Tsunamis - 7 of 6
Tsunamis FAQs - 6 Found
Three primary sources of information can be used to answer the question "Could It Happen Here? Tsunamis That Have Struck U.S. Coastlines": (1) tsunami catalogs of historical events, (2) the age of geologic deposits left by great earthquakes and tsunamis (see related Sound Waves article "Group Aims to Distinguish Tsunami Deposits from Large-Storm Deposits in the Geologic Record", and (3) computer simulations of tsunamis from potential great earthquakes and landslides around the world.
This FAQ focuses on the first source, historical information, taken mainly from the worldwide catalog of historical tsunamis maintained by NOAA's National Geophysical Data Center (NGDC). This catalog includes two types of measurements: runup observations from eyewitness accounts, and wave-height readings from tide-gauge stations, most often located in harbors. The term "runup" refers to the vertical height a wave reaches above sea level as it washes ashore, "wave height" to the vertical measurement of the wave before it reaches shore, and "inundation distance" to the horizontal distance a tsunami reaches landward from the shoreline.
Hawaii has a long recorded history of tsunamis—both "teletsunamis" (also called "far-field tsunamis") from earthquakes around the Pacific rim, and "local tsunamis" from earthquakes and landslides near Hawaii. The Pacific Disaster Center reports that tsunamis have accounted for more lost lives in Hawaii than the total of all other local disasters. In the 20th century, an estimated 221 people were killed by tsunamis on the islands of Hawaii. One of the largest and most devastating tsunamis that Hawaii has experienced was a teletsunami in 1946 from an earthquake along the Aleutian subduction zone. Runup heights reached a maximum of 33 to 55 ft and 159 people were killed. Damage was more than $26 million ($255 million in today's dollars). Other important teletsunamis include one from the 1960 magnitude 9.5 earthquake in southern Chile and one from the 1964 magnitude 9.2 earthquake in the Gulf of Alaska. The May 22, 1960, Chile earthquake generated a 35-ft-high wave, causing 61 deaths and $23 million damage (about $150 million in today's dollars). Hawaii has also been hit by local tsunamis, primarily from earthquakes and large-scale subsidence along the south flank of Kilauea.
Because Alaska, including the Aleutian Islands, is bordered on the south by a major subduction zone capable of generating large earthquakes, Alaska has sustained many damaging tsunamis. By far, the one that stands out is the tsunami generated by the 1964 magnitude 9.2 earthquake in the Gulf of Alaska. Not only was a Pacific-wide tsunami generated by this great earthquake, but landslides in coastal fiords, such as Port Valdez, also generated localized, extremely damaging waves. The 1964 tsunami caused damage and loss of life across the Pacific. The West Coast & Alaska Tsunami Warning Center in Palmer, AK, indicates that the 1964 tsunami was the most disastrous tsunami to hit the U.S. west coast, causing many fatalities and financial losses.
U.S. West Coast
The historical record of tsunamis along the U.S. west coast consists mainly of teletsunamis generated by large earthquakes around the Pacific Rim. Of the teletsunamis that have struck the West Coast, the 1964 Gulf of Alaska tsunami caused the most extensive damage, particularly in Crescent City, CA, where at least 10 deaths occurred. Potentially tsunamigenic fault structures exist locally offshore the U.S. west coast, most notably the Cascadia subduction zone—an offshore fault system about 1,200 km (750 mi) long that extends from northern California to southern Canada and accommodates motion between the Pacific and North American tectonic plates at a rate of about 40 mm/yr (1.6 in./yr). This subduction zone is believed to have most recently ruptured in a magnitude 9.0 earthquake in 1700; the resulting tsunami was recorded in historical accounts in northern Japan. Geologic evidence of submerged vegetation indicates that large or great earthquakes (magnitude 8 to 9) have occurred on average every 500 years along this zone. Great ruptures along this subduction zone would most likely cause local and possibly oceanwide tsunamis that could affect the Western United States.
U.S. Gulf Coast
In historical times, tsunami waves recorded along the Gulf Coast have all been less than 1 m high. Those reported from the 1964 Gulf of Alaska earthquake as felt in Louisiana and Texas are technically termed seiches—oscillations of a body of water typically caused by atmospheric disturbances but in this case caused by ground motion from the earthquake. Seiches can also occur in lakes from earthquake movements.
U.S. East Coast
Because the only major subduction zones in the Atlantic Ocean are along the Caribbean Sea, tsunamis have been relatively infrequent here in comparison with the Pacific Ocean. The most famous Atlantic tsunami was the 1755 Lisbon tsunami, generated by an earthquake on a fault offshore Portugal. Teletsunamis from that earthquake were reported in Newfoundland (Canada) and islands in the Caribbean Sea. The most noteworthy local tsunami in North America resulted from the 1929 magnitude 7.3 Grand Banks earthquake near Newfoundland. In this complex event, most, if not all, of the tsunami energy may have been triggered by a submarine landslide. The maximum tsunami runup was 2 to 7 m, which was concentrated on the coast of Newfoundland, although it was recorded as far south as South Carolina. A couple of tsunamis reported from Caribbean earthquakes had runups less than 1 m.
For more general information on tsunamis and what to do during a tsunami warning, please visit the web sites sponsored by the Federal Emergency Management Agency, the National Weather Service, and the National Oceanic and Atmospheric Administration. For tips from the stories of people who have survived tsunamis, please see USGS Circular 1187, "Surviving a Tsunami—Lessons from Chile, Hawaii, and Japan," (PDF files in English and Spanish can be downloaded from this site).
USGS Science Topics - Tsunamis: Sea waves generated by submarine earthquakes, volcanic eruptions, or landslides, which are generally imperceptible in deep water but may be very destructive when striking the shoreline.