know more about the KILLER WAVES

28 MAY 2008

How do they form?

Tsunamis are formed as a result of earthquakes, volcanic eruptions, or landslides that occur under the sea. When these events occur under the water, huge amounts of energy are released as a result of quick upward bottom movement. For example, if a volcanic eruption occurs, the ocean floor may very quickly move upward several hundred feet. When this happens, huge volumes of ocean water are pushed upward and a wave is formed. A large earthquake can lift thousands of square kilometers of sea floor which will cause the formation of huge waves. The Pacific Ocean is especially prone to tsunamis as a result of the large amount of undersea geological activity.

How big do they get?

In the open ocean tsunamis may appear very small with a height of less than 1 meter (3 feet). Tsunamis will sometimes go undetected until they approach shallow waters along a coast. These waves have a very large wavelength (up to several hundred miles) that is a function of the depth of the water where they were formed. Although these waves have a small height, there is a tremendous amount of energy associated with them. As a result of this huge amount of energy, these waves can become gigantic as they approach shallow water. Their height, as they crash upon the shore, depends on the underwater surface features. They can be as high as 30 m (100 feet) or more. In 1737 , a huge wave estimated to be 64m (210 feet) in height hit Cape Lopatka, Kamchatka (NE Russia). The largest Tsunami ever recorded occurred in July of 1958 in Lituya Bay, Alaska. A huge rock and ice fall sent water surging up to a high water mark of 500m (1640 feet). It's no wonder that these waves can cause such massive destruction and loss of life.

How fast do they move?

In the deep open sea, tsunamis move at speeds approaching a jet aircraft. As they approach the shore, they slow down. When a tsunami arrives at the shore, it usually does so as a rapidly rising tide moving at about 70 km/hour (45 miles/hour).

How much destruction do they cause?

Beyond the tremendous destruction of life that tsunamis cause, they have also caused massive physical damage. They have entirely destroyed buildings and left towns looking like a nuclear war zone. They have lifted boats high out of the water and violently hurled them against the shore, smashing them to pieces. They have bent parking meters all the way down to the ground. In one incredible story, during the huge tsunami in Lituya Bay, Alaska (mentioned above), a boat with two people in it was carried from the bay, over tree tops and over the land out into the ocean. The people survived to tell the tale.

Can we detect them before they hit?

Yes. About 35 years ago, 24 countries around the Pacific set up the Pacific Tsunami Warning System. A group of seismic monitoring stations and a network of tide gauges are used for detection. The biggest problem with this system is that it is difficult to predict how large and destructive the resulting waves will be. Scientists are currently working on better predictive tools.