Volcanoes and Earthquakes

55 Pages·2009·25.961 MB·English

by  Britannica, Encyclopædia

VVOOLLCCAANNOOEESS
AANNDD EEAARRTTHHQQUUAAKKEESS
BBrriittaannnniiccaa IIlllluussttrraatteedd SScciieennccee LLiibbrraarryy
Encyclopædia Britannica, Inc.
Chicago ■ London ■ New Delhi ■ Paris ■ Seoul ■ Sydney ■ Taipei ■ Tokyo
BBrriittaannnniiccaa IIlllluussttrraatteedd
SScciieennccee LLiibbrraarryy
© 2009 Editorial Sol 90
All rights reserved.
Idea and Concept of This Work: Editorial Sol 90
Project Management: Fabián Cassan
Photo Credits: Corbis, ESA, Getty Images, Graphic News,
NASA, National Geographic, Science Photo Library
Illustrators: Guido Arroyo, Pablo Aschei, Gustavo J. Caironi,
Hernán Cañellas, Leonardo César, José Luis Corsetti, Vanina
Farías, Joana Garrido, Celina Hilbert, Isidro López, Diego
Martín, Jorge Martínez, Marco Menco, Ala de Mosca, Diego
Mourelos, Eduardo Pérez, Javier Pérez, Ariel Piroyansky, Ariel
Roldán, Marcel Socías, Néstor Taylor, Trebol Animation, Juan
Venegas, Coralia Vignau, 3DN, 3DOM studio
Composition and Pre-press Services: Editorial Sol 90
Translation Services and Index: Publication Services, Inc.
Portions © 2009 Encyclopædia Britannica, Inc.
Encyclopædia Britannica, Britannica, and the thistle logo are
registered trademarks of Encyclopædia Britannica, Inc.
Britannica Illustrated Science Library Staff Encyclopædia Britannica, Inc.
Editorial Jacob E. Safra, Chairman of the Board
Michael Levy, Executive Editor, Core Editorial
John Rafferty, Associate Editor, Earth Sciences Jorge Aguilar-Cauz, President
William L. Hosch, Associate Editor, Mathematics and
Computers Michael Ross, Senior Vice President, Corporate Development
Kara Rogers, Associate Editor, Life Sciences
Rob Curley, Senior Editor, Science and Technology Dale H. Hoiberg, Senior Vice President and Editor
David Hayes, Special Projects Editor
Marsha Mackenzie, Director of Production
Art and Composition
Steven N. Kapusta, Director
Carol A. Gaines, Composition Supervisor
Christine McCabe, Senior Illustrator International Standard Book Number (set):
978-1-59339-860-6
Media Acquisition International Standard Book Number (volume):
Kathy Nakamura, Manager 978-1-59339-863-7
Britannica Illustrated Science Library:
Copy Department Volcanoes and Earthquakes 2009
Sylvia Wallace, Director
Julian Ronning, Supervisor Printed in China
Information Management and Retrieval
Sheila Vasich, Information Architect
Production Control
Marilyn L. Barton
Manufacturing
Kim Gerber, Director www.britannica.com
Volcanoes and
Earthquakes
Contents
CCoonnttiinnuuoouuss
MMoovveemmeenntt
PPaaggee 66
Volcanoes
Page 24
Study and
Prevention
Page 44
Earthquakes
Page 58
Study and
Prevention
Page 74
helplessness, of endurance in the face of be more destructive than the earthquake
chaos. Unlike storms and volcanic eruptions, itself. On Dec. 26, 2004, the world
earthquakes are unpredictable, unleashed witnessed one of the most impressive
within seconds, and without warning. They natural disasters ever. An undersea quake
spread destruction and death, forcing with a magnitude of 9 on the Richter scale
millions to flee from their homes. The day shook the eastern Indian Ocean, causing
after the catastrophe revealed a terrifying tsunamis that reached the coastal areas of
scene: debris everywhere, a number of eight Asian nations, causing about 230,000
people injured and dead, others wandering deaths. The earthquake was the fifth
desperately, children crying, and over three strongest since the invention of the
million survivors seeking help after losing seismograph. Satellite images show the
everything. Throughout history Earth has region before and after the catastrophe.
been shaken by earthquakes of greater or
T
lesser violence. These earthquakes have hroughout history, nearly all ancient
caused great harm. One of the most famous peoples and large societies have
is the earthquake that rocked San Francisco thought of volcanoes as dwelling
in 1906. Registering 8.3 on the Richter scale, places of gods or other supernatural beings
the temblor left nearly three thousand dead to explain the mountains' fury. Hawaiian
and was felt as far away as Oregon to the mythology, for instance, spoke of Pele, the
north, and Los Angeles in southern goddess of volcanoes, who threw out fire to
California. cleanse the earth and fertilize the soil. She
was believed to be a creative force.
The Power Nowadays, specialists try to find out when a
Kashmir, 2005 T
Farmer Farid Hussain, 50, grasps he purpose of this book is to help you volcano might start to erupt, because within
the hand of his wife, Akthar Fatma,
better understand the causes of hours after an eruption begins, lava flows
after the earthquake that rocked
the Himalayas on the Indian of Nature fractures and the magnitude and can change a lush landscape into a barren
subcontinent. Eighty thousand
violence of the forces deep within the earth. wilderness. Not only does hot lava destroy
people were killed, and thousands
of families were left homeless. The full-color, illustrated book you hold in everything in its path, but gas and ash
your hands contains shocking scenes of expelled in the explosion also replace oxygen
cities convulsed by earthquakes and in the air, poisoning people, animals, and
S
ome photos speak for themselves. volcanoes, natural phenomena that, in mere plants. Amazingly, life reemerges once again
Some gestures communicate more seconds, unleash rivers of fire, destroy from such scenes of destruction. After a
than words ever could, like these buildings, highways and bridges, and gas and time, lava and ash break down, making the
clasped hands, which seek comfort in the water lines and leave entire cities without soil unusually fertile. For this reason many
face of fear of the unknown. The picture was electricity or phone service. If fires cannot farmers and others continue to live near
taken Oct. 8, 2005, when aftershocks were be put out quickly, the results are even more these “smoking mountains,” in spite of the
still being felt from the strongest earthquake devastating. Earthquakes near coastlands latent danger. Perhaps by living so close to
ever to strike Kashmir, in northern India. can cause tsunamis, waves that spread the danger zone, they have learned that no
Those clasped hands symbolize terror and across the ocean with the speed of an one can control the forces of nature, and the
panic; they speak of fragility and airplane. A tsunami that reaches a coast can only thing left to do is to simply live.
Continuous Movement
PAHOEHOE LAVA SCORCHING FLOW 8-9 OCEAN TRENCHES 16-17
A type of Hawaiian lava
that flows down the slopes THE LONG HISTORY OF THE EARTH 10-11 WRINKLES IN THE EARTH 18-19
of Mt. Kilauea to the sea.
STACKED LAYERS 12-13 FOLDS 20-21
THE JOURNEY OF THE PLATES 14-15 WHEN FAULTS RESOUND 22-23
I
n the volatile landscape of
the sea. When the molten rock enters nothing stays the same from one investigation of lava samples under the
Volcano National Park in Hawaii,
the water, the lava quickly cools and moment to another. One day rivers of microscope helps volcanologists
the beginning and end of life
hardens into rock that becomes part lava blaze down the volcano's slopes, discover the rock's mineral
seem to go hand in hand.
of the coastline. By this process, and the next day there are new, silver- composition and offers clues about
Outpourings of lava often reach
volcanic islands grow constantly, and colored rocks. The ongoing how the volcano may behave.
8 CONTINUOUS MOVEMENT VOLCANOES AND EARTHQUAKES 9
Scorching Flow
M
ost of the Earth's interior is in a liquid and incandescent state at extremely high
Rock Cycle
temperatures. This vast mass of molten rock contains dissolved crystals and SEDIMENTARY METAMORPHIC
Once it cools, lava forms igneous rock. ROCK ROCKS
water vapor, among other gases, and it is known as magma. When part of the This rock, subjected to weathering and Rock formed by Their original
magma rises toward the Earth's surface, mainly through volcanic activity, it is called lava. natural processes such as metamorphism eroded and structure is changed
and sedimentation, will form other types of compacted materials. by heat and pressure.
As soon as it reaches the surface of the Earth or the ocean floor, the lava starts to cool
rocks that, when they sink back into the
and solidify into different types of rock, according to its original chemical composition. Earth's interior, again become molten rock.
TURNS TURNS
This process takes millions of years and is
This is the basic process that formed the surface of our planet, and it is the reason the BACK INTO BACK INTO
known as the rock cycle.
LAVA LAVA
Earth's surface is in constant flux. Scientists study lava to understand our planet better.
2. IGNEOUS ROCK
Rock formed when lava
Streams of Fire solidifies. Basalt and
granite are good examples
Lava is at the heart of every volcanic eruption. The characteristics of lava vary, depending on of igneous rocks.
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 1. LAVA
which lava travels depends to a great extent on the steepness of the sides of the volcano. Some lava The state in which magma
flows can reach 90 miles (145 km) in length and attain speeds of up to 30 miles per hour (50 km/hr). flows to the Earth's outer SOLID LAVA
crust, either reaching the
Lava solidifies at temperatures below
surface or getting trapped 1,700º F (900º C). The most viscous
INTENSE HEAT within the crust. type of lava forms a rough landscape,
Lava can reach temperatures littered with sharp rocks; more fluid
above 2,200º F (1,200º C). The lava, however, tends to form flatter and
hotter the lava, the more fluid it is. smoother rocks.
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.
1,800º F
(1,000º C)
is the average temperature
of liquid lava.
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
Mineral Composition
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.
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
Andesitic Lava Rhyolitic Lava
in viscosity have resulted in one of the most commonly used
classification systems of lava: basaltic, andesitic, and rhyolitic, Silicates 63% Silicates 68%
in order from least to greatest silicate content. Basaltic lava 52% 48%
forms long rivers, such as those that occur in typical Hawaiian Other Other
volcanic eruptions, whereas rhyolitic lava tends to erupt Content 37% Content 32%
explosively because of its poor fluidity. Andesitic lava, named
after the Andes mountains, where it is commonly found, is an Silicates Other Content
intermediate type of lava of medium viscosity.
10 CONTINUOUS MOVEMENT VOLCANOES AND EARTHQUAKES 11
The Long History of the Earth
3.8
THE AGE OF THE
When the first crust
T BILLION YEARS AGO cooled, intense volcanic SUPER VOLCANOES
he nebular hypothesis developed by astronomers suggests that the Earth was formed 4 activity freed gases Indications of komatite,
ARCHEAN EON
in the same way and at the same time as the rest of the planets and the Sun. It all from the interior of the a type of igneous
planet, and those gases rock that no longer
began with an immense cloud of helium and hydrogen and a small portion of heavier STABILIZATION formed the atmosphere exists.
BILLION YEARS AGO
The processes that formed and the oceans.
materials 4.6 billion years ago. Earth emerged from one of these “small” revolving clouds,
METEORITE COLLISION the atmosphere, the oceans,
where the particles constantly collided with one another, producing very high temperatures. Meteorite collisions, at a rate and protolife intensified.
Later, a series of processes took place that gave the planet its present shape. 1to5d0a tyi,m eveas paosr agtreeda tt haes tphraimt iotfive Astta bthileiz seadm, aen tdi mthee, tfhires tc rust
ocean and resulted in the rise of plates of Earth's crust
all known forms of life. appeared. Because of their
weight, they sank into
Earth's mantle, making way
From Chaos to Today's Earth
for new plates, a process
4.5 that continues today.
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.
BILLION YEARS AGO
The changes have been unceasing, and,
according to experts, there will be COOLING
many more changes in the future.
The first crust formed as it
was exposed to space and The oldest rocks
cooled. Earth's layers became appeared.
differentiated by their density.
4.6 BILLION FORMATION
YEARS The accumulation of matter into solid
bodies, a process called accretion, ended,
AGO
and the Earth stopped increasing in volume.
60 540 1.0
MILLION YEARS AGO MILLION YEARS AGO BILLION YEARS AGO
FOLDING IN THE PALEOZOIC ERA SUPERCONTINENTS 2.2 2.3
TERTIARY PERIOD
Rodinia, the first
FRAGMENTATION
The folding began that would produce supercontinent, formed, but it
the highest mountains that we now The great landmass formed that would completely disappeared about
BILLION YEARS AGO BILLION YEARS AGO
have (the Alps, the Andes, and the later fragment to provide the origin of the 650 million years ago.
Himalayas) and that continues to continents we have today. The oceans WARMING “SNOWBALL” EARTH
generate earthquakes even today. reached their greatest rate of expansion.
Earth warmed again, and the Hypothesis of a first,
glaciers retreated, giving way to great glaciation.
the oceans, in which new
1.8
organisms would be born. The
ozone layer began to form.
BILLION YEARS AGO
PROTEROZOIC EON
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.
12 CONTINUOUS MOVEMENT VOLCANOES AND EARTHQUAKES 13
Stacked Layers
The Gaseous Envelope
E The air and most of the weather events that affect our lives occur only in
Less than Greater than
very 110 feet (33 m) below the Earth's surface, the temperature increases by 1.8 degrees the lower layer of the Earth's atmosphere. This relatively thin layer, called
310 miles 310 miles
Fahrenheit (1 degree Celsius). To reach the Earth's center—which, in spite of temperatures 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.
above 12,000° F (6,700° C), is assumed to be solid because of the enormous pressure (500 km) (500 km)
exerted on it—a person would have to burrow through four well-defined layers. The gases that Less than Less than Less than THERMOSPHERE EXOSPHERE
6 miles 31 miles 62 miles Very low density. Below No fixed outer limit. It
cover the Earth's surface are also divided into layers with different compositions. Forces act on 155 miles (250 km) it contains lighter gases
the Earth's crust from above and below to sculpt and permanently alter it. (10 km) (50 km) (100 km) is made up mostly of such as hydrogen and
nitrogen; above that helium, mostly ionized.
TROPOSPHERE STRATOSPHERE MESOSPHERE level it is mostly oxygen.
Contains 75 percent Very dry; water vapor The temperature is
of the gas and almost freezes and falls out -130º F (-90° C), but
all of the water vapor of this layer, which it increases gradually
in the atmosphere. contains the ozone layer. above this layer.
Earth's crust KEY Sedimentary Rock Igneous Rock Metamorphic Rock
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
THE CONTINENTAL THE MID-OCEAN RIDGES
to 44 miles (70 km) under mountain ranges. Volcanoes on
SHELF The ocean floor is regenerated with new
land and volcanic activity in the mid-ocean ridges generate
In the area where basaltic rock formed by magma that solidifies
new rock, which becomes part of the crust. The rocks at the
the oceanic crust in the rifts that run along mid-ocean ridges.
bottom of the crust tend to melt back into the rocky mantle.
comes in contact with
a continent, igneous OCEANIC ISLANDS
rock is transformed Some sedimentary rocks are
THE SOLID EXTERIOR
into metamorphic rock added to the predominantly
The crust is made up of
MOUNTAIN RANGES by heat and pressure. igneous rock composition.
igneous, sedimentary, and
Made up of the three
metamorphic rock, of
types of rock in about
various typical compositions,
equal parts.
according to the terrain.
UPPER MANTLE
370 miles
LITHOSPHERE 93 miles
(600 km) Includes the solid (150 km)
outer part of the
upper mantle, as
well as the crust.
LOWER MANTLE
1,430 miles
(2,300 km)
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).
CRUST
3-44
ASTHENOSPHERE 280 miles
Underneath is the (450 km)
miles OUTER CORE asthenosphere,
GRANITIC made up of partially
1,410 miles
BATHOLITHS molten rock.
Plutons can solidify (5-70 km)
underground as (2,270 km)
masses of granite.
Composed mainly of INNER CORE
molten iron and nickel
756 miles
COASTAL ROCK among other metals at
Lithified layers of temperatures above
sediments, usually 8,500º F (4,700° C). (1,216 km)
PLUTONS
clay and pebbles,
Masses of rising INTERNAL ROCK The inner core behaves
that come from the
magma trapped The inside of a as a solid because it is
erosion of high
within the Earth's mountain range under enormous pressure.
mountains.
crust. Their name is consists of igneous
derived from Pluto, rock (mostly
the Roman god of granite) and
the underworld. metamorphic rock.