Abstract

At 10–100 m scales, glaciated landscapes are lumpy, sporting rocky bedforms with abraded upvalley faces and sharp, quarried downvalley edges. Using models that operate at two time scales, I address glacial landform development at these scales in order to explore the dependence of bed topography and erosion rate on glacier and rock properties. Sliding at the bed, a prerequisite for both abrasion and quarrying, is strongly modulated by water pressures. Short-time-scale models designed to capture the transient hydro-sliding system beneath a temperate glacier quantify the temporal and spatial pattern of effective stress on the glacier bed. The bed is subjected to repetitive stressing focused on the edges of bed steps, the frequency and magnitude of stress events increasing with ice thickness. The numerical model of bed evolution at longer time scales incorporates both abrasion and quarrying of fracture-bound blocks. The probability of quarrying of a block by a particular stress event is taken to depend inversely upon both block size and the depth of the niche in which it sits. Upglacier-migrating rock bedforms with 10–100 m wavelengths inevitably emerge, reflecting efficient quarrying of blocks from downvalley-facing steps in the bed. The relative importance of abrasion and quarrying, and bed roughness, are controlled by fracture spacing, and major steps in the valley floor are attributable to transitions in fracture spacing.

Citation

Anderson, R. S. (2014): Evolution of lumpy glacial landscapes. Geology 42(8): 679–682. DOI: 10.1130/G35537.1