Broad Facts About Tsunamis

Tsunamis result when a large body of water is displaced and moves out in waves from a disruptive source. Tsunamis can be very destructive, destroying habitats, ecosystems, human resources and ultimately changing the topography and profiles of landmasses. Tsunamis happen as a result of powerful natural forces and can be triggered by slides, earthquakes or seaquakes and volcanic activity.

Tsunami Origins

• Seaquakes have a direct influence on the formation of tsunamis. When continental plates collide, slip and break loose, the result produces tremendous forces that disturb the water column. Island and coastal landslides can displace huge volumes of soil and rock when they plunge into the ocean. Volcanic activity can cause underwater slides and fractures in the crust, sending out huge shock waves. Asteroids and meteorites have the potential to strike open water and send out destructive waves.

Wave Propagation

• When a strong physical force acts upon a huge volume of water, a series of waves, or a wave train, is generated, which flows out from the epicenter, or source, of the disturbance. The waves react in a ripple effect.

Sound

• The sound associated with the approach and landing of tsunami waves on the shoreline has been likened to the noise of a freight train or a loud roar.

Tsunami Speed and Height

• Tsunamis generated in great ocean depths will produce waves that may be 1 foot or smaller upon the top surface layer of water. They can move at speeds of up to 500 mph. They normally slow down when they reach shallows, beach and bay areas, but their wave troughs can rise up to 100 feet over the shoreline.

Length and Duration

• Tsunami waves can extend for 60 miles or more in length. Tsunami waves can arrive in sets, some sets arriving long after the initial shock wave. Multiple sets can last for hours and continue to flood inland areas with repeated surges.

Receding Water

• Tsunami waves produce a backward draw of water from shallow beaches, estuaries and bays. The tsunami creates a negative backward flow, drawing water into the primary wave as it flows inland and gains height. Several flood events and water recessions can result from a single tsunami.

Flooding

• Depending upon the size of the disturbance that creates the tsunami, the inland flooding can reach distances of up to 1,000 feet and much more, depending upon the topography of the land. Tsunami waves can travel up rivers and streams for great distances. Tsunamis can erase rock jetties, beaches, atolls and shallow peninsulas, changing the profile of the land permanently.

Death and Destruction

• The Indian Ocean tsunami of 2004 released energy equivalent to 23,000 atomic bombs. The tsunami wave train traveled to the coastlines of 11 countries, wiping out infrastructure and taking the lives of 283,000 people. The property damages incurred ranged in the billions.

Tsunami Hot Spots

• The majority of the largest tsunamis occur in the Indian and Pacific oceans. The Pacific Ocean has a boundary of frequent tectonic activity called the Ring of Fire, which puts the Hawaiian islands, Japan, the Asian continent and the west coast of the United States directly in harm's way.