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The Meteor Crater from 36,000 feet Meteor Crater is a meteorite impact crater approximately east of Flagstaff and west of Winslow in the northern Arizona desert of the United States. Because the United States Board on Geographic Names commonly recognizes names of natural features derived from the nearest post office, the feature acquired the name of "Meteor Crater" from the nearby post office named Meteor.〔("J. P. Barringer's acceptance speech." ) ''Meteoritics'', volume 28, page 9 (1993). Retrieved on the SAO/NASA Astrophysics Data System.〕 The site was formerly known as the Canyon Diablo Crater and fragments of the meteorite are officially called the Canyon Diablo Meteorite.〔La Pas, L. (1943). ("Remarks on four notes recently published by C. C. Wylie" ), ''Popular Astronomy'', volume 51, page 341〕 Scientists refer to the crater as Barringer Crater in honor of Daniel Barringer, who was first to suggest that it was produced by meteorite impact.〔Grieve, R.A.F. (1990) "Impact Cratering on the Earth", ''Scientific American'', 262 (4), 66–73.〕 The crater is privately owned by the Barringer family through their Barringer Crater Company, which proclaims it to be "best preserved meteorite crater on Earth".〔(【引用サイトリンク】title=Barringer Meteorite Crater * Meteorites Craters and Impacts )〕〔(【引用サイトリンク】title=Meteor Crater )〕 Despite its importance as a geological site, the crater is not protected as a national monument, a status that would require federal ownership. It was designated a National Natural Landmark in November 1967.〔(【引用サイトリンク】url=http://www.nature.nps.gov/nnl/site.cfm?Site=BAME-AZ )〕 Meteor Crater lies at an elevation of about above sea level. It is about in diameter, some 170 m deep (570 ft), and is surrounded by a rim that rises above the surrounding plains. The center of the crater is filled with of rubble lying above crater bedrock.〔 One of the interesting features of the crater is its squared-off outline, believed to be caused by existing regional jointing (cracks) in the strata at the impact site. ==Formation== The crater was created about 50,000 years ago during the Pleistocene epoch, when the local climate on the Colorado Plateau was much cooler and damper. The area was an open grassland dotted with woodlands inhabited by woolly mammoths and giant ground sloths. The crater was over 10,000 years old when the first humans saw it, at the earliest, 40,000 years ago. Since the crater's formation, the rim is thought to have lost 15–20 meters of height at the rim crest due to natural erosion. Similarly, the basin of the crater is thought to have approximately 30 meters of additional postimpact sedimentation from lake sediments and of alluvium. These erosion processes are the reason we see very few remaining craters on Earth, since many have been erased by this geological process. The relatively young age of Meteor Crater, paired with the Arizona climate, have allowed this crater to remain as we see it today. The lack of erosion that preserved the crater's shape helped lead to this crater being the first crater recognized as an official impact crater from a natural celestial body.〔(【引用サイトリンク】title=Meteorite Crater - The shape of the land, Forces and changes, Spotlight on famous forms, For More Information )〕 The object that excavated the crater was a nickel-iron meteorite about across. The speed of the impact has been a subject of some debate. Modeling initially suggested that the meteorite struck at up to 20 kilometers per second (45,000 mph) but more recent research suggests the impact was substantially slower, at 12.8 kilometers per second (28,600 mph). It is believed that about half of the impactor's bulk was vaporized during its descent. Impact energy has been estimated at about 10 megatons. The meteorite was mostly vaporized upon impact, leaving little in the crater.〔Schaber, Gerald G. ("A Chronology of Activities from Conception through the End of Project Apollo (1960–1973)" ), 2005, U.S. Geological Survey Open-File Report 2005-1190. (PDF)〕 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「Meteor Crater」の詳細全文を読む スポンサード リンク
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