Geology Reference
In-Depth Information
Figure 6.9.
Rock glaciers. (A) Muragl rock glacier, Switzerland. This well-investigated rock glacier
is deforming at surface velocities of up to 50 cm per year (see Kaab and Kneisel, 2006). (B) Clast-
supported angular rock debris in an ice matrix in the basal part of the Larsbreen rock glacier in
Longyeardalen, Svalbard. This photo is supplied courtesy of Professor O. Humlum.
debris-covered glaciers (Johnson, 1974; Potter, 1972), the majority of rock glaciers dis-
cussed in the literature are essentially periglacial, or permafrost-related, features (Barsch,
1978, 1988; Haeberli, 1985).
Rock glaciers represent an extreme example of permafrost creep that occurs when rela-
tively warm, ice-rich debris (Figure 6.9B) deforms on relatively steep mountain slopes.
Rock glaciers are also thought signifi cant because they are often used to infer the lower
altitudinal limit of alpine permafrost.
6.4.1. Creeping Permafrost
It is well known that frozen ground can deform under the infl uence of gravity (Johnston,
1981, pp. 81-99; Yershov, 1990, pp. 145-156). Deformation is due mainly to the creep of
