Glaciers erode U-shaped valleys with a flat floor and steep sides. The glacier uses the processes of plucking and abrasion to widen, steepen, deepen and smooth V-shaped river valleys into a 'U' shape.

See that U-shaped valley? That’s Lairig Ghru. It was carved out by a glacier, a huge river of ice, during the ice age - just like corries and other glacial features. As glaciers move downhill ...