A cirque, also known as a corrie (Scotland) or cwm (Wales), is a large, bowl-shaped feature cut into the top of a mountain by a glacier. In times before the Ice Age, there were shallow hollows in mountainsides caused by rivers making their headwaters. But during an Ice Age, ice filled these hollows. Any small stones and other material on the land was frozen to the bottom of the ice. Then, as it got thicker its weight caused it to slip. As the ice slipped, so it scraped the debris across the surface, making the hollow deeper. Over time this formed a bowl - a cirque.

In place which still have ice, you can still see the ice in its corrie. But in places where the ice has gone, such as in the English Lake District, the bowl is often marked by a small, circular lake, called a tarn in the Lake District.