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|date = UTC |time = UTC 〔 |duration = |magnitude = 7.8 Mw 〔〔〔 |depth = 〔 |location = |type = Strike-slip 〔 |affected = Lituya Bay, Alaska |damages = |intensity = XI (''Extreme'') 〔 |pga = |tsunami = runup 〔 |landslide = |foreshocks = |aftershocks = |casualties = 5 〔 }} The 1958 Lituya Bay megatsunami occurred on , following an earthquake with a moment magnitude of 7.8 and a maximum Mercalli Intensity of XI (''Extreme''). The event took place on the Fairweather Fault and triggered a rockfall of 2,000 feet of rock and ice (30 million cubic metres, 40 million cubic yards, and about 90 million tons) to fall from several hundred metres into the narrow inlet of Lituya Bay, Alaska. The impact was heard away,〔Dave Kiffer, ("Surviving the Biggest Wave Ever" ), 2008〕 and the sudden displacement of water resulted in a megatsunami that destroyed vegetation up to above the height of the bay and a wave that traveled across the bay with a crest reported by witnesses to be on the order of in height.〔 This is the most significant megatsunami and the largest known in modern times. The event forced a re-evaluation of large wave events, and recognition of impact, rockfall and landslide events as a previously unknown cause of very large waves. A 2010 model examined the amount of infill on the floor of the bay, which was many times larger than that of the rockfall alone, and also the energy and height of the waves, and the accounts given by eyewitnesses, concluded that there had been a "dual slide" involving a rockfall, which also triggered a release of 5 to 10 times its volume of sediment trapped by the adjacent Lituya Glacier, as an almost immediate and many times larger second slide, a ratio comparable with other events where this "dual slide" effect is known to have happened. Lituya Bay has a history of megatsunami events in modern times — the 1958 event is one of many evidenced, but due to its remoteness was the first for which sufficient data was captured at the time, to confirm the nature of the event.〔http://www.santacruzsentinel.com/general-news/20110409/gary-griggs-our-ocean-backyard-tsunami-rocked-alaskas-lituya-bay-in-1958〕〔 ==Lituya Bay== (詳細はfjord located on the Fairweather Fault in the northeastern part of the Gulf of Alaska.〔 It is a T-shaped bay with a width of and a length of . Lituya Bay is an ice-scoured tidal inlet with a maximum depth of . The narrow entrance of the bay has a depth of only .〔 The two arms that create the top of the T-shape of the bay are the Gilbert and Crillon inlets and are a part of a trench on the Fairweather Fault. In the past 150 years Lituya Bay has had three other tsunamis of over 100 ft: 1854 (), 1899 () and 1936 ().〔.〕 Near the crest of the Fairweather Mountains sit the Lituya and the North Crillon glaciers. They are each about long and wide with an elevation of . The retreats of these glaciers form the present "T" shape of the bay, the Gilbert and Crillon inlets.〔 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「1958 Lituya Bay megatsunami」の詳細全文を読む スポンサード リンク
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