Red Tarn: A Bowl Carved by Ice

This is Red Tarn, tucked into the hollow beneath Helvellyn that looks like an armchair carved into the mountainside. The shape is no accident. It is the work of glaciers. The steep headwall of Helvellyn and the sharp ridges of Striding and Swirral Edges are the giveaway. Together they form a semi-circle. Geologists call this a cirque. In the Lake District, the local names are cove or comb(e), in Scotland corrie, and in Wales cwm.

These features usually began as simple hollows on a slope, perhaps formed by a stream or a landslide. During the ice ages, snow and ice collected in them. Small glaciers take shape. These then scrape, grind, and tear at the rock, deepening and widening the hollow. The freeze-thaw of water around the edges adds to the destruction. Each glacial phase did more work. As the hollow grew, it trapped more snow. More snow meant larger glaciers, and larger glaciers meant more erosion. The result is the striking bowl-shaped landscape seen here.