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 6 kilometers (3.7 mi) 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.
The depression is interpreted as a meteor impact crater formed about 14.3 million–14.5 million years ago in the Miocene.[1] [2] The crater is most commonly referred to simply as the Ries or Ries crater. The original crater rim had an estimated diameter of 24 kilometers (15 mi). The present floor of the depression is about 100 to 150 m (330 to 490 ft) below the eroded remains of the rim.
It was originally assumed that the Ries was of volcanic origin. In 1960 Eugene Shoemaker and a colleague showed that the depression was caused by meteorite impact. The key evidence was the presence of coesite (shocked quartz), which, in natural unmetamorphosed rocks can only be formed by the shock pressures associated with meteorite impact. The coesite was found in the building stone (suevite) of the Nördlingen town church, constructed from locally derived stone.[3] The suevite was formed from mesozoic sediments. [4] [5]
Another impact crater, the much smaller (3.8 km diameter) Steinheim crater[6], is located about 42 km (26 mi) 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 1.5 kilometers (4,900 ft) (Ries) and 150 meters (490 ft) (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 20 km/s (45,000 mph). The resulting explosion had the power of 1.8 million Hiroshima bombs, an energy of roughly 2.4x10^21 joules.
The Ries crater impact event is believed to be the source of moldavite tektites found in Bohemia and Moravia (Czech Republic). [7] The tektite melt originated from a sand-rich surface layer and was ejected to distances up to 450 km (280 mi) downrange of the crater.
Stone buildings in Nördlingen contain millions of tiny diamonds, all less than 0.2 mm (0.0079 in) across. The impact that caused the Nördlinger Ries crater created an estimated 72,000 tonnes (79,000 short tons) of them when it impacted a local graphite deposit. Stone from this area was quarried and used to build the local buildings.[8]
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