Basic Principles

Extreme spatial variability with respect to microclimatic conditions, abundance of well-drained coarse sediments and bare rock on steep slopes, snow redistribution by wind and avalanches, and the reduced influence of vegetation cause permafrost in alpine topography (Fig. 14.1) to be strikingly different from permafrost in high-latitude lowlands, and to react in a specific way to climate change and global warming. Complications already start on the highest peaks with very steep to vertical and largely snow-free rock walls, where subsurface heat diffusion can be assumed to play a predominant role: permafrost inside such mountain peaks can be effectively decoupled from geothermal heat because of pronounced lateral fluxes caused by its often strongly asymmetrical three-dimensional (3D) geometry and thermal structure (Gruber et al. 2004b; Noetzli et al. 2007). Furthermore, warming trends can penetrate from two or more sides to greater depths below the surface.

Fig. 14.1 The village of Tasch and the Mischabel Group in the Matter Valley, Valais Alps, Switzerland, with numerically simulated permafrost distribution (blue; red = uncertainty zone and probably warm/degrading/already thawed permafrost). Note dams for rock fall protection on left and debris flow on right slope above village. In 2001, a debris flow from a moraine lake in marginal permafrost of the lateral valley (centre of image) caused heavy damage to the village (satellite imagery: © ESA/Eurimage, CNES/Spotimage, swisstopo/NPOC; permafrost simulation/visualization: S. Gruber, S. Biegger, University of Zurich)

Fig. 14.1 The village of Tasch and the Mischabel Group in the Matter Valley, Valais Alps, Switzerland, with numerically simulated permafrost distribution (blue; red = uncertainty zone and probably warm/degrading/already thawed permafrost). Note dams for rock fall protection on left and debris flow on right slope above village. In 2001, a debris flow from a moraine lake in marginal permafrost of the lateral valley (centre of image) caused heavy damage to the village (satellite imagery: © ESA/Eurimage, CNES/Spotimage, swisstopo/NPOC; permafrost simulation/visualization: S. Gruber, S. Biegger, University of Zurich)

On less inclined slopes, a spatially and temporally most variable snow cover acts as a complex interface between the warming atmosphere and the ground surface. It thereby greatly affects the radiation balance via the albedo — especially in spring and early summer — as well as the exchange of sensible heat through thermal insulation (Lutschg et al. 2004). Even greater complexities exist on the widespread slopes covered by coarse-grained, well-drained debris, because openwork active layers enable lateral and vertical heat advection through movements of air and water to play an important role (Bernhard et al. 1998; Delaloye et al. 2003; Vonder Muhll et al. 2003; Hanson and Hoelzle 2004). Additionally, the low thermal conductivity of such deposits causes a relative ground cooling when compared to other materials, because of a lower contrast between the thermal conditions during winter (snow and ground) and summer (only ground, Gruber and Hoelzle 2008).

Ice contents far in excess of the pore volume are common in perennially frozen sands and silts. They not only cause perennially frozen debris to creep at considerable rates and to form striking landforms of cohesive flow (rock glaciers) in otherwise non-cohesive material (talus, moraines), but also retard permafrost thaw through latent heat exchange. Finally, permafrost in high mountain areas often interacts with various forms of perennial surface ice such as persisting avalanche cones, perennial snow banks and glacierets as well as with polythermal to cold mountain, cirque and hanging glaciers (Haeberli 2005; Gruber and Haeberli 2007). In these cases, the warming-induced evolution of subsurface ice is intimately coupled with the vanishing of surface ice.

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