Environmental Engineering Reference
In-Depth Information
Plate 25.8 Remnant boulder field, tors and summit
altiplanation terrace (background) at about 1 km altitude in Y
Glyderau, North Wales, frost-weathered in steeply dipping
tuffs and siltstones.
Photo: Ken Addison.
ALPINE SLOPE DEVELOPMENT
The evolution of high mountain slopes is subject, like all slope processes, to variation and
much argument and modelling. There is, however, progressive removal of the rock wall
at the expense of a developing talus/colluvial foot slope (Figure 25.17). Rock walls may
be crowned by peaks or broader crests, dominated by frost weathering and shedding
debris by solifluction and deflation. The rock wall is eroded at average rates of 1-10 cm
yr −1 , two to four orders of magnitude higher than the crest which it steadily consumes.
Initial rockwall height and steepness depend on the extent of glacial erosion and
rockmass strength. Angles exceed 45°-50° in general, with major cliff elements over 65°
and main valleys 0·5-2 km deep. Rock walls rarely extend continuously over this range
and may be stepped in response to structural features or episodes of valley deepening.
Rock falls and rock slides lead to eventual rock-wall destruction, exploiting the failure
criteria of inherently
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