Abstract Karst landscapes and karst aquifers, which are composed of a variety of soluble rocks such as salt, gypsum, anhydrite, limestone, dolomite and quartzite, are fascinating areas of study. As karst rocks are abundant on the Earth’s surface, the fast evolution of karst landscapes and the rapid flow of water through karst aquifers present challenges from a number of different perspectives. This collection of 25 papers deals with different aspects of these challenges, including karst geology, geomorphology and speleogenesis, karst hydrogeology, karst modelling, and karst hazards and management. Together these papers provide a state-of-the-art review of the current challenges and solutions in describing karst from a scientific perspective.

Abstract The development of subsurface voids and cavities in soluble rocks is controlled by the hydrological and chemical processes in the host rock. Water (enriched with carbon dioxide) percolates through fractures and bedding partings of the host rock and removes material from the rock surface. As this enlargement is a highly heterogeneous process, only some fractures and bedding partings become significantly enlarged, evolving towards larger voids and caves. The size of the enlarged voids, often reaching the metre scale, can result in mechanically unstable structures, which, when close to the surface, are prone to collapse and thus are a hazard to infrastructure. We explored two caves in the anhydrite host rock of the Permian Zechstein sequences in northern Germany using geophysical measurements: the Kalkberghöhle close to Bad Segeberg (Hamburg region) and the Jettenhöhle close to Osterode (Harz region). Based on the results of gravity and electrical measurements, we were able to identify the cave voids and to characterize the local geological setting. Using these indirect geophysical observations, we deduced a structural model for both cave sites by numerical modelling. Our structural models were successfully calibrated against the Bouguer gravity data.