Glacial deposition along an ice‐contact slope: an example from the southern lake district, chile

Abstract

Glacially derived sediments and structures vary systematically with topographic position along ice‐contact slopes near the margin of former temperate piedmont glaciers in the southern Lake District, Chile. Features along lower positions of the slopes include glaciolacustrine sediments and large‐scalethrusting. Middle slope features include low‐angle subglacial thrusting of thin slices of lacustrine sediment. Upper slope features include high‐angle thrusting, and lodgement and flow till. Locally, the same ordering of these features occurs in vertical sequence.A common theme that unifies the processes represented by these features is the distribution of hydrostatic pressure. Thicker ice (producing higher glacier overburden pressures) and aquicludes of fine‐grained sediments toward the center of the basin result in high hydrostatic pressures, whereas thin ice and porous out‐wash reduce these pressures at the top of the ice‐contact slopes.However, such a distribution cannot completely explain the observed vertical sequences; hence, local variations in hydrostatic pressure because of lithologic contrasts probably play a role. Nowhere along the ice‐contact slope are pervasively deformed glacial sediments observed; therefore they cannot be invoked to explain the low glacier profiles of these piedmont glacier lobes.