4. Glacial Erosion - Corries and associated landforms Flashcards
Briefly explain what a corrie is/ its appearance.
A corrie/cirque is an armchair-shaped rock hollow, with a steep back wall and an over-deepened basin with a rock lip. It often contains a small lake (tarn). In the British Isles, corries are mainly found on north, northeast, and east-facing slopes where reduced insolation allows more accumulation of snow.
Explain the associated landforms of a Corrie.
If several corries develop in a highland region, they will jointly produce other erosional features. When two corries lie back to back or alongside each other, enlargement will often leave a narrow, steep-sided ridge between the two hollows, called an arête. An example is Striding Edge on Helvellyn in the Lake District.
If more than two corries develop on a mountain, the central mass will survive as a pyramidal peak, which often takes on a very sharp appearance (has a sharply pointed summit) due to frost shattering/freeze-thaw action. An example is the Matterhorn in the Alps.
Explain the formation of a corrie.
Corrie formation is the result of several interacting processes. The original process is believed to be nivation, which acts upon a shallow, preglacial hollow and enlarges it into an embryo corrie (this make take a long time and be spread across several glacial periods within an ice age). As the hollow grows, the snow becomes thicker and is increasingly compressed to form firn (partially compacted névé) and then ice. The back wall becomes steeper through the action of plucking. The **rotational movement **of the ice, together with the debris supplied by plucking and frost shattering/freeze-thaw action on the back wall, abrades the floor of the hollow which over-deepens the corrie.
As the hollow deepens, the thinner ice at its edge does not produce the same amount of downcutting and a rock lip develops on the threshold of the feature. Some thresholds have their height increased by morainic deposits formed when the glacier’s snout was in that position. After the last ice has melted, the corrie fills with meltwater and rainwater to form a small lake (tarn).
Draw a diagram to show the formation of a Corrie.
