In a warming atmosphere mountains warm up as well. The permafrost in cold mountains is highly sensitive to such temperature changes. Under frozen conditions, rock strength and slope stability are especially high but now tend to lose this extra-strength with increasing temperatures. With the loss of ice in cracks and fissures of rocks, water can infiltrate, enhance heating and further reduce slope stability.

Permafrost warming at depth takes place via heat diffusion, in places markedly slowed down by latent heat exchange from local ice melt. This extremely slow combination of processes induces strong, deep and long-lasting delays in thermal disturbance at depth. In strongest contrast to glaciers vanishing within decades to a century or two, complete permafrost thawing can take centuries to millennia. Permafrost in cold mountains will still exist – although deeply disturbed - when glaciers will long have disappeared.

Destabilization of the permafrost slope at Kleines Nesthorn initiated the catastrophic destruction by a large rock-ice avalanche of the village of Blatten, Valais Alps, Switzerland, on 28 May 2025. A combined thermo-mechanical 2D model calculation for the detachment zone before its failure indicates a characteristic asymmetric permafrost in a ridge with a warm and a cold side. Depths of permafrost on the cold destabilized slope reached up to more than 100 meters below surface. Since the Little Ice Age, warming and related stability reduction have reached down to roughly 50 - 100 meters below surface, hence affecting large frozen rock masses.

At Kleines Nesthorn, permafrost warming and related mechanical weakening at centennial to decadal and annual time scales may most probably have ultimately triggered the failure of a rock mass, which had reached sub-critical topographic and geological stability conditions through much longer time scales. Such a situation and development in time are likely to occur in many places of the Alps and of cold mountains worldwide.