BREAKDOWN

A tsunami is a sea wave generated by an undersea earthquake or possibly an undersea landslide or volcanic eruption. When the ocean floor is tilted or offset during an earthquake, a set of waves is created. Most tsunamis originate along the circum-Pacific Ring of Fire, a zone of volcanoes and seismic activity. Since 1819, about 40 tsunamis have struck the Hawaiian Islands. A tsunami can have wavelengths, or widths, of 100 to 200 km and may travel hundreds of kilometers across the deep ocean, reaching speeds of about 725 to 800 km/h Upon entering shallow coastal waters, the wave, which may have been only about half a meter (a foot or two) high out at sea, suddenly grows rapidly. When the wave reaches the shore, it may be 15 m (50 ft) high or more. Tsunamis have tremendous energy because of the great volume of water affected. They are capable of annihilating entire coastal settlements.

Tsunamis that strike coastal locations in the Pacific Ocean Basin are most always caused by earthquakes.

Some tsunamis can be very large. In coastal areas their height can be as great as 30 feet or more (100 feet in extreme cases), and they can move inland several hundred feet.

All low-lying coastal areas can be struck by tsunamis.

A tsunami consists of a series of waves. Often the first wave may not be the largest. The danger from a tsunami can last for several hours after the arrival of the first wave, and they move faster than a person can run.

Sometimes a tsunami causes the water near the shore to recede, exposing the ocean floor. The force of some tsunamis is enormous. Large rocks weighing several tons along with boats and other debris can be moved inland hundreds of feet by tsunami wave activity.

Homes and other buildings are destroyed. All this material and water move with great force and can kill or injure people.

Tsunamis can occur at any time, day or night, travelling up rivers and streams that lead to the ocean.