Mountain Landforms and Geomorphic Processes - Mountain Geography: Physical and Human Dimensions - page 253

is saturated and flowage occurs (Benedict 1970, 1976). On drier slopes, the effects of
frost creep can often be seen, resulting in small steps and terraces. Below timberline,
the downslope curvature of tree trunks may be good evidence of creep, although heavy
snowfall, among other factors, may also be important (Phipps 1974).
Solifluction
Solifluction is derived from the Latin words solum (soil) and fluere (to flow) (Andersson
1906). It is best developed in cold climates where permafrost or a subsurface frozen
layer prevents the downward percolation of water. Under these conditions, the soil be-
comes saturated, cohesion among soil particles is reduced, and the viscous mass be-
gins to deform downslope in a porridge or concrete-like fashion (Williams 1957; Barsch
1993). Some have used the term gelifluction to describe such a process; others have
referred to the process as solifluction when permafrost is not involved (French 1996).
In some cases, solifluction can do more work to the alpine hillslope than rockfall and
avalanche processes (Smith 1992). Solifluction and creep processes combine to produce
forms such as turf and stone banked lobes, benches, and terraces (Benedict 1970). Soli-
fluction lobes are one of the slower forms of mass wasting, with average rates of move-
ment from 0.5 to 5.0 cm/yr (Benedict 1970, 1976; Fig. 5.10). In the Canadian Rockies,
rates of solifluction averaged 0.47 cm/yr between 1980 and 1990 (Smith 1992). The
greatest downslope movement occurs near the ground surface, whereas the greatest
differential movement arises in an intermediate layer 20-50 cm below the ground sur-
face. There is very little movement below the active layer (Price 1991). Solifluction, frost
action, frost creep, and other weathering processes act to reduce overall slope and cre-
ate altiplanation ( cryoplanation ) terraces (Péwé 1970; Reger and Péwé 1976).
FIGURE 5.10 Solifluction lobes on Niwot Ridge, Colorado. The lobes, denoted by darker vegetation
from greater soil moisture, create a stepping, porridge-like appearance on the hillslope. (Photo
by J. R. Janke.)