FAQ's about Tsunamis

As with many natural phenomena, tsunamis can range in size from micro-tsunamis detectable only by sensitive instruments on the ocean floor to mega-tsunamis that can affect the coastlines of entire oceans, as with the Indian Ocean tsunami of 2004. If you hear a tsunami warning or if you feel strong shaking at the coast or very unusual wave activity (e.g., the sea withdrawing far from shore), it is important to move to high ground and stay away from the coast until wave activity has subsided (usually several hours to days). For more general information on tsunamis and what to do during a tsunami warning, please visit sites sponsored by FEMA, the National Weather Service, NOAA, and the USGS.

Go to the Natural Hazards Gateway, which includes:

• Earthquakes
• Floods
• Geomagnetism (solar flares, etc.)
• Hurricanes
• Landslides
• Seismic Zone Mapping
• Sinkholes
• Tsunamis
• Volcanoes
• Wildfires

Pacific Tsunami Warning Center
West Coast and Alaska Tsunami Warning Center

• Current Messages
• Recent Tsunamis

Other organizations in tsunami monitoring and research include:

• British Columbia Provincial Emergency Program
• Tsunami! - University of Washington
  
• International Tsunami Information Center

• Tsunami Fact Sheet from FEMA
  
• Tsunami Hazard Mitigation from the University of Washington
• The Physics of Tsunamis - FAQ from the University of Washington

(UC Berkeley)

Tsunamis are large, potentially destructive sea waves, most of which are formed as a result of submarine earthquakes, but which may also result from the eruption or collapse of island or coastal volcanoes and the formation of giant landslides on marine margins. These landslides, in turn, are often triggered by earthquakes. Environmental damage by these tsunamis include coral reef destruction, contamination of wells and other sources of fresh water by salt water, denudation of trees and other types of dry-land vegetation, accelerated beach erosion, and fish and other marine life fatalities due to abnormal wave action. The flooding and powerful wave action of the tsunami may potentially cause damage to man-made containment vessels of petroleum products, chemicals, and garbage landfills, resulting in toxic leakage, which in turn has the potential to pollute both coastal land and ocean environment.

Tsunami waves can be generated from displacements of water resulting from rock falls, icefalls and sudden submarine landslides or slumps. Major earthquakes are suspected to cause many underwater landslides, which may contribute significantly to tsunami generation. For example, many scientists believe that the 1998 tsunami, which killed thousands of people and destroyed coastal villages along the northern coast of Papua-New Guinea, was generated by a large underwater slump of sediments, triggered by an earthquake.

The 1964 Alaska earthquake caused 115 deaths in Alaska alone, with 106 of those due to tsunamis generated by tectonic uplift of the sea floor, and by localized subareal and submarine landslides. The earthquake shaking caused at least 5 local slide-generated tsunamis within minutes after the shaking began. For an eyewitness account of the tsunami caused by the movement and landslides of the 1964 Alaska earthquake, please see: http://www.npr.org/templates/story/story.php?storyId=5007860

Current research in the Canary Islands concludes that there have been at least five massive volcano landslides that occurred in the past, and that these same large events may occur in the future. These giant landslides have the potential of generating large tsunami waves, at close and also very great distances and would have the potential to devastate large areas of coastal land, as far away as the eastern seaboard of North America.

Rock falls and rock avalanches in coastal inlets, such as those that have occurred in the past at Tidal Inlet, Glacier Bay National Park, Alaska have the potential to cause regional tsunamis that pose a hazard to coastal ecosystems and human settlements. On July 9, 1958, a magnitude M 7.9 earthquake on the Fairweather Fault triggered a rock avalanche at the head of Lituya Bay, Alaska. The landslide generated a wave that ran up 524 m on the opposite shore and sent a 30-m high wave through Lituya Bay, sinking two of three fishing boats and killing two persons.

Source of Information:

Geist, E. L., 1998, Source characteristics of the July 17, 1998 Papua New Guinea tsunami: EOS, Transactions of the American Geophysical Union, v. 79 (supplement), p. 571.

Committee on the Alaska Earthquake of Division of Earth Sciences, National Research Council, Seismology and Geodesy, 1972,Plafker, George, USGS, U.S. Geological Survey Professional Paper. 543-I. Tectonics of the March 27, 1964, Alaska Earthquake.

Siebert, Lee, 2004, Landslides resulting from structural failure of volcanoes, Catastrophic Landslides:  Effects, Occurrence and mechanisms, Evans, Stephen G., and Jerome V. DeGraff, eds., Reviews in Engineering Geology, Volume XV, Geological Society of America, Boulder, Colorado USA.

Wieczorek, Gerald F., Jakob, Matthias, Motyka, Roman, Zirnheld, Sandra L., and Patricia Craw, 2003, Preliminary assessment of landslide-induced wave hazards:  Tidal Inlet, Glacier Bay National Park, Alaska, U.S. Geological Survey Open-file report 03-100.

Please see Can It Happen Here?

The Pacific Tsunami Warning Center is responsible for tsunami monitoring in the Pacific Basin. Their website is at http://www.prh.noaa.gov/ptwc/. Tragically, no such system existed for the Bay of Bengal where the devastating earthquake and tsunami occurred in December 2004.

1. 1797: A magnitude 8.4 earthquake near the central part of the western Sumatra generated a tsunami that flooded Padang. More than 300 fatalities.

2. 1833: A magnitude 8.7 earthquake near the south coast of the western Sumatra triggered a huge tsunami that flooded the southern part of western Sumatra. Numerous victims.

3. 1843: A tsunami that came from the southeast and flooded the coast of the Nias Island. Many fatalities.

4. 1861: A magnitude 8.5 earthquake affected all the western coast of Sumatra. Several thousand fatalities.

5. 1881: A magnitude 7.9 earthquake in the Andaman Island region generated a 1 m high tsunami on India's eastern coast. (http://cires.colorado.edu/~bilham/Oldham1881account.htm

6. 1883: Krakatau explosion. 36,000 fatalities, primarily on the islands of Java and Sumatra.

7. 1941: A magnitude ~7.7 Adaman Islands earthquake. Anecdotal accounts exist of a tsunami, however, no official records exist.

References:
Tsunami Laboratory, Institute of Computational Mathematics and Mathematical Geophysics
(http://tsun.sscc.ru/tsulab/20041226tsun.htm)
National Geophysical Data Center (http://www.ngdc.noaa.gov/seg/hazard/hazards.shtml)
K. Sieh (http://www.gps.caltech.edu/~sieh/publications.htm)
R. Bilham (http://cires.colorado.edu/~bilham/IndonesiAndaman2004.htm)
Oritz and Billham, 2003 JGR, VOL. 108, NO. B4, pp 2215

Please see Tsunamis That Have Struck U.S. Coastlines.

Although both are sea waves, a tsunami and a tidal wave are two different unrelated phenomenona. A tidal wave is a shallow water wave caused by the gravitational interactions between the Sun, Moon, and Earth. A tsunami is a sea wave caused by an underwater earthquake or landslide (usually triggered by an earthquake) displacing the ocean water.