Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 243

will be less cohesion in the soil, and thus stable slopes may become active. Recent
warming has accelerated the processes associated with recent deglaciation: glacial
avalanches, landslides, slope instability, and outburst floods (Evans and Clague 1994).
Sheet slides and skin flows could increase as a result of moisture oversaturation and
high pore water pressure associated with melting permafrost or early snowmelt. Rock
glaciers may become unstable and create hazards as debris is no longer consolidated
by ice (Barsch 1993). Kääb and Vollmer (2000) used computer-aided aerial photogram-
metry to map disasters and hazard potentials in a section of the Swiss Alps. Glacier lake
outbursts in 1968 and 1970 from the Gruben area caused floods up to 400,000 m 3 and
debris flows moving material at 15 m 3 s −1 , leading to heavy damage in the village of
Saas Balen. Creeping permafrost or rock glaciers can eventually move into steep chan-
nels, creating a dam that could block a river or cross a hiking path.
Because of the fragility of mountain environments, it is almost impossible for systems
to return to their initial state after disturbance (Beniston 2000). The same conclusion
can be drawn with respect to permafrost. The sensitivity, or the range of stress a system
can experience without damage; the vulnerability, or the extent to which it may be dam-
aged by stress; and the adaptability, or the degree to which it may adjust to stress, are
factors that must be examined in detail.
Frost Heave and Thrust
When ice lenses (horizontal accumulations of ice crystals) build beneath the surface,
they cause the ground to expand in the direction of the ice-crystal growth. The most
common direction is vertical ( heave ), toward the soil surface, since this is the source of
the cold. Expansion may also take place laterally ( thrust ) because of the variations in
conductivity of heterogeneous materials (Washburn 1980). Frost heave and thrust are
the major causes of stirring and disruption of the soil. As the soil freezes, water is at-
tracted to the freezing plane, where it accumulates in the form of ice lenses that push
the soil upward.