Distinguishing ice-rich and ice-poor permafrost to map ground temperatures and ground ice occurrence in the Swiss Alps

摘要

Mountain permafrost is invisible, and mapping it is stilla challenge. Available permafrost distribution maps often overestimate thepermafrost extent and include large permafrost-free areas in theirpermafrost zonation. In addition, the representation of the lower belt ofpermafrost consisting of ice-rich features such as rock glaciers or ice-richtalus slopes can be challenging. These problems are caused by considerabledifferences in genesis and thermal characteristics between ice-poorpermafrost, occurring for example in rock walls, and ice-rich permafrost.While ice-poor permafrost shows a strong correlation of ground temperaturewith elevation and potential incoming solar radiation, ice-rich ground doesnot show such a correlation. Instead, the distribution of ice-rich ground iscontrolled by gravitational processes such as the relocation of ground iceby permafrost creep or by ground ice genesis from avalanche deposits orglacierets covered with talus. We therefore developed a mapping method which distinguishes between ice-poorand ice-rich permafrost and tested it for the entire Swiss Alps. Forice-poor ground we found a linear regression formula based on elevation andpotential incoming solar radiation which predicts borehole groundtemperatures at multiple depths with an accuracy higher than 0.6 ∘C. The zone of ice-rich permafrost was defined by modelling the depositionzones of alpine mass wasting processes. This dual approach allows thecartographic representation of permafrost-free belts, which are boundedabove and below by permafrost. This enables a high quality of permafrostmodelling, as is shown by the validation of our map. The dominatinginfluence of the two rather simple connected factors, elevation (as a proxyfor mean annual air temperature) and solar radiation, on the distribution ofice-poor permafrost is significant for permafrost modelling in differentclimate conditions and regions. Indicating temperatures of ice-poorpermafrost and distinguishing between ice-poor and ice-rich permafrost on anational permafrost map provides new information for users.