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Newberry Volcano (with Newberry Caldera) is a large potentially active〔 shield volcano located east of the Cascade Range and about southeast of Bend, Oregon, within the Newberry National Volcanic Monument. It is not a typical shield volcano because, in addition to erupting basaltic lavas, it also has erupted andesitic and even rhyolitic lava. The volcano is in diameter and has a total volume of .〔(【引用サイトリンク】 Newberry Volcano, Oregon )〕 It possesses a large oval-shaped caldera in diameter, called the Newberry Caldera. Within the caldera there are two lakes (Paulina Lake and East Lake), many pyroclastic cones, lava flows, and obsidian domes. A deep gash in the northern flank, dubbed "The Fissure", is the end of a long series of fractures called the Northwest Rift Zone. Approximately 6,100 years ago, basaltic lava flows erupted from the fissure and covered part of Newberry's northwest flank. Newberry Volcano was named for John Strong Newberry, who explored central Oregon for the Pacific Railroad Surveys in 1855.〔.〕 During the Apollo program, parts of the volcano that resemble the Moon's surface were used to train the astronauts. The Horse Lava Tube System, the Arnold Lava Tube System, and Lava Butte are all on the flanks of the volcano. == Geology == The Newberry Volcano lies at the northwest end of both the Brothers Fault Zone, and the High Lava Plains (area of blue lines on diagram at right) of volcanic features in central Oregon that have been developing since about 16 Ma. Volcanism in the High Lava Plains is bimodal, having both basaltic (mafic) and rhyolitic (silicic) types of lava. Some of the rhyolites show a progression in ages from about 10 Ma in the east to the geologically recent Newberry Caldera in the west. This track, and its implication of a moving source, roughly mirrors the similar track of the Yellowstone Hotspot from the McDermitt Caldera on the Oregon—Nevada border, on which basis the Newberry volcanism has been attributed to a so-called hotspot (a plume of hot material arising from the earth's mantle). But whereas the Yellowstone Hotspot reflects the motion of the North American plate across a hotspot, the Newberry track does not. Although the cause of the intense regional volcanism around 16 Ma is hotly debated,〔See (www.MantlePlumes.org ) for a taste of the debate.〕 the age progression across the High Lava Plains is now attributed to a reservoir of hot material that expanded over time, and the linearity of the trend attributed to exploitation of a deep, pre-existing weakness in the crust associated with the Brothers Fault Zone.〔; ; ; ; .〕 A great deal of volcanic activity has occurred at Newberry Volcano, which itself has one of the largest collections of cinder cones, volcanic domes, lava flows, and fissures in the world. Most of the cinder cones are high and have shallow saucer-shaped summit craters. They are typically surrounded by basalt or andesite that erupted from their bases forming large lava beds. The northern flank holds three distinct lava tube systems that formed in pāhoehoe: the Horse Lava Tube System, Arnold Lava Tube System, and the Lava Top Butte basalt.〔; ; (Oregon High Desert Grotto ).〕 On the northwest flank of the volcano and located next to Highway 97 south of Bend, Lava Butte is a good example of this kind of cinder cone and an aā lava bed. There are also about 20 rhyolite domes or fissures on the eastern, southern, and western flanks. Larger examples include 580,000-year-old McKay Butte on the west flank, 80,000-year-old China Hat and 850,000-year-old East Butte on the far eastern base. During the late Pleistocene and Holocene periods, there have been six eruptive episodes: four of them rhyolitic, on the eastern half of the caldera; and two basaltic, on the flanks. * South Obsidian Eruptive Episode: An estimated 12,000 years ago, an obsidian dome and related obsidian flow erupted in the southeast part of the caldera. * East Rim Eruptive Episode: About 11,200 years ago (10,000 14C years B.P.), mafic cinders, scoria, spatter, and lava flows erupted from a fissure on the east rim of the caldera. * Interlake Eruptive Episode: A series of rhyolitic eruptions began in the caldera approximately 7,300 years ago (6,200 14C years B.P.). They produced a widespread phreatomagmatic pumiceous tephra deposit, obsidian flows, large and small pumice cones, and a pumice ring. This eruptive episode probably lasted for about 200 years. * Northwest Rift Eruptive Episode: About 7,000 years ago (6,100 14C years B.P.), basaltic andesite lava and cinder cones erupted from extensive fissure vents on the northwest and south flanks of Newberry. Spatter and cinders also erupted from a fissure on the north caldera wall. The lava flows range up to long and are more voluminous at lower elevations. This eruptive episode probably lasted for less than 50 years. * East Lake Eruptive Episode: About 3,500 years ago, obsidian flows and associated pumice deposits in the caldera erupted from caldera ring fractures. * Big Obsidian Eruptive Episode: About 480 A.D. (1,470 14C years B.P.), a three-part sequence of rhyolitic eruptions began which included an air-fall tephra, ash-flow tephra, and an obsidian flow from a common vent at the base of the south caldera wall. The initial Plinian eruption 480 A.D. (1,580 14C years B.P.) produced the Newberry pumice fall deposit which blanketed the east flank of the volcano and areas to the east. About 210 years later, the Paulina Lake ash flow (1,310 14C years B.P.) spread from near the south caldera wall to Paulina Lake. The final phase of the eruption produced the Big Obsidian Flow, which covers . Newberry's highest point is located above the southern caldera floor on Paulina Peak, which is just a peak on the southern rim. The volcano's south flank descends into the basaltic flatlands of central Oregon. 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「Newberry Volcano」の詳細全文を読む スポンサード リンク
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