The origin of the Nördlinger Ries

About 14.5 million years ago an asteroid, about 1 kilometre in size, accompanied by a 150 m sized satellite, races towards the Earth (Figure 1). Both crash at a speed of more than 70,000 km/h into the Alb and create two craters with diameters of 25 and 4 km, respectively: The “Nördlinger Ries” and the “Steinheim Basin”.

At the point of impact the pressure reaches several million bar and the temperature is more than 20,000 °C (Figure 2). The asteroid and parts of the target rock immediately vaporize or melt. A pressure front (shock wave) races at supersonic speed through the lower parts of the target (Figure 3) and causes severe effects on the rocks, e.g. the formation of high-pressure minerals such as coesite, stishovite and diamond. In the first few seconds after impact a transient crater with a depth of 4.5 km is formed (Figure 4). The ejected rock masses are deposited as a coherent ejecta blanket (Bunte Breccia), extending as far as 50 km from the point of impact. At the same time a plume of hot ejecta shoots into the atmosphere.

The deep crater existed only for a few seconds. The floor of the crater where rocks of the crystalline basement are exposed rises up in the centre of the crater (Figure 5). At the same time, large blocks of rock slide down the steep sides of the crater wall, thereby enlarging the crater so that the original crater wall becomes more and more obscured. The central uplift collapses and forms an elevated inner ring inside the enlarged flat crater. The rock movements end after only a few minutes. On the floor of the transient crater a turbulent flow of molten and fractured rocks forms a thick layer of suevite. Meanwhile the hot vapor cloud collapses depositing another layer of suevite in the crater on top of the suevite formed by ground surging. In addition suevite is deposited on top of the ejecta blanket outside the crater in some isolated areas (Figure 6).

Scientists point out that the Ries was created by the impact of an asteroid. Colloquially an asteroid is often referred to as a “meteorite” although this is not strictly correct. For this reason, however, we will also occasionally refer to a “meteorite” in our descriptions.

Phase 1: ´35 milliseconds before impact

Phase 4: Formation of the deep “transient crater” after about 10 seconds

Phase 2: 10 milliseconds after impact

Phase 5: Collapse of the “transient crater” and deposition of ejected rock masses after 1 minute

Phase 3: Beginning of crater formation after 60 milliseconds

Phase 6: End of crater formation and deposition of suevite after 10 minutes

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