Since 1996, we have instrumented boreholes at more than twenty permafrost locations in the Swiss Alps. Our permafrost measurement network provides essential information about the state of the permafrost and helps to understand the complex interactions between the ground surface and the underlying substrate.
Most of the boreholes are located in ice-bearing scree slopes, rock walls and rock glaciers and in the immediate vicinity of buildings and other structures at high elevations. We measure the temperatures inside the boreholes, as well as at the ground surface. We often gather data on snow depth, air temperature and radiation from an automatic weather station nearby. SLF’s measurement network extends over large parts of the Swiss Alps and is partly incorporated into PERMOS, the Swiss Permafrost Monitoring Network.
The measurements are used to study the impact of the climate on permanently frozen ground and improve the forecasting of events such as natural hazards or damage to structures. We examine the depth of the active layer, the thermal regime of the permafrost and the intensity of slope movements. As well as looking at long-term changes, we also record and analyse the impact of extreme events, such as the summer 2015 heat wave. We need these data in order to simulate future ground temperature patterns with numeric models. Such analysis requires long, high-quality data series with as few gaps as possible. This is a major challenge for the manufacturers of measuring instruments, since instruments at high elevations are exposed to harsh conditions – including cold, snow pressure, avalanches, lightning and rockfall.
Response time in the ground
We compare the permafrost temperatures at the various locations at depths of at least 10 m, where they are not influenced by factors near the surface, such as daily fluctuations in temperature. At this depth, it takes around six months for a response to seasonal influences at the ground surface to be registered. This means that at a depth of 10 m, the response to the summer’s conditions will only be seen the following winter. Depending on the elevation and the local conditions, the temperatures measured at a depth of 10 m are more or less between -3°C and 0°C. Alongside air temperature and radiation, snow distribution has a major influence on the ground surface temperature: snowy winters induce higher ground temperatures, while less snow makes for lower ground temperatures.
Impact of climate change on permafrost
It is difficult to make general assertions about the state of the permafrost in the Alps because ground temperatures and ice content can vary greatly depending on the location and the local conditions. Nevertheless, it has been confirmed that the permafrost is warming, and that this is causing ice loss, slope movements and infrastructure instability in some places. This trend is especially pronounced in rock walls: since they have good heat transfer properties, they respond more quickly and more directly to changes in the climate than e.g. scree slopes. Extremely hot summers may accelerate this development considerably.