Glacial Erosion

Basal sliding erodes the rock surface underlying a glacier. Meltwater freezes in cracks, and pieces of bedrock are pried loose and incorporated into the ice (similar to frost wedging). These pieces of rock grind against each other and the bedrock underneath. The intensity of the grinding is proportional to the weight and pressure of the glacier. Faceted rocks are those rocks along the base that are worn flat from erosion. The surfaces of the bedrock and the rock fragments are polished just like rocks in a rock tumbler are. Rocks embedded in the ice scratch long, deep grooves in the bedrock called striations, which indicate the direction of ice movement. The constant grinding of rocks in the glacier creates a fine‐grained rock powder that turns the meltwater white when released by ablation.

Other erosional features associated with glaciers include increased mass wasting from rapid downcutting of valley sides, frost wedging that creates rockfalls, and avalanches that contribute additional rock and soil material.