When a glacier travels over bedrock, it can gouge out chunks of rock and then move them “downstream” by glacial plucking.

As gravity assists the weight of the glacier to move downhill, the friction between the ice and the rock creates a thin layer of meltwater which then seeps into cracks. As the meltwater freezes, it expands, widening the crack. Over time, sections of rock are separated from the bedrock surrounding it. The continued friction from the ice will “pluck out” chunks of the rock over time. It may then be dragged downstream with the path of the ice, deposited eventually as part of the glacial moraine (by which time it may have been ground down to smaller pieces yet).

At the foot and sides of a glacier, we encounter lateral and terminal moraines, and in former glaciated terrain, we can find eskers, kames, terraces, and other depositional shapes.

We can also see signs of glacial striation when a rock has been dragged along bedrock, grooving out a channel or scratch along the path of the ice movement. Once we learn to identify these features, its easy to see many examples while out wilderness hiking.