Deline P. (1), Chiarle M. (2), Curtaz M. (3), Kellerer-Pirklbauer A. (4), Lieb G.K. (4), Mayr V. (5), Mortara G. (2), Ravanel L. (1), 2011, Hazards related to permafrost and to permafrost degradation, pp.67–105, 2011,
URL: http://www.cnr.it/prodotto/i/324013

Rockfalls (<0.1 M m3) generate risks for mountaineering activity in the Alps, while rock avalanches (> 0.1-1 M m3) can threaten valley inhabitants at very long distance from the source area. Permafrost is present in Alpine rockwalls at high elevation (e.g. above c. 3000 m and 3500 m a.s.l. on north- and south-facing slopes, respectively). Its climatically-driven degradation is probably one of the main triggers of recent, present and future rockfalls and rock avalanches. Rockwall permafrost and its degradation are not directly observable. Monitoring with temperature sensors at different depths, aspects, and slope angles, and with geophysical methods (PermaNET WP4), and rock temperature modelling (PermaNET WP5) are crucial. But the relationship between permafrost changes and high mountain rockwall instability remained for a long time not well-established, because_ · Frequency and volume of instability events in high mountains are poorly known because of the lack of systematic observations. · Physical processes linking permafrost, its degradation and rockfalls are not fully understood. The hypothesis that the increase of high mountain rockwall instability relates to permafrost changes gains recently force because_ · Massive ice was observed in several starting zones; · Mean annual air temperature has increased by more than 1°C in the Alps during the 20th Century, with an accelerated warming trend since the 1980s, whereas ice-bonded joints and water-saturated rock become weaker in 'warm' permafrost (i.e. close to 0°C). Studies establish a clear relationship between climate and rockfall occurrence in the Mont Blanc massif_ · After the end of the Little Ice Age (1860), rockfalls started at the end of the 1940s, in correspondence with a very warm period. After this 1rst peak, rockfall frequency increased continuously since the 1970s. · Hottest summers (1976, 1983, 2003, 2009) were characterized by a very high rockfall frequency. · In some cases (Drus), rockfall magnitude tends to increase from 1950 to 2005. Our different study cases (Mont Blanc massif, Matterhorn, Mt. Mittlerer Burgstall) suggest that_ · Elevation of scars is often close to the lower limit of the permafrost (depending on aspect and slope), where its degradation is more active. · Ridges, spurs, and pillars are prone to collapse, probably because of heat fluxes from well-exposed rock faces. Snow cover, controlled by the slope and the wind, is an important control factor of the permafrost degradation in rockwalls.

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