Valley floor landforms

Windermere in the Lake District
Windermere in the Lake District

As a glacier flows over the land, it flows over hard rock and softer rock. Softer rock is less resistant, so a glacier will carve a deeper trough. When the glacier has retreated, (melted) water will collect in the deeper area and create a long, thin lake called a ribbon lake. Many of the lakes in the English Lake District are ribbon lakes, eg Windermere. The areas of harder rock left behind are called rock steps.

If the glacier hits a particularly resistant outcrop of rock it will flow over and around it. This leaves a rock mount smoothed by abrasion from the glacier. These come in two types:

Roches moutonnée

Roches moutonnée often have steep, jagged faces created by plucking on the lee (far) side and a gradual incline which is smoothed and polished by abrasion on the other (stoss) end. It may have striations on it indicating the direction of glacier movement.

Formation of a roche moutonee

Crag and tail

Crag and tail tends to be larger than a roche moutonnée. Crag and tail is the opposite of the roche moutonnée as the ice hits the steep resistant rock outcrop first. This protects the lee (far) side of the obstacle from erosion. Edinburgh castle is built on crag and tail.

The crag and tail formation and Edinburgh castle