Crater Formation (Rebecca Smith - USW)
The crater is a complex crater as can be seen in the diagram below which shows a cross sectional view of the crater. It has a central uplift in the middle of a shallow, flat crater floor which is surrounded by the inner ring, megablock zone and the outer crater rim. Central uplifts are made of one or more rings with a peak in the middle and they are composed of rock that has been brought up from great depth. The inner crater basin has been filled in with deposits of suevite, then after the impact lake deposits filled the crater in further. The inner ring is made up of shock metamorphosed material that has been overturned and upturned by the impact. Megablocks are large blocks of rock that were displaced when the crater formed. It is still not known for certain how megablocks are formed but there are two leading theories. The first is that during the crater excavation stage they were thrown out and deposited at the same time as the ejecta blanket. The other theory is that during the modification stage they slumped inwards.
Complex crater formation can be broken down into stages. The first of these is contact with the surface and compression of the rock. A supersonic shock wave is created at the point of contact which goes through the impactor and the surface it has hit. This shockwave compresses the impactor and the target and as a result the target undergoes shock related changes such as transforming the quartz mineral in the rock into shocked quartz and it melts the impactor. Next excavation takes places as the crater grows and material is ejected out, in the Nördlinger Ries impact about 150 km3 of rock wasAn image depicting complex crater formation. thrown out and it fell in the area surrounding the crater up to 40 km away. Near the crater the debris was up to 200m thick. The crater that is created is unstable so modification takes place, during this stage the walls of the crater collapse under gravity and the rim collapses inwards and the centre is uplifted. The central uplift is a result of material attempting to return to a state of gravitational equilibrium. This process is shown in the image above.
This is a cross sectional diagram of the crater showing the structure of the crater and where different types of rock can be found.
"Interesting fact - Many buildings in the town of Nördlinger are made out of stone quarried from the crater. The stone contains millions of tiny diamonds smaller than 0.2 mm in size, so many buildings in Nördlinger have diamonds in their stone".