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The Crater Glacier〔The official name for this feature is "Crater Glacier", as decided by an 8-4 vote of the U.S. Board on Geographic Names, Domestic Names Committee, in June 2006. This supersedes the earlier decision by the Washington State Board on Geographic Names in March 2005 to name it "Tulutson Glacier", and is now the official name required for use in all US government documents and publications. See 〕 (also known as Tulutson Glacier) is a geologically young glacier that is located on Mount St. Helens, in the U.S. state of Washington. The glacier formed after the 1980 Eruption and due to its location, the body of ice grew rapidly, unknown to the public for nearly 20 years. The glacier once contained ice caves in the smooth ice before the 2004-2008 volcanic activity. The growth of the lava dome and volcanic eruptions from 2004 to 2008 significantly altered the appearance of the glacier.〔 In the same time period, several agencies decided to put an official name on the glacier which, at first, was Tulutson Glacier. A later decision made Crater Glacier the official glacier name. Despite the volcanic activity, the glacier continued to advance and by mid-2008, the glacier completely encircled the lava domes.〔〔〔 - Glacier is still connected south of the lava dome.〕〔 In addition, new glaciers (rock or ice) have formed around Crater Glacier as well.〔 == Description == True to its name, the glacier lies inside the north-facing crater left by the 1980 eruption of Mount St. Helens and the glacier's elevation is about . A massive central lava dome emplaced from 1980 to 1987 occupies the center of the crater, and the glacier formed in the shape of a horseshoe around the dome, with two terminal moraines on the eastern and western sides. Heavy winter snowfall, repeated snow avalanches, rockfalls, and sun-shading by the surrounding cliffs to the south, led to the exceptionally rapid growth of this glacier. Thus, the glacier composition is estimated to be six-tenths ice and four-tenths rock,〔 with an average thickness of 328 feet (100 m) and a maximum thickness of around 656 feet (200 m); nearly as deep as Mount Rainier's Carbon Glacier.〔 None of the ice is older than the year 1980, however, the volume of the new glacier is about the same as all the pre–1980 glaciers combined.〔 The surface of the glacier looks dark and dirty in the summer due to the numerous rockfalls from the steep, unstable crater walls along with ash from eruptions, all of which help to insulate and protect the growing glacier. The 2004-2008 volcanic activity created a series of domes that nearly split the glacier into two lobes at the south end of the crater.〔 In spite of the four-year lava dome building period, the glacier remains North America's youngest and fastest growing glacier.〔 With the joining of the termini on the north end of Crater Glacier in May 2008, the body of ice completely encircles the lava domes.〔〔 Meltwater from the glacier gives rise to Loowit Creek.〔(【引用サイトリンク】title=Loowit Falls )〕 ;Pre-2004 eruption glacier caves of Crater Glacier In 2000, glacier caves were discovered on the then-smooth glacier surface. Many of these glacier caves were big enough to explore, like the glacier caves on the summit of Mount Rainier. Most of the glacier caves were located near the 1980s lava dome, where hot steam and volcanic gas emissions from hidden fumaroles on the crater floor or lava dome melted holes in the young glacial ice.〔 About 7,900 feet or 2.4 km of underground caves and passageways in the glacier were mapped and studied.〔 ;Other glaciers and new rock glaciers Since 2004, new glaciers have formed on the crater wall above Crater Glacier feeding rock and ice to Crater Glacier below. In addition, there are two rock glaciers to the north of the eastern lobe of Crater Glacier and one north of the western lobe. Two of these rock glaciers have merged with the Crater Glacier, with one on the west and one on the east. The other rock glacier on the eastern slopes of the crater wall is very close to touching the glacier. 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「Crater Glacier」の詳細全文を読む スポンサード リンク
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