Preliminary Quantitative Study of Alpine Subnival Boulder Pavements, Colorado Front Range, U.S.A.

Abstract

Alpine subnival boulder pavements occur as two types: Type I, those associated with a stream; Type II, those with no stream present. Type I may be subdivided into Type Ia, pavements that are approximately rectangular with their long axes roughly orthogonal to snow-delivering winds; and Type Ib, pavements that are fan-like in plan with a centrally located stream. Type Ia pavements have three internal zones: zone 1, occupied by the stream; zone 2, the sheltered margin with deep snowpack accumulation; and zone 3, the downwind margin with only shallow snowpack accumulation. Type Ib pavements have only zones 1 and 2. Using this typology and zonation, together with data from five pavements in the Indian Peaks, Colorado Front Range, three hypotheses were tested statistically. Hypothesis 1, that streams scour fines from beneath a coarse surficial layer, is accepted. Hypothesis 2, that pavement roughness is inversely related to seasonal snowpack mass, remains uncertain. Such a relationship does occur, but is probably secondary to stream scour. Hypothesis 3, that pavements may be either autochthonous or allochthonous, remains indeterminate.