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〕 | established = | visitation_num = 535,508 | visitation_year = 2014 | visitation_ref = | governing_body = National Park Service }} Crater Lake National Park is a United States National Park located in southern Oregon. Established in 1902, Crater Lake National Park is the fifth oldest national park in the United States and the only national park in Oregon. The park encompasses the caldera of Crater Lake, a remnant of a destroyed volcano, Mount Mazama, and the surrounding hills and forests. The lake is deep at its deepest point, which makes it the deepest lake in the United States, the second deepest in North America and the ninth deepest in the world.〔 Crater Lake is often referred to as the seventh deepest lake in the world, but this former listing excludes the approximately depth of subglacial Lake Vostok in Antarctica, which resides under nearly of ice, and the recent report of a maximum depth for Lake O'Higgins/San Martin, located on the border of Chile and Argentina. However, when comparing its average depth of to the average depth of other deep lakes, Crater Lake becomes the deepest in the Western Hemisphere and the third deepest in the world. The impressive average depth of this volcanic lake is due to the nearly symmetrical deep caldera formed 7,700 years ago during the violent climactic eruptions and subsequent collapse of Mount Mazama and the relatively moist climate that is typical of the crest of the Cascade Range. The caldera rim ranges in elevation from . The United States Geological Survey benchmarked elevation of the lake surface itself is . This National Park encompasses .〔 Crater Lake has no streams flowing into or out of it. All water that enters the lake is eventually lost from evaporation or subsurface seepage. The lake's water commonly has a striking blue hue, and the lake is re-filled entirely from direct precipitation in the form of snow and rain. ==Geology== Volcanic activity in this area is fed by subduction off the coast of Oregon as the Juan de Fuca Plate slips below the North American Plate (see plate tectonics). Heat and compression generated by this movement has created a mountain chain topped by a series of volcanoes, which together are called the Cascade Range. The large volcanoes in the range are called the High Cascades. However, there are many other volcanoes in the range as well, most of which are much smaller. About 400,000 years ago, Mount Mazama began its existence in much the same way as the other mountains of the High Cascades, as overlapping shield volcanoes. Over time, alternating layers of lava flows and pyroclastic flows built Mazama's overlapping cones until it reached about in height. As the young stratovolcano grew, many smaller volcanoes and volcanic vents were built in the area of the park and just outside what are now the park's borders. Chief among these were cinder cones. Although the early examples are gone—cinder cones erode easily—there are at least 13 much younger cinder cones in the park, and at least another 11 or so outside its borders, that still retain their distinctive cinder cone appearance. There continues to be debate as to whether these minor volcanoes and vents were parasitic to Mazama's magma chamber and system or if they were related to background Oregon Cascade volcanism. After a period of dormancy, Mazama became active again. Then, around 5700 BC, Mazama collapsed into itself during a tremendous volcanic eruption, losing in height. The eruption formed a large caldera that, depending on the prevailing climate, was filled in about 740 years, forming a beautiful lake with a deep blue hue, known today as Crater Lake.〔 〕 The eruptive period that decapitated Mazama also laid waste to much of the greater Crater Lake area and deposited ash as far east as the northwest corner of what is now Yellowstone National Park, as far south as central Nevada, and as far north as southern British Columbia. It produced more than 150 times as much ash as the May 18, 1980 eruption of Mount St. Helens. This ash has since developed a soil type called andisol. Soils in Crater Lake National Park are brown, dark brown or dark grayish brown sandy loams or loamy sands which have plentiful cobbles, gravel and stones. They are slightly to moderately acidic and their drainage is somewhat excessive. 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 Lake National Park」の詳細全文を読む スポンサード リンク
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