Roaming Ries Crater

Posted on May 8, 2024 by stephhalwa
The group of students and staff who attended the Ries Crater field course. They are siting at the top of a hill in Wallerstein, which is located on the inner peak ring in Ries. 

In early April, some of the University of Manchester Planetary Geology pathway students in their 3rd year took a trip to explore the formation and geology of Ries Crater in southern Germany. The group stayed in the quaint Bavarian town of Nördlingen, which is about the same size (~1 km in diameter) as the impactor which formed the crater. Ries crater formed ~14.8 million years ago (Schwarz et al., 2020) from the collision of an extra-terrestrial impactor. The resulting explosion from the impact event likely rivalled the power of 250 000 atomic bombs (Böhme et al., 2002), obliterating all life within a radius of 100 000 km. The site has been popular as an analogue for training astronauts and was visited by Apollo 14 astronauts Alan Shepard and Edgar Mitchel in 1970.

The town of Nördlingen as seen from the top of St George’s Church, which is situated within (slightly SW of the centre) Ries crater.

The group started off looking at the suevite, a rock type which is famous for only being found at Ries crater. Suevite is an impactite, a rock which is formed from deposition during the impact event. The town church (St. George’s church) is famous for being built out of suevite. The group were then taken to various field sites and quarries, where different impact rock types were exposed, including the famous ‘bunte’ breccia – Bunt means colourful in German, these deposits originate from different rock formations of different colours, hence appear colourful.

A fragment of suevite, which is an impactite formed during the impact event. This rock consists of clasts of target lithologies (different types of rocks present before the impact), and melted material held together in a light-coloured matrix. The clasts are mostly (90-95 %) crystalline igneous rocks (e.g. granites) which are excavated from the deepest parts of the crater.
The students investigating the outcrop at Wengenhausen, which is near the inner ring of the Ries impact crater. The white rock on the left of the cliff face is brecciated granite, while the yellowish rock on the right is polymict (lots of different types of clasts) impact breccia. The yellow bed above the granite is post-crater lake limestone, deposited from the lake which filled the crater long after the impact event.

The group prevailed through various weather conditions, both very hot and very cold and windy, with only minor sunburns, and lots of rocks (especially shatter cones) as bounties for their efforts.

The last site was a small crater close to Ries called Steinheim, where the students wandered round finding impactites to add to their rock collections. Here they are comparing who found the best shatter cone (picture below).
An example of a shatter cone found in Steinheim crater. Shatter cones form in the rock beneath the impact. Their appear in a conical shape with thin grooves, which is the result of shock waves travelling through the rock (Sagy et al., 2004). They form when a rock is exposed to pressures between 2- 30 Pa (Pascals), and thus are only related to nuclear explosions and meteorite impact events.

References

Böhme, M., Gregor, HJ., Heissig, K. (2002). The Ries and Steinheim Meteorite Impacts and their Effect on Environmental Conditions in Time and Space. In: Geological and Biological Effects of Impact Events (eds. Buffetaut, E., Koeberl, C.). Impact Studies. Springer, Berlin, Heidelber.

Sagy, A., Fineberg, J., Reches, Z. (2004). “Shatter cones: Branched, rapid fractures formed by shock impact”. Journal of Geophysical Research. 109 (B10): B10209. 

Schwarz, W. H., Hanel, M., Trieloff, M. (2020). U‐Pb dating of zircons from an impact melt of the Nördlinger Ries crater. Meteoritics & Planetary Science. 55 (2): 312–325 

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