Robert Kenner is an enthusiastic permafrost researcher. For the past eight years at SLF, his focus has been on the permanently frozen ground in the Swiss Alps – for example, in the Ritigraben near Grächen (Canton Valais). There, over the past thousands of years, a rock glacier has formed, consisting of a mixture of debris and ice.
Rock glaciers creep slowly down towards the valley. In recent decades, however, they have been moving faster due to climate change. This increases the risk of natural hazard events. Robert explains: “The faster a rock glacier creeps, the more likely rockfall and debris flows become.”
Using measurements in boreholes, as well as laser scans, aerial photography and GPS, Robert found that the rock glacier in the Ritigraben is moving mainly in a layer about 20 metres deep, the so-called shear horizon. The rock glacier is now creeping four times faster than in the year 2000, and its movements have a distinctly seasonal pattern. It reaches the highest velocities between August and November, before slowing down in winter up until the beginning of the snow-melt, when it quickly accelerates again. Moreover, after heavy rainfall, the rock glacier may, for a short period, move 16 times faster than normal.
Water seems to play an important role in influencing the creeping velocity. Robert: “We assume that rain and melt-water can penetrate the rock glacier more easily today than previously because the ice has become warmer with climate change.” This leads to less friction in the shear horizon and thus an increase in the creep velocity. Some rock glaciers are depositing more debris in steep channels – and thus further increasing the risk of rockfall and debris flows. (Christine Huovinen, Diagonal 1/18)