Rocks in focus: Geologists warn of dangers in Saxon Switzerland

Rocks in focus: Geologists warn of dangers in Saxon Switzerland

Since the fire in Saxon and Bohemian Switzerland in 2022, a team of geologists from Freiburg has been intensively involved in investigating the stability of rocks and the associated dangers for people in the mountains. These fires have not only changed the landscape, but have also caused acute risks in tourist areas such as the Elbe Sandstone Mountains, as [tu-freiberg.de] reports. The TU Bergakademie Freiberg and the TU Dresden are leading the research. They are investigating the influence of such fires on the strength of sandstone and granite, which is of great importance for the safety of hikers and the infrastructure in these regions.

As part of their studies, two projects were dedicated to the investigation of mass movements in mountains. One of these projects is being carried out in collaboration with Charles University in Prague, in particular examining the internal structure of the rocks, including the fortified tower of the Rathen rock stage. Another project with HTW Dresden analyzes mass movements, threats to infrastructure and the stability of embankments in the Caucasus. The data collected flows into a geographic information system (GIS) and into security concepts in order to record the dangers for visitors and residents as precisely as possible.

Investigations and methods

One of the current projects, entitled “Firerisk”, focuses on unconsolidated sandstone rocks in the Elbe Sandstone Mountains. These rocks are characterized by a solid sandstone shell, but their internal structure is often unclear. In order to better understand the structural properties of these rocks, non-destructive methods such as geophysical measurements and image analysis of aerial photographs are being further developed. In addition, large-scale fire tests are planned in which different temperatures and durations will be tested in order to determine the material properties of the sandstone.

The results of this research are crucial for geotechnical fire models that are used to calculate the stability and behavior of rocks and debris flows under different fire scenarios.

Hazard management and preventive measures

The dangers posed by rock falls and mass movements require comprehensive risk reduction measures. According to [geologie.sachsen.de], the initial state of the rock walls should be documented in order to record changes. Experts also recommend hiring an expert to assess the risk, especially in areas at risk of falling rocks or rockslides.

• Absturzgefährdete lose Steine sollten entfernt werden.
• Es empfiehlt sich, Steinschlagschutzgehölze unterhalb der Felswände zu pflanzen.
• Die Errichtung von Schutzzäunen wird ebenfalls als wirksam erachtet.
• Für Neubauten in gefährdeten Bereichen sollten keine Auflasten im Kopfbereich des Hangs vorgenommen werden.

In addition, if there is a low risk of falling rocks, precautionary measures such as solid construction of the walls and roof elements should be taken. Detailed engineering geological investigations are essential in order to adequately assess the risk situation.

The current extreme weather events and the dense population in mountains increase the urgency of these investigations. According to [pollux-fid.de], the risks from rock falls are not only important for forest owners or locals, but also for tourists. Monitoring rock slopes at risk of falling rocks is the central focus of the GeoRiS project, which is funded by the federal states and the European Union. High-resolution photogrammetric measurement methods are used to monitor the development of stability and to initiate targeted safety measures based on this.