100 years of monitoring in the Swiss National Park reveals overall decreasing rock glacier velocities

The rock glaciers of the Swiss National Park were the first in the world where in-situ measurements of surface displacement were undertaken, starting with the pioneering work of Chaix in 1918. Our research is focused on the four rock glaciers described by Chaix, bridging the historical data gap that existed between their early 20th-century measurements and the most recent observations. Through the application of photogrammetric techniques, we geomorphologically analyze the spatiotemporal evolution of rock glaciers in the region, and disentangle the interplay with their adjacent glaciers. We show that these rock glaciers are in different phases of degradation with a general trend of deceleration and loss of volume. Our findings reveal historical kinematic changes influenced by the hydrological contributions of adjacent glaciers, which were closely connected since the Little Ice Age but are now severely degraded. The observed hydrological control, suggests that ongoing climate-induced glacier degradation will likely result in a future scenario with limited new accelerations. Instead, a steady water flow from adjacent glaciers may sustain a gradual secondary creep, progressively slowing as permafrost degradation continues, driven by predicted warming and dry climatic conditions in the Alps.