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Tectonic Hazards - Part 2

  • Tsunamis in Japan
  • Managing the Effects of Earthquakes
  • Types of Volcanoes
  • Formation of Iceland
  • Managing the Effects of Volcanic Eruptions
  • Living near a Tectonic Hazard

What caused the Japan 2011 tsunami?

A tsunami is a large wave of water (sometimes over 10 metres high) and is caused by a displacement (movement) of a large amount of water.


There are several causes for tsunamis including earthquakes, volcanic eruptions and landslides. Yes, there are volcanoes on the ocean floor, especially at constructive plate margins. 

A magnitude 9.0 earthquake occurred at a destructive subduction margin when the Pacific Plate slipped 50 metres as it collided with the North American Plate. Look at the plate tectonic map above.


This movement in the Japan ocean trench caused a sudden uplift of the sea floor, sending a displaced column of water into the air. This water comes back down and travels as a series of high speed waves that slow down as the wave approached land. However, the wave gains height. This wave is a tsunami.

How can the effects of earthquakes be reduced?


There are four management strategies to reduce the effects of tectonic hazards. 

  • Monitoring 
  • Prediction 
  • Protection 
  • Planning

Monitoring Earthquakes


Earthquakes occur without warning. Whilst scientists have a good understanding of where they occur (along plate margins and fault lines within rock), they are yet to find reliable ways of monitoring arthquakes. Seismometers are used to measure minor earthquakes before the main earthquakes.

Predicting Earthquakes


Due to a lack of effective monitoring it is not possible to accurately predict earthquakes. Scientists use historical records of earthquakes to look for patterns and trends to determine if a large earthquake is likely. 

Protection from Earthquakes


Protection is the main way to reduce risks from earthquakes.

  • Buildings and bridges are built to resist the ground shaking as a result of an earthquake. 
  • It is possible to construct tsunami walls at the coast to protect people and important buildings. Japan have built tsunami walls up to 12 metres high. 

Planning for Earthquakes


Planning and preparing what to do during and after an earthquake helps the authorities, emergency services and individuals to act quickly and calmly.

  • Regular earthquake drills help people keep alert and be prepared. 
  • The Red Cross provides a checklist of what people should have in an emergency survival kit.
  • Hazard maps can be created to show where earthquakes are likely, this will prevent buildings being built in earthquake prone areas.

How do volcanoes form?


A volcano is where magma (melted rock) erupts through the earth's crust. Above ground, the magma is called lava. Volcanoes mostly occur along destructive (subduction) and constructive plate margins. 


Cracks or weaknesses in the earth's crust allows magma to rise from the mantle. Pressure builds up, which is released suddently allowing the magma to explode. This is a volcanic eruption. When the lava cools, it forms igneous rock such a basalt. Subsequent eruptions create new islands and land masses. 


Composite volcanoes occur at destructive (subduction) plate margins whereas shield volcanoes occur at constructive plate margins. 

Features of a Composite Volcano

  • Tall
  • Conical shaped and symmetrical
  • Steep sides
  • Made up of layers of ash and lava
  • Contains thick magma
  • Very explosive

Locations of Composite Volcanoes

  • Found on Destructive plate boundaries
  • E.g. Mount St Helens

Features of a Shield Volcano

  • Low
  • Flat
  • Symmetrical
  • Gentle slopes
  • Wide base
  • Created by runny, fast flowing lava
  • Less explosive

Locations of Shield Volcanoes

  • Found on Constructive plate boundaries and hotspots.
  • E.g. Mauna Loa

How was Iceland made?


Volcanoes can appear very quickly. On the 14th November 1963, the cook on a fishing trawler south of Iceland noticed black clouds rising from the surface of the sea. Within 24 hours the Island of Surtsey had been formed off the southern coast of Iceland. 

Iceland is one of the youngest land masses on Earth and is still very much in the making. 12 miles below Iceland is a magma plume, a column of super heated rock. It allows heat to rise up from the Earth’s core through the mantle. Repeated volcanic eruptions on the Mid-Atlantic ridge (a constructive plate margin) are how Iceland is believed to have been created. When the tectonic plates are moved as a result of convection currents in the mantle and ridge push at the surface, magma continue to rise and solidify. This creates new crust. Iceland was formed over 24 million years.

What is a supervolcano?


Supervolcanoes occur where magma rises from the mantle to the earth's crust at a hotspot or destructive (subduction) plate margins. The magma cannot break through the crust, which causes pressure to build up in a large magma chamber until the crust can no longer take the pressure. Yellowstone Caldera is an example of a supervolcano. 

Although there are only small number of supervolcanoes, eruptions cover large areas with lava and ash. Eruptions can have a long-term impact on weather with the possibility of triggering a mini ice age whcih could cause species to become extinct.

How can the effects of volcanoes be reduced?


There are four management strategies to reduce the effects of tectonic hazards. These are the same for earthquakes.

  • Monitoring 
  • Prediction 
  • Protection 
  • Planning



It is possible to monitor volcanoes. As magma rises through a volcano it gives warning signs that an eruption is possible. Scientists monitor active volcanoes all over the world. 

  • Remote sensing – satellites detect heat and changes to the volcano’s shape.
  • Seismicity – seismographs record earthquakes.
  • Gas – instruments detect gases released as magma rises.
  • Hydrology - scientists measure the temperature of water in streams and rivers to see if it has increased.



Monitoring allows predictions to be made. In 2010 an increase in earthquake activity beneath the Eyjafjallajökull volcano in Iceland enabled scientists to make an accurate prediction about the eruptions that took place in March and April that year.



There is not much that can be done to protect people and property from a powerful volcanic eruption.

  • Earth embankments or explosive can divert lava flows away from buildings.



Just like earthquakes, hazard maps have been produced for many of the world’s most dangerous volcanoes, showing areas most at risk. They can be used in planning to restrict certain land uses or to identify which areas need to be evacuated when an eruption is about to happen.

Why do people live near tectonic hazards?


People live near tectonic hazards for a variety of reasons. 

  • Poverty - some people do not have a choice. The land is often cheap.
  • Low frequency of events - earthquakes and eruptions are rare and people take the risk not expecting them to happen. 
  • Geothermal energy - 25% of Iceland's electricity is from geothermal energy. 
  • Agriculture - the slopes of volcanoes are very fertile and good for crop growth. 
  • Plate margins often coincide with very favourable areas for settlement, such as coastal areas where ports have developed.
  • Better building design and warning systems mean there is less risk as people are protected and have time to evacuate. 

Where do earthquakes and volcanoes occur?


Earthquakes are found in belts along all plate margins (destructive, constructive, conservative). Some are found away from margins due to human activity such as fracking.


Volcanoes are found in belts along constructive and destructive plate margins. For instance, the Pacific Ring of Fire. Some are found away from plate margins at hotspots (areas where the crust is so thin, magma erupts), for example Hawaii.