The Münsterdorf sinkhole cluster: void origin and mechanical failure

Since 2004, collapse sinkholes occur on the sports field of Münsterdorf, a village north of Hamburg in Germany. The sinkholes, around 2-5 m in diameter and 3-5 m deep, develop in peri-glacial sand, which at around 20 m depth is underlain by Cretaceous chalk. The chalk has been pushed up close to the surface by a salt diapir. The sinkhole formation initiated suddenly and occurs with a frequency of one every 2 years. We use a variety of geophysical results (e.g. gravity, electrical resistivity imaging, ground-penetrating radar) from previous fieldwork campaigns together with a new data set from direct-push-based methods to infer mechanical and hydrological properties of the material beneath the sports field (peri-glacial sand, glacial marl, Cretaceous chalk). Based on the derived material properties, we develop a mechanical model for the sinkhole collapse, starting from simple analytical considerations and then moving towards a three-dimensional distinct-element model explaining the sudden onset of collapse sinkholes for the sports field. The mechanical model supports our hypothesis that the sudden onset of sinkholes is triggered by changes in groundwater level.