<P> The 1958 Lituya Bay megatsunami occurred on July 9 at 22: 15: 58 following an earthquake with a moment magnitude of 7.8 and a maximum Mercalli intensity of XI (Extreme). The earthquake took place on the Fairweather Fault and triggered a rockslide of 40 million cubic yards (30 million cubic meters and about 90 million tons) into the narrow inlet of Lituya Bay, Alaska . The impact was heard 50 miles (80 km) away, and the sudden displacement of water resulted in a megatsunami that washed out trees to a maximum elevation of 1,710 feet (520 m) at the entrance of Gilbert Inlet . This is the largest and most significant megatsunami in modern times; it forced a re-evaluation of large - wave events and the recognition of impact events, rockfalls, and landslides as causes of very large waves . </P> <P> 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 . Scientists 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, a ratio comparable with other events where this "dual slide" effect is known to have happened . Lituya Bay has a history of megatsunami events, but the 1958 event was the first for which sufficient data was captured at the time . </P> <P> Lituya Bay is a 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 2 miles (3 km) and a length of 7 miles (11 km). Lituya Bay is an ice - scoured tidal inlet with a maximum depth of 722 feet (220 m). The narrow entrance of the bay has a depth of only 33 feet (10 m). 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 (395 ft or 120 m), 1899 (200 ft or 61 m) and 1936 (490 ft or 150 m). </P> <P> Near the crest of the Fairweather Mountains sit the Lituya and the North Crillon glaciers . They are each about 12 miles (19 km) long and 1 mile (1.6 km) wide with an elevation of 4,000 feet (1,200 m). The retreats of these glaciers form the present "T" shape of the bay, the Gilbert and Crillon inlets . </P>

The largest recorded tsunami with a wave 1720 feet tall in lituya bay alaska