Tsunamis, often incorrectly called tidal waves, can be caused by undersea earthquakes or landslides either undersea or above falling into the sea triggered by something like a volcano or earthquake.
Deep Ocean:
 Speed: 300-600 MPH
 Height: A few inches to 3 ft.
 Period: 5 minutes - 2 hr.
 Wave Length:
   Earthquake generated: 12 - 180 mi. (20 - 300 km.)
   Landslide generated: 200 yards - 20 mi.
Near Shore:
 Speed: 15-20 MPH
 Height: 10 to 100 feet
Wind-driven waves typically reach 10 metres. However, these waves only involve water close to the ocean surface and are separated by at most several hundred metres with a period of 10 sec.

Tsunami waves have a very deep reach, 4000 metres or more with a wave length of 3-500 miles. They involve the entire depth of the ocean. Their energy is thousands of times more than a monster storm.
Because the rate at which a wave loses its energy is inversely related to its wave length, tsunamis not only propagate at high speeds, they can also travel great, transoceanic distances with limited energy losses.

Tsunamis do not necessarily make their final approach to land as a series of giant breaking waves. They may be more like a very rapidly rising tide. This may be accompanied by much underwater turbulence, sucking people under and tossing heavy objects around. Entire beaches have been stripped away by tsunamis.

Information at NOAA's (National Oceanic and Atmospheric Administration) StormReady.com:
There were 21 damaging Tsunamis and 76 non-damaging Tsunamis from 1990-1999
Tsunamis with the highest death toll:

Deaths Year Location Notes
225,000 2004 Indian Ocean 9.0 Earthquake near Sumatra, Indonesia, affecting more than 10 countries in SE Asia and NE Africa. Sri Lanka, India, and Indonesia were worst hit.
83,000 1908 Messina, Italy 7.5 Earthquake
70,000 1755 North Atlantic - Lisbon, Portugal 100,000 died from tsunami, earthquake and fire
40,000 1782 S. China Sea Includes deaths in Taiwan
36,500 1883 S. Java Sea Krakatau Volcano. Tsunami over 120 ft. high 100 K died from earthquake and tsunami.
30,000 1707 Tokaido-Nankaido, Japan
26,360 1896 Sanriku, Japan
25,674 1868 N. Chile
15,030 1792 Sw. Kyushu Island, Japan
13,486 1771 Ryukyu Trench
8,000 1976 Moro Gulf, Philippines
5,233 1703 Tokaido-Kashima, Japan
5,000 1605 Nankaido, Japan
5,000 1611 Sanriku, Japan
3,800 1746 Lima, Peru
3,620 1899 Banda Sea, Indonesia
3,000 1692 Jamaica
3,000 1854 Nankaido, Japan
3,000 1933 Sanriku, Japan*
2,243 1674 Banda Sea, Indonesia
2,182 1998 Papua New Guinea Underwater Landslide
2,144 1923 Tokaido, Japan
2,000 1570 Chile
1,997 1946 Nankaido, Japan
1,700 1766 Sanriku, Japan
Others of interest:
1,000 1960 South Central Chile 9.5 Earthquake (revised from 8.6 due to new scale for large earthquakes) 61 died when the tsunami hit Hilo Hawaii. From 1,000 to 2,290 total died from the earthquake and tsunami. (Article)
165 1946 Hawaii 7.5 earthquake in Aleutian Isl. caused waves over 30 ft. in Hilo, Hawaii
100? 1854 Lituya Bay, Alaska Wave up to 400 ft. high from landslide
122 1964 Gulf of Alaska
27-51 1929 Newfoundland's Burin Peninsula 7.2 earthquake causing glacial debris at the edge of Georges Bank by the St. Lawrence River to collapsed down the continental slope of North America, creating a 40-foot wave.
Note: Statistics quoted before 20 th Century are approximate

You ain't seen nothing yet.
There is the possibility that any time in the next few thousand years an eruption of volcano of Cumbre Vieja on La Palma in the Canary Islands could cause a massive landslide creating a mega-tsunami which travel across the Atlantic in about 9 hours and send a 30-70 foot tall wave across the East Coast of the US from Boston to Miami and into the Caribbean traveling up to 20 miles inland.
The volcano's last eruption in 1949 made its western flank highly unstable. It could literally split apart next time the volcano erupts. It has shown no signs of activity since that eruption.
Scientists say the entire area of unstable slope may not fall at once. Instead, smaller landslides may occur over time. These landslides would produce waves one-fourth to half the height of the mega tsunami.
Monitoring might at best provide two weeks warning of the disaster.
Mega-tsunami at the bbc.
Giant Wave will hit Britain at 500 MPH at news.telegraph
Cumbre Vieja Volcano -- Potential collapse and tsunami
Volcanic Landslide Could Send Mega Tsunami to U.S. East Coast at disasterrelief.org
Tsunami: Why America's Coast Would Be Toast at propagandamatrix.com.

Cracks discovered in the ocean floor just north of Cape Hatteras in North Carolina in 2004 could warn of an unpredictable disaster. The cracks, a 25-mile-long series of roof shingle-shaped ridges located 300 to 600 feet below the ocean surface may cause the seabed to crumble, creating a submarine landslide, or "slump," triggering a tsunami with waves 20-feet high in some places.

See more at:
Timeline: Tsunami disasters at CNN
Pacific Tsunami Warning Center
Intergovernmental Oceanographic Commission (IOC)
National Geographic
Ocean Atlas
Red Cross
 International Tsunami Information Center - Library (
Tsunami Great Waves) at the  National Oceanic and Atmospheric Administration (NOAA).

last updated 29 Jan 2005