Thawing of the permafrost
Depending on the geographical orientation, the soil at altitudes above 2,400 metres in Switzerland is permanently frozen. This phenomenon is known as permafrost. Due to climate change, the permafrost limit could rise in the decades to come. The thawing process could trigger rockfall and rock avalanches, landslides and debris flows in the mountains.
The thaw layer is an indicator of the thermal activity in the permafrost. If the soil that is usually frozen warms up, the thaw layer increases in size. This increase is caused not only by the rise in air temperature but also by changes in the temporal distribution of the insulating snow cover over the course of the year. Early snow cover in the autumn can trap the summer heat in the soil. As opposed to this, the persistence of the snow cover in spring forms a shield against the heat and sun rays and the low winter temperatures influence the frozen soil for longer.
During the heatwaves of 2003, the thaw depth was considerably greater in two measurement locations – i.e. Mount Schilthorn and Barba Peider – than in other years. The extreme values recorded in 2003 were not repeated in the subsequent years. However, in the hot year of 2014, the values of all previous years, including 2003, were exceeded at three locations: Murtel-Corvatsch (4.2 m), Gentianes (4.4 m) and Schilthorn (8.9 m).
Based on the knowledge currently available, the permafrost presents a very delayed reaction to climate change with increasing depth. Thus the melting of the permafrost located deep in the underground could take decades or centuries.
In addition to the thaw layer, temperature changes in the borehole are a relevant indicator of the state. Many permafrost boreholes are exhibiting a warming trend at the 5-10 m depth. This trend has increased in recent years. Additionally, most rock glaciers are exhibiting increased activity and a higher speed. Some exceptions may exist and can be explained by local effects.
- Related indicators
- Annual mean temperature
Permafrost measurements are coordinated in Switzerland by PERMOS (Permafrost Monitoring Switzerland). The PERMOS monitoring network is composed of borehole locations that record the temperature at a specific depth of a borehole ("borehole logging") so that the maximum thaw depth can be ascertained. The monitoring network also includes dynamic-kinematic locations where geomorphological observations are recorded, particularly of rock glaciers, debris flows and rockfalls.