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The Nördlinger Ries is a large circular depression in western Bavaria, Germany, located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located about southwest of the centre of the depression. The word "Ries" is not a German word; it is believed that the term is derived from Raetia, since the tribe of Raetians lived in the area in pre-Roman times. == Ries impact crater == The depression is interpreted as a meteor impact crater formed about 14.3 million–14.5 million years ago in the Miocene.〔Johannes Baier: (''Zur Herkunft und Bedeutung der Ries-Auswurfprodukte für den Impakt-Mechanismus'' ). - Jber. Mitt. oberrhein. geol. Ver., N. F. 91, 9-29, 2009.〕 The crater is most commonly referred to simply as the Ries or Ries crater. The original crater rim had an estimated diameter of . The present floor of the depression is about below the eroded remains of the rim. It was originally assumed that the Ries was of volcanic origin. In 1960 Eugene Shoemaker and Edward C. T. Chao showed that the depression was caused by meteorite impact.〔E.M. Shoemaker and E.C.T. Chao (1961). ''New Evidence for the Impact Origin of the Ries Basin, Bavaria, Germany.'' J. Geophys. Res., 66(10), 3371–3378. 〕 The key evidence was the presence of coesite, which, in unmetamorphosed rocks, can only be formed by the shock pressures associated with meteorite impact. The coesite was found in the locally derived suevite building stone of the Nördlingen town church.〔"Exploring Space: The Quest for Life", 2005, Nova.〕 The suevite was formed from mesozoic sediments shocked by the bolide impact.〔Johannes Baier: ''Die Auswurfprodukte des Ries-Impakts, Deutschland'', in ''Documenta Naturae'', Vol. 162, München, 2007. ISBN 978-3-86544-162-1; Johannes Baier: ''Zur Herkunft der Suevit-Grundmasse des Ries-Impakt Kraters'', in ''Documenta Naturae'', Vol. 172, Munich, 2008. ISBN 978-3-86544-172-0〕〔Johannes Baier: (''Die Bedeutung von Wasser während der Suevit-Bildung (Ries-Impakt, Deutschland)'' ). - Jber. Mitt. oberrhein. geol. Ver., N. F. 94, 55-69, 2012.〕 Another impact crater, the much smaller (3.8 km diameter) Steinheim crater,〔Johannes Baier & Armin Scherzinger: (''Der neue Geologische Lehrpfad im Steinheimer Impakt-Krater'' ). - Jber. Mitt. oberrhein. geol. Ver, N. F. 92, 9-24, 2010.〕 is located about west-southwest from the centre of Ries. The two craters are believed to have formed nearly simultaneously by the impact of a binary asteroid. Recent computer modeling of the impact event indicates that the impactors probably had diameters of about (Ries) and (Steinheim), had a pre-impact separation of some tens of kilometers, and impacted the target area at an angle around 30 to 50 degrees from the surface in a west-southwest to east-northeast direction. The impact velocity is thought to have been about . The resulting explosion had the power of 1.8 million Hiroshima bombs, an energy of roughly 2.4 joules. The Ries crater impact event is believed to be the source of Moldavite tektites found in Bohemia and Moravia (Czech Republic).〔Günther Graup, Peter Horn, Horst Köhler & Dieter Müller-Sohnius: Source material for moldavites and bentonites. In Naturwissenschaften. Vol. 67, Berlin, 1981.〕 The tektite melt originated from a sand-rich surface layer that was ejected to distances up to downrange of the crater. Stone buildings in Nördlingen contain millions of tiny diamonds, all less than across. The impact that caused the Nördlinger Ries crater created an estimated of them when it impacted a local graphite deposit. Stone from this area was quarried and used to build the local buildings.〔John Emsley (2001). ''Nature's Building Blocks''. Oxford University Press, pp. 99. ISBN 0-19-850341-5.〕 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「Nördlinger Ries」の詳細全文を読む スポンサード リンク
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