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KS3 Geography - Tectonic Hazards: Tsunamis

A guide to tectonic hazards for your Year 9 course, compiled by your Librarians.

Causes of tsunamis

     The name "tsunami" came from Japanese. It means harbor wave. It is usually caused by volcanic or earthquake activity under the ocean, sometimes it can also be caused by giant landslides.

      When an earthquake, volcano or landslide happens on the ocean floor, water is displaced. This water forms the start of the tsunami. When the waves reach shallower water:

  • their height can increase by several metres
  • the shallow water slows the wave
  • the waves get closer together

 

      The most obvious sign of a tsunami is the coastal water retreats just before the waves reach the shore. This is actually the trough of the wave following behind.

      Tsunami can eventually crash onto the shoreline. The effects on a community can be devastating.

Impact of tsunamis

   The main impact a tsunami has is flooding. The waters are also able to erode the foundations of coastal structures. The effects of the tsunami range from destruction and damage, death, injury, disease, environmental and financial cost, and long lasting psychological problems for the inhabitants of the region.

Case study 1: 26/12/2004 Indian Ocean Tsunami

   On 26 December 2004 a tsunami occurred in the Indian Ocean. It was the result of the Indio-Australian Plate subducting below the Eurasian Plate. It was caused by an earthquake measuring more than magnitude 9. The earthquake caused the seafloor to uplift, displacing the seawater above.

  • In open ocean the tsunami measured less than 1m high.
  • The tsunami travelled at speeds up to 800km per hour.
  • When the Tsunami reached the shores, the height of the wave increased to 15m in some areas.

   

Facts & Impacts
A quarter of a million people died.
Two million people were made homeless.
People were swept away in the waters, which arrived rapidly and with little warning.
Thirteen countries were affected, the worst being Indonesia.
Indonesia was hit by the tsunami first. Fourty-five minutes later the tsunami reached Thailand.
Mangrove swamps helped to act as a barrier to reduce the energy of the water in some areas.
Short-term aid, such as water purification tablets, temporary housing and medical supplies were given from international countries.
Islands reliant on tourism and fishing, such as the Maldives, had to rebuild their industries.
An early warning system between countries surrounding the Indian Ocean has been set up.

Tsunami safety

 

PLAN FOR A TSUNAMI:
  • Have a disaster plan.
  • Know whether you’re at risk for danger.
  • Plan an evacuation route.
  • Prepare a disaster supplies kit for your home and car. Include a first aid kit, canned food and a can opener, bottled water, battery-operated radio, flashlight, protective clothing and written instructions on how to turn off electricity, gas, and water.
DURING A TSUNAMI:
  • Follow the instructions issued by local authorities.
  • You will probably want to evacuate immediately.
  • Get to higher ground and as far inland as you can.
AFTER A TSUNAMI:
  • Help injured or trapped people.
  • Stay out of a building if water remains around it. Tsunami waters can cause buildings to sink, floors to crack, or walls to collapse.
  • When re-entering homes, use extreme caution.
  • Check for gas leaks.
  • Open windows and doors to help dry things out.
  • Look for fire hazards.

Can tsunami be predicted?

     Since earthquakes cannot be predicted, we do not know when a tsunami will happen before the earthquake occurs. Once a large potentially tsunamigenic earthquake does occur, we can forecast tsunami arrival times and wave heights through the use of computer modeling.

     Scientists have made great strides in monitoring and predicting the ongoing threat of tsunamis. One center continuously monitoring seismic events and changes in the tide level is the Pacific Tsunami Warning Center (PTWC) located in Ewa Beach, Hawaii. This center is of particular importance because submarine earthquakes in this region have created waves that moved throughout the Pacific Ocean before striking elsewhere.

Animation of tsunamis

A brief presentation on tsunamis

Animation of 2004 Indian Ocean tsunami

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Case study 2: 11/03/2011 Japan eathquake & tsunami

CASE STUDY SUMMARY
 
Date: 11 March, 2011
Primary Hazard: Earthquake (Magnitude = 9.0)
Secondary Hazards: Tsunami (average wave height 5-12m), Nuclear Meltdown
Areas Affected: North-East Japan, Tsunami: Pacific Basin
No of Deaths: 15,800 Approx
Buildings Destroyed: >125,000
People Displaced: >500,000
Economic Cost (Est.): US $235 Billion

Tsunami quiz

Test your knowledge about tsunamis!

How much do you know about tsunami?

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Tsunami activities

See how the tsunami of 2004 developed, from its birth at the seafloor to its impact on coasts around the Indian Ocean.

With the world map, explore eight of the deadliest tsunamis of the past and see where the next big one could strike..

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Interactive guide to survive a tsunami

Try this complete tsunami guide which covers detailed information about tsunamis: introduction, survival tips, research and history.