De La Salle College

Geography Department

Ms.Diane Sammut

PLATE TECTONICS

TOPIC FOUR

2

We will be focusing on...

Page

The theory of Plate Tectonics 3

Cross-section of the Earth 5

Tectonic plates 7

Plate boundaries 8

Constructive plate boundaries 10

Destructive plate boundaries 12

Collision zones 14

Conservative plate boundries 16

Volcanoes 20

Living in a danger zone 26

Mount St.Helens 28

Supervolcanoes and hotspots 33

Mount Etna 34

Earthquakes 38

Kobe, Japan 42

Tsunami 46

Predict and prepare 48

Glossary 50

3

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been replaced by the science of plate tectonics.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.

Wegener based his theory on the following evidences :

• _______________________________________________________________________________

• _______________________________________________________________________________

• _______________________________________________________________________________

4

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5

Cross-section of the Earth

LAYER PROPERTIES

The Earth is divided into four main layers, the crust, the mantle, the outer core and the inner core.

6

OCEANIC CRUST CONTINENTAL CRUST

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

• Denser (therefore comparably heavier)

• Sinks (therefore can be destroyed)

• Newer

• Thicker (this crust is deeper and thicker)

• Less Dense (therefore comparably lighter)

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

• Older

There are two types of crust, oceanic and continental.

Generally oceanic crust is found under the oceans and

continental under land. Although plates are usually a

combination of oceanic and continental crust, there are some

key differences between the two types of crust. the key

differences are listed below.

HOW DO WE KNOW WHAT’S INSIDE THE EARTH?

Most of the Earth's mass must be located towards the

centre of the planet. The theory is that when Earth

formed 4.5 billion years ago, a lot of the iron present

in our universe must have worked its way down to the

core. It is suggested that the iron was gradually

squeezed down through the rocks of the Earth over

millions of years, until it reached the core. So, what

makes scientists think it begins 3000km down? There's

a one-word answer: seismology. When an earthquake

happens, it sends shockwaves throughout the planet.

Seismologists record these vibrations. They act as if we hit one side of the planet with a gigantic

hammer, and listened on the other side for the noise. Depending on the route those vibrations

take, they pass through different bits of the Earth, and this affects how they "sound" at the other

end. It was realised that at times some vibrations were going missing. These S-waves can only

reverberate through solid material, and can't make it through liquid. They must have come up

against something molten in the centre of the Earth. By mapping the S-waves' paths, it turned

out that rocks became liquid around 3000km down. Later it was noticed that another kind of

waves, called P-waves, unexpectedly travelled through this liquid core and could be detected on

7

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.

ACTIVITY

2.1

Number the boxes near the plate names and label the plates on the map accordingly :

8

Plate boundaries Scientists now have a fairly good understanding of how the plates move and how such movements relate

to earthquake activity. Most movement occurs along narrow zones between plates where the results of

plate tectonic forces are most evident. There are four types of plate boundaries:

where new crust is generated as the plates pull away from

each other.

where crust is destroyed as one plate dives under another.

where crust is neither produced nor destroyed but chang-

es shape.

where crust is neither produced nor destroyed as the

plates slide horizontally past each other.

9

POIN

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F IN

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10

Constructive plate boundaries

As the plates move apart (very slowly), magma

rises from the mantle. The magma erupts to the

surface of the Earth. This is also accompanied by

earthquakes. When the magma reaches the surface,

it cools and solidifies to form a new crust

of igneous rock. This process is repeated many

times, over a long period of time.

Eventually the new rock builds up to form a

volcano. 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.

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.

SURTSEY—ICELAND

11

Living on the Mid-Atlantic ridge

Iceland lies on a constructive plate margin. It is

part of a submarine mountain chain called the

Mid-Atlantic Ridge, which stretches for

thousands of kilometres through the middle of the

Atlantic Ocean.

Did you know that Iceland is growing in size?

As the two plate move apart new land is formed

every time there is an eruption. Despite being at

risk from occasional earthquake and volcanic

eruptions, the people of Iceland gain a number of

benefits from living on top of this plate boundary.

Just a few kilometres below the surface is a huge

body of heat that provides them with the following:

• _________________________________________________________

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• _________________________________________________________

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• _________________________________________________________

_________________________________________________________

• _________________________________________________________

_________________________________________________________

• _________________________________________________________

_________________________________________________________

• _________________________________________________________

_________________________________________________________

• _________________________________________________________

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ACTIVITY

2.2

THE BENEFITS OF ICELAND’S UNDERGROUND

12

Destructive plate boundary

At a destructive boundary the plates are moving

towards each other. This usually involves

a continental plate and an oceanic plate.

The oceanic plate is denser than the continental

plate so, as they move together, the oceanic plate

is forced underneath the continental plate. The

point at which this happens is called

the subduction zone. As the oceanic plate is

forced below the continental plate it melts to form

magma and earthquakes are triggered. The magma

collects to form a magma chamber. This magma

then rises up through cracks in the continental

crust. As pressure builds up, a volcanic eruption

may occur.

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.

MARIANA TRENCH

13

The Pacific Ring of Fire

a) Using a yellow pencil on a map of the world shade the areas where you think the most earthquakes

occur.

b) Using an orange pencil on a map of the world shade the areas where you think the most volcanoes

occur.

c) Label each of the following: North America continent, South America continent, Australia

continent, Asia continent, Pacific Ocean, Sea of Japan, Mt Rainier and Mt Fuji

Use the information in the data table below to mark the location of each earthquake on the map.

• Draw a circle at each earthquake location.

• Mark the locations of the volcanoes on the map with a triangle.

EARTHQUAKES VOLCANOES

ACTIVITY

2.3

14

Collision zone 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.

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

THE HIMALAYAS

15

World fold mountains

Look up and label the fold mountain ranges marked on the map above :

A

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ACTIVITY

2.4

16

Conservative plate boundary At conservative margins mountains are not made,

volcanic eruptions do not happen and crust is not

destroyed. Instead, two plats either slide past each

other in opposite directions, or two plates slide past

each other at different speeds. As they move past

each other stress energy builds as the plates snag

and grind on one another.

When this stress energy is eventually released it

sends shock waves through the earth’s crust

forming faults. We know these shock waves as

earthquakes, and a good example of this is the

San Andreas fault in California, where the Pacific

plate is moving NW at a faster rate than the North

American plate.

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.

SAN ANDREAS FAULT

17

California today...and someday

BOX 1 BOX 2 BOX 3

PROCEDURE :

1. Colour Pacific Ocean blue and land brown.

2. Cut out the three pictures of California.

3. Cut the first picture apart along the San Andreas Fault and glue in place in Box 1.

4. Cut out the second picture and along the fault. Move Pacific plate slightly Northward and glue

in Box 2.

5. Cut out the third picture and along the fault. Move Pacific plate further up from the position of

the previous one in Box 3.

6. Label each box with the following;

North American plate Pacific plate

Juan de Fuca plate San Andreas Fault

California Mexico

Arizona Nevada

Oregon

ACTIVITY

2.5

18

19

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What are volcanoes? 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).

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23

Types of volcanoes Geologists and professional volcanologists usually

classify volcanoes into four different types, based

on their shape, magnitude, structure, material, and

type of eruption.

EX :

EX :

EX :

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ACTIVITY

2.6

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25

Volcanoes

ACTIVITY

2.7

1. Answer the following seven questions. write your answers in the boxes below and draw an arrow

from each box to the correct feature on the diagram.

a) What name is given to the molten rock below the earth’s surface?

b) Name the molten rock that flows down the side of the volcano.

c) Name the funnel shaped opening at the top of a volcano.

d) What are the lumps of molten rock thrown out of a volcano called?

e) Name the opening through which molten rock flows to the surface.

f) What material makes up a volcano?

g) What shape is a volcano?

2.

Finish off the statements below :

a) A volcano that no longer erupts is said to be ____________________________________________

b) A volcano that erupts regularly is said to be ____________________________________________

c) Steep sided volcanoes are usually made from ___________________________________________

d) Volcanoes with gently-sloping sides are usually made from ________________________________

e) The volcano that erupted with a loud bang in 1883 was ___________________________________

f) The active volcano on the island of Hawaii is called ______________________________________

g) The dates of Mount Etna’s two recent eruptions were ____________________________________

h) Mount Etna is located on the island of _________________________________________________

i) Three other volcanoes in Italy are ____________________________________________________

26

Living in a danger zone

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.

ADVANTAGES DISADVANTAGES

27

Sinabung volcano in

Sumatra, Indonesia

rumbles away in

June 2015, but

local farmers

appear

unconcerned.

Many villagers

remained in the

area an would not

only live near the

“red zone” (the

restricted area

within 3km of the

summit) but also

regularly venture

28

Mount St. Helens

Mount St Helens, Washington State, NW USA is

located in the Cascade mountain range and prior

to its eruption in 1980 it had been active for over

100 years. The area around the mountains is a

National Park which is mainly used for tourism,

forestry, salmon farming and some agriculture –

therefore the population density of the area is

relatively low. The volcano which is a composite

cone, sits on a destructive boundary where the

Juan de Fuca plate meets the North American

plate. Mount St Helens erupted on May 18th 1980

following a period of activity which began in

March 1980 with an earthquake measuring 4.0 on

the richter scale. What followed was 3 months of

seismic activity as magma rose within the

mountain. As the magma rose, a large bulge grew

on the north flank of the volcano, this was due to a

blockage in the main vent resulting in the growth

of a cryptodome (mound of viscous lava) in the

side of the volcano. On May 18th, an earthquake

measuring 5.1 on the richter scale caused a

landslide on the northern flank of the volcano,

which in turn exposed the cryptodome below,

resulting in a sudden release of pressure and a

cataclysmic eruption in the form of a lateral

(sideways) blast. The blast zone consisted of 230

square miles with the eruption leaving a 'lunor'

landscape in its wake.

29

POINT OF INFO

30

EFFECTS ON THE LANDSCAPE

• 400 metres was blown off the top of the

mountain and a one mile horse shoe-shaped

crater was left that was 500m deep.

• Every plant and animal within 25km north of

the volcano was killed – approximately 7000

animals died. Every tree within 30km of the

volcano was flattened.

• The water produced from melting ice and

snow on top of the volcano create lahars

(mudflows of ash and water), which choked

rivers and killed all fish and water life. Spirit

Lake was filled with mud. 12 million salmon

died.

• The eruption also destroyed 250 homes, 47

bridges, 15 miles of railways and 185 miles of

highway.

• Nuée ardente (hot ash and gas) destroyed

forests and logging camps.

EFFECT ON PEOPLE AND THE

ECONOMY

• 63 people were killed, mainly by poisonous

gases.

• Ash clogged up car engines and farm

machinery. The cost of ash damaged to

farmers crops and machinery totalled £100

million.

• 15cm of ash fell causing traffic chaos and

airline flights to be cancelled.

• The timber industry in the area was destroyed by

the flattening of trees which significantly

damaged them.

• Telephone lines and electricity supplies were

knocked out.

• Tourists no long visited the area causing a

reduction in the local economy.

CONSEQUENCES OF THE ERUPTION

31

SHORT-TERM AID

• Rescuing stranded people, providing shelter for

those who has lost their homes, giving medical

supplies to those who were injured. The aid

operation rescued 198 people. Unfortunately, the

landscape had changed so much that maps were

no longer accurate, this slowed down the rescue

efforts.

LONG-TERM AID

• A million tonnes of ash were removed from

roads, buildings and airports. Removing the ash

cost over $1million in the town of Yakima and it

took ten weeks.

• Millions of trees were replanted because there

was a huge loss of timber which would cost

$300million.

• Compensation was given to farmers because what

they produced on their farms was destroyed by

being covered by ash. This would cost about

$70million.

• New tourist facilities were built because there

were less tourists, meetings and conferences in

the area after the eruption. It was important to get

these people back as they input a lot of money

into the economy.

• A channel was dredged to remove logs and

levees were rebuilt to reduce floods which could

happen in the future. This is because the

Columbia River shipping channel was closed.

This caused the port of Portland $3million per

month in lost trade.

• A new highway was built and major repairs were

undertaken because 250km of roads and 25km of

railways were damaged, costing $7million.

• Money was given to rebuild houses after 200

homes were destroyed.

• Money was given to redevelop the salmon

hatcheries after 12 million baby salmon were

killed.

RESPONSES TO THE ERUPTION

32

Date : ____________________ Name/location of volcano :

______________________

Tectonic plates :

_________________________________________________________

Type of plate boundary :

__________________________________________________

Causes : __________________________________________

ACTIVITY

2.8

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

Research some information about a famous volcanic eruption :

Volcanic eruption profile

33

Super volcanoes and hot spots

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

Most islands are found at tectonic plate

boundaries either from spreading centres (like

Iceland) or from subduction zones (like Japan).

There are few 'hot spots' on Earth and the one

under Hawaii is right in the middle of one of the

largest plates on Earth - the Pacific Plate.

A geologic 'hot spot' is an area in the middle of a

plate where molten magma breaks through the

thin crust A hot spot under the American plate is

why Yellowstone National Park has geysers and

other thermal features. If the hot spot is under the

seafloor (as it is in Hawaii) it produces undersea

volcanoes. Some of these volcanoes build up to

the surface of the ocean and become islands.

Over millions of years the plate may move

across the 'hot spot' and the original volcano

become extinct but a new volcano will begin to

form in the area of the 'hot spot.'

Yellowstone is one example of a super volcano. 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. The super volcano at Yellowstone is formed because of a

volcanic hotspot. Every year millions of visitors come to see the related

features, such as geysers and hot springs.

YELLOWSTONE

34

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.

MAP A

35

When Mount Etna erupts...

ACTIVITY

2.9

Work in groups to fill in the information required about what happens when Mount Etna erupts. Use the

information cards to help you.

1. a) Name four volcanoes in Italy.

__________________________________________________________________________________

b) Which large town is nearest to Mount Etna? ____________________________________________

c) Which two plates meet over Italy? ____________________________________________________

d) Are the plates moving apart or towards each other? ______________________________________

2. a) Which villages were threatened by the 1983 and1992 lava flow?

__________________________________________________________________________________

b) What was the length of the 1992 lava flow? ____________________________________________

c) What was the length of the longest lava flow? __________________________________________

3. Describe what happens when Mount Etna erupts by sorting the boxes below into the correct order,

then label the drawing below:

Lava pours down the mountainside Buildings and property damaged

Rescue service goes into action Volcano gently rumbles and steams

Loud explosion as volcano erupts Ash, bombs and lava blasted out of volcano

36

ACTIVITY

2.9

4. List six positive effects from the eruption of Mount Etna:

• _______________________________________________________________________________

• _______________________________________________________________________________

• _______________________________________________________________________________

• _______________________________________________________________________________

• _______________________________________________________________________________

• _______________________________________________________________________________

5. Fill in the table below. Sort the negative effects into the correct column:

6. The two farmers below live near to Mount Etna. Complete the sentences to explain their views.

Some problems caused by Mount Etna eruptions

FARMING TOURISM OTHER

Cont.

37

ACTIVITY

2.9

7. Zaffarena is a farming village 10km from the summit of Mount Etna. In 1991 an eruption lasted four

months.

a) When did the eruption start? _______________________________________________________

b) On what dates were army teams brought in? ___________________________________________

c) When was Zaffarena finally declared safe? ____________________________________________

d) How close to the village did the lava get?

______________________________________________________________________________

e) What three ways were tried to stop the lava?

______________________________________________________________________________

______________________________________________________________________________

______________________________________________________________________________

f) Why was building dams with bulldozers difficult?

______________________________________________________________________________

______________________________________________________________________________

g) What method of protection finally saved the village?

______________________________________________________________________________

8. Write down six points how damage and danger from an eruption can be reduced.

• ______________________________________________________________________________

• ______________________________________________________________________________

• ______________________________________________________________________________

Cont.

38

Earthquakes Earthquakes are caused by the release of built-up

pressure inside the Earth's crust. An earthquake's

power is measured on the Richter scale using an

instrument called a 'seismometer'.

The effects of an earthquake can be devastating -

they can destroy settlements, change landscapes,

and cause many deaths.

An earthquake is caused by 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.

39

Richter scale 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.

40

Effects of eartquakes

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)

Effects are often classified as primary and

secondary impacts. Primary effects occur as a direct

result of the ground shaking while secondary

effects occur as a result of the primary effects.

SOCIAL IMPACTS ECONOMIC IMPACTS ENVIRONMENTAL IMPACTS

Short-term

impacts

Long-term

impacts

41

Different impacts of eartquakes

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.

Climate

Influences survival rates

and the rate at which

disease can spread.

aftershock number to quantify the size of an earthquake

epicentre The size of an earthquake as measured by the energy released.

fault The zone of activity that surrounds the Pacific Ocean and the Pacific

plate.

focus A collapse of a mass of earth from a mountain or a cliff.

landslide A smaller earthquake following the main shock of a larger earthquake.

magnitude An instrument that measures earthquakes. It measures their size and their

duration. Also known as a seismometer.

Ring of fire A fracture in a rock formation along which there has been movement of

the rocks on either side of the fracture.

Richter scale The point on the earth’s surface, directly above the focus of an earth-

quake.

seismograph The place of origin of an earthquake.

Match earthquake words with their definition :

42

Kobe, Japan

Kobe is located in the south east of Japan, near a

destructive plate margin. It is a megacity and has

one of the largest container ports in the world.

Although further from a plate margin than most of

the cities in Japan, Kobe is still found on a fault

line.

The earthquake that hit Kobe during the winter of

1995 measured a massive 7.2 on the Richter

scale . At this plate margin, the Pacific plate is

being pushed under the Eurasian plate, stresses

build up and when they are released the Earth

shakes. This is known as an earthquake happening

along a subduction zone. The focus was only

16km below the crust and this happened on

the 17th Jan 1995 at 5.46am. 10 million people

live in this area.

The effects of this earthquake were catastrophic

for a more economically developed country

(MEDC).

Despite some buildings having been made

earthquake proof during recent years many of the

older buildings simply toppled over or

collapsed. A lot of the traditional wooden

buildings survived the earthquake but burnt down

in fires caused by broken gas and electricity lines.

43

PRIMARY EFFECTS

• The collapse of 200,000 buildings and

numerous bridges along the 130km bullet train

route.

• During the 20 second earthquake, the ground

moved up to 50 centimetres horizontally and up

to 1 metre vertically.

• Collapse of 1km of the Hanshin Expressway.

• 120 out of 150 quays destroyed at the port of

Kobe were destroyed.

SECONDARY EFFECTS

• Electricity, water and gas supplies were cut.

• Fires caused by broken gas pipes raged for

several days destroyed wooden buildings

• Roads were at gridlock, delaying ambulances and

fire engines.

• 230,000 people were made homeless and had to

live in temporary shelters (un-heated gyms or

open parks) at a time when night-time

temperature dropped to –2°C

• There was a shortage of supplies (ex. blankets,

water, food).

• Large industries in the area forced to close down

(ex. Panasonic, Mitsubishi)

• Final death toll was at 5500 people.

CONSEQUENCES OF THE EARTHQUAKE

44

• Water, electricity, gas, telephone services were

fully working by July 1995.

• The railways were back in service by August

1995.

• A year after the earthquake, 80% of the port was

working but the Hanshin Expressway was still

closed.

• By January 1999, 134,000 housing units had

been constructed but some people were still

having to live in temporary accommodation.

• New laws were passed to make buildings and

transport structures even more earthquake proof.

• More instruments were installed in the area to

monitor earthquake movements.

• Most new buildings and roads have, in the last

20 years, been designed to be earthquake proof,

schools and factories have regular earthquake

drills, etc. Despite this, many older buildings

still collapsed or caught fire. This led to many

blocked roads and massive problems of

homelessness.

• Telephones and other communication services

were put out of action making communication

slow and difficult.

• Electricity and water supplies were badly

damaged over large areas. This meant no power

for heating, lights, cooking, etc. Clean, fresh

water was in short supply until April 1995. The

government and city authorities were criticised

for being slow to rescue people and for refusing

offers of help from other countries.

• Many people had to sleep in cars or tents in

cold winter conditions.

RESPONSES TO THE EARTHQUAKE

45

ACTIVITY

2.10

Research some information about a famous earthquake :

Earthquake profile

Date : ____________________ Name/location of volcano : ______________________

Tectonic plates : _________________________________________________________

Type of plate boundary : __________________________________________________

Causes : __________________________________________

_________________________________________________

_________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

_________________________________________________________________________

46

The wave of destruction A tsunami is a huge wave, usually caused by

volcanic or earthquake activity under the ocean,

which can eventually crash onto the shoreline.

The effects on a community can be devastating.

When an earthquake, volcano or landslide

happens on the ocean floor, water is displaced.

This water forms the start of the tsunami.

When the waves reach shallower water:

• their height can increase by several metres

• the shallow water slows the wave

• the waves get closer together

It is hard to see that a tsunami is approaching.

The most obvious sign is the coastal water

retreats just before the waves reach the shore.

This is actually the trough of the wave following

behind.

The main impact a tsunami has is flooding. The

waters are also able to erode the foundations of

coastal structures.

47

Indian Ocean Tsunami Log on the following website and answer the questions :

http://www.bbc.co.uk/bitesize/ks3/geography/physical_processes/plate_tectonics/revision/9/

1. When did the tsunami

occur and in which ocean? ___________________________________________

2. What caused the tsunami?

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

3. Briefly describe the tsunami.

____________________________________________________________________________________

____________________________________________________________________________________

4. How many countries were affected? _______________________________________________

5. Name 5 countries which were affected by the tsunami. Which country was the worst affected?

____________________________________________________________________________________

____________________________________________________________________________________

6. Which type of industries were affected most?

____________________________________________________________________________________

____________________________________________________________________________________

7. How did countries cope with the disaster?

____________________________________________________________________________________

____________________________________________________________________________________

____________________________________________________________________________________

ACTIVITY

2.11

48

Predict and prepare

It's not possible to prevent earthquakes and

volcanic eruptions. However, careful

management of these hazards can minimise the

damage that they cause. Prediction is the most

important aspect of this, as this gives people time

to evacuate the area and make preparations for

the event. Unfortunately volcanic eruptions and

earthquakes cannot be prevented. Managing

hazards such as earthquakes and volcanoes can be

done by prediction and preparation.

PREDICTING AN ERUPTION

As a volcano becomes active, it gives off a number

of warning signs. These warning signs are picked up

by volcanologists (experts who study volcanoes)

and the volcano is monitored.

PREPARING FOR AN ERUPTION

Everyone who could be affected needs to know the

plan and what they should do if it needs to be put

into action. Planning for a volcanic eruption

includes:

• creating an exclusion zone around the volcano

• being ready and able to evacuate residents

• having an emergency supply of basic

provisions, such as food

• funds need to be available to deal with the

emergency and a good communication

system needs to be in place.

49

PREDICTING AN EARTHQUAKE

Earthquakes are not as easy to predict as volcanic

eruptions. However, there are still some ways of

monitoring the chances of an earthquake:

• Laser beams can be used to detect plate

movement.

• A seismometer is used to pick up

the vibrations in the Earth's crust. An increase

in vibrations may indicate a possible

earthquake.

• Radon gas escapes from cracks in the Earth's

crust. Levels of radon gas can be monitored - a

sudden increase may suggest an earthquake.

PREPARING FOR AN ERUPTION

Many of the prediction techniques used to monitor

earthquakes are not 100 per cent reliable. Planning

and preparing for an earthquake is therefore very

important.

• People living in earthquake zones need to know

what they should do in the event of a

quake. Training people may involve

holding earthquake drills and educating people

via TV or radio.

• People may put together emergency kits and

store them in their homes. An emergency kit

may include first-aid items, blankets and tinned

food.

• Earthquake-proof buildings have been

constructed in many major cities. Such

buildings are designed to absorb the energy of

an earthquake and to withstand the movement

of the Earth.

• Roads and bridges can also be designed to

withstand the power of earthquakes.

50

Glossary

aftershock a smaller earthquake following the main shock of a large earthquake.

continental drift the gradual movement of the continents across the earth's surface through geological time.

convection currents very hot material at the deepest part of the mantle rising, then cooling, sinking again and then heating, rising and repeating the cycle over and over.

crust the outer layer of the earth made up of solid rock layer upon which we live.

core the hottest part at the centre of the Earth which with its immense heat energy, the inner core is like the engine room of the planet

earthquake a sudden violent shaking of the ground, typically causing great destruction, as a result of movements within the earth's crust or volcanic action.

epicentre the point on the earth's surface vertically above the focus of an earthquake.

fault a fracture along which the rocks have been displaced.

focus the point of origin of an earthquake unerneath the crust.

fold mountains form mainly by the effects of folding on layers within the upper part of the Earth's crust.

geothermal energy thermal energy generated and stored in the Earth.

hot spot a place deep within the Earth where hot magma rises to just underneath the surface, creating a bulge and volcanic activity.

igenous rock a type of rock formed through the cooling and solidification of magma or lava.

lahars a destructive mudflow on the slopes of a volcano.

landslide a collapse of a mass of earth or rock from a mountain or cliff.

lava the resulting rock after solidification and cooling of magma coming out of a volcano.

magma molten rock located deep within the mantle of the Earth that comes to the surface through the eruption of volcanoes .

51

mantle the layer between the earth’s crust and the outer core made up of semi-molten rock.

metamorphic rock rock that was once one form of rock but has changed to another under the influence of heat or pressure.

nueé ardente a cloud of gas, ash, and lava fragments ejected from a volcano, typically as part of a pyroclastic flow.

plate a massive, irregularly shaped slab of solid rock which floats on the mantle.

plate boundary/margin the locations where two tectonic plates meet.

plate tectonics the theory that Earth's outer shell is divided into several plates that glide over the mantle.

pyroclastic flow a dense, destructive mass of very hot ash, lava fragments, and gases ejected explosively from a volcano and typically flowing at great speed.

Richter scale a numerical scale for expressing the magnitude of an earthquake.

seismometer an instrument that measures and records details of earthquakes, such as force and duration.

seismic waves A wave in the earth produced by an earthquake.

subduction zone a plate boundary where two plates converge, and one plate is forced beneath the other.

trench a long, narrow, deep depression in the ocean bed, typically one running parallel to a plate boundary and marking a subduction zone.

vent the main outlet for the magma to escape.