Station: [27] The Ries Crater

In the middle of the Swabian / Franconian Jura, there’s an unusual, almost circular depression that’s roughly 25 kilometres or 15 miles across. It’s called the "Nördlinger Ries". For a long time, it was thought to be a volcanic crater. But in 1961, US researchers found minute traces of minerals that had been altered by extremely high pressure. It was proof that the Ries was a crater formed by the impact of a large meteorite.

But there were no tangible remains of any meteorite, so the impact theory was long rejected. However, we now know that the energy converted during an impact increases with the size of the meteorite. So during major strikes in particular, the entire body of the meteorite is vaporised.

The Ries impact event generated all the features typical of a relatively large meteorite crater. For instance, you find a complex, unsorted mix of rocks ejected near the surface: what’s known as variegated breccia.

On the other hand, rocks from deeper impact areas have been part vaporised, part melted, or shattered by the shock, right down to their crystal lattice. This type of rock has been given the name "suevite", which is derived from the Latin word for Schwaben, or Suabia. The term is now used all over the world for impact rocks, or impactites, of this type. Previously molten fragments, called "Flädle" for their elongated shape, are especially characteristic of suevite. The shape came about as they were ejected into the air.

As the shock waves from meteorite strikes spread, they may also create impact structures called "shatter cones" in the rock. Finds like these are also regarded as evidence of a meteorite impact.

Other evidence of large impact events involves widely scattered drops of molten material. During the Ries impact, these greenish, solidified vitreous particles were flung as far as the present-day Czech Republic. Based on the area where they were found on the Vltava River, formerly the Moldau, these vitreous rocks are called "Moldavites".

A lake formed in the crater after the impact event. The limestone along the lake shore is rich in fossils. The finds demonstrate that life soon returned to a landscape devastated by the impact.