Tsunami

Tsunamis carry great destructive potential and pose a serious threat to coastal communities in their path.

A tsunami is a series of ocean waves produced by sudden movements of the ocean floor, landslides, or volcanic activity. In the deep ocean, tsunami waves may travel across the ocean as fast as a jet plane (more than 500 miles per hour) but look like ripples perhaps only a few inches high—likely not noticeable to someone on a boat or ship. For more information on how tsunamis form and travel across the ocean, including animated graphics, visit the NOAA Tsunami website.

Illustration Depicting Tsunami


As tsunami waves approach shore, they begin to slow down and build up in height. The shape of the waves is changed by the depth of the water and the slope of the coast.

Illustration Depicting Tsunami Wavelength


To someone standing on the shore watching a tsunami approach (not recommended!), it might look like a fast-moving (20–30 mph) wall of water 10 feet high or more. Large tsunamis are rare, but when they happen they carry great destructive potential and pose a serious threat to coastal communities in their path.

Tsunamis have no “season,” and can strike at any time of day or night, in good weather or bad. They occur in every ocean and sea, but most tsunamis (about 85 percent) happen in the Pacific Ocean. Tsunamis cannot be prevented; however, their impacts on coastal communities can be mitigated through planning, preparedness, timely warnings, and effective response. Keep in mind: any tsunami today happens on top of the 8-inch rise in average global sea level since 1900. By the year 2100, tsunamis will happen on top of another 8 inches to 6.6 feet of sea level rise.1

Map Showing Tsunami Sources 1410 B.C. to A.D. 2011

NOAA’s National Geophysical Data Center (NGDC) and co-located World Data Center for Geophysics and the International Tsunami Information Center, a UNESCO/IOC-NOAA partnership, have collaborated to produce a map showing tsunami sources. The information comes from the NGDC Historical Tsunami Database that includes information on tsunami source events throughout the world that range in date from 1410 B.C. to A.D. 2011. The tsunami definitions are from the Tsunami Glossary 2008 published by UNESCO.

This table provides a qualitative tsunami hazard assessment for U.S. states and territories:2

Region Hazard Based on Runups Hazard Based on Frequency Hazard Based on Local Earthquakes Number of Reported Deaths Since 1900
Hawaii Very High Very High High 326
Alaska Very High Very High High 222
Puerto Rico and the Virgin Islands High High High 172
U.S. West Coast High High High 25
U.S. Pacific Island Territories Moderate High High 1
U.S. Atlantic Coast Very Low to Low Very Low Very Low to Low None
U.S. Gulf Coast Very Low Very Low Very Low None
credit: Paula Dunbar (NOAA) and Craig Weaver (USGS)

 

Banner Image Credit
A tsunami evacuation map on a board by the sea in Depoe Bay, Lincoln County, Oregon. By Oregon State University (Flickr). CC BY-SA 2.0, http://creativecommons.org/licenses/by-sa/2.0, via Wikimedia Commons
Last modified
6 July 2016 - 11:34am