Nordlinger Ries Crater (Rebecca Smith - USW)
The Nördlinger Ries Crater is situated in the south of Germany in the Bavaria state and the centre is about 6km northeast of Nördlinger city as can be seen in the image to the right.The impact was of a 1.5km diameter asteroid travelling at about 72,000 km/h which happened about 14.3 – 14.5 million years ago. The asteroid penetrated 1km into earth’s crust. It is a complex crater and the outer ring has a 25km diameter and the inner crater is 12km in diameter. The impact energy is thought to be roughly equal to the energy of 1.8 million Hiroshima bombs which is 2.4×1021 joules.
"Interesting fact - The two major rock formations that make up part of the ejecta of the crater, the suevite and Bunte breccia were used as training ground for some of the Apollo astronauts".
For over 100 years, until 1960 when Eugene Shoemaker showed that the formation was caused by a meteorite impact, it was assumed that the Ries depression was caused by volcanic activity. There are six pieces of evidence that can be found to prove that a formation was created by an impact and not by a volcanic event and there are as follows:Shatter cones – these are cone shaped structures found in the rock beneath impact craters, the apex (point) of the cone is at the top. A pressure of 2 – 30 Giga Pascals is needed to create these. Only meteorite impacts and underground nuclear explosions can create these features.Multiple planar deformation features – microscopic features in grains of silicate materials such as quartz or feldspar that are caused by a shock wave from the impact.
They are narrow planes of glassy material in parallel sets that have distinct orientation with respect to the crystal structure of the grain.High pressure mineral polymorphs – the high pressures caused by impacts can form high pressure polymorphs of various minerals such as quartz, titanium dioxide and carbon. Quartz can become either coesite or stishovite and carbon can become diamond.Morphometric structures – size, shape and morphology of the structure.Pseudotachylytes and breccias - Pseudotachylytes are fine grained glassy fault rocks that are made up of a very fine grained matrix that occur in veins. Breccia is rock that is made of fragments of minerals or rock held together by a fine grained matrix. They contain contamination of extraterrestrial material such as iridium and osmium anomaliesImpact melt sheets, dikes and melt breccias – A dike is a sheet of rock that has formed in a crack in pre-existing rock. In impacts molten rock caused by the event goes into cracks in pre-existing rock and crystallizes. Melt breccias is similar to breccia apart from the matrix that holds the fragments together. In melt breccia the cementing breccia is made from crystallized impact melt.Two types of titanium dioxide high pressure polymorphs were found at the Nördlinger Ries crater.
Shocked quartz was also found at the Nördlinger Ries crater, shocked quartz is only found at impact sites and not volcanic formations therefore when it was discovered at Nördlinger Ries by Eugene Shoemaker it was proof that this was the result of an impact not volcanic activity. There is impact breccia at the site composed of granite and gneiss along with shatter cones. Computer simulations indicate that the meteor would have been about 1.5 km in diameter and hit the surface at an angle of 30 – 50 degrees and came in from a west-southwest to east-northeast direction. The area that it hit was composed of about 500 – 800m thick sedimentary rock with granite and gneiss underneath.