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Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide , and for this reason they are often referred to as tidal waves. Tsunamis generally consist of a series of waves with periods ranging from minutes to hours, arriving in a so-called "wave train".  Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous and they can affect entire ocean basins; the 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history with over 230,000 people killed in 14 countries bordering the Indian OceanPowerPoint Presentation: has a wavelength of about 200 kilometres (120 mi). Such a wave travels at well over 800 kilometres per hour (500 mph), but owing to the enormous wavelength the wave oscillation at any given point takes 20 or 30 minutes to complete a cycle and has an amplitude of only about 1 metre (3.3 ft).  This makes tsunamis difficult to detect over deep water. Ships rarely notice their passage. The reason for the Japanese by a Tsunamis cause damage by two mechanisms: the smashing force of a wall of water travelling at high speed, and the destructive power of a large volume of water draining off the land and carrying all with it, even if the wave did not look large. While everyday wind waves have a wavelength (from crest to crest) of about 100 metres (330 ft) and a height of roughly 2 metres (6.6 ft), a tsunami in the deep ocean name "harbor wave" is that sometimes a village's fishermen would sail out, and encounter no unusual waves while out at sea fishing, and come back to land to find their village devastated huge wavePowerPoint Presentation: Tsunami generated by landslides In the 1950s, it was discovered that larger tsunamis than had previously been believed possible could be caused by giant landslides . Underwater landslides that generate tsunamis are called sciorrucks .  These phenomena rapidly displace large water volumes, as energy from falling debris or expansion transfers to the water at a rate faster than the water can absorb. Their existence was confirmed in 1958, when a giant landslide in Lituya Bay , Alaska , caused the highest wave ever recorded, which had a height of 524 metres (over 1700 feet). The wave didn't travel far, as it struck land almost immediately. Two people fishing in the bay were killed, but another boat amazingly managed to ride the wave. Scientists named these waves megatsunami . Scientists discovered that extremely large landslides from volcanic island collapses can generate megatsunamis that can cross oceansPowerPoint Presentation: Drawback If the first part of a tsunami to reach land is a trough—called a drawback—rather than a wave crest, the water along the shoreline recedes dramatically, exposing normally submerged areas. A drawback occurs because the water propagates outwards with the trough of the wave at its front. Drawback begins before the wave arrives at an interval equal to half of the wave's period. Drawback can exceed hundreds of metres, and people unaware of the danger sometimes remain near the shore to satisfy their curiosity or to collect fish from the exposed seabedPowerPoint Presentation: The 2011 earthquake off the Pacific coast of Tōhoku ( 東北地方太平洋沖地震 Tōhoku-chihō Taiheiyō Oki Jishin ? ),  also known as the 2011 Tohoku earthquake,  the Great East Japan Earthquake,   [fn 1] and the 3.11 Earthquake, was a magnitude 9.0 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC ) on Friday, 11 March 2011,    with the epicenter approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 32 km (20 mi).   It was the most powerful known earthquake ever to have hit Japan , and one of the five most powerful earthquakes in the world since modern record-keeping began in 1900.    The earthquake triggered powerful tsunami waves that reached heights of up to 40.5 metres (133 ft) in Miyako in Tōhoku's Iwate Prefecture ,   and which, in the Sendai area, travelled up to 10 km (6 mi) inland.  The earthquake moved Honshu 2.4 m (8 ft) east and shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in). [PowerPoint Presentation: On 12 March 2012, a Japanese National Police Agency report confirmed 15,861 deaths,  6,107 injured,  and 3,018 people missing  across twenty prefectures , as well as 129,225 buildings totally collapsed, with a further 254,204 buildings 'half collapsed', and another 691,766 buildings partially damaged.  The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse.   Japanese Prime Minister Naoto Kan said, "In the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan."  Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.  Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion.  The Bank of Japan offered ¥ 15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions.  The World Bank 's estimated economic cost was US$235 billion, making it the most expensive natural disaster in world historyPowerPoint Presentation: The earthquake, caused by 5 to 8 meters upthrust on a 180-km wide seabed at 60 km offshore from the east coast of Tōhoku,  resulted in a major tsunami that brought destruction along the Pacific coastline of Japan's northern islands. Thousands of lives were lost when entire towns were devastated. The tsunami propagated throughout the Pacific Ocean region reaching the entire Pacific coast of North and South America from Alaska to Chile . Warnings were issued and evacuations carried out in many countries bordering the Pacific. However, while the tsunami affected many of these places, the extent was minor.    Chile's Pacific coast, one of the furthest from Japan at about 17,000 km (11,000 mi) distant, was struck by waves 2 m (6.6 ft) high,    compared with an estimated wave height of 38.9 meters (128 ft) at Omoe peninsula, Miyako city, Japan ‘’’’’’’’’’’’’’’’’’’’’’’’’’PowerPoint Presentation: THE END You do not have the permission to view this presentation. In order to view it, please contact the author of the presentation.