spreading was studied

    for many years: new crust constantly forms at the

    bottom of the ocean. The ocean floor has deep trenches,plains, and mountain ranges. The mountain ranges are higher

    than those found on the continents but with different

    characteristics. The spines of these great mountain ranges,The Crust Under the Oceans

    MAGNETISM

    Normal

    magnetism

    Reversed

    magnetism

    called mid-ocean ridges, exhibit incredible volcanic activity in

    rift zones. The rift zones are fissures in relatively narrow

    regions of the crust, along which the crust splits and spreads.

    One hundred eighty million years ago, the paleocontinent

    Gondwana broke apart, forming a rift from which the Atlantic

    Ocean grew, and is still growing.

    How the Mid-Ocean

    Ridge Was Formed

    Europe

    North

    America

    Central

    America

    South

    America Australia

    Africa

    AsiaThe Three Greatest Folding Events

    The Earth's geological history has included three major mountain-

    building processes, called “orogenies.” The mountains created during

    the first two orogenies (the Caledonian and the Hercynian) are much lower

    today because they have undergone millions of years of erosion.

    Formation of the Himalayas

    The highest mountains on Earth were formed following the collision of

    India and Eurasia. The Indian Plate is sliding horizontally underneath

    the Asiatic Plate. A sedimentary block trapped between the plates is cutting

    the upper part of the Asiatic Plate into segments that are piling on top of

    each other. This folding process gave rise to the Himalayan range, which

    includes the highest mountain on the planet, Mount Everest (29,035 feet

    [8,850 m]). This deeply fractured section of the old plate is called an

    accretion prism. At that time, the Asian landmass bent, and the plate doubled

    in thickness, forming the Tibetan plateau.

    A portion of the crust subjected to a sustained

    horizontal tectonic force is met by resistance,and the rock layers become deformed.

    The outer rock layers, which are often more rigid,fracture and form a fault. If one rock boundary

    slips underneath another, a thrust fault is formed.

    1 2 3

    430 Million Years

    CALEDONIAN OROGENY

    Formed the Caledonian range.

    Remnants can be seen in Scotland, the

    Scandinavian Peninsula, and Canada

    (which all collided at that time).

    HERCYNIAN OROGENY

    Took place between the late Devonic and

    the early Permian periods. It was more

    important than the Caledonian Orogeny. It

    shaped central and western Europe and

    produced large veins of iron ore and coal.

    This orogeny gave rise to the Ural

    Mountains, the Appalachian range in North

    America, part of the Andes, and Tasmania.

    Trilobites

    300 Million Years

    MATERIALS Mostly granite, slate,amphibolite, gneiss, quartzite, and schist.

    MATERIALS

    High proportions of

    sediment in Nepal,batholiths in the Asiatic

    Plate, and intrusions of new

    granite: iron, tin, and tungsten.

    Distortions of the Crust

    The crust is composed of layers of solid rock. Tectonic

    forces, resulting from the differences in speed and direction

    between plates, make these layers stretch elastically, flow, or

    break. Mountains are formed in processes requiring millions of

    years. Then external forces, such as erosion from wind,ice, and water, come into play. If slippage releases rock

    from the pressure that is deforming it elastically, the rock

    tends to return to its former state and can cause earthquakes.

    VOLCANOES AND EARTHQUAKES 19 18 CONTINUOUS MOVEMENT

    MATERIALS Mudstone, slate, and

    sandstone, in lithified layers.

    60 MILLION YEARS AGO

    The Tethys Sea gives way as the plates

    approach. Layers of sediment begin to rise.

    40 MILLION YEARS AGO

    As the two plates approach each other,a subduction zone begins to form.

    20 MILLION YEARS AGO

    The Tibetan plateau is pushed up by

    pressure from settling layers of sediment.

    THE HIMALAYAS TODAY

    The movement of the plates continues to fold the

    crust, and the land of Nepal is slowly disappearing.

    Amonites

    60 MILLION

    YEARS

    A COLLISION OF CONTINENTS

    Indian

    Plate

    Asiatic

    Plate

    Tethys Sea Lighter

    sediments

    Heavy

    sediments

    Tethys Sea Tibet Heavy

    sediments

    Tibet Heavy

    sediments

    Tibet Nepal India

    ALPINE OROGENY

    Began in the Cenozoic Era and continues today.

    This orogeny raised the entire system of

    mountain ranges that includes the Pyrenees,the Alps, the Caucasus, and even the

    Himalayas. It also gave the American Rockies

    and the Andes Mountains their current shape.

    India today

    10 MILLION

    YEARS AGO

    20 MILLION

    YEARS AGO

    30 MILLION

    YEARS AGO

    The composition of rock layers shows the origin

    of the folding, despite the effects of erosion.

    SOUTHEAST

    ASIA

    Brachiopods

    T

    he movement of tectonic plates causes distortions and breaks in the Earth's

    crust, especially in convergent plate boundaries. Over millions of years,these distortions produce larger features called folds, which become

    mountain ranges. Certain characteristic types of terrain give clues

    about the great folding processes in Earth's geological history.

    Folding in the Earth's CrustVOLCANOES AND EARTHQUAKES 21

    MUDSTONE

    SANDSTONE

    LIMESTONE

    Composition

    Before mountain ranges were lifted up by the collision of ancient

    continents, constant erosion of the land had deposited large

    amounts of sediments along their coasts. These sediments later formed

    the rock that makes up the folding seen here. As that rock's shape clearly

    shows, tectonic forces compressed the originally horizontal sediments

    until they became curved. This phenomenon is seen along Cardigan Bay

    on the ancient coast of Wales.

    SANDSTONE

    20 CONTINUOUS MOVEMENT

    Folds

    T

    he force that forms the mountains also molds the rocks within them. As

    the result of millions of years of pressure, the layers of crust fold into

    strange shapes. The Caledonian Orogeny, which began 450 million years

    ago, created a long mountain range that joined the Appalachian mountains of

    the United States to the Scandinavian peninsula. All of northern England was

    lifted up during this process. The ancient Iapetus Ocean once lay between

    the colliding continents. Sedimentary rocks from the bed of this ocean

    were lifted up, and they have kept the same forms they had in the past.

    THREE CONTINENTS

    The Caledonian orogeny

    was formed by the

    collision of three ancient

    continents: Laurasia,Gondwana, and Baltica.

    In between them,the Iapetus Ocean

    floor contained

    sediments that now

    form the bedrock of

    the coast of Wales.

    1.

    A MOUNTAIN RANGE

    The long Caledonian range is seen

    today in the coasts of England,Greenland, and Scandinavia. Since the

    tectonic movements that created them

    have ended, they are being worn away

    and sculpted by constant erosion.

    2.

    MILLION

    YEARS 395

    MILLION

    YEARS

    440

    The name of the geological period

    in which this folding occurred.

    Silurian

    Place

    Length

    Rock

    Fold

    WALES, UNITED

    KINGDOM

    Latitude: 51° 30’ N

    Longitude: 003° 12’ W

    Cardigan Bay

    40 miles (64 km)

    Sedimentary

    MonoclinalThe great San Andreas fault in the

    western United States is the backbone of

    a system of faults. Following the great

    earthquake that leveled San Francisco in 1906,this system has been studied more than any

    other on Earth. It is basically a horizontal

    transform fault that forms the boundary

    between the Pacific and North American tectonic

    plates. The system contains many complex lesser

    faults, and it has a total length of 800 miles

    (1,300 km). If both plates were able to slide past

    each other smoothly, no earthquakes would

    result. However, the borders of the plates are in

    contact with each other. When the solid rock

    cannot withstand the growing strain, it breaks

    and unleashes an earthquake.

    Fatal Crack

    F

    aults are small breaks that are produced along the Earth's crust. Many, such as the

    San Andreas fault, which runs through the state of California, can be seen readily.

    Others, however, are hidden within the crust. When a fault fractures suddenly, an

    earthquake results. Sometimes fault lines can allow magma from lower layers to break

    through to the surface at certain points, forming a volcano.

    VOLCANOES AND EARTHQUAKES 23 22 CONTINUOUS MOVEMENT

    When the Faults Resound Streambeds Diverted

    by Tectonic Movement

    Through friction and surface cracking, a

    transform fault creates transverse faults

    and, at the same time, alters them with its

    movement. Rivers and streams distorted by the

    San Andreas fault have three characteristic forms:

    streambeds with tectonic displacement, diverted

    streambeds, and streambeds with an orientation

    that is nearly oblique to the fault.

    Fault borders do not usually form straight

    lines or right angles; their direction along

    the surface changes. The angle of vertical

    inclination is called “dip.” The classification of a

    fault depends on how the fault was formed and

    on the relative movement of the two plates that

    form it. When tectonic forces compress the crust

    horizontally, a break causes one section of the

    ground to push above the other. In contrast,when the two sides of the fault are under tension

    (pulled apart), one side of the fault will slip down

    the slope formed by the other side of the fault.

    Relative Movement Along Fault Lines

    Fault plane

    350 miles

    (566 km)

    The distance that the opposite sides

    of the fault have slipped past each

    other, throughout their history.

    140 years

    NORTH AMERICAN

    PLATE

    PACIFIC PLATE

    The average interval between major

    ruptures that have taken place along

    the fault. The interval can vary

    between 20 and 300 years.

    Juan de

    Fuca Plate

    San Andreas

    Fault

    East

    Pacific Ridge

    Queen Charlotte Fault

    1 2

    Diverted Streambed

    The stream changes course

    as a result of the break.

    Displaced Streambed

    The streambed looks

    “broken” along its fault line.

    1

    Normal

    Fault

    This fault is the product of

    horizontal tension. The

    movement is mostly vertical,with an overlying block (the

    hanging wall) moving

    downward relative to an

    underlying block (the

    footwall). The fault plane

    typically has an angle of 60

    degrees from the horizontal.

    2

    Reverse Fault

    This fault is caused by a horizontal

    force that compresses the ground. A

    fracture causes one portion of the

    crust (the hanging wall) to slide over

    the other (the footwall). Thrust faults

    (see pages 18-19), are a common form

    of reverse fault that can extend up to

    hundreds of miles. However, reverse

    faults with a dip greater than 45° are

    usually only a few yards long.

    3

    Oblique-Slip

    Fault

    This fault has horizontal as well as vertical

    movements. Thus, the relative displacement

    between the edges of the fault can be

    diagonal. In the oldest faults, erosion

    usually smoothes the differences in the

    surrounding terrain, but in more recent

    faults, cliffs are formed. Transform faults

    that displace mid-ocean ridges are a

    specific example of oblique-slip faults.

    Strike-Slip

    Fault

    In this fault the relative movement of the plates

    is mainly horizontal, along the Earth's surface,parallel to the direction of the fracture but not

    parallel to the fault plane. Transform faults

    between plates are usually of this type. Rather

    than a single fracture, they are generally made up

    of a system of smaller fractures, slanted from a

    centerline and more or less parallel to each other.

    The system can be several miles wide.

    Fault

    plane

    Elevated block

    Hanging

    wall

    Footwall

    Hanging

    wall

    Footwall

    Dip angle

    SAN FRANCISCO

    OAKLAND

    PACIFIC

    OCEAN

    FOOTWALL FOOTWALL

    San

    Andreas

    Calaveras

    Greenville

    Mt.

    Diablo

    Concord-Green Valley

    San

    Gregorio

    Rodgers Creek

    Hayward

    OPPOSITE

    DIRECTIONS

    The northwestward

    movement of the

    Pacific Plate and the

    southeastward movement

    of the North American Plate

    cause folds and fissures

    throughout the region.

    PAST AND FUTURE

    Some 30 million years ago, the Peninsula

    of California was west of the present

    coast of Mexico. Thirty million years

    from now, it is possible that it may be

    some distance off the coast of Canada.

    WEST

    COAST

    OF THE

    UNITED

    STATES

    Greatest

    displacement (1906)

    Maximum

    width of fault

    Length of California

    Length of fault

    770 miles (1,240 km)

    800 miles (1,300 km)

    60 miles (100 km)

    20 feet (6 m) AFTERMATH OF FURY 36-37

    JETS OF WATER 38-39

    RINGS OF CORAL 40-41

    FROZEN FLAME 42-43

    Volcanoes

    Mount Etna has always been

    an active volcano, as seen

    from the references to its

    activity that have been

    made throughout history. It

    could be said that the volcano has not

    given the beautiful island of Sicily a

    moment's rest. The Greek philosopher

    Plato was the first to study Mount Etna.

    He traveled to Italy especially to see it

    up close, and he subsequently described

    how the lava cooled. Today Etna's

    periodic eruptions continue to draw

    hundreds of thousands of tourists, who

    enjoy the spectacular fireworks

    produced by its red-hot explosions. This

    phenomenon is visible from the entire

    east coast of Sicily because of the

    region's favorable weather conditions

    and the constant strong winds.

    FLAMING FURNACE 26-27

    CLASSIFICATION 28-29

    FLASH OF FIRE 30-31

    MOUNT ST. HELENS 32-33

    KRAKATOA 34-35

    MOUNT ETNA

    With a height of 10,810 feet

    (3,295 m), Etna is the largest and

    most active volcano in Europe.Flaming Furnace

    26 VOLCANOES VOLCANOES AND EARTHQUAKES 27

    Volcanoes are among the most powerful manifestations of

    our planet's dynamic interior. The magma they release at

    the Earth's surface can cause phenomena that devastate

    surrounding areas: explosions, enormous flows of molten rock,fire and ash that rain from the sky, floods, and mudslides.

    Since ancient times, human beings have feared volcanoes,even seeing their smoking craters as an entrance to the

    underworld. Every volcano has a life cycle, during which

    it can modify the topography and the climate and

    after which it becomes extinct.

    Explosive

    eruptions can

    expel huge

    quantities of lava,gas, and rock.

    LIFE AND DEATH OF A VOLCANO:

    THE FORMATION OF A CALDERA

    1.

    ERUPTION

    OF LAVA

    CLOUD

    OF ASH

    STREAMS OF LAVA

    flow down the flanks

    of the volcano.

    CRATER

    Depression or hollow

    from which eruptions

    expel magmatic

    materials (lava, gas,steam, ash, etc.)

    VOLCANIC CONE

    Made of layers of

    igneous rock, formed

    from previous eruptions.

    Each lava flow adds a

    new layer.

    MAIN CONDUIT

    The pipe through

    which magma rises.

    It connects the

    magma chamber

    with the surface.

    MAGMA CHAMBER

    Mass of molten rock at

    temperatures that may exceed

    2,000° F

    (1,100° C)

    In an active volcano, magma

    in the chamber is in constant

    motion because of

    fluctuations of

    temperature and pressure

    (convection currents).

    Magma can reach the

    surface, or it can stay

    below ground and exert

    pressure between the

    layers of rock. These

    seepages of magma

    have various names.

    SEEPAGE OF

    GROUNDWATER

    EXTINCT

    CONDUIT

    SECONDARY

    CONDUIT

    PARASITIC

    VOLCANO

    UNDER THE VOLCANO

    In its ascent to the surface, the magma

    may be blocked in various chambers at

    different levels of the lithosphere.

    A void is left

    in the conduit

    and in the

    internal chamber.

    2.

    The cone breaks up

    into concentric

    rings and sinks into

    the chamber.

    Volcanic

    activity may

    continue.

    3.

    A depression, or caldera, forms

    where the crater had been, and it

    may fill up with rainwater. 4.

    Ocean crust

    SCALE

    IN MILES

    (KM)

    60

    (100)

    220

    (350)

    1,790

    (2,880)

    3,200

    (5,140)

    3,960

    (6,370)

    Continental crust

    Lithosphere

    Asthenosphere

    Mesosphere

    Liquid core

    Solid core

    MAGMA

    1 When two plates

    converge, one moves

    under the other

    (subduction).

    2 The rock melts and

    forms new magma.

    Great pressure builds up

    between the plates.

    Many volcanoes are caused by phenomena occurring in

    subduction zones along convergent plate boundaries.

    MOUNTAIN-RANGE VOLCANOES

    SILL

    Layer of magma forms

    between rock layers.

    DIKE

    Vertical Channel

    of Magma.

    PLUG OF AN

    EXTINCT

    VOLCANO

    ACTIVE

    VOLCANO

    INTRUSION OF MAGMA

    Composite volcanic

    cones have more

    than one crater.

    3 The heat and pressure in the crust force the

    magma to seep through cracks in the rock and

    rise to the surface, causing volcanic eruptions.CINDER CONE

    Cone-shaped, circular

    mounds up to 980 feet

    (300 m) high. They are

    formed when falling debris

    or ash accumulates near

    the crater. These volcanic

    cones have gently sloping

    sides, with an angle

    between 30° and 40°.

    VOLCANOES AND EARTHQUAKES 29 28 VOLCANOES

    Classification

    No two volcanoes on Earth are exactly alike, although they have

    characteristics that permit them to be studied according to six basic

    types: shield volcanoes, cinder cones, stratovolcanoes, lava cones,fissure volcanoes, and calderas. A volcano's shape depends on its origin,how the eruption began, processes that accompany the volcanic activity,and the degree of danger the volcano poses to life in surrounding areas.

    LAVA DOME

    The sides are formed by

    the accumulation of “hard”

    lava, made viscous by its

    high silicon content.

    Instead of flowing, it

    quickly hardens in place.

    STRATOVOLCANO

    (COMPOSITE VOLCANO)

    Nearly symmetrical in appearance,formed by layers of fragmented

    material (ash and pyroclasts)

    between lava flows. A stratovolcano

    is structured around a main conduit,although it may also have several

    branch pipes. This is usually the most

    violent type of volcano.

    SHIELD VOLCANO

    The diameter of these

    volcanoes is much

    greater than their

    height. They are formed

    by the accumulation of

    highly fluid lava flows, so

    they are low, with gently

    sloping sides, and they

    are nearly flat on top.

    Magma

    chamber

    Convex

    Sides

    Layers of

    ash

    Branch

    Pipe

    Sill

    Dike

    Parasitic

    Volcano River of

    Lava

    Lava

    slope

    Caldera

    that contains

    a lake

    Plug of extinct

    volcano

    Formation

    of new

    cone

    Shock

    wave

    Crater of

    Stratovolcano

    Main

    Conduit

    Extinct

    volcano

    FORMATION OF

    THE VOLCANIC PLUG

    INITIAL

    EROSION

    THE NECK

    FORMS.

    Lava

    solidifies

    and forms

    resistant

    rock.

    Erosion of

    the cone

    The plug

    is not

    affected. The surrounding

    terrain is flat.

    The volcanic

    neck remains.

    CALDERA VOLCANO

    Large basins, similar to craters but greater than

    0.8 mile (1 km) across, are called calderas. They

    are found at the summit of extinct or inactive

    volcanoes, and they are typically filled with deep

    lakes. Some calderas were formed after

    cataclysmic explosions that completely destroyed

    the volcano. Others were formed when, after

    successive eruptions, the empty cone could no

    longer hold up the walls, which then collapsed.

    THE MOST COMMON

    Stratovolcanoes, or composite cones,are strung along the edges of the

    Pacific Plate in the region known

    as the “Ring of Fire.”

    FISSURE VOLCANOES

    Long, narrow openings found

    mainly in mid-ocean ridges. They

    emit enormous amounts of

    highly fluid material and form

    wide slopes of stratified basaltic

    stone. Some, such as that of the

    Deccan Plateau in India, cover

    more than 380,000 square miles

    (1 million sq km).

    CHAPEL OF ST. MICHAEL

    Built in Le Puy, France, on top

    of a volcanic neck of hard

    rock that once sealed the

    conduit of a volcano. The

    volcano's cone has long

    since been worn away

    by erosion; the lava

    plug remains.

    IGNEOUS INTRUSIONS: A PECULIAR PROFILE

    1 2 3

    MOUNT FUJI

    Composite

    volcano 12,400

    feet (3,776 m)

    high, the highest

    in Japan. Its

    last eruption

    was in 1707.

    MAUNA ULU

    Fissure volcano,about 5 miles (8 km)

    from the top of

    Kilauea (Hawaii). This

    is one of the most

    active volcanoes in

    the central Pacific.

    CALDERA

    BLANCA

    Located on

    Lanzarote, Canary

    Islands, in the

    fissure zone known

    as the Monta?as

    de Fuego (Fire

    Mountains).

    MOUNT

    KILAUEA

    Shield volcano

    in Hawaii. One

    of the most

    active shield

    volcanoes on

    Earth.

    MOUNT

    ILAMATEPEC

    Cinder cone located

    45 miles (65 km)

    west of the capital of

    El Salvador. Its last

    recorded eruption

    was in October 2005.

    FEET (80 M)

    The height of

    the plug, from

    base to peak.

    262VOLCANOES AND EARTHQUAKES 31 30 VOLCANOES

    Flash of Fire

    Avolcanic eruption is a

    process that can last from

    a few hours to several

    decades. Some are devastating,but others are mild. The severity

    of the eruption depends on the

    dynamics between the magma,dissolved gas, and rocks within the

    volcano. The most potent

    explosions often result from

    thousands of years of

    accumulation of magma and gas,as pressure builds up inside the

    chamber. Other volcanoes, such as

    Stromboli and Etna, reach an

    explosive point every few months

    and have frequent emissions.u

    THE ESCAPE

    When the mounting

    pressure of the magma

    becomes greater than the

    materials between the

    magma and the floor of the

    volcano's crater can bear,these materials are ejected.

    IN THE CONDUIT

    A solid layer of fragmented

    materials blocks the magma

    that contains the volatile

    gases. As the magma rises

    and mixes with volatile

    gases and water vapor, the

    pockets of gases and steam

    that form give the magma

    its explosive power.

    Water

    Vapor

    Plume of ash

    Cloud of burning

    material from about

    330 to 3,300 feet

    (100-1,000 m) high

    The column can

    reach a height of

    49,000 feet

    (15 km)

    Cloud can reach

    above 82,000 feet

    (25 km).

    Dome Low, like a

    shield volcano, with

    a single opening

    Pyroclastic

    Fragments

    Low volume

    Lava Flows

    Highly fluid,of basaltic

    composition.

    WHERE

    In mid-ocean

    ridges and on

    volcanic islands.

    Fissure

    Often

    several

    miles long

    Lava

    Seeps

    out slowly

    Large,Frequent

    Lava Flows

    Burning cloud

    moving down

    the slope

    Lava

    flow

    Volcanic

    ash

    Snow

    and ice

    (11.5 Km) HIGH

    SMOKE COLUMN

    Lava plug

    Lava

    flow

    Burning

    clouds

    Abundant

    pyroclastic

    fragments

    Lava flows

    Viscous and

    dome-shaped

    lava

    Lava

    Andesitic or

    rhyolitic

    MAGMA

    MAGMA

    Gas

    Particles

    Molten

    Rock

    CRATER

    BOMB

    LAPILLI

    ASH

    CONDUIT

    MAGMA CHAMBER

    IN THE CHAMBER

    There is a level at which

    liquefaction takes place and

    at which rising magma,under pressure, mixes with

    gases in the ground. The

    rising currents of magma

    increase the pressure,hastening the mixing.

    EXPLOSIVE ACTIVITY

    TYPES OF EXPLOSIVE

    ERUPTION

    LAVA FLOW MT. KILAUEA, HAWAII LAKE OF LAVA MAKA-O-PUHL, HAWAII COOLED LAVA (PAHOEHOE) MT. KILAUEA, HAWAII

    TYPES OF EFFUSIVE ERUPTION FROM OUTER SPACE

    A photo of the eruption of Mt.

    Augustine in Alaska, taken by the

    Landsat 5 satellite hours after

    the March 27, 1986, eruption.

    Comes from the combination of high levels of gas with

    relatively viscous lava, which can produce pyroclasts and

    build up great pressure. Different types of explosions are

    distinguished based on their size and volume. The greatest

    explosions can raise ash into a column several miles high.

    EFFUSIVE ACTIVITY

    Mild eruptions with a low frequency of explosions. The

    lava has a low gas content, and it flows out of openings

    and fissures.

    HOW IT HAPPENS

    3.

    2.

    PYROCLASTIC PRODUCTS

    In addition to lava, an eruption can

    eject solid materials called

    pyroclasts. Volcanic ash consists of

    pyroclastic material less than 0.08

    inch (2 mm) in size. An explosion can

    even expel granite blocks.

    WHERE

    Along the

    margins of

    continents and

    island chains.

    BOMB

    LAPILLI

    ASH

    2.5 inches (64 mm) and up

    0.08 to 2.5 inches (2 mm

    to 64 mm)

    Up to 0.08 inch (2 mm)

    4.

    LAVA FLOWS

    On the volcanic island of

    Hawaii, nonerupting flows

    of lava abound. Local terms

    for lava include “aa,”

    viscous lava flows that

    sweep away sediments, and

    “pahoehoe,” more fluid lava

    that solidifies in soft waves.

    STROMBOLIAN

    The volcano Stromboli in

    Sicily, Italy, gave its

    name to these high-

    frequency eruptions. The

    relatively low volume of

    expelled pyroclasts

    allows these eruptions

    to occur approximately

    every five years.

    HAWAIIAN

    Volcanoes such as Mauna

    Loa and Kilauea expel large

    amounts of basaltic lava

    with a low gas content, so

    their eruptions are very mild.

    They sometimes emit

    vertical streams of bright

    lava (“fountains of fire”) that

    can reach up to 330 feet

    (100 m) in height.

    FISSURE

    Typical in ocean rift zones,fissures are also found on the

    sides of composite cones such

    as Etna (Italy) or near shield

    volcanoes (Hawaii). The

    greatest eruption of this type

    was that of Laki, Iceland, in

    1783: 2.9 cubic miles (12 cu

    km) of lava was expelled from

    a crack 16 miles (25 km) long.

    VULCANIAN

    Named after Vulcano in

    Sicily. As eruptions eject

    more material and become

    more explosive, they

    become less frequent. The

    1985 eruption of Nevado

    del Ruiz expelled tens of

    thousands of cubic yards

    of lava and ash.

    VESUVIAN

    Also called Plinian, the

    most violent

    explosions raise

    columns of smoke and

    ash that can reach into

    the stratosphere and

    last up to two years,as in the case of

    Krakatoa (1883).

    PELEAN

    A plug of lava blocks the

    crater and diverts the

    column to one side after a

    large explosion. As with Mt.

    Pelée in 1902, the pyroclastic

    flow and lava are violently

    expelled down the slope in a

    burning cloud that sweeps

    away everything in its path.

    5. 1.

    7 MilesVOLCANOES AND EARTHQUAKES 33 32 VOLCANOES

    Mount St. Helens

    Warning Signs

    Two months before the great

    explosion, Mount St. Helens

    gave several warning signs: a series of

    seismic movements, small explosions,and a swelling of the mountain's north

    slope, caused by magma rising toward

    the surface. Finally on May 18, an

    earthquake caused a landslide that

    carried away the top of the volcano.

    Later, several collapses at the base of

    the column caused numerous

    pyroclastic flows with temperatures of

    nearly 1,300° F (700° C).

    9,680 feet

    (2,950 m)

    -1,315 feet

    (-401 m)

    8,363 feet

    (2,549 m)

    GLACIER

    TONGUE

    CONE

    OLD DOME

    (1980-86)

    PRECOLLAPSE

    SUMMIT

    NEW DOME

    Influx of

    magma.

    Graben:

    Depression

    caused by

    movement in

    the Earth's

    crust

    Blocked

    Crater

    Side

    block of

    the cone

    Profile

    before the

    collapse

    Profile

    after the

    collapse

    Unchanged

    profile.

    Secondary

    dome of

    earlier rocks.

    Precollapse

    swelling.

    Having no

    escape route,the magma

    exerts pressure

    sideways and

    breaks through

    the north slope.

    The crater

    exploded.

    The side block gave

    way, causing a powerful

    pyroclastic flow.

    A vertical

    column of

    smoke and ash

    rose 12 miles

    (19 km) high.

    In the eruption Mount

    St. Helens lost its conical

    stratovolcano shape and

    became a caldera.

    Pulverized and incinerated

    by the force of the lava

    and the pyroclastic flow.

    Temperatures rose above

    1,110° F (600° C).

    8miles

    13 km

    Range of the shock wave from the

    pyroclastic flow. The heat and ash left

    acres of forest completely destroyed.

    15 miles

    24 km

    600 sq km

    SWELLING

    The uninterrupted flow of magma toward

    the volcano's surface caused the north

    slope of the mountain to swell, and later

    collapse in an avalanche.

    1.

    232 SQUARE

    MILES

    SURFACE DESTRUCTION

    The effects were devastating:

    250 houses, 47 bridges, rail

    lines, and 190 miles (300 km)

    of highway were lost.

    BEFORE THE ERUPTION

    The symmetrical cone, surrounded

    by forest and prairies, was admired

    as the American Fuji. The eruption

    left a horseshoe-shaped caldera,surrounded by devastation.

    DURING THE EXPLOSION

    The energy released was the

    equivalent of 500 nuclear

    bombs. The top of the

    mountain flew off like the cap

    of a shaken bottle of soda.

    Cut Top

    Like the cork in a bottle

    of champagne, the top

    of the mountain burst

    off because of pressure

    from the magma.

    The Forest

    Burned trees covered

    with ash, several miles

    from the volcano

    Type of Volcano

    Size of Base

    Type of Activity

    Type of Eruption

    Most Recent Eruptions

    Fatalities

    OLYMPIA

    WASHINGTON

    STATE

    Stratovolcano

    5.9 mi (9.5 km)

    Explosive

    Plinian

    1980, 1998, 2004

    57

    PRESSURE ON THE NORTH SLOPE

    The swelling of the mountain was no

    doubt caused by the first eruption,almost two months before the final

    explosion.

    2.

    INITIAL ERUPTIONS

    The north slope gave way to the great

    pressure of the magma in an explosive

    eruption. The lava traveled 16 miles

    (25 km) at 246 feet (75 m) per second.

    3.

    EXPLOSION AND VERTICAL COLLAPSE

    At the foot of the volcano, a valley 640

    feet (195 m) deep was buried in volcanic

    material. Over 10 million trees were

    destroyed.

    4.

    Within the territory of the United States, active volcanoes

    are not limited to exotic regions such as Alaska or

    Hawaii. One of the most explosive volcanoes in

    North America is in Washington state. Mount St. Helens,after a long period of calm, had an eruption of ash

    and vapor on May 18, 1980. The effects were

    devastating: 57 people were killed, and lava

    flows destroyed trees over an area of

    232 square miles (600 sq km). The

    lake overflowed, causing

    mudslides that destroyed

    houses and roads. The

    area will need a

    century to

    recover.

    GLACIER 34 VOLCANOES VOLCANOES AND EARTHQUAKES 35

    BEFORE

    In May the volcano began showing

    signs in the form of small quakes and

    spouting vapor, smoke, and ash. None

    of this served to warn of the terrible

    explosion to come, and some even

    took trips to see the volcano's

    “pyrotechnics.”

    AFTER

    A crater nearly 4 miles (6.4 km) in diameter was left where the volcano

    had been. About 1927, new volcanic activity was observed in the area.

    In 1930, a cone emerged. Anak Krakatoa (“daughter of Krakatoa”)

    appeared in 1952; it grows at a rate of nearly 15 feet (4.5 m) per year.

    DURING

    At 5:30 a.m. the island

    burst from the

    accumulated pressure,opening a crater 820 feet

    (250 m) deep. Water

    immediately rushed in,causing a gigantic tsunami. MEGATONS

    The energy released,equivalent to 25,000

    atomic bombs such

    as the one dropped

    on Hiroshima.

    500

    Rakata

    Danan

    Perbuatan

    Anak Krakatoa

    Rakata

    Panjang

    Sertung

    Crater's edge

    I

    n early 1883, Krakatoa was just one of

    many volcanic islands on Earth. It was located

    in the Straits of Sundra, between Java and

    Sumatra in the Dutch East Indies, now known as

    Indonesia. It had an area of 10.8 square miles (28 sq km) and

    a central peak with a height of 2,690 feet (820 m). In August

    1883, the volcano exploded, and the island was shattered in

    the largest natural explosion in history.

    Long-Term Effects

    Krakatoa

    Krakatoa was near the subduction

    zone between the Indo-Australian

    and Eurasian plates. The island's inhabitants

    were unconcerned about the volcano

    because the most recent previous eruption

    had been in 1681. Some even thought the

    The Island That Exploded

    Aftereffects

    The ash released into the atmosphere

    left enough particles suspended in the

    air to give the Moon a blue tinge for years

    afterward. The Earth's average temperature

    also decreased.

    volcano was extinct. On the morning of

    Aug. 27, 1883, the island exploded. The

    explosion was heard as far away as

    Madagascar. The sky was darkened, and

    the tsunamis that followed the explosion

    were up to 130 feet (40 m) high.

    The height of the

    column of ash.

    miles

    34

    FRACTION

    Two thirds of the

    island was

    destroyed, and only

    a part of Rakata

    survived the

    explosion.

    PYROCLASTICS

    The pyroclastic flows were

    so violent that, according

    to the descriptions

    of sailors, they

    reached up to 37

    miles (80 km)

    from the island.

    1

    3

    2 Stratosphere Madagascar

    English

    Channel

    Atmosphere

    The ash expelled

    by the explosion

    lingered for years

    PRESSURE WAVE

    The atmospheric pressure

    wave went around the

    world seven times.

    WATER LEVEL

    The water level

    fluctuated as far away

    as the English Channel.

    The height of the tsunami

    waves, which traveled at 700

    miles per hour (1,120 kmh).

    130 feet

    (40 m)

    (55 km)

    KRAKATOA

    Latitude 6° 06′ S

    Longitude 105° 25′ E

    Surface Area

    Remaining Surface Area

    Range of the Explosion

    Range of Debris

    Tsunami Victims

    10.8 square miles (28 sq km)

    3 square miles (8 sq km)

    2,900 miles (4,600 km)

    1,550 miles (2,500 km)

    36,0001 Lighter particles

    separate from

    heavier ones and rise

    upward, forming a

    blanket-shaped cloud.

    Deposit

    Nonturbulent

    dense flow

    2 Ahead of the

    burning c ......