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

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.

Types of plate boundaries

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 plateNorth American plate

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

South American plate (continental crust)

Hot liquid rock (magma) rises.

Hot liquid rock (magma) rises

Creates shield volcanoes

Young Fold Mountains

North American Plate moving slower than, and slightly towards, Pacific Plate

Pacific Plate moving faster than the North American Plate

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

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.

Young Fold Mountains are 10 to 25 million years of age e.g. Rockies, Alps and Himalayas.

TourismSince 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.

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.

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 boundaryWide base and gentle slopesMade of layers of lava only

Regular and frequent eruptionsRunny lava with low silica content

Not very violentMauna Loa, Hawaii

Lava travels longer distances before cooling

Destructive plate boundaryTall cone with steep slopes and a narrow

baseMade of alternative layers of ash and lava

Irregular eruptions with long dormant periods

Thick lava with high silica content (viscous)

Violent explosionsMount 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

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

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.

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, 18 th 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.

Yellowstone

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 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. 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.

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.

The Richter Scale

Richter scale no.

No. of earthquakes

per yearTypical effects of this magnitude

< 3.4 800 000 Detected only by seismometers3.5 - 4.2 30 000 Just about noticeable indoors4.3 - 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

Mid-plate earthquakes

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.

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, 17 th January 1995

LEDC Case Study: Kashmir Earthquake, 8 th 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.

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.

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.

Asian Tsunami/Indian Ocean Earthquake, 26 th 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

Tsunami Normal wave

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.

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.

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

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 techniquesHundreds of small earthquakes are caused as magma rises up through cracks in the Earth's crust.

Seismometers are used to detect earthquakes.

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.

Warning signs Monitoring techniquesTemperatures 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.