Glaciation and ice landscapes
Geography · Key Stage 3 · The School
How ice erodes
Glaciers erode in two main ways. PLUCKING: meltwater freezes onto rock, and as the ice moves it tears fragments away. ABRASION: those trapped fragments are dragged across the bedrock and grind it down like sandpaper, leaving scratches called striations that record the direction the ice travelled.
What ice leaves behind
Glacial landforms are distinctive: U-SHAPED VALLEYS, broad and steep-sided, unlike a river's V; CORRIES, armchair hollows high on a mountain where ice first gathered; ARÊTES, knife-edge ridges between two corries; and MORAINE, the unsorted rubble a glacier dumps when it melts. Together they identify a landscape as glaciated at a glance.
Britain without glaciers
Britain has no glaciers now, but Snowdonia, the Lake District and the Highlands are full of these landforms because ice covered much of the country repeatedly during the last two and a half million years, most recently ending around 11,500 years ago. The landscape is a record of a climate that no longer exists here.
Stand in a Snowdonia valley. It is U-shaped with steep sides and a flat floor — a river cuts a V, only ice cuts a U. There are hanging valleys entering high up the sides, left by smaller glaciers. There is a corrie with a small lake at the head, and a ribbon lake along the floor behind a rock bar. Erratics — boulders of the wrong rock type — sit on the slopes. Five pieces of evidence, and no glacier for 11,500 years.