ROCK/ICE AVALANCHES FROM DEGRADING PERMAFROST INTO NEW LAKES IN DEGLACIATING MOUNTAIN RANGES

Continued atmospheric temperature rise in cold mountains causes rapid vanishing of glaciers but much slower degradation and thawing of permafrost. As a consequence, many still existing glacier and permafrost landscapes are now transforming into new landscapes of bare bedrock, loose debris, sparse vegetation, numerous new lakes and steep slopes with slowly degrading/thawing permafrost. In the European Alps, for instance, present glaciers on average loose about 2 km³ per year from their remaining total ice volume of about 80 ± 20 km³. Already in the second half of the century, less ice could be left in surface than in subsurface ice (recently estimated at about 25 km³). Total future lake volume was modeled to increase to a total volume of few km³. Comparable scenarios are likely to take place in many other cold mountain chains.

During extended future time periods, the new high-mountain landscapes will be characterized by pronounced disequilibria within their geo- and ecosystems, including long-term stability reduction of steep/icy mountain slopes as a slow and delayed reaction to stress redistribution following de-buttressing by vanishing glaciers and to changes in mechanical strength and hydraulic permeability caused by permafrost degradation and thaw. Many of the new lakes and systems of lakes come into existence in close neighborhood to, or even directly at the foot of, deep-frozen slopes with thermal conditions far out of equilibrium and correspondingly decreasing stability. Such conditions are likely to persist for centuries if not millennia to come.

The frequency of high-magnitude rock/ice avalanches seems to rise and the probability of high-magnitude events to reach large water bodies and to cause far-reaching flood waves systematically increases. Options for reduction of long-term risk include adapted spatial planning, early-warning systems, artificial lake-level lowering, and flood retention optimally in connection with multipurpose structures for hydropower production and/or irrigation. A key challenge for scientific research is thereby to define “hot spots” of risk by integrative approaches including process consideration as well as socio-economic vulnerability aspects. This may help deciding where priorities for hazard prevention must be set.