In the high Alps, where snow and ice have long provided a stable foundation, a quiet but growing crisis is reshaping the landscape. Permafrost, a layer of soil or rock that remains below freezing for at least two years, is warming at an alarming rate. In the Alps, this frozen ground is found at different altitudes depending on the slope's orientation. North-facing slopes can have permafrost as low as 1,900 meters, while south-facing slopes require climbing to around 2,300 meters. At higher elevations, permafrost becomes more continuous. However, as global temperatures rise, this once-stable foundation is beginning to melt, triggering rockfalls and threatening the safety of both people and structures. The warming of Alpine permafrost has been measured at more than 1 degree Celsius per decade at a depth of 10 meters. As the ice that once acted as a natural cement between rock fragments melts, it weakens the structure of the mountain. This leads to large-scale rockfalls, some as big as several thousand cubic meters. In Switzerland, more than a third of mountain huts are now at risk of collapse or damage due to permafrost thaw, prompting efforts to relocate or reinforce them. One example is the Rothorn hut near Zermatt, which was moved from its original location to avoid the threat of melting permafrost. To better understand the changes happening beneath the surface, scientists have set up monitoring systems in key areas of the Alps. At the Aiguille du Midi, a high-altitude peak in the French Alps, researchers have measured significant temperature differences between shaded and sunny sides of the mountain, with temperatures varying by up to 3 degrees Celsius at a depth of 10 meters. In other areas, such as the Deux-Alpes region, long-term measurements show that permafrost is warming even at depths of 30 meters. These observations are part of a broader network known as PermaFRANCE, which tracks changes in frozen ground across the region. The consequences of this thaw are not limited to huts and research stations. Classic climbing routes, such as the normal route up Mount Blanc, have been closed due to the increased risk of falling rocks. In 2026, the Tête Rousse and Goûter huts—key stops on the route—were shut down by local authorities after a series of rockfalls. Mountain guides have had to adjust their practices, often starting climbs earlier in the day to avoid unstable conditions. Infrastructure such as cable cars, power lines, and ski resort access roads, built on or near permafrost, are also being re-evaluated for safety. The long-term implications of this warming are still uncertain. Many mountain huts built in the 1960s and 1970s assumed that permafrost would remain stable indefinitely. Now, with permafrost thawing at an accelerating pace, the question of how many of these structures will need to be relocated looms. As the Intergovernmental Panel on Climate Change (IPCC) has noted, the decline of glaciers, snow, and permafrost is likely to increase risks for mountain communities, with more frequent landslides and rockfalls. The story of the Alps' changing permafrost is only just beginning to be told, but the mountain itself has been writing it for much longer.