Global Distribution of Volcanoes and Earthquakes

Restless Earth

Map to show the location of volcanoes

around the world

Map to show the distribution of

earthquakes around the world

If the exam asks you to describe the

pattern of earthquakes and volcanoes.

This is a skills question not a knowledge

question – you should not use the word

‘because’. Simply say what you see:

Volcanoes and earthquakes are not evenly

spread across the earth

They both occur on land and in the sea

They can occur together and

independently of each other

They tend to occur in lines

An examples of volcanoes and

earthquakes occurring in lines in along the

west coast of North & South America

Diagram to show the structure of the earth

Map to show the worlds main plate

boundaries

The structure of the Earth

The Earth is made up for four layers:

1. The crust – solid rock which is

between 0km and 80km thick

2. The mantle – made of molten rock

that flows like a liquid

3. The outer core – a liquid made up of

silicate, nickel and iron

4. The inner core – a solid made up of

nickel and iron. Up to 5500ºC

Types of plate boundaries

The Mantle – convectional currents

The mantle causes plates to move. The mantle gets hotter the closer to the core it gets, due

to pressure. As it acts like a liquid, the hottest mantle rises towards to crust. As it rises, it

begins to cool, condenses and sinks back down towards the core, where the process repeats

itself. This causes convection currents. These convection currents either circle towards or

away from each other (as shown in the diagram). Currents that circle towards each other

cause the crust floating on top to move towards each other, whilst currents that move away

cause the crust on top to move away from each other. This is what causes plates to move.

The Crust

There are two types of crust; oceanic

and continental. Oceanic crust is made

up of basalt and is denser than

continental crust which is made of

granite and cannot be destroyed.

Magma from

mantle creates

volcanic island

arcs e.g. Mid-

Atlantic Ridge

Eurasian plate

North American

plate

Creates shield

volcanoes

The Nazca Plate

moves towards South

American plate and

is forced underneath

it (subducts). It is

oceanic crust, so is

heavier.

Friction and

heat from

mantle melts

rock

Oceanic crust

being forced

downwards

causes severe

earthquakes.

Violent volcanic

eruptions. Produces

composite volcanoes.

South American

plate (continental

crust)

Hot liquid

rock

(magma)

rises.

North American

Plate moving

slower than, and

slightly

towards, Pacific

Plate

Pacific Plate moving

faster than the

North American

Plate

Hot liquid rock

(magma) rises

Rocks formerly on

ocean bed are

pushed together,

buckled and forced

up to form Himalayan

Mountains. They are

the same

weight/crust, so

neither plate is

subducted.

Indo-Australian

Plate (continental

crust)

Eurasian Plate

(continental

crust)

Collision margin

Pressure builds up and when it is suddenly release it

produces seismic waves and violent earthquakes

Young Fold Mountains are 10 to 25 million years of age

e.g. Rockies, Alps and Himalayas.

Young Fold Mountains

Young Fold Mountains are mountains formed from

the folding of the earth's crust. Fold mountains are

formed when two plates move together (collision or

destructive plate margin). This can be where two

continental plates or a continental and an oceanic

plate move towards each other. The movement of the

two plates forces sedimentary rocks upwards into a

series of folds. Fold mountains are usually found

along the edges continents. This is where the

thickest deposits of sedimentary rock generally

accumulate. When plates and the continents riding on

them collide, the accumulated layers of rock crumple

and fold like a tablecloth that is pushed across a

table.

During long periods of quiet sedimentary rocks

formed from the build up of sediments deposited by

rivers into the sea (depression/geosynclines). Over

time these compressed together to form

sedimentary rocks. When the two plates collide

these rocks are forced upwards and fold upwards

(anticline) and downwards (syncline). In some places

the folds are pushed over on one side (overfolds).

Fold Mountains - The Alps

The Alps are home to eleven million

people and thus the most densely

populated mountain area in the world.

The economy of this region is based on

the exploitation of the coniferous

forest and pasturing dairy cattle, and

tourism plays an important role.

Farming and Forestry

Coniferous trees are the main trees forested in

the Alps. They are ideally suited to the Alpine

environment. Their conical shape makes the tree

stable in windy conditions. The downward

sloping, springy branches allows the snow to

slide of the tree without damaging its branches.

The wide meadows of The Alps make the area

ideal for sheep farming. In the more extreme

upland areas goat herding is the main type of

farming. The cold climate and difficult relief

make it almost impossible for arable farming to

occur.

Tourism

Since the end of the WWII, the Alps

have become the winter and summer

play ground of European urban dwellers.

In winter the Alps are a very popular

destination amongst winter tourists. Ski

resorts such as Val d'Isere and Les

Deux Alps have been purpose-built.

These areas are very crowded in the

winter but tend to be quieter in the

summer. However, traditional ski

resorts tend to be busy throughout the

year.

In summer between June and

September the Alps are heavily

populated with walkers, cable-car riders

and paragliders.

The huge number of tourist visitors to

the Alps has led to them becoming the

most threatened mountain chain in the

world. This is in terms of its fragile

ecological and physical system.

HEP Schemes

Hydroelectric power schemes are common in the

Alps. The combination of tectonic and glacial

processes make the area ideally suited for HEP

schemes. HEP schemes often involve many

different watersheds. It is an area of excess

water and deep U-shaped valleys. Since the

development of HEP at the end of the 19th and

the beginning of the 20th centuries these

valleys have been dammed and used to develop

HEP.

The development of HEP in The Alps led to the

establishment in the lower valleys of electricity-

dependent industries, manufacturing such

products as aluminium, chemicals, and speciality

steels.

Types of volcanoes

Shield

Composite

Constructive plate boundary

Wide base and gentle slopes

Made of layers of lava only

Regular and frequent eruptions

Runny lava with low silica content

Not very violent

Mauna Loa, Hawaii

Lava travels longer distances before cooling

Destructive plate boundary

Tall cone with steep slopes and a narrow base

Made of alternative layers of ash and lava

Irregular eruptions with long dormant periods

Thick lava with high silica content (viscous)

Violent explosions

Mount St. Helens

Lava may cool inside the vent – the next

eruption is very explosive to remove the plug

Mauna Loa Shield Volcano Mt St Helens Composite Volcano

Causes:

The North and South American Plates

are being subducted under the

Caribbean Plate (Destructive)

The melted plate, mixed with sea

water, is less dense than the rest of

the mantle. So the melted magma

rises upwards

The dissolved gases are released when

the magma gets higher up. That’s

because the pressure is lower in the

crust.

The released gases pushed out the

dust and ash from previous eruptions.

That’s what made the first eruptions

in July 1995. And the volcano has

been active ever since.

LEDC Case Study: Montserrat eruption, July 1995 – June 1997

Montserrat is a small island in the

Caribbean, and is still a British colony.

Many of the residents are quite poor,

practising subsistence farming. Before

the eruption, the population was 12,000.

50% of people lived in the capital,

Plymouth.

In July 1995, the Soufriere Hills

volcano erupted for the first time in

350 years.

Short term effects:

Ashfall from the eruption has caused

severe disruption to life on the island.

In August 1995 people were evacuated to

the north of the island, and were forced to

live in halls and churches, sharing toilets,

with nothing to do. Others had to live in

makeshift shelters with inadequate

sanitation.

In April 1996 the capital city of Plymouth

was evacuated.

In June 1997 the south of the island was

covered by rivers of hot ash, gases, mud

and rock, known as PYROCLASTIC FLOWS.

These caused huge fires, killing 19 people.

The long term effects

The country’s tourist industry ground to a halt.

The ports and airport had to close, restricting trade and affecting Montserrat’s economy.

Two-thirds of Montserrat’s homes and three-quarters of its infrastructure (roads,

telephone lines, etc.) were lost due to ashfall or fire.

Two-thirds of Montserrat’s homes and three-quarters of its infrastructure (roads,

telephone lines, etc.) were lost due to ashfall or fire.

Long term effects

The area is now a tourist attraction.

This means the local economy is

wealthier than it was before the

eruption.

There is now an increased risk of

flooding due to ash and mud blocking

river valleys.

MEDC Case Study: Mount St. Helens eruption, 18th May 1980

Mount St. Helens is a volcano in the

Cascade Mountain Range in the USA.

They are FOLD MOUNTAINS on a

destructive plate boundary.

Short term responses/solutions

Scientists monitored the volcano and set up warning systems

UK government sent £17 million of emergency aid

Red Cross set up temporary schools

People evacuated to the north of the island and then to other countries. Some went on

boats paid for by the UK and USA. The British navy took some people. By November

1997 the population had fallen to 3500.

USA sent troops for the evacuation

Charities also sent emergency food for farm animals.

Long term responses/solutions

By 2005, the south of the island was still out of bounds and scientists were still

monitoring the area.

People have now been allowed to move back further north. By 2005 the population was

over 8000.

Red Cross built a home for the elderly

The UK government, at a cost of £122.8 million, funded a three-year redevelopment

programme for houses, schools, medical services, infrastructure and agriculture.

People were also offered mortgages to start new businesses.

The population structure changed, because more of the younger people made new lives

elsewhere, and more of the elderly had either not left in the first place, or returned.

Some vegetation began to re-grow in the south of the island. The soil will eventually

become fertile as the ash and lava break down.

Tourists may come back and the volcano itself may become a tourist attraction.

Causes:

20 March 1980 there was an earthquake

under the mountain, caused by the magma

beginning to move.

More earthquakes followed in the days

afterwards

27 March, gas and steam belched out of

the top of the mountain.

3 April, a bulge started to appear on the

side of the mountain, and continued to

grow. By 12 April it was 100 metres high.

On May the volcano erupted out of its side

and top. A pyroclastic flow occurred,

moving at 300 km per hour.

Supervolcanoes

Supervolcanoes occur on a much bigger scale than normal volcanoes. They emit at

least 1000km³ of material compared to a normal volcanoes such as Mount St. Helens

which only emitted 1km³. They can occur away from plate boundaries, whereas

normal volcanoes only occur on destructive or constructive plate boundaries.

Supervolcanoes do not look like normal volcanoes with its cone shape; they have large

depressions called calderas with a rim of higher land around the edges.

Responses:

Short term - Prior to the main eruption, scientists issued warnings to the local people that

they might have to evacuate the area. On 30 April scientists gave another warning and the

local authorities put a 30 km danger zone around the volcano that people were not allowed to

enter.

Long term - The US government gave $951 million in aid to rebuild industry in the area and

compensate people.

Short term effects

The pyroclastic flow flattened and burnt trees over 360 square km. 7000 animals were

killed in the forests. 12 million salmon in a fish farm were killed. 61 people died, mainly

scientists and photographers.

Hot magma melted the snow on the mountain, causing mudslides which flowed down river

valleys at 35 metres per second.

A cloud of smoke, dust and ash went upwards and made a cloud 24 km up into the sky.

Planes had to be diverted. Roads became unusable and destroyed crops and farm

machinery. This cost of the damage caused by the ash was $175 million.

After the eruption, the mountain appeared very different. The side had blown out and

the top had collapsed. It was 365 metres lower than it used to be!

This is Old Faithful

Geyser. A geyser is when

water erupts into the air

under pressure.

Yellowstone

Yellowstone is in Montana, in the USA. Yellowstone is a hot spot, where plumes of

magma rise towards the earths crust. The last eruption of Yellowstone was 630,000

years ago. Its caldera is 80km long, 40km wide and 8km deep. There is evidence that

the magma beneath Yellowstone is shifting, the caldera is bulging up near Lake

Yellowstone. The ground has risen in places by 70cm.

Earthquakes

What is an earthquake?

Earthquakes usually occur at plate boundaries. Powerful forces from inside the earth

(convections currents) cause each plate to move in a different direction to its

neighbour. The rock stores up the energy as strain energy. Eventually, the pressure

gets too much. One mass of rock gives way and slips. The stored energy is released in

waves called seismic waves. These waves get weaker as they radiate away from the

epicentre.

The focus of the earthquake is the point where the waves started.

The epicentre is the point directly above it on the Earth’s surface.

As the rock settles into its new position, there will be lots of smaller

earthquakes called aftershocks.

If an eruption occurred it would…

Destroy 10,000km² of land

Kill 87,000 people

15cm of ash would cover buildings with 100km

1 in 3 people affected would die

Ash would affect transport link, farming and

electricity/water supplies

Mud flows would occur

The UK would have ash falling over the country after

five days

Crops would fail as sunlight is blocked out by the ash.

2,000 tonnes of sulphuric acid would be ejected into our

atmosphere and this would deflect sunlight back into

space and would trigger a catastrophic volcanic winter

which could results in temperatures decreasing between

12ºC and 16ºC. This could cause monsoon rains to fail

and ultimately lead to mass starvation.

Measuring earthquakes

Earthquakes are measured using

machines called seismometers. These

record the shaking as waves on a

graph. This can tell scientists how

much energy the earthquake gave out.

This is known as the earthquake’s

magnitude. It can be shown on the

Richter Scale.

The Richter Scale

Richter

scale no.

No. of

earthquakes per

year

Typical effects of this magnitude

< 3.4 800 000 Detected only by seismometers

3.5 - 4.2 30 000 Just about noticeable indoors

4.3 - 4.8 4 800 Most people notice them, windows rattle.

4.9 - 5.4 1400 Everyone notices them, dishes may break, open doors swing.

5.5 - 6.1 500 Slight damage to buildings, plaster cracks, bricks fall.

6.2 6.9 100 Much damage to buildings: chimneys fall, houses move on foundations.

7.0 - 7.3 15 Serious damage: bridges twist, walls fracture, buildings may collapse.

7.4 - 7.9 4 Great damage, most buildings collapse.

> 8.0 One every 5 to

10 years Total damage, surface waves seen, objects thrown in the air.

The Mercalli Scale

An increase of 1 on this scale means the shaking is 10 times

grater, and about 30 times more energy is given out.

The Mercalli Scale (below) is less widely used, but is another method of describing the

strength of an earthquake. The problem with it can be that it describes the EFFECTS of

the earthquake and not the magnitude itself. The effects of two earthquakes of identical

magnitude would differ greatly if one earthquake occurred in an MEDC and one in an LEDC

due to differing building standards and hazard preparation and response between the two

countries.

Mid-plate earthquakes

Whilst most major earthquakes occur along plate boundaries, there are some which

do not. We call these mid-plate earthquakes. There are four main reasons for these

earthquakes:

Underground subsidence following deep mining.

Lubrication of an ancient fault by moving water or oil.

Dam and reservoir construction, partly due to the increased pressure exerted

on a fault from above and also the likelihood of water seeping into the

groundwater zone and lubricating a fault.

Scientists now believe that extreme pressures exerted at plate margins

actually cause a web of cracks to form right across the plate, rather like a

windscreen that crazes when hit by a stone. This means that marginal tensions

can be released mid-plate as well as at the plate margin itself.

MEDC Case Study: Kobe earthquake, 17th January 1995

LEDC Case Study: Kashmir Earthquake, 8th

October 2005

Where and when? 8.40am on 8 October, 2005.

A massive earthquake hits Kashmir in Pakistan.

It’s focus is 26km down. It measures 7.6 on the

Richter scale. The shaking lasts for 60 seconds.

Aftershocks (some up to 6 on the Richter scale)

continue for 2 days.

Why? Kashmir is on the border of India and

Pakistan, in a mountainous area (part of the

Himalayas). This area is where two plates are

colliding, at a COLLISION PLATE BOUNDARY. The Indian plate is colliding with the

Eurasian plate.

Short term effects:

Buildings collapsed, signs fell of walls,

windows shattered, furniture fell over,

roads cracked and bridges toppled.

These caused injury and death.

In Kashmir, over 70,000 people were

killed, 100,000 were injured and 3.3

million homes were destroyed.

Landslides also occurred.

The effects were so severe because

buildings in the towns were not built

very strongly.

As Saturday is a normal school day in

the region, most students were at

school when the earthquake struck.

Many were buried under collapsed

school buildings.

Water pipes broke, and people did not

have a clean water supply. This caused

diseases like cholera and typhoid to

spread, which again caused more deaths.

People also developed respiratory

infections like pneumonia. There were

also deaths from cold in the harsh

winter, as they only had thin tents to

sleep in.

Long term effects:

In the urban areas, many people lost their

jobs as their offices or shops were

damaged.

Electricity lines were brought down, so

reconstruction was made harder.

Schools were damaged, and students lost

their books, negatively affecting their

education.

3.3 million people lost their homes and

were forced to live in temporary shelters

until rebuilding could start in the spring.

The overall cost of the damage is

expected to be over $5 billion.

Tsunamis

Tsunamis are triggered by earthquakes. A Tsunami is a special type of wave where

the entire depth of the sea or ocean is set into motion by an event, normally an

earthquake, which displaces the water above it and creates huge waves. In deep

water, the waves move at high speed, but when they reach shallower water near the

coast, they begin to slow down but build in height. A normal wave is created by wind

only moving the surface water not the whole volume of the sea/ocean.

Immediate responses:

Local people started trying to rescue those who were trapped

The Indian Red Cross distributed 21 500 blankets, 300 kitchen sets and medical supplies.

The army and emergency services arrived to help did people out.

Helicopters from the military were used to take the injured to first aid centres on

flatter ground.

The border between India and Pakistan was opened in a few places to allow food

emergency supplies to cross.

Tents were given out by charities like Muslim Aid and the Pakistani and Indian armies.

Pakistan Airways carried emergency food and supplies from other countries for free.

Military hospitals were opened for civilian casualties.

Rescue and medical teams arrived from other countries (eg Russia and the UK) to try to

find survivors and treat the injured.

Long term responses:

The Red Cross re-established water supplies in Muzaffarabad.

The tents weren’t enough for the cold winter, so the army and the Red Crescent built pre-

fabricated homes using corrugated tin for people to live in until they had rebuilt their

houses.

Schools will need to be re-built and re-supplied.

Teachers may be trained in counselling to help traumatized children.

Sanitation will be needed for the temporary houses.

Building laws will be tightened up to make sure that next time there will be less damage

and fewer deaths.

Tsunami Normal wave

Asian Tsunami/Indian Ocean Earthquake, 26th December 2004

On the 26th December 2004 the Indo-Australian plate subducting under the Eurasian

plate moved (destructive plate margin) causing an earthquake measuring 9.3 on the

Richter scale (some measured it at 9.1).

It was one of the worst disasters in history killing nearly 300,000 people, 650,000

were seriously injured and up to 2 millions were made homeless. Public buildings were

wiped out and many people posted photos of loved ones in hope of trying to find them.

Identification of the dead was a major problem. Rescue and emergency services were

swamped by the disaster. Injured people were untreated for days and bodies

littered the streets before being buried in mass graves

Immediate responses

Fresh water, water purification tablets, food, sheeting and tents arrived from

international communities.

$7 billion was donated worldwide to the affected countries.

People in the UK donated £372 million and the government promised £75 million in

aid.

The UN’s World Food Programme provided food aid for more than 1.3 million

people

Long term responses/solutions

The Disasters Emergency Committee (DEC) spent £230 million on rebuilding

projects in Sri Lanka and Indonesia.

The Indian Ocean Tsunami Warning System was set up in June 2006 so that

people know how to respond and so that local authorities have plans in place should

another tsunami occur. Warnings go out via radio, TV, email, bells & megaphones.

The Green Coast Project in Aceh, Indonesia are restoring and replanting mangrove

swamps which help protect against tsunamis. They absorb the wave’s power

naturally. This has also helped to provide a livelihood for people as they are a

good breeding ground for fish as well.

Indonesia:

236,169 people died. Western

Sumatra was the closest

inhabited area to the

earthquake’s epicentre and was

devastated. UP to 70% of some

coastal populations were killed or

missing. At Banda Aceh the wave

reached nearly 17 metres high.

Sri Lanka:

The southern and eastern

coastlines were ravaged,

with homes, crops and

fishing boats destroyed.

400,000 people lost their

jobs and 31,147 people

died. The wave reached

6m high in places.

Thailand:

The west coast was

severely hit, including

the islands like Phi Phi

and Phuket, the dead

there included 1700

foreigners from 36

countries.

Earthquakes:

Economic: People work in the area and can’t afford (or don’t want to) lose their jobs by

moving. Los Angeles, for example, is a rich city with (for most people) a good lifestyle

and well-paid jobs.

Technological: People feel secure that prediction will give them enough warning and,

even if it doesn’t, that technology will mean their homes are safe and the emergency

services will be able to cope.

Perception: People don’t see relatively uncommon earthquakes as big risks. Regular

things like car accidents and crime are often seen as being more likely to happen to

you, so are more ‘dangerous’.

Social: People have their families, friends, schools and favourite places nearby, and

don’t want to lose them.

Why do people choose to live in tectonic areas?

Managing tectonic hazards

It's not possible to prevent earthquakes and volcanic eruptions from happening, but

careful management 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. It is often LEDC countries that are hardest hit by the

impact of earthquakes and volcanoes.

Predicting and preparing for volcanoes

Unfortunately there is nothing that can be done to stop volcanic eruptions or

earthquakes. Prevention is not an option. This leaves two possible ways of managing

hazards such as earthquakes and volcanoes:

1. prediction

2. preparation

Volcanoes:

Fertile soil when the lava weathers

Tourist attractions, e.g. trips to the rim of the crater, hotel accommodation, souvenir

shops.

Minerals, e.g. sulphur, borax and pumice.

Lava flows build new land, e.g. Iceland, Hawaii.

Hot springs for bathing, heating.

Heat used to generate electricity.

Predicting eruptions

As a volcano becomes active, it gives off a number of warning signs. These warning

signs are picked up by vulcanologists (those who study volcanoes) and the volcano is

monitored. The key techniques for monitoring a volcano are outlined in the table

below.

Eruption detection and monitoring

Warning signs Monitoring techniques

Hundreds of small earthquakes are caused as

magma rises up through cracks in the Earth's

crust.

Seismometers are used to detect

earthquakes.

Temperatures around volcano rise as activity

increases.

Thermal imaging techniques and satellite

cameras can be used to detect the heat

around a volcano.

When a volcano is close to erupting it starts to

release gases. The higher the sulphur content of

these gases the closer volcano is to erupting.

Gas samples may be taken and chemical

sensors used to measure sulphur levels.

As technology improves, the techniques available for predicting and monitoring

volcanic activity are becoming more and more accurate. Volcanoes such as Mt. St.

Helens in the USA or Mt. Etna in Italy are closely monitored at all times. This is

because they are active or have been active in recent years. This means that people

can benefit from early-warning signs of an eruption. However, as well as prediction,

people need to be prepared for an eruption.

Preparing for an eruption

A detailed plan is needed for dealing with a possible eruption. Everyone who could be

affected by the eruption needs to know the plan and what they should do if it needs

to be put into action.

Planning for a volcano 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

Predicting earthquakes

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: A machine that detects vibrations in the earth's crust 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; an increase may suggest an earthquake.

Many of the prediction techniques used to monitor earthquakes are not

considered 100% reliable. Planning and preparing for an earthquake is

therefore very important. As with volcanoes, there are many ways of preparing

for an earthquake. These are outlined in the table below.

Preparing for earthquakes

Preparation Explanation

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

e.g. The transamerica Pyramid in San Francisco. Buildings such as this

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.

Earthquakes and volcanoes in LEDCs

Less Economically Developed Countries (LEDCs) often suffer more from the effects

of volcanoes and earthquakes than More Economically Developed Countries (MEDCs).

This is because LEDCs have weaker communication systems, lower standards of

building, together with limited funds to deal with either evacuation before the

disaster, or to deal with the aftermath of the emergency. See the diagram below.