Distinguishing ice-rich and ice-poor permafrost to map ground temperatures and ground ice occurrence in the Swiss Alps
2019
Abstract. Mountain permafrost is invisible, and mapping it is still
a challenge. Available permafrost distribution maps often overestimate the
permafrost extent and include large permafrost-free areas in their
permafrost zonation. In addition, the representation of the lower belt of
permafrost consisting of ice-rich features such as rock glaciers or ice-rich
talus slopes can be challenging. These problems are caused by considerable
differences in genesis and thermal characteristics between ice-poor
permafrost, occurring for example in rock walls, and ice-rich permafrost.
While ice-poor permafrost shows a strong correlation of ground temperature
with elevation and potential incoming solar radiation, ice-rich ground does
not show such a correlation. Instead, the distribution of ice-rich ground is
controlled by gravitational processes such as the relocation of ground ice
by permafrost creep or by ground ice genesis from avalanche deposits or
glacierets covered with talus. We therefore developed a mapping method which distinguishes between ice-poor
and ice-rich permafrost and tested it for the entire Swiss Alps. For
ice-poor ground we found a linear regression formula based on elevation and
potential incoming solar radiation which predicts borehole ground
temperatures at multiple depths with an accuracy higher than 0.6 ∘ C. The zone of ice-rich permafrost was defined by modelling the deposition
zones of alpine mass wasting processes. This dual approach allows the
cartographic representation of permafrost-free belts, which are bounded
above and below by permafrost. This enables a high quality of permafrost
modelling, as is shown by the validation of our map. The dominating
influence of the two rather simple connected factors, elevation (as a proxy
for mean annual air temperature) and solar radiation, on the distribution of
ice-poor permafrost is significant for permafrost modelling in different
climate conditions and regions. Indicating temperatures of ice-poor
permafrost and distinguishing between ice-poor and ice-rich permafrost on a
national permafrost map provides new information for users.
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