Evidence for advancing glaciers

Rôche moutonnées form as a glacier flows over bedrock. Sediments entrained in flowing glacial ice abrade and polish the bedrock on the stoss side (facing towards the moving glacier) and pluck rocks off the lee side (facing away from the moving glacier). Abrasion on the stoss side gives the bedrock a soft gentle slope, and where the plucked rocks are removed on the lee side you get a very steep slope (about 10x more materials is fractured off the lee side). These features can exist at different scales. Looking across to the Adirondacks, most of the ridgeline exhibits this pattern – a gentle north-facing slope and a sharp drop to the south. But look at a smaller scale and you can often find the same thing. The image at the bottom is a small (~3″ across) example of a roche moutonnee on the exposed bedrock on the summit of Deer Leap in Bristol.

For more on roche moutonnees, check out this blog post.