The fracture, which runs vertically through the limestone summit, is now measured at more than two meters wide and approximately 100 meters deep. Other recent measurements describe the main fracture as 40 meters long, 8 meters deep, and 3 meters wide. These large fractures in the summit area were first documented in the late 19th century, but a progressively accelerating rockslide has developed since the 1950s. In 2018, the main fracture on the southeast side had already opened by 2 to 4 meters, with dimensions of roughly 5 meters in width and 30 meters in length. Since then, the crack has continued to open at a rate of a few millimeters per month. Heavy rainfall in June and rising temperatures are believed to have accelerated this process recently.
The geological structure of the Hochvogel presents specific vulnerabilities. The peak features extensive vertical fractures that run perpendicular to the general dip of the rock, creating an intensely fractured fabric. Scientists have identified about six subunits of rock, ranging in volume from 8,000 to 148,000 cubic meters, located along a failure plane on two large, northeast-to-southwest trending fracture systems. If a full collapse were to occur, up to 260,000 cubic meters of limestone debris could fall into the Hornbach Valley in Austria. The main sliding plane extends more than 60 meters downwards, with a minimum surface area of 2,000 square meters.
Seismic Monitoring of “Stick-Slip” Motion
To track these changes, authorities have installed a network of seismic stations equipped with a real-time high-alpine monitoring system. Lead author Michael Dietze, a post-doctoral researcher at the GFZ Helmholtz Centre Potsdam, noted that this technology allows for the first time a continuous, near real-time sensing and recording of the cyclical phenomena occurring within the rock. “We can now for the first time sense, record and process this cyclical phenomenon continuously and almost at real time,” Dietze said.
The data reveals a recurrent sawtooth-like frequency pattern in seismic activity. Researchers attribute the rise in frequency to stress increases within the rock mass. When the frequency drops, sensors record an increased rate of crack cues, a phenomenon associated with rock being torn apart. This cyclical increase and decrease of stress through jerky movement is known as stick-slip motion, which is considered a typical precursor to large mass movements. While the southern part of the mountain has already subsided by several meters in recent years, scientists remain divided on whether the rock falls will continue gradually or result in a single, catastrophic collapse. However, the consensus among the researchers is that the mountain will eventually collapse in the form of a landslide.
The discovery of additional instability has not been limited to the summit. Kristian Rath, a local mountaineer and author, recently identified a new crack on the neighboring Kesselspitze peak. He forwarded his observations to the geologists at the Technical University of Munich, who are already closely monitoring the Hochvogel. Professor Michael Krautblatter, a landslide expert at the university, acknowledged the importance of such local observations, noting that frequent hikers often notice changes before they are detected by remote sensors. However, Krautblatter cautioned against jumping to conclusions, pointing out that while the Hochvogel is under intense scrutiny due to its specific geometry and history, cracks are common throughout the Alpine region.
Broader Implications for Alpine Safety
The Hochvogel serves as a focal point for understanding how extreme weather and climate shifts are making the Alps more dangerous. The combination of droughts, heat, and intense rainfall events is exacerbating the destabilization of fractured rock masses. While rock falls have already begun, authorities state there is currently no threat to the population living in the surrounding areas. The threatened zones include the Zugspitze area in Germany and the Hornbach Valley in Austria.
The situation at the Hochvogel highlights the increasing difficulty of predicting geological events in a warming climate. As temperatures rise and precipitation patterns become more erratic, the forces acting on these mountain structures are intensifying. The continuous monitoring of the Hochvogel provides critical data for understanding the mechanics of mountain collapse, offering insights that may help safeguard other vulnerable alpine environments. The next phase of assessment will focus on whether the current acceleration continues, potentially altering the timeline for the predicted collapse of the summit.
