PLATE TECTONICS

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The theory of Plate

Tectonics

Continental drift describes one of the earliest ways geologists thought continents

moved over time. Today, the theory of continental drift has been replaced by the

science of plate tectonics.

The theory of continental drift is most associated with the scientist Alfred Wegener.

In the early 20th century, Wegener published a paper explaining his theory that the

continental landmasses were “drifting” across the Earth, sometimes ploughing through

oceans and into each other. He called this movement continental drift.

Pangaea existed about 240 million years ago. By about 200 million years ago this

supercontinent began breaking up. Over millions of years, Pangaea separated into

pieces that moved away from one another. These pieces slowly assumed their

positions as the continent we recognize today.

Today, scientists think that several supercontinents like Pangaea have formed and

broken up over the course of the Earth’s lifespan. These include Pannotia, which

formed about 600 million years ago, and Rodinia, which existed more than a billion

years ago.

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Wegner’s evidence proving the movement of continents.;

A.

B.

C.

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THE STRUCTURE OF THE PLANET

Our home planet, the Earth, may look like one huge rock, but it is actually like an

onion when cut through its cross-sectional area – it has different layers with

different compositions. Billions of years ago, Earth was formed from a hot ball of

nebula gases and as time goes by, the Earth’s surface cooled down and there

emerged different life forms. However, the inner part of the Earth remained very

hot.

CRUST

•This is where life exists and is covered with different kinds of landforms like

mountains, valleys, hills, air, and different bodies of water.

•This is the cool outer layer of our planet with an average temperature of around

22°C.

•It is the Earth’s thinnest layer.

•The crust’s state is solid.

•Continental crust is composed of granite, sedimentary rocks, and metamorphic

rocks.

•Oceanic crust is made up of iron, oxygen, silicon, magnesium, and aluminium.

•The continental crust is 8 to 70 kilometres thick and is mostly composed of granite.

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•The ocean bed has a layer beneath it, which is the oceanic crust, that is

more or less eight kilometres thick and is mostly composed of a rock called

basalt.

•Igneous rocks are formed from magma (liquid rock) that were cooled and

hardened inside the Earth.

•Metamorphic rocks are the rocks that have been exposed to different

factors, such as high pressure and very high temperatures.

•Sedimentary rocks are formed from broken rocks are formed from chemical

sediments and debris.

•Intrusive rocks are cooled rocks that have risen close to the Earth’s surface.

•The layers underneath the crust can be investigated by observing how the

seismic waves through the Earth behave during and after earthquakes and

volcanic eruptions.

•A seismograph is used to measure these waves

TECTONIC PLATES

•This is a combination of the crust and the outer mantle – which both make

the lithosphere.

•They move very slowly – so slowly that is measured to only a

•couple of inches a year.

•Faults are made when a tectonic plate touches or meets another plate.

•An earthquake can happen when the plates move and their boundaries bump

OCEANIC CRUST CONTINENTAL CRUST

• Thinner (this crust is not as deep or thick)

• Denser (therefore compara-bly heavier)

• Sinks (therefore can be de-stroyed)

• Newer

• Thicker (this crust is deeper and thicker)

• Less Dense (therefore comparably lighter)

• Doesn’t Sink (therefore can’t be destroyed)

• Older

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MANTLE

The mantle makes up about 85% of the Earth’s weight.

•It consists of rocks in molten form, just like play-dough.

•It is made of molten iron, minerals and other semi-solid rocks that will still flow

under pressure.

•Back in 2007, scientists from the Japanese ship called Chikyu drilled up to 23,000

feet (7,000 meters) below the seabed between the Cape Verde Islands and the

Caribbean Sea.

•

UPPER MANTLE

•Its temperature ranges from 1,400°C – 3,000°C.

•It has both liquid and solid states.

•It is mainly composed of iron, oxygen, silicon, magnesium, and aluminium.

•This layer is 670 kilometers thick below the Earth’s surface.

•The rocks present in the upper region of this layer are stiffer compared to its

lower area because it’s cooler.

The lower part of this layer is made up of both solid and melted rock.

LOWER MANTLE

•The temperature of this layer is around 3,000°C.

•It’s in a solid state.

•It is mainly composed of iron, oxygen, silicon, magnesium, and aluminium.

•It is 670 to 2,890 kilometres thick below the surface.

•This layer is made of solid rock.

The rocks present in this layer are hot enough to melt, but are in a solid state

because of the pressure pushing down on this layer.

OUTER CORE

•Has a temperature that ranges from 4,000°C to 6,000°C.

•Its state is liquid.

•Mainly composed of iron, nickel, sulphur, and oxygen.

•This liquid layer is about 5,150 kilometres thick.

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INNER CORE

•4.5 billion years ago, when the Earth was formed, the heavy material sunk to the

middle and these formed the inner core.

•The inner core has a temperature that ranges from 5,000°C – 6,000°C and is the

hottest part of the Earth.

•It is in a solid state.

•It is mainly composed of iron and nickel.

•It is a huge metal ball that is 2,500 kilometres wide.

•The metal at the inner core is still solid despite the very high temperature be-

cause of the immense pressure surrounding it

•The spinning of the inner core at a different speed compared to the rest of the

planet is the reason behind Earth’s magnetic field.

EARTH’S MAGNETIC FIELD

This is the reason why compass needles point to the North Pole regardless of which

way you turn.

•The magnetic field creates a protective barrier around Earth that shields the

planet from the sun’s solar winds which are very damaging.

Solar winds are streams of charged particles ejected by the Sun.

•When the magnetic field traps the solar winds, they collide with air molecules

above Earth’s magnetic poles.

•The air molecules with the solar winds begin to glow and creates an aurorae, or al-

so called the northern and southern lights.

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Primary, Secondary and Surface Waves

Earthquakes produce three types of seismic waves: primary waves, secondary waves,

and surface waves. Each type moves through materials differently. In addition, the

waves can reflect, or bounce, off boundaries between different layers. The waves can

also bend as they pass from one layer into another. Scientists learn about Earth’s

layers by studying the paths and speeds of seismic waves traveling through Earth.

Primary Waves

The fastest seismic waves are called primary waves, or P waves. These waves are the

first to reach any particular location after an earthquake occurs. Primary waves travel

through Earth’s crust at an average speed of about 5 kilometres per second. Primary

waves can travel through solids, liquids, and gases.

Secondary Waves

Secondary waves are the second seismic waves to arrive at any particular location

after an earthquake, though they start at the same time as primary waves. Secondary

waves travel through Earth’s interior at about half the speed of primary waves

Secondary waves are also called S waves. Secondary waves can travel through rock,

but unlike primary waves they cannot travel through liquids or gases. When scientists

learned that secondary waves cannot pass through Earth’s outer core, they realized

that the outer core is not solid.

Surface Waves (Long Waves)

Surface waves are seismic waves

that move along Earth’s surface, not

through its interior. They make the

ground roll up and down or shake

from side to side. Surface waves

cause the largest ground

movements and the most damage.

Surface waves travel more slowly

than the other types of seismic

waves.

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Tectonic plates

The Earth's crust is broken up into

pieces called plates. Heat rising and

falling inside the mantle

creates convection currents generated

by radioactive decay in the core. The

convection currents move the plates.

Where convection currents diverge

near the Earth's crust, plates move

apart.

Where convection currents converge,

plates move towards each other.

The movement of the plates, and the

activity inside the Earth, is called plate

tectonics.

Plate tectonics cause earthquakes and

volcanoes. The point where two plates

meet is called a plate boundary.

Earthquakes and volcanoes are most

likely to occur either on or near plate

boundaries.

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PLATE BOUNDERIES

What are Plate Boundaries?

Constructive/Divergent Boundaries:

Divergent boundaries are those that move away from one another. When they

separate, they form what is known as a rift. As the gap between the two plates widen,

the underlying layer may be soft enough for molten lava underneath to push its way

upward. This upward push results in the formation of volcanic islands. Molten lava that

succeeds in breaking free eventually cools and forms part of the ocean floor.

Constructive boundaries tend to be found under the sea, ex. the Mid Atlantic Ridge.

Here, chains of underwater volcanoes have formed along the plate boundary. One of

these volcanoes may become so large that it erupts out of the sea to form a volcanic

island, ex. Surtsey and the Westman Islands near Iceland.

In Plate Tectonic Theory, the lithosphere is broken into tectonic plates, which

undergo some large scale motions. The boundary regions between plates are aptly

called plate boundaries. Based upon their motions with respect to one another,

these plate boundaries are of three kinds: Constructive, Destructive,

Conservative and Collision.

SURTSEY ICELAND

On November 14,1963 a cook aboard a trawler sailing south of Iceland spotted a

column of dark smoke rising from the surface of the sea. Thinking is was a boat on

fire and the captain turned his vessel to investigate. They found an island in the

process of being born: volcanic eruptions originating from below the sea surface,

belching black columns of ash. The new island was later named Surtsey. Eventually,

ash had blocked sea water from the crater area. Lava formed a hard cap of solid

rocks over the lower slopes which prevented the waves from washing away the

island.

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Convergent/destructive Boundaries:

Convergent boundaries are those that move towards one another. When they collide,

subduction usually takes place. That is, the denser plate gets subducted or goes

underneath the less dense one. Sometimes, the plate boundaries also experience

buckling. Convergent boundaries are responsible for producing the deepest and tallest

structures on Earth.

Among those that have formed due to convergent plate boundariesare K2 and Mount

Everest, the tallest peaks in the world. They formed when the Indian plate got

subducted underneath the Eurasian plate. Another extreme formation due to the

convergent boundary is the Mariana Trench, the deepest region on Earth.

MARIANAS TRENCH

Mariana Trench is a deep-sea trench in the floor of the

western North Pacific Ocean, just east of the Mariana

Islands . It is the deepest trench known on Earth. It stretches

for more than 2,540km with a width of 69 km . The greatest

depths are reached in Challenger Deep, a steep-walled valley

on the floor of the main trench. The deepest part of the ocean

is called the abyssal zone. Even though it is very cold it has

hot water vents from moving plates so it is able to host

thousands of species of invertebrates and fish including such

oddities as the Angler Fish.

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THE PACIFIC RING OF FIRE

Recently the United States

has been rocked by eight

earthquakes in quick

succession , with three

tremors hitting in California

and others felt in Oklahoma

Alaska, Nebraska and

Texas.

The quake was the

strongest felt in Southern California for more than four years.

The US Geological Survey said back in 2008 that there was a 99% chance of a huge

quake hitting California, which sits on the infamous "Ring of Fire", in the not to

distant future. Alaska in the US also sits in the Ring of Fire, which causes many

volcano eruptions and earthquakes.

California also lies on the San Andreas fault, where two of the earth’s huge tectonic

plates meet.

What is the Ring of Fire?

The Ring of Fire is a Pacific region home to over 450 volcanoes, including three of the

world’s four most active volcanoes - Mount St. Helens in the USA, Mount Fuji in Japan

and Mount Pinatubo in the Philippines. It is also sometimes called the circum-Pacific

belt.

Around 90% of the world's earthquakes occur in

the Ring of Fire, and 80% of the world’s largest

earthquakes.

The 40,0000 kilometre horse-shoe-shaped ring

loops from New Zealand to Chile, passing through

the coasts of Asia and the Americas on the way.

KRAKATAO

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Why does the Ring of Fire trigger earthquakes? The world’s deepest earthquakes happen in subduction zone areas as tectonic plates

scrape against each other - and the Ring of Fire has the world’s biggest concentration

of subduction zones.

As energy is released from the earth’s molten core, it forces tectonic plates to move

and they crash up against each other, causing friction. The friction causes a build-up

of energy and when this energy is finally released it causes an earthquake. If this

happens at sea it can cause devastating tsunamis.

Tectonic plates usually only move on average a few centimetres each year, but when

an earthquake strikes, they speed up massively and can move at several metres per

second. It takes tens of thousands of years for the energy to build up, but only a

matter of seconds for it to be release.

How dangerous is the Ring of Fire?

Well, it’s not called the Ring of Fire for nothing, and volcanic and earthquake activity

is almost constant somewhere along the ring so there is some risk attached to living in

the regions affected. Kilauea, which is considered the most active volcano in the

world is in the Pacific Ring of Fire. Mount Fuji, the US’s Mount Saint Helens and

Mount Rainier in the American North West, as well as Krakatoa in Indonesia and

Mauna Loa in Hawaii are all volcanoes that are well known and some that could be very

dangerous to the nearby population .

In August 1883 Krakatoa erupted with devastating effects, expelling huge clouds of

gas and ash, generating massive tsunamis, and killing more than 36,000 people.

According to reports at the time the eruption launched ash clouds up to 22 miles high

blacking out the sun for three days - and the blasts from the volcano could be heard

up to 3,000 miles away.

The debris in the atmosphere was so great that it filtered the amount of sunlight

reaching Earth and caused global temperatures to fall by 1.2 Celsius the next

year. Temperatures did not get back to normal until five years later in 1888.

Most of the thousands of people who died in the Krakatoa eruption were killed by the

huge tsunamis - up to 120 feet high - that were created when the volcano collapsed

into the ocean.

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At a conservative plate margin, the

plates move past each other or are side

by side moving at different speeds. As

the plates move, friction occurs and

plates become stuck. Pressure builds up

because the plates are still trying to

move. When the pressure is released, it

sends out huge amounts of energy,

causing an earthquake. The earthquakes

at a conservative plate boundary can be

very destructive as they occur close to

the Earth's surface. There are no

volcanoes at a conservative plate margin.

The San Andreas Fault marks the junction between the North American and Pacific

Plates. The fault is 1300 km long and extends to at least 25 km in depth. Although

both plates are moving in a north westerly direction, the Pacific Plate is moving faster

than the North American Plate. Pressure builds up for years and when it is released

the plates slip suddenly and shallow focus earthquakes are generated. San Francisco

has historically suffered significant earthquakes, notably in 1906 and 1989. The

average rate of movement along the San Andreas Fault is between 30mm and 50mm

per year over the last 10 million years. If current rates of movement are maintained

Los Angeles will be adjacent to San Francisco in approximately 20 million years.

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When two plates that carry continental crust move towards

each other, the result is a mountain range. Although one plate

does get stuffed beneath the other, the continental crust is

thick and does not easily subduct like oceanic lithosphere. It

crumples, bends, breaks and becomes very thick, creating fold

mountains like the Alps and the Himalayas.

The rocks caught within a continental collision are heated and squeezed until they

change from their original rock type. These are called metamorphic rocks which

include slate and marble. These are often seen in old, eroding mountain ranges such

as the Appalachians.

Collision zone

THE HIMALAYAS

The Himalayan mountain range and Tibetan plateau have formed as a result of

the collision between the Indian Plate and Eurasian Plate which began 50

million years ago and continues today. The Himalayas are still rising by more

than 1 cm per year as India continues to move northwards into Asia, which

explains the occurrence of shallow focus earthquakes in the region today.

However the forces of weathering and erosion are lowering the Himalayas at

about the same rate. The Himalayas and Tibetan plateau trend east-west and

extend for 2,900 km, reaching the maximum elevation of 8,848 metres

(Mount Everest).

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Volcanoes are openings (vents) in the

ground where magma (molten rock) from

deep inside the earth forces its way to

the surface. The magma may appear as

flows of molten lava, as volcanic bombs, as

fragment of rock or simply ash and dust.

Mountains that are made of these

materials are called volcanoes.

Volcanoes may be active, dormant or

extinct.

• If a volcano has erupted recently and is

likely to erupt again, it is described as

active. There are over 700 active

volcanoes around the world (ex. Mount

Etna, Italy).

• Volcanoes that have erupted in the past

2,000 years but not recently, are said to

be dormant or sleeping. These may be

dangerous as it is difficult to predict

when they are going to erupt again (ex.

Mount Ararat, Turkey)

• Many volcanoes are unlikely ever to erupt

again. They are said to be extinct because

their volcanic activity has finished. Such

volcanoes may have erupted over 50

million years ago and have mostly been

worn away by erosion (ex. Mount Snowdon,

Wales).

What are volcanoes

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The three main types of volcanoes are:

• stratovolcano (or composite volcano) — a conical volcano consisting of layers of solid

lava flows mixed with layers of other rock.

• cinder cone volcano — doesn’t have any horizontal layers, and is instead a steep conical

hill of tephra (volcanic debris) that accumulates around and downwind from the vent..

• shield volcano — a type of volcano built entirely or mostly from fluid lava vents. They

are named like this because when viewed from above, you can see just how massive and

imposing they are – like a warrior’s shield.

Super volcanoes

A super volcano is a volcano on a massive scale. It is different from a volcano because:

• It erupts at least 1,000 km3 of material (a large volcano erupts around 1 km3).

• It forms a depression, called a caldera (a volcano forms a cone shape). • A super volcano often has a ridge of higher land around it.

• A super volcano erupts less frequently - eruptions are hundreds of thousands of years apart.

•Yellowstone is one example of a supervolcano. Three huge eruptions have happened in

the last 3 million years. The last eruption was 630,000 years ago, and was 1,000 times

bigger than the Mount St Helens eruption in 1980.The large volume of material from

the last Yellowstone eruption caused the ground to collapse, creating a depression

called a caldera. The caldera is 55 km by 80 km wide. The next eruption is predicted

to have catastrophic worldwide effects.

•Every year millions of visitors come to see the related features, such as geysers and

hot springs. Old Faithful is one example of a geyser.

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Why do people live close to volcanoes?

Volcanoes have a wide range of effects on humans. These can be problematic or

beneficial. It is usually the destructive nature of volcanoes which is more widely

documented. However, many people rely on volcanoes for their everyday survival.

Today, many millions of people live close to volcanoes for this very reason.

People live close to volcanoes because Geothermal energy can be harnessed by using

the steam from underground which has been heated by the Earth's magma. This

steam is used to drive turbines in geothermal power stations to produce electricity

for domestic and industrial use. Countries such as Iceland and New Zealand use this

method of generating electricity.

Volcanoes attract millions of visitors

around the world every year. Apart

from the volcano itself, hot springs

and geysers can also bring in the

tourists. This creates many jobs for

people in the tourism industry. This

includes work in hotels, restaurants

and gift shops. Often locals are also

employed as tour guides.

[Lava] from deep within the earth contains minerals which can be mined once the lava

has cooled. These include gold, silver, diamonds, copper and zinc, depending on their

mineral composition. Often, mining towns develop around volcanoes.

Volcanic areas often contain some of the

most mineral rich soils in the world. This is

ideal for farming. [Lava] and material

from [pyroclastic flows] are weathered to

form nutrient rich soil which can be

cultivated to produce healthy crops and rich

harvests.

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Mount St. Helens

The first sign of activity began in the spring of 1980

with a series of small earthquakes began. After

thousands of additional earthquakes and steam

explosions, a cataclysmic eruption occurred on 18 May

1980.

Mount St Helens lies close to a destructive plate

boundary where the smaller Juan de Fuca plate is be-

ing forced into the mantle by the larger North Ameri-

can plate.

Friction and heat cause the plate to melt and, as it melts, molten rocks are formed.

The molten rock builds up until it has the chance to reach the surface through cracks

in the Earth’s crust.

Impact on landscape and population

Landscape

•The mountain was reduced from a height of 2950m to 2560m as the eruption created

the largest landslide ever recorded.

•All plant and animal life within a 25km radius of the volcano was killed, including fully

grown trees.

•Mudflows poured down the valleys choking rivers with rock debris, killing fish and

ripping trees from their roots.

Population

Sixty one people died due to mudflows, being crushed to death and poisonous gases, while 198 had to be rescued.

•Mudflows destroyed bridges, houses and logging camps.

•The explosion flattened buildings and trees and knocked out power supplies and

telephones.

•Ash clouds resulted in airline flights being cancelled.

•Ash caused £100 million of damage to farm machinery and crops.

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Methods of prediction and planning

Volcanoes are difficult to predict

but, although they were unable to

give a precise date scientists tried

to predict the eruption of Mount St

Helens by measuring the frequency

of earthquakes on the mountain.

The greater the frequency, the

nearer the eruption and measuring

the size of the volcanic cone shows

the build-up of magma in the vent.

crater. However, even before the

eruption of Mount St Helens,

scientists thought that the it might

still be a few weeks away.

The authorities were able to

evacuate people from the areas

surrounding Mount St Helens, after

the areas affected by the previous

eruption and they set up

an exclusion zone around the

volcano. Emergency services were

also on hand to rescue those people

needing help.

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Mount Etna

Late in 1991 the people living near Mount

Etna began to worry. They had felt many

small earthquakes and could hear the

occasional rumbling noise from deep inside

the mountain. Steam from the main crater

was causing great clouds to develop. There

was sometimes heavy rain with thunder and

lighting. Etna was preparing itself for yet

another eruption!

Mount Etna is located on the island of

Sicily. It is the biggest volcano in Europe

and one of the most active in the world. It

has erupted 46 times in the last 100 years

and continuously rumbles and steams. When

Etna erupts it produces lava, ash, volcanic

bombs and gases. They come from the

crater at the top and from several smaller

craters lower down the mountainside.

The ash can be chocking and may cover the

area in a white dusty blanket. The lava and

bombs are more dangerous. They can kill

people and animals and destroy buildings

and farmland.

Like most other volcanoes, Etna is located

on a plate boundary. The boundary that

runs through Italy is a destructive plate

margin where the African plate is

subducting under the Eurasian plate.

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EARTHQUAKES What causes an earthquake?

An earthquake is the shaking and vibration of the Earth's crust due to movement of

the Earth's plates (plate tectonics). Earthquakes can happen along any type of plate

boundary.

Earthquakes occur when tension is

released from inside the crust. Plates

do not always move smoothly alongside

each other and sometimes get stuck.

When this happens pressure builds up.

When this pressure is eventually

released, an earthquake tends to

occur.

The point inside the crust where the

pressure is released is called the focus. The point on the Earth's surface above

the focus is called the epicentre.

Earthquake energy is released in seismic waves. These waves spread out from the

focus. The waves are felt most strongly at the epicentre, becoming less strong as

they travel further away. The most severe damage caused by an earthquake will

happen close to the epicentre.

Measuring the power and strength of an earthquake

The power of an earthquake is measured using a seismometer. A seismometer detects

the vibrations caused by an earthquake. It plots these vibrations on a seismograph.

The strength, or magnitude, of an earthquake is measured using the Richter scale.

The Richter scale is numbered 0-10+ with 10+ being the greatest strength or

magnitude. Earthquakes measuring just 1 or 2 on the scale are very common and can

happen everyday in places like San Francisco. These earthquakes are so small that

people cannot feel them, they can only be picked up by a seismometer.

Earthquakes measuring around 7 or 8 on the Richter scale can be devastating. The

earthquake in China's south-western Sichuan province in May 2008 measured 7.8 on

the Richter scale.

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Scientists measure earthquakes using

the Richter scale. This scale,

invented in 1934 by California

scientist Charles Richter, measures

the magnitude of an earthquake, and

the result is a number from 0 to 10,

as measured on a machine called a

seismograph.

The scale is not a normal number

scale, however; rather, it is a

logarithmic scale. This means that an

earthquake that measures 2 on the

Richter scale is 10 times as powerful

as an earthquake that measures 1. In

addition, each whole number increase

means 32 times more energy is

released.

The Richter scale measures

earthquakes in whole numbers and

tenths numbers. Most earthquakes

register 2.5 or less and are too small

to be experienced by people.

Seismographs register these quakes,

though.

Scientists estimate that 900,000 of

such "small" quakes occur every year.

Up to 30,000 of quakes measuring 2.5

to 5.4 occur in a year as well, and

these cause minor damage and are

certainly noticed by people. The

higher the number on the Richter

scale, the fewer earthquakes occur

every year. Quakes registering 8.0 or

higher occur, on average, only once

every 5 to 10 years.

THE RICHTER SCALE

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Distance from the epicentre The effects of an earthquake are more severe at its centre.

Magnitude

The higher on the Richter scale, the more severe the

earthquake is. Level of development

(MEDC or LEDC)

MEDCs are more likely to have the resources

and technology for monitoring, prediction

and response.

Population may not be well educated about

what to do in the event of a volcanic eruption

or an earthquake.

Construction standards tend to be poor in LEDCs. Homes and

other buildings may suffer serious damage when a disaster occurs.

Population density (rural or urban area)

The more densely populated an area, the more likely there are to be deaths and casualties.

Communication

Good infrastructure and accessibility helps rescue teams reach area of disaster.

Time of day

Influences whether people are in their homes, at work or

travelling. A severe earthquake at rush hour in a densely

populated urban area could have devastating effects.

Factors affecting the impacts of an earthquake

Climate

Influences survival rates and the rate at which disease can spread.

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Effects of an earthquake Earthquakes can destroy settlements and kill many people. Aftershocks can cause even more damage to an area. It is possible to classify the impacts of an earthquake, by taking the following factors into account:

• short-term (immediate) impacts

• long-term impacts

• social impacts (the impact on people).

• economic impacts (the impact on the wealth of an area)

environmental impacts (the impact on the landscape)

Social impacts Economic impacts Environmental impacts

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People may be killed or injured. Homes may be destroyed. Transport and communication links may be disrupted. Water pipes may burst and water supplies may

be contaminated.

Shops and business may be destroyed. Looting may take place. The damage to transport and communication links can make trade

difficult.

The built landscape may be destroyed. Fires can spread due to gas pipe explosions. Fires can damage areas of woodland. Landslides may occur. Tsunamis may cause flooding in coastal areas.

Short-term im-mediate

Long-term impacts

Disease may spread. People may have to be re-housed, sometimes in refugee camps.

The cost of rebuilding a settlement is high. Investment in the area may be focused only on repairing the damage caused by the earthquake. Income could be lost.

Important natural and human landmarks may be lost.

Effects are often classified as primary and secondary impacts. Primary effects occur as a direct result of the ground shaking, eg buildings collapsing. Secondary effects occur as a result of the primary effects, eg tsunamis or fires due to ruptured gas mains

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The wave of destruction Tsunamis

Tsunami is a Japanese word which means 'harbour wave'. A tsunami is a large sea wave

caused by the displacement of a large volume of water. They can be caused by triggered

by moving sections of the Earth's crust under

the ocean.

In the last decade there have been a number

of devastating tsunamis. Two large ones caused

particularly extensive devastation: the Indian

Ocean tsunami (26 December 2004) and the

Japanese tsunami (11 March 2011).The Indian

Ocean tsunami of 2004 was caused by plates

moving and slipping under the ocean.

Tsunami formation

• Convection currents in the mantle move the plates towards each other.

• Pressure builds up as the denser Indo-Australian plate is forced under the

overriding Burma plate.

• An earthquake occurs.

• Water is displaced, creating a wave which spreads out.

• As the wave approaches the shore, the wave height increases and the wave

length shortens.

Earthquake occurs and a tsunami forms

Water is displaced and waves move through the ocean at speed

Tsunami slows as water reaches the shore, but waves increase in height

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Case study: TSUNAMI

On Sunday 26 December 2004, a magnitude 9 earthquake occurred off the West Coast

of Northern Sumatra in the Indian Ocean.

This caused the Indian Ocean tsunami that

affected 13 countries and killed

approximately 230,000 people.

This tsunami was particularly devastating because;

•The earthquake which caused the tsunami was magnitude 9.

•The epicentre was very close to some densely populated coastal communities, eg

Indonesia.

•They had little or no warning. The only sign came just before the tsunami struck when

the waterline suddenly retreated, exposing hundreds of metres of beach and seabed.

• There was no Indian Ocean tsunami warning system in place. This could have saved

more people in other countries further away from the epicentre.

•Many of the countries surrounding the Indian Ocean are LEDCs so they could not

afford to spend much on preparation and prevention.

•In some coastal areas, mangrove forests had been removed to make way for tourist

developments and therefore there was less natural protection.

Social impacts of the tsunami (effects on people)

•230 000 deaths.

•1.7 million homeless.

•5-6 million needing emergency aid, eg food and water.

•Threat of disease from mixing of fresh water, sewage and salt water.

•1,500 villages destroyed in northern Sumatra.

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Economic impacts of the tsunami (effects on money and jobs)

• Ports ruined.

• Fishing industry devastated - boats, nets and equipment destroyed. An estimated 60%

of Sri Lanka’s fishing fleet destroyed.

• Reconstruction cost billions of dollars.

• Loss of earnings from tourism - foreign visitors to Phuket dropped 80% in 2005.

• Communications damaged, eg roads, bridges and rail network

Environmental impacts of the tsunami

• Crops destroyed.

• Farm land ruined by salt water.

• 8 million litres of oil escaped from oil plants in Indonesia.

• Mangrove forests along the coast were destroyed.

• Coral reefs and coastal wetlands damaged.

Responses to the tsunami

Non-Governmental Organisations (NGOs) and local authorities typically

have immediate and secondary responses to devastation of this kind.

Immediate responses

• Search and rescue.

• Emergency food and water.

• Medical care.

• Temporary shelter.

• Re-establishing infrastructure and communications.

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Secondary responses

• Re-building and improving infrastructure and housing.

• Providing jobs and supporting small businesses.

• Giving advice and technical assistance.

Responses to the 2004 Indian Ocean tsunami can also be divided into short and

long term

Short-term responses

• In many areas local communities were cut off and had to help themselves.

The authorities ordered quick burial or burning of the dead to avoid the spread

of disease.

• Food aid was provided to millions of people, eg from the World Food Programme.

• $7 billion (just under £4.5billion) of aid was promised by foreign governments -

but there were complaints that not all money pledged was given.

• The British public gave £330 million through charities, eg the average Action aid

donation was £84 - their best ever response.

Long-term responses

• Reconstruction is still taking place.

• International scale: an Indian Ocean tsunami warning system has now been set up.

• Local scale: some small-scale sustainable development projects have been set up by

charities to aid recovery and help local people help themselves to rebuild and set up

small businesses.