Sliding motion of glaciers: Theory and observation

摘要: The sliding motion of glacier ice over bedrock, which contributes about half the flow velocity temperate glaciers, is analyzed for arbitrary bedrock topography low roughness. Fourier-analyzed represented by a roughness spectral function ζ(h, k) defined in terms mean square topographic amplitude. From an essentially exact solution problem linear ice-flow rheology, approximate actual nonlinear rheology built on assumption that second strain-rate invariant depends only distance from ice-bedrock contact. transition wavelength λ0 between regelation and plastic flow, constant theory, replaced theory velocity- roughness-dependent parameter λα plays similar role. Detailed results are given three special types k): (1) white (|ζ| constant); (2) truncated all wavelengths above certain lower limit); (3) single wavelength; (4) cross-corrugated sinusoidal waves. tested against field observations sliding. Given υ, basal shear stress τ, rheological parameters, predicts values ζ different k). When compared with inferred observed outcrops, predicted somewhat too small, whereas at 3.53 meters, they expected size (ζ ∼ 0.05). Predicted range 3 to 112 cm; high υ (>20 m yr−1) generally gives 10–40 cm, (<6 30–70 cm. thickness layer (1–10 mm) agrees observation, but appear be small. Extensive separation sole due tensile stresses set up sliding, icefalls, valley glaciers little predicted, unless meltwater under head pressure comparable has access bed. not needed account typical velocities, provided spectrum truncated. Observed features glaciated indicate truncation, glacial abrasion. For spectrum, dependence τ much more highly than full spectrum; this implies relatively sensitivity changes or surface slope.