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Long Valley Caldera is a depression in eastern California that is adjacent to Mammoth Mountain. The valley is one of the earth's largest calderas, measuring about long (east-west) and wide (north-south), and up to deep. Long Valley was formed 760,000 years ago when a huge volcanic eruption released very hot ash that later cooled to form the Bishop tuff that is common to the area. The eruption was so colossal that the magma chamber under the now-destroyed volcano was emptied to the point of collapse. The collapse caused a larger secondary eruption of pyroclastic ash that burned and buried thousands of square miles. Ash from this eruption blanketed much of the western part of what is now the United States. ==Geography== The caldera is a giant bowl-shaped depression, approximately wide, surrounded by mountains, but open to the southeast. The elevation of the bottom of the bowl ranges from , being higher in the west. Near the center of the bowl, there is a resurgent dome formed by magmatic uplift. The southeastern slope from the caldera down towards Bishop, California is filled with the Bishop Tuff, solidified ash that was ejected during the stupendous eruption that created the caldera. The Bishop tuff is thousands of feet thick and is cut by the Owens River Gorge, formed during the Pleistocene when the caldera filled with water and overtopped its rim. The rim of the caldera is formed from pre-existing rock, rising about above the caldera floor.〔 However, the eastern rim is less high, only about .〔 Mammoth Mountain is a lava dome complex in the southwestern corner of the caldera, consisting of about 12 rhyodacite and dacite overlapping domes.〔 These domes formed in a long series of eruptions from 110,000 to 57,000 years ago, building a volcano that reaches in elevation. The Mono–Inyo Craters are a -long volcanic chain situated along a narrow, north–south-trending fissure system extending along the western rim of the caldera from Mammoth Mountain to the north shore of Mono Lake. The Mono-Inyo Craters erupted from 40,000 to 600 years ago, from a magma source separate from the Long Valley Caldera. The caldera has an extensive hydrothermal system. Casa Diablo Hot Springs at the base of the resurgent dome hosts a geothermal power plant. Hot Creek cuts into part of the resurgent dome and passes through hot springs. The warm water of Hot Creek supports many trout, and is used at the Hot Creek Fish Hatchery. The creek was closed to swimming in 2006 after geothermal activity in the area increased, and was still closed as of 2012.〔〔(【引用サイトリンク】title=New Activity at Hot Creek Geologic Site )〕 There are a number of other hot springs in the area, some of which are open to bathers. 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「Long Valley Caldera」の詳細全文を読む スポンサード リンク
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