Explain the formation of a corrie

Corries are geological features that are formed through glaciation. The glacier sticks to the sides of the valley and, as it moves, pulls away large chunks of rock in a process known as plucking. During the colder months, water gets into cracks in the rocks and freezes. When the temperature rises and the rock thaws, the expansion of the ice breaks the rock apart - this is freeze-thaw weathering, or frost-shattering. These pieces of shattered rock fall to the bottom of the valley and underneath the glacier. As the glacier advances and retreats, the debris is carried and scrapes along the bottom of the valley, eroding the rock underneath. These three glacial processes remove and erode the rocks in the surrounding landscape.

This abrasion, over time, scours out a basin shape on the mountain. This leaves behind a corrie - a deep basin with high, steep sides. It may fill with water to form a feature known as a corrie lochan.

(There is a diagram that could be used alongside this written answer)