How a Tsunami


          Lindsey Springer                 


Part of Waves of Devastation, a class website on the Indian Ocean Tsunami & Global Environmental Injustice, produced by students of Geography 378 (International Environmental Problems & Policy) at the University of Wisconsin-Eau Claire, USA, Spring 2005.

Professor Zoltan Grossman







Global environmental justice

Natural disasters

How a tsunami happens


Past tsunamis

Pacific Ocean warnings

Indian Ocean warnings




Sri Lanka


Other countries

Environmental impacts:

Freshwater supplies







Human & environmental impacts:

Indigenous peoples




Civil wars

Conservation education


A class project by students in



Problems & Policy

(Geography 378, Spring 2005, University of Wisconsin-Eau Claire)


Assistant Professor

of Geography Zoltan Grossman

(715) 836-4471

P.O. Box 4004,

Eau Claire, WI 54702 USA





The term tsunami has its origins in the Japanese language; an English equivalent is "seismic sea waves." Tsunamis are often incorrectly interchanged with the term" tidal waves," which refer to high waves of water caused by changes in the flow and surge of the ocean. Tsunamis, on the other hand, can be caused by a few different means: 1) the down drop or upthurst of the Earth’s crust which results in an earthquake; 2) a large-scale undersea landslide; 3) a submarine volcanic eruption of a certain degree; or potentially, 4) a large meteor impact at sea. The vast majority of tsunamis result from earthquakes.

 (Source: The Great Waves).





How Earthquakes Cause Tsunamis

The illustration below shows a subduction earthquake (one where a denser plates shifts below its neighboring plate, at left). Energy is transferred and the displaced water forms a wave. As the wave travels and enters shallower water in the coastal area, it begins to increase in amplitude (National Geographic).

Killer Wave! Tsuanmi--National Geographic Kids

Tsunamis are not always colossal waves when they come into the shore. In fact, "... most tsunamis do not result in giant breaking waves (like normal surf waves at the beach that curl over as they approach shore). Rather, they come in much like very strong and very fast tides (i.e., a rapid, local rise in sea level)." (USGS website) Nevertheless, there is destruction of life and of property by floating debris and impact of water. The tsunami produces a series of rushing waves and also a series of withdrawals.


Tsuanamis and Earthquakes-Basics- USGS

If you think about throwing a rock in water, a ripple is formed. It is the same principle involving a meteor or an earthquake, except they form bigger ripples. If you think about that ripple, it seems to disappear as time goes on--but in actuality, it does not stop. In the picture below we can see that a tsunami is very fast (the speed often compared with that of a jet) and it has a height of 20 inches.

However, we need to take into consideration the effect of the tsunami reaching the shore. The speed is diminished but the wave height is increased drastically.

To view a QuickTime visualization: Tsunami Visualization

For more information about earthquake formation see Tectonics.

How Volcanoes Cause Tsunamis

There are two different ways that volcanoes can cause seismic waves. One possibility is for a land-based volcano to break down and collapse, forcing large amounts of ash and debris into the water. This sudden change and displacement of the water column transfers to kinetic energy and results in waves. More debris can create a bigger increase in wave amplitude and number.

Geosciene Australia

Tsunamis can also be induced by submarine volcanoes. These underwater volcanoes can collapse downwards or spew forth lava heating the surrounding water quickly. 

How Landslides Cause Tsunamis

Landslides are similar to volcanoes that avalanche into the sea. They occur in the water and often are triggered by earthquakes. There is an instance in 1958 where a tsunami was caused by rockfall in Lituya Bay, Alaska. In this instance, a gigantic boulder was loosed by an earthquake and fell into the bay causing a tsunami that went out to sea. (Tsunami Research Center: USC)

See: Past Tsunamis for  more historic tsunami information.

Geography of Tsunamis

World Oceans Map

An average of 85% of all tsunamis have been observed in the Pacific Ocean in the "Ring of Fire." George Maul participated in an expert panel discussion on tsunami locations, in association with Smithsonian magazine . In his presentation he offered data (shown below) representing the distribution of tsunamis in the world's oceans and seas:

Location %
Atlantic East Coast 1.6
Atlantic West Coast 0.4
Mediterranean 10.1
Caribbean 13.8
Bay of Bengal 0.8
East Indies 20.3
Oceania 25.4
Japan-Russia 18.6
Pacific East Coast 8.9

Location and Percentage Distribution of Tsunami  

Social & Environmental Justice

When looking at the effects of the 2004 tsunami in the Indian Ocean, there was a death toll of up to 300,000 lives with the addition of 5,000,000 people who were affected by the tsunami (Tsunami Laboratory). It is unavoidable to have property and land destruction, but the large number deaths as a result of this disaster was avoidable.

Within minutes of the submarine earthquake that cause this tsunami, the Pacific Tsunami Warning Center knew the danger that was approaching the coastal areas. They tried to warn the threatened countries, who did not get the message in enough time. The fact remains that there was no warning system in the Indian Ocean. If there was, perhaps valuable time would have been bought for those in the coastal areas (Reducing the Death Toll from the Tsunami).

See: Pacific Ocean warnings or Atlantic Ocean warnings.

Tsunami education is another factor that could have saved lives, thereby reducing the death toll. There should be an awareness of how to recognize signs of a tsunami, and a degree of preparation for people in high-risk areas. If the same tsunami had occurred in the North Pacific Ocean, there would not have been as large a death toll, due to the Pacific Ocean countries' warning system, evacuation plans, and public education. Disasters are never fair, but if many people can be saved by funding the warning systems and public education, it is worth the cost.

For more in-depth information of what happened to individual countries, see: Indonesia, Thailand, Sri Lanka, India, or Other Countries.


For more information on this topic:

Dynamic Earth YY Education:

Geoscience Australia: How do Tsunamis Occur:

Killer Wave! Tsuanmi--National Geographic Kids:

Myles, Douglas. "The Great Waves". United States; McGraw-Hill

      Book Company.

International Tsunami Information Center: Tsunami.htm

Reducing the Death Toll From Tsunami:

Tsunamis and Earthquakes-Basics-USGS WCMG:

Tsunami Laboratory, Novosibirsk, Russia: 

Tsunami Research Center--USC: View of Lityua Bay and Description of Tsunami:

Tsunami Visualization (QuickTime Demonstration):


Virtual Vacationland: “Hands on” Activity: