Skip to content

Tectonic hazards


Key idea Specification content
Earthquakes and volcanic eruptions are the result of physical processes Plate tectonics theory.

Global distribution of earthquakes and volcanic eruptions and their relationship to plate margins. Physical processes taking place at different types of plate margin (constructive, destructive and conservative) that lead to earthquakes and volcanic activity.

The effects of, and responses to, a tectonic hazard vary between areas of contrasting levels of wealth. Primary and secondary effects of a tectonic hazard.

Immediate and long-term responses to a tectonic hazard.

Use named examples to show how the effects and responses to a tectonic hazard vary between two areas of contrasting levels of wealth.

Management can reduce the effects of a tectonic hazard.


Reasons why people continue to live in areas at risk from a tectonic hazard.

How monitoring, prediction, protection and planning can reduce the risks from a tectonic hazard.


Tectonic Hazards


Natural hazards

A natural hazard is a threat of a naturally occurring event that will have a negative effect on people or the environment. Many natural hazards are interrelated, e.g. earthquakes can cause tsunamis and drought can lead directly to famine. If this threat becomes a serious reality then it becomes a disaster. A natural hazard becomes a natural disaster when it affects people – deaths.


In this unit of work we will study two tectonic hazards (earthquakes and volcanoes) and one atmospheric hazard – tropical cyclones (hurricanes).

Plate tectonics

The topic of plate tectonics is largely based on Alfred Wegner’s theory of continental drift. Wegner was a German geophysicist and meteorologist who in 1912 hypothesised that the world’s continents were moving. The movement of the earth’s crust is now generally known as plate tectonic theory.



Plate Movements and Convection Currents
The earth’s tectonic plates are in motion, moving like giant ‘rafts’ on top of the semi-molten mantle below. However this movement is slow and rates vary from less than 2.5cm /yr to over 15cm/yr.

The movement of the earth’s crustal plates is believed to be due to convection currents which occur in the semi-molten mantle. These convection currents are created by heat from within the earth.

The structure of the Earth



Tectonic Plates and the Earth’s Crust

The crust of the earth is broken into giants pieces. These giant pieces are called tectonic plates, or often just plates. There are seven major or primary plates (African, Eurasian, North American, South American, Pacific, Indo-Australian and Antarctica). There are seven smaller secondary plates (Nazca, Cocos, Caribbean, Scotia, Arabian, Philippine and Juan de Fuca). Because the plates are so big they have faults and cracks in them so are sometimes divided into smaller tertiary plates as well. The earth’s plates are being constantly moved by convection currents found in the mantle.

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 crusts.

Oceanic crust
Oceanic crust is younger
Oceanic crust is normally thinner
Oceanic crust is denser (heavier)
Oceanic crust can be destroyed
Oceanic crust can be made


Continental crust
Continental crust is older
Continental crust is normally thicker
Continental crust is less dense (lighter)
Continental crust can’t be made
Continental crust can’t be destroyed.

Plate Boundaries

Plate boundaries can be classified in several ways. Plate boundaries moving towards each other are called convergent, plate boundaries moving apart are called divergent and plate boundaries moving alongside each other are called transform. However, at IGCSE we need to know the specific names of plate boundaries. You need to know four types:


Constructive Plate Boundary


At a constructive or divergent plate boundary two oceanic plates are moving apart. Constructive plate boundaries are found under the ocean e.g. Atlantic Ocean and cause the process of sea floor spreading (basically the ocean floor getting wider). The movement apart of the plates allows magma to escape from the mantle below. When the magma touches the ocean it cools and forms new land creating an oceanic ridge. The world’s best example of an ocean ridge is the Mid-Atlantic ridge. Overtime ridges can break the surface of the water and form new islands e.g. Iceland. Because the plates are moving apart, there is not a large build of friction so earthquakes tend to be fairly gentle. Volcanoes tend to be less violent than at destructive plate boundaries but can be more constant. Volcanoes can also cause the problems of lahars in Iceland. This is basically the lava melting the snow above and causing a mudslide.


Destructive Plate Boundary


A destructive or convergent plate boundary is when oceanic and continental crust collide. The denser oceanic crust is forced (subducted) under the continental plate. Huge amounts of heat from the mantle and also friction cause the oceanic plate to start melting in the subduction zone. The continental plate can not be destroyed so is forced up to make fold mountains e.g. Andes in South America. As the oceanic plate melts, it expands, becoming less dense. This causes some of the magma to rise to the surface through the fold mountains creating volcanoes. Where the oceanic plate subducts under the continental plate a very deep ocean trench is created. This is basically a deep valley in the sea. Ocean trenches are the deepest sections of the world’s oceans. Big earthquakes are found at destructive plate boundaries because of the build up of pressure between the two plates.

If a destructive plate boundary is found at sea, the continental crust (or less dense oceanic crust) is forced up to make an island arc instead of fold mountains. There are many examples of island arcs including the Caribbean, Indonesia, Japan and New Zealand.

Collision Plate Boundary


A collision or convergent plate boundary happens when two continental plates collide. Because neither plate can be destroyed they are forced upwards and downwards. The upwards section make fold mountains (the Himalayas were made like this) and the downwards section makes mountain roots. You get big earthquakes at collision boundaries because there is a massive build up of friction and pressure. However, because no plate is being destroyed, magma is not being created, so you do not get volcanoes.


Conservative Plate Boundary


A conservative or transform boundary happens when two continental plates move alongside each other. Because plates are not being forced up or down, there are no major landforms found at these boundaries. Also because the crust is not being destroyed, no magma is being created so there are no volcanoes. However, there can be a huge build up of pressure between the two plates so massive earthquakes occur. The most famous conservative plate boundary is the ‘San Andreas Fault’ where the North American and Pacific plates are moving past each other.



Earthquakes and volcanoes – distribution

The distribution of earthquakes and volcanoes are similar in that they occur along tectonic plate boundaries.

The map below highlights where volcanoes are located.

This map (below) indicates the global distribution of earthquakes.

Similarities in the global distribution of earthquakes and volcanoes yet again can be seen in the map below.

Earthquakes and volcanoes are found on plate margins (boundaries) and we therefore find that they are located in similar locations around the world. Although their distributions and causes are similar, earthquakes and volcanoes are very different hazards. Their hazard characteristics are not at all alike.


An earthquake is a sudden and brief period of intense ground shaking. The movement of the ground can be both vertical and horizontal. Thousands of earth movements (tremors and quakes) occur every year, but most can only be detected by instruments called seismographs. On average there are between 40 and 50 earthquakes every year. Depending on their strength and intensity, they can cause widespread damage, destruction and loss of life – especially if they happen in a densely populated area.


Measuring earthquakes

The power of an earthquake is measured using a seismometer. A seismometer detects the vibrations caused by an earthquake. It plots these vibrations on a seismograph.
The strength, or magnitude, of an earthquake is measured using the Richter scale. The Richter scale is numbered 0-10. The Richter magnitude scale (often shortened to Richter scale) was developed to assign a single number to quantify the energy that is released during an earthquake.


The Mercalli Scale is based on what people experience and the amount of damage done.
The focus and epicentre


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. Equally the amount of damage caused depends on the depth of the focus and the type of rock (geology). The earthquake in Haiti is an example of this where the focus was close to the surface and the geological structure was soft rock (sand). This leads to the rock structure acting like a liquid – liquefy. In these situations buildings and bridges simply collapse.

Reducing the impact of an earthquake

  • Currently impossible to predict when an earthquake will happen. But if you can, it would give people time to evacuate which would reduce the number of injuries and deaths.
  • There can be clues that an earthquake is about to happen, such as lots of small tremors, cracks appearing in rocks and strange animal behaviour (e.g. rats abandoning nests).
  • It’s possible to predict where future earthquakes may happen using data from past earthquakes e.g. mapping where earthquakes have happened shows which places are likely to be affected again,  or where there is a gap where there haven’t been major EQs along a fault line there is a probability of an earthquake occurring there-these places can prepare themselves for the impacts of an earthquake.

Building techniques

  • Buildings can be designed to withstand earthquakes. e.g. by using materials like reinforced concrete or building special foundations that absorb an earthquake’s energy.
  • Constructing earthquake-resistant buildings reduces the number of buildings destroyed by an earthquake, so fewer people will be killed, injured, made homeless and made unemployed.
  • Future developments, e.g. new shopping malls, can be planned to avoid the areas most at risk from earthquakes. This reduces the number of buildings destroyed by an earthquake.
  • Firebreaks can be made to reduce the spread of fires.
  • Emergency services can train and prepare for disasters, e.g. by practising rescuing people from collapsed buildings and by stockpiling medicine and other equipment. This reduces the number of people killed.
  • Governments can plan evacuation routes to get people out of dangerous areas quickly and safely after an earthquake. This reduces the number of people killed/injured by things like fires.
  • Governments and other organisations can educate people on what to do in the case of an earthquake. (e.g. stand in a doorway) and how to evacuate. This reduces deaths. –Schools and companies should practise earthquake drills regularly.
  • People can be told how to make a survival kit containing things like food, water, a torch, a radio and batteries. The kits reduce the chance of people dying if they’re stuck in the area.
  • Poorer countries that have been affected by earthquakes can receive aid from governments or organisations-it can be things like food, water, money or service people (e.g. doctors/rescuers)
  • Aid helps to reduce the impacts, e.g. money-aid is used to rebuild homes, reducing homelessness.


Another after effect of an earthquake is a tsunami. Earthquakes with epicentres under the sea can generate large and destructive waves. The Asian tsunami of 2004 had its epicentre just of the west coast of Sumatra and generated a wave up to 30m high. This caused immense damage and the casualty toll was close to 300 000 people. One of the deadliest disasters in history.


The Japanese earthquake and tsunami, 2011


Earthquakes – case studies

Case Study of the Management of a Tectonic Event in an HIC: Kobe Earthquake, 1995


Cause of the earthquake:
The earthquake was caused by the Philippines Plate being subducted under the Eurasian Plate.
The focus was very shallow; it was only about 15km.
The epicentre was very close to Kobe, around 20km away.

Short term impacts of the earthquake
Nearly 200,000 buildings were destroyed.
A 1km stretch of the elevated Hanshin Expressway collapsed.
120 of the 150 quays in the port of Kobe were destroyed.
Electricity, gas and water supplies were disrupted.
Fires caused by broken pipes and ruptured electricity lines, swept the city.
An estimated 230,000 people were made homeless.
The number of deaths was put officially at 5500.
At lest 40,000 people suffered serious injury.


How Was The Earthquake Disaster Managed?

Before the earthquake: Prediction
The Japanese government established the Imperial Earthquake Investigation Committee in 1892 in response to the Nobi earthquake (1891) which caused significant damage in Japan. However, they failed to predict the Great Hanshin Earthquake.
Even though Japan has one of the most advance Earthquake prediction systems, they failed to predict it. Kobe had not had a major earthquake for more than 400 years so there was less prediction equipment there than in other areas of Japan.
Although people on duty could see that there were many tremors (prior to the earthquake), they did not raise the alarm. It could be that they were getting complacent because they had not received a huge earthquake for a long time.

Before the earthquake: Preparation
– Illusion of preparedness made people complacent-caught unaware.
– There were still many old, traditional houses in Kobe. They had heavy tiles on the roofs to withstand typhoons; but they injured many people when the wood supporting the roof collapsed.
– Most new buildings built had been designed to be earthquake proof; but because of liquefaction, they still toppled over. The houses were not retrofitted, resulting in many elderly people injured. Transport infrastructure not retrofitted either.
– They didn’t have sufficient emergency supplies. Especially water-couldn’t fight fire efficiently.
Schools and factories had regular earthquake drills

After the earthquake: Response In The Short Term
· They had to get clean, fresh water from other parts of the country.
· The Japanese government evacuated people into temporary shelters because they still faced the dangers of fires and unstable buildings. The government was criticized for being so slow in mobilizing the army-sluggish response.
· Bulldozers were brought in to clear fallen buildings.
· The local fire department put out the fires.
· Civilians helped to rescue others who were trapped.
· Medical aid centres were set up.

After the earthquake: Response In The Medium & Long Term
By January 1999, 134,000 housing units had been constructed. All homes and buildings had to be built to strict regulations and they were made more earthquake resistant. (Flexible frames, steel support.)
Water, electricity, gas and telephone services were fully working by July 1995.
Within a year, 80% of the port was working but the Hanshin Expressway was still closed.

The railways were back in service by August 1995.
More instruments were installed in the area to monitor seismic activity.
Major transport routes were reinforced so they do not get destroyed or damaged in the event of another major earthquake.
Earthquake resistant shelters were constructed in local parks.
The city plan was more spaced out, buildings were further apart so that if one collapsed, it would not create a domino effect. Buildings were not allowed to be built on unstable land.
Developed more open space in the city so that people had a large area to evacuate to.
Japan refused international aid for a while then finally let them in.

Afghanistan 1998 Earthquake – LIC


Afghanistan is located in South Asia and sits on a collision plate boundary. The Indian and Iranian plate are colliding with the Eurasian plate. Although this does not cause any volcanoes, it does cause very big earthquakes. On 4th February 1998 northern Afghanistan was struck by a 6.1 magnitude earthquake. The province at the epicentre was Takhar which is a remote province with poor transport and communications.


Reports of the earthquake took three days to reach the capital Kabul. A day later a number of international charities reached the area and stated that over 20 villages had been destroyed and up to 4000 were dead. It was not until 16th February that weather had cleared enough for emergency helicopters to reach the area. When helicopters reached the area, it was discovered a further 7 villages had been destroyed, 10,000 people were injured and a further 15,000 homeless.


Even though the earthquake to hit Afghanistan was not massive, it still caused a lot of death and damage. This is because Afghanistan is one of the poorest countries in the world which has suffered conflict for decades. Much of Afghanistan is mountainous and transport and communication links are poor. There is little money to spend on medical care and there were no trained rescue services – Afghanistan had to rely on outside help. Building design in Afghanistan is also poor and much of the adult population is illiterate.

Kashmir earthquake (2005)

Pakistan Earthquake_Information_for_Pakistan

The 2005 Kashmir earthquake occurred at 08:52:37 Pakistan Standard Time on 8 October and was centered the Pakistan administered Kashmir near the city of Muzaffarabad and also affected the Khyber Pakhtunkhwa province of Pakistan. It registered a magnitude of 7.6. As of 8 November, the government stated the official death toll was 75,000.

Pakistan hilltop_view_of_balakot

The earthquake also affected countries in the surrounding region where tremors were felt in Tajikistan and western China, while officials say nearly 1,400 people also died in Jammu and Kashmir and four people in neighbouring Nangarhar Province of Afghanistan. The severity of the damage caused by the earthquake is attributed to severe upthrust, coupled with poor construction.

Pakistan man-grieves-earthquake-kasmir-2005

Haiti earthquake 2010

Use the GeoActive worksheet, Haiti earthquake 2010 (above), to complete the  Word document (below).




Features of a volcano


A volcano forms around a crack or fissure in the Earth’s surface, allowing molten rock, steam, ashes and gases to escape. Lava rises from a magma chamber underground through a pipe called a vent. A crater is formed on the surface from successive eruptions. If the eruption is sudden, the release of pressure and high temperature cause explosions of steam, gas and ash. Pyroclastic flows of superheated gas can travel at 200mph, destroying everything in their path. Volcanic bombs – large and small fragments of rock – can be hurled hundreds of metres into the air. Clouds of ash may fill the sky then fall, covering everything beneath. Hot ash can mix with snow and ice and can cause destructive mudflows called lahars.

Lava Flows: Most traditionally associated with volcanoes, but probably one of the least dangerous hazards to humans. Lava flows only travel up to a couple of km/hr so it is possible to move out of their way. However, they can bury and incinerate any land or property that they travel over.


Pyroclastic Flows: These are giant clouds of ash and gas. They are extremely dangerous because they can travel up to 500 km/hr, reach distances of 30km and can be over 700 degrees centigrade in temperature. They will burn, knock over or bury anything in their path.


Lahars: These are a secondary hazard and normally occur on snow covered volcanoes. Hots ash and gas melt the snow and then mix. They then travel down the volcano as a fast moving mudflow which can drown or bury anything in their path.


Ash Clouds: Not as fast moving as a pyroclastic flow, but ash clouds can still be very disruptive. The weight of falling ash can collapse buildings and destroy crops. They can reduce sunlight by blocking out the sun and even cause problems for air travel like the recent Iceland volcano.


Lava or Volcanic Bombs (tephra): When volcanoes erupt they often throw out semi molten pieces of rocks. As long as humans are a safe distance they don’t really pose any problems. However, because of their heat they can start fires.


Poisonous Gases: When volcanoes erupt they can release poisonous gases like carbon monoxide and sulphur dioxide. These can kill humans or animals if they are too close, but they can also contribute to the greenhouse effect.


Volcanoes are a lot easier to predict than earthquakes because they normally give some warning signs. Scientists (vulcanologists) will look for some of the following changes to try and predict a likely volcano.
Change in the shape or size of volcano
Change in the temperature of a volcano
Change in the amount and type of gases being released
Earthquake activity
Changes in plant and animal life
Changes in local hydrology e.g. temperature and chemical composition of nearby rivers.

Living Near Volcanoes

Even though volcanoes are extremely hazardous places, many people still choose to live on, or near them. Some of the reasons why people do this include:
Their beauty, places like Mount St. Helen’s are beautiful to look at and enjoy.
Minerals, it is possible to mine minerals like sulphur from volcanoes
Geothermal potential (cheap and clean renewable energy) e.g. Iceland.and El Salvador
Tourism – tourists like to view and walk up volcanoes e.g. Santa Ana volcano or Pacaya volcano
There is often hot springs near volcanoes which tourists and locals can enjoy e.g. Mt. Arenal in Costa Rica or the hundreds of onsens in Japan.
Land around volcanoes is very fertile because of all the minerals, therefore many people choose to farm the land.
Poverty, people simply can’t afford to live anywhere else apart from the marginal land on volcanoes
Complacency or naivety because the volcano has not erupted for a long time.
Confidence that they will be given adequate warning to evacuate
Family home. Family have always lived in the area and don’t want to leave
Shortage of space and high population density. San Salvador is slowly growing up El Boqueron because of the shortage of space.

Mount Arenal Volcano in Costa Rica (tourism)


Mount Arenal is Costa Rica’s most active volcano. It has been erupting on and off since 1968. Around the volcano and especially in the nearby town of La Fortuna, hundreds of jobs have been created by people visiting the volcano hoping to see it erupt. There are now close to 100 hotels in the area as well as horse riding stables, mountain biking, canopy trails, nature reserves, rafting centres, restaurants, quad biking and much more. A large number of hot spring resorts have also developed in the area.

Geothermal Power in Iceland


Iceland sits on a constructive plate boundary in the middle of the Atlantic Ocean. Iceland itself was actually created by magma escaping from the mantle. Iceland has five geothermal power stations that create 24% of Iceland’s energy needs. In addition geothermal power heats the houses and water of 87% of buildings in Iceland. In addition to heating and geothermal power, volcanic activity has also created a large tourism industry and created a number of hot springs, including the world famous Blue Lagoon.

Mount St. Helens Natural Beauty


Mount St. Helens is located in the Cascades mountain range in the Rockies. It sits on a destructive plate boundary. Mount St. Helens lies in a beautiful area, the mountains themselves are beautiful but also Spirit Lake at its foot. Mount St. Helens has become home to people who like the outdoors. It has also become a tourist destination and is good for fishing. People feel relatively safe living near the volcano because it is so well monitored. However, despite warnings over 50 people still lost their lives in the 1980 eruptions. Most would not leave either because they were scientists studying the volcano or residents who could not bring themselves to leaving their home.

El Boqueron, San Salvador


El Boqueron has created a number of benefits for local residents. The fertile slopes on the side of El Boqueron has allowed coffee farming to take place. Also the road up the side of El Boqueron has increased tourism, both to visit the restaurants, visit the view points and look at the crater and wildlife. More people are also choosing to live on its slopes because of shortage of space in downtown San Salvador, but also because it is cooler, safer (in terms of criminality) and less congested. Because El Boqueron has not erupted for nearly 100 years, citizens feel safe living under it.

Case studies

Montserrat- Chances Peak, Montserrat, 1995-97 – an LIC


Montserrat is a small island in the Caribbean. There is a volcanic area located in the south of the island on Soufriere Hills called Chances Peak. Before 1995 it had been dormant for over 300 years. In 1995 the volcano began to give off warning signs of an eruption (small earthquakes and eruptions of dust and ash). Once Chances Peak had woken up it then remained active for five years. The most intense eruptions occurred in 1997.

During this time, Montserrat was devastated by pyroclastic flows. The small population of the island (11,000 people) was evacuated in 1995 to the north of Montserrat as well as to neighbouring islands and the UK.
Despite the evacuations, 19 people were killed by the eruptions as a small group of people chose to stay behind to watch over their crops.
Volcanic eruptions and lahars have destroyed large areas of Montserrat. The capital, Plymouth, has been covered in layers of ash and mud. Many homes and buildings have been destroyed, including the only hospital, the airport and many roads.


Short-term responses and results
Abandonment of the capital city.
The British government gave money for compensation and redevelopment.
Unemployment rose due to the collapse of the tourist industry.

Long-term responses and results
An exclusion zone was set up in the volcanic region.
A volcanic observatory was built to monitor the volcano.
New roads and a new airport were built.
Services in the north of the island were expanded.
The presence of the volcano resulted in a growth in tourism.
Volcanic activity has calmed down in recent years and people have begun to return to the island.

Mount St Helens – 1980 HIC


Mount St. Helens is located in the Cascades mountain ranges which is part of the North American Rockies. It sits on a destructive plate boundary where the Pacific plate and Juan de Fuca plate subduct under the North American plate. Mt St. Helens had been dormant for nearly 120 years when on the morning of 18th May 1980 a 5.0 earthquake triggered a huge landslide and pyroclastic flow. The pyroclastic flow travelled for 25km and flattened everything in its path. Ash and gas continued to be released from the volcano over the course of the day and reached the east coast of the US three days later.


Sixty one people lost their lives in the tragedy, mainly residents refusing to leave and scientists monitoring the volcano. Spirit lake was destroyed along with 250km of fishing rivers. 250km2 of forest was destroyed and 10 million trees had to be replanted. No animals survived in the blast zone and many crops were destroyed by falling dust.

%d bloggers like this: