MAIN Science Earth Sciences Tsunamis

Taken from the Japanese words for "tsu" (harbor) and "nami" (wave), a tsunami (pronounced tsoo-nah-mee) is a wave or series of waves that over the centuries have wreaked havoc on vulnerable seaside communities.

Also sometimes referred to as tidal waves, tsunamis have little to do with the pull of the moon on ocean tides, but are most commonly caused by undersea earthquakes or volcanic eruptions.

Tsunamis can also be caused by massive coastal landslides or large asteroid impacts. Most, however, occur around the Pacific Ring of Fire known for its active earthquake and volcanic activity that most recently spawned the Indian Ocean tsunami in 2004.

Depending on the severity of the shock that causes them, tsunamis can range from a mere ripple that goes relatively unnoticed — to awesome 100-foot waves clocked at speeds of up to 600mph or that equal to the speed of a commercial airliner.

Tsunami warning signs

While Mother Nature provides little advance warning of a tsunami, buoys have been set in place around the Pacific (and following the 2004 tsunami, the Indian Ocean) that forewarn of an undersea earthquake or other disturbance that may result in a giant wave.

Otherwise, the traditional way to know if a tsunami is headed toward shore is when the shoreline dramatically recedes, an alarming sign that the crest of the wave may be seconds or minutes away from breaking.

The "sixth sense" exhibited by local animals - who seem to know hours before a tsunami strikes - is yet another early warning system that has intrigued scientists for decades. While no conclusive evidence shows how they are aware of the danger, it is thought that audio signals - beyond human hearing - alert animals to quickly head inland before disaster strikes.

History of tsunamis

While the 2004 Indian Ocean tsunami is strong in most recent memory, Japan is always at the forefront in discussions about the history of tsunamis, having been recorded there as early as 684 A.D.

Among the most destructive tsunamis ever recorded in Japan was the 100-foot wave that struck Honshu resulting in around 27,000 fatalties in 1896.

However, almost a decade earlier, eruptions from the Krakatoa volcano in 1883 sparked a tsunami in Java and Sumatra that resulted in some 36,000 drownings and mass destruction to the coastline.

Other notable tsunamis that have occured over the last century:

• April 1, 1946: An earthquake in Alaska kills more than 150 people in Hawaii when a resulting giant wave speeds across the Pacific to hit the Hilo coast. It is soon dubbed the April Fools tsunami due to people in Hawaii thinking that tsunami warnings were an April fools prank.
• May 22, 1960: With a magnitude of 8.6, the world's largest recorded earthquake in Chile results in a tsunami that decimates the Chilean coast. A 75-foot wave races across the Pacific to kill hundreds more in Hawaii.
• March 27, 1964: The Good Friday earthquake results in a a 201-foot high wave in the Valdez Inlet and sends tsunami shockwaves up and down the coast as far south as Crescent City, California.
• Aug. 23, 1976: The Moro Gulf Tsunami in the southwest Philippines kills 8,000 following a powerful earthquake.
• July 17, 1998: A tsunami in Papua New Guinea is the most devastating tsunami since the 1976 Moro Gulf, Philippines, tsunami resulting in 2,200 deaths.
• December 26, 2004 - An undersea earthquake in the Indian Ocean sets off a powerful series of tsunamis killing more than 225,000 people in eleven countries.

More about tsunamis around the Web:

Tsunami - Wikipedia - Causes, effects plus historical information on the world's worst tsunamis, along with a photo gallery and extensive list of related resources.

Tsunamis and Earthquakes at the USGS - Research at the U.S. Geological Survey featuring basic information on tsunamis with related photos and videos, a look a the 2004 Indian Ocean quake, the 1998 Papua New Guinea tsunami, and occurences in the U.S. Pacific Northwest.

Savage Earth - Waves of Destruction - Companion site to the PBS TV special with sample videos, photos and information on how tsunamis are created and their potential for devastation.

Tsunami Facts: How They Form, Warning Signs, and Safety Tips - Good overview from National Geographic with photos and related resources.

Tsunami: the Great Waves - Online informational brochure with facts, information, early warnings signs, safety tips and historical information with related photos, resources.

What Causes a Tsunami? - Kid-friendly illustrations and information on causes, effects and more on the science behind the phenomenon, with related resources from TIME Magazine.