An arête is a knife-edge ridge. It is formed when two corries run back to back. As each glacier erodes either side of the ridge, the edge becomes steeper and the ridge becomes narrower.
A pyramidal peak is formed where three or more corries and arêtes meet. Glaciers erode backwards towards each other, carving out the rocks by plucking and abrasion. Freeze thaw weathers the top of the mountain, creating a sharply pointed peak.
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.
The interlocking spurs in the narrow V-shaped river valley are cut-off by the ice, creating truncated spurs. After glaciation, a misfit stream/river or ribbon lake can sometimes occupy the floor of the U-shaped valley.