Nördlinger Ries

For human settlement within the Nördlinger Ries region, see Donau-Ries. Nördlinger RiesRelief map of Nördlinger RiesLocation within GermanyLocationNördlingen, Donau-Ries, Bavaria and Baden-Württemberg, Germany48°53′N 10°34′E / 48.883°N 10.567°EImpact crater structureConfidenceConfirmedDiameter24 km (15 mi)Age14.808 ± 0.038 Ma, Middle MioceneExposedYesDrilledYesBolide typeAchondrite Satellite image of the Nördlinger Ries (large circular structure on the right) and the Steinheim Basin (lower left) The Nördlinger Ries (German pronunciation: [ˈnœʁtlɪŋɐ ˈʁiːs]) is an impact crater[1] and large circular depression in western Bavaria and eastern Baden-Württemberg. It is located north of the Danube in the district of Donau-Ries. The city of Nördlingen is located within the depression, about 6 kilometres (3.7 mi) south-west of its centre. Ries is derived from Raetia, since the tribe of Raetians lived in the area in pre-Roman times.[2][3] View of Nördlinger Ries Suevite from Nördlinger Ries The depression is a meteorite impact crater formed 14.808 ± 0.038 million years ago in the Miocene.[4][5] The crater is most commonly referred to simply as the Ries crater or the Ries. The original crater rim had an estimated diameter of 24 km (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, glacial or tectonic origin. Oliver Sachs introduced, in this context, the term "pioneer era" (up to 1870) and marked the beginning of early modern research on the Ries (from 1870), meaning the period when the first detailed theories about the formation of the Nördlinger Ries became known.[6][7][8] In 1960 Eugene Shoemaker and Edward C. T. Chao showed that the depression was caused by meteorite impact.[9] 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 suevite from Otting quarry,[10][9] but even before, Shoemaker was encouraged by St. George's Church in Nördlingen, which is built of locally derived suevite.[10] The suevite was formed from mesozoic sediments shocked by the bolide impact.[11][12][13] The Ries impact crater was a rampart crater, thus far a unique finding on Earth.[14] Rampart craters have almost exclusively been found on Mars. Rampart craters exhibit a fluidized ejecta flow after the impact of the meteorite, most simply compared to a bullet fired into the mud, with the ejecta resembling a mudflow. Another impact crater, the much smaller (3.8 km (2.4 mi) diameter) Steinheim crater,[15] is located about 42 km (26 mi) west-southwest from the center of Ries. It had previously been thought that the two craters formed simultaneously by the impact of a binary asteroid 14.8 million years ago, but a study published in 2020 suggests that Steinheim could actually be about 500,000 years younger than Nördlinger Ries.[16] Recent computer modeling of the impact event indicates that the impactors probably had diameters of about 1.5 km (4,900 ft) (Ries) and 150 m (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.[citation needed] The impact velocity is thought to have been about 20 km/s (72,000 km/h; 45,000 mph).[citation needed] The resulting explosion had the power of 40 million Hiroshima bombs, an energy of roughly 2.4×1021 joules.[citation needed] The Ries crater impact event is believed to be the source of moldavite tektites found in southern Bohemia and Moravia (Czech Republic).[17] The tektite melt originated from a sand-rich surface layer that was ejected to distances up to 450 km (280 mi) downrange of the crater. The shape of the strewnfield suggests that the direction of impact was from the west-southwest.[18] Stone buildings in Nördlingen contain millions of tiny diamonds, all less than 0.2 mm (0.008 in) across. The impact that caused the Nördlinger Ries crater created an estimated 72,000 tonnes (72,000,000 kg) of them when it impacted a local graphite deposit. Stone from this area was quarried and used to build the local buildings.[19] After the impact, the crater filled with water, forming a lake ~400 km2 in area, almost the size of Lake Constance.[20] The lake silted up after about two million years. The present Ries basin was only exposed by erosion during the Ice Ages.[21] The Ries impact (also known as the Ries event) was an asteroid impact that occurred approximately 15 million years ago in what is now southern Germany.[22] The resulting impact crater, the Nördlinger Ries, has a diameter of about 24 km (15 mi), indicating the release of an enormous amount of energy. The nearby Steinheim Basin and a number of smaller craters on the Franconian Jura and in the Lake Constance area are, according to more recent findings, not contemporaneous with the Nördlinger Ries and are therefore not part of the Ries event.[23] The Nördlinger Ries is one of the best-studied impact craters on Earth. Since 1960, when it was proven that the formation of the Ries crater resulted from the impact of an asteroid,[24] scientists have developed a highly detailed understanding of the events that took place during its formation 14.6 ± 0.2 million years ago[25] (during the Miocene Langhian stage).[26][27][28][29] A recent geophysical study was able to demonstrate, based on the different impact rocks, that the Ries impactor struck from the north-northwest.[30][31] In just a few seconds, a celestial body — an asteroid approximately 1.5 km (0.93 mi) in diameter — travelling at 20 km/s (72,000 km/h or 45,000 mph) passed through the Earth's atmosphere. As a meteor whose apparent magnitude exceeded that of the Sun, it approached the Earth's surface almost undamped from a westerly direction.[32] The much smaller Steinheim Basin, located about 40 km (25 mi) southwest and formed by a second body, is now known to be several hundred thousand years younger and thus not contemporaneous. Fractions of a second before the asteroid hit the surface at an angle of about 30°, the air between the asteroid and the ground was compressed and heated. Surface soil, sand, and gravel instantly vaporised and, together with the compressed air, were forced sideways from beneath the asteroid in a process known as jetting. Molten surface material was ejected at high velocity up to 450 km (280 mi) away. The melted sands came to rest in a confined area in what is now Bohemia and Moravia, where these solidified melt droplets, known as moldavites, are still found today.[33] The impactor penetrated the Mesozoic sedimentary cover and reached a depth of about one kilometre into the crystalline basement. The total penetration depth is estimated at approximately 4 km.[34] Both the asteroid and the surrounding rock were compressed to less than half their original volume. At pressures of several million bar (500 GPa) and temperatures up to 30,000 °C, the asteroid and the surrounding rock vaporised almost instantly, within fractions of a second after contact. The shock wave propagated through the rock around the impact site at supersonic speed. With increasing distance, the stress on the rocks from pressure and temperature decreased; the rocks were only partially melted or transformed under high pressure and high temperature. Through the process known as shock-wave metamorphism, quartz was converted into coesite or stishovite, and diaplectic glasses also formed. For kilometres around the impact point, the rock was deformed and liquefied under the extreme pressure. Approximately two seconds after impact, the main excavation phase began: once the shock wave had passed, the rock rebounded, the new crater floor rose, and a central uplift formed in the centre. Debris from inside the crater was ejected in the form of a conical curtain (ejecta curtain) along ballistic trajectories, while in the crater rim zone larger blocks were pushed across the surface (roll-glide mechanism).[35] During ejection, rocks from a wide variety of stratigraphic levels were mixed together and formed a continuous ejecta blanket extending up to 40 km from the crater, initially reaching thicknesses of up to 100 metres. Today, these ejecta deposits surrounding the Ries crater are known as the Bunte Breccia (colourful breccia). The explosion, whose energy was equivalent to several hundred thousand Hiroshima bombs, excavated a transient crater approximately 8 km in diameter and 4 km deep. The fireball rose from the crater, carrying with it pulverised and partially molten rock.