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Such a tsunami can potentially rise to heights of hundreds of meters, travel at 550 miles per hour (890 km/h) in mid-ocean and potentially reach 20 km inland in low-lying regions. A wave of this nature propagates as a vertical shift a metre or so throughout the volume of water in deep ocean, with a crest to crest distance of hundreds of kilometers, and so is barely noticeable. However the huge amount of energy in it generates a much higher wave as it approaches shallow water.
Underwater earthquakes do not normally generate such large tsunamis unless they also trigger an underwater landslide — typically they have a height of less than ten metres.
The occurrence of such colossal disasters was first considered by two geologists searching for oil in Alaska, when they observed evidence of unusually large waves in the nearby bay. Five years later, landslides were revealed to be the source of the waves. These landslides would hit the water so fast that the displaced water could not settle before the rocks had, which increased the strength of the resulting wave. Subsequently, this was found to pertain to much larger landslides as well, including collapsing island masses.
The geological record shows that events such as megatsunamis are very rare, but are extremely devastating to anything near the receiving shore when they do occur. Some are so large that they can devastate the coasts of entire continents. The last such event (that we know of) occurred approximately 4,000 years ago on Réunion island, to the east of Madagascar.
A smaller megatsunami did occur in Lituya Bay, Alaska in 1958. This is an ice-scoured inlet 220 meters deep with an entrance only 10 meters wide. The topology of the inlet is particulary suited to producing local megatsunami. A magnitude 7.5 earthquake on July 8 nearby generated a landslide within the inlet which produced a wave that washed out trees 200 meters above normal sea level. Comparison with previous photographs indicated that several hundred feet of ice had been removed from the front of a nearby glacier by a 520 meter high wave.
Some have conjectured that historic megatsunamis underlie the deluge mythsFor generic information on some great floods of historical times, see the article deluge. Epic of Gilgamesh in Akkadian The Great Flood the Universal Deluge involving Noah in Genesis or Utnapishtim in the Epic of Gilgamesh is a widespread but not universa that are common to most cultures throughout the world.
Volcanic Islands such as Réunion and HawaiiFor the 1959 novel and 1966 movie, see Hawaii (novel). Hawaii ( Hawaiian/ Hawaiian English: Hawai‘i with the ‘okina is the archipelago of the Hawaiian Islands in the Pacific Ocean. Hawaii constitutes the 50th state of the United States, and as of the 2000 are susceptible to causing megatsunamis because often they are structurally little more than large, unstable piles of loosely aggregated material heaped up by successive eruptions. Evidence for this has been found in the form of extensive underwater debris aprons around them composed of the material which has slipped into the ocean. In recent years some five such debris aprons have been found in Hawaii alone.
Some geologists believe the most likely candidate for the source of the next megatsunami is the island of La PalmaThis article discusses one of the Canary Islands. For other similar names, see Palma. La Palma a Spanish island, is one of the Canary Islands in the Atlantic Ocean off Africa. It is located at 28°40' N, 17°52 W. Description La Palma is one of the Canary I, in the Canary IslandsComunidad Autonoma deCanarias ( In Detail) Capitals Las Palmas de Gran Canaria Santa Cruz de Tenerife Area total % of Spain Ranked 13th 7 447 km² 1,5% Population Total (2003) % of Spain Density Ranked 8th 1 843 755 4,4% 247,58/km² Demonym English Spanish. During the 19491949 is the common year starting on Saturday. see link for calendar) Events January-February January 4 RMS Caronia of the Cunard Line departs Southampton for New York on her maiden voyage January 4 February 22 Series of winter storms in Nebraska, Wyoming, eruption the western half of the Cumbre ViejaCumbre Vieja ( Spanish: "Old Summit") is a volcanic ridge on the island of La Palma in Spain's Canary Islands. Geology The last three eruptions in the ridge were in 1712, 1949, and 1971. Scientists warn that a future eruption, which could come at any time ridge slipped several metres downwards into the Atlantic Ocean. It is believed that this process was driven by the pressure caused by the rising magma heating and vaporising water trapped within the structure of the island, causing the island's structure to be pushed apart. During an eruption that is anticipated to occur sometime within the next few thousand years the western half of the island, weighing perhaps 500 billion tonnes, will catastrophically slide into the ocean. This will inevitably generate a megatsunami which will travel across the Atlantic and strike the Caribbean and the Eastern American seaboard several hours later with a wave possibly 90 meters (300 feet) high, resulting in massive coastal devastation.
The aftermath would hold obvious implications for affected populations, governments and for the global economy. While potentially not as devastating as a supervolcano, a megatsunami would be an unprecedented disaster in whatever region of the World it occurred.
Megatsunamis are a favorite subject of many films, given their undoubted visual impact; these megatsunamis are often caused by asteroid impacts or other extraterrestrial causes, rather than by landslides. Examples of this are the movies Deep Impact, The Day After Tomorrow and the longer versions of The Abyss.