Geology, glacier retreat and permafrost degradation as controlling factors of slope instabilities in a high-mountain rock wall: the Monte Rosa east face

Abstract

Abstract. The Monte Rosa east face, Italian Alps, is one of the highest flanks in the Alps (2200-4500 m a.s.l.). Steep hanging glaciers and permafrost cover large parts of the wall. Since the end of the Little Ice Age (about 1850), the hanging glaciers and firn fields have retreated continuously. During recent decades, the ice cover of the Monte Rosa east face experienced an accelerated and drastic loss in extent. Some glaciers have completely disappeared. New slope instabilities and detachment zones of gravitational mass movements developed and enhanced rock fall and debris flow activity was observed. This study is based on multidisciplinary investigations and shows that most of the detachment zones of rock fall and debris flows are located in areas, where the surface ice disappeared only recently. Furthermore, most of these detachment zones are located in permafrost zones, for the most part close to the modelled and estimated lower boundary of the regional permafrost distribution. In the view of ongoing or even enhanced atmospheric warming and associated changes it is therefore very likely that the slope instabilities in the Monte Rosa east face will continue to represent a critical hazard source.

Recent and future warm extreme events and high-mountain slope stability

“…The east face of Monte Rosa extends from about 2200 m to over 4600 m a.s.l., and was the site of two spectacular avalanches in 2005 and 2007 (Fischer et al 2006). The slope increases upward, reaching greater than 55 • in the exposed gneissic bedrock sections and greater than 40 • in the sections with glaciers (figure 12).…”

“…Studies based on sequential historical photographs have shown that the ice cover on the east face of the mountain changed a little during the twentieth century until about 1980, when it began to rapidly decrease (Haeberli et al 2002;Fischer et al submitted b). Slope instability involving both ice and rock increased around 1990 and has continued to the present (Fischer et al 2006 The 2005 event was a large ice avalanche (1.1 × 10 6 m 3 ) that initiated from a steep glacier terminating at 3500 m a.s.l. and reached the foot of the face, where a large supraglacial lake had formed in 2002, but had drained in 2003 (figure 12).…”

“…Previous studies show that the lower limit of permafrost is at about 3000 m a.s.l. on north-to northeast-facing slopes, and up to 500 m higher on east-facing sections (Zgraggen 2005;Fischer et al 2006;Huggel 2009). …”

“…Indications of possible effects of climate change on slope stability has come from an increasing number of large-size rock falls and rock avalanches from permafrost areas in the Alps over the past two decades (Barla et al 2000;Fischer et al 2006;Fischer & Huggel 2008;Sosio et al 2008). Many of these events have not yet been studied in detail, and the causes and trigger processes are not adequately understood.…”

Exposure dating and reinterpretation of coarse debris accumulations (‘rock glaciers’) in the Cairngorm Mountains, Scotland

“…The possibility that failure was triggered by warming of ice in bedrock joints reducing the stability of the rock mass (e.g. Dramis et al, 1995;Haeberli et al, 1997;Davies et al, 2001;Fischer et al, 2006;Gruber and Haeberli, 2007) seems unlikely as failure occurred during cold periods associated with widespread permafrost, but cannot be excluded owing to the low precision of the exposure ages.…”