The word tsumani is a Japanese word, which literally means harbor wave. These are potentially the most catastropic of all ocean waves. Tsunamis are caused by undersea earthqukes, and have waves similar to the ones that appear when you drop an object into water, and all the circles form. They have tremendous energy because of the great volume of water that is affected. Tsunamis can have wave lengths that are up to 120 miles across. They can reach speeds of 450-500 miles per hour when they are traveling across the ocean. One way to tell if a tsunami might be coming is if the water level changes. Usually, a tsunami is only a few feet high when it is out at sea, but it starts to grow when it enters coastal waters, and may be as tall as 50 feet when it reaches shore. These waves can easily wipe out coastal settlements. For example, in 1883, 120 feet waves from the Krakatoa eruption, killed 36,000 perople. About fourty tsunamis have struck Hawaii since 1819. On April 1, 1946, an earthquake in the Aleutian Islands of Alaska sent a wave ashore on Unimak Island that killed five people. Hours later, the tsunami reached Hawaii where it killed 159 people. More people have died since 1945 because of tsunamis than as a direct result of an earthquake. Also, tsunamis do not arrive as one big wave; they arrive as a series of successive 'crests', these being 10-45 minutes apart, typically.

Tsunamis fall into the category of title waves. Although titlewaves can be caused by undersea earthquakes, volcanic eruptions, landslides, collasped ocean islands whose displacemenot of massis large enough to cause high wave, and even impacts of asteroids or comets, tsunamis can only be caused by earthquakes. Tsunamis can move fast enough to keep up with a jetliner at times. (about 500 miles an hour). However tall they look at sea, if a pilot were to fly his plane directly over a moving tsunami, the wave probably wouldn't even be noticeable.

The first picture is of a tsunami wave begining to crash, courtesy of http://www.germantown. k12.il.us/gifs/tsunami2.gif The second image is of a tsunami that is still out at sea, but approaching shore, courtesy of http://homer.hcrhs.k12.nj.us/esoup/esvol10/tsunami/ocean.jpg