Glaciation Pack F Flashcards
What is a cirque?
An arm-chair shaped hollow with a steep back and a rock basin
- Macro scale landform
What makes a hollow deep enough to collect more snow?
Nivation enlarges the hollow by a combination of freeze-thaw weathering and meltwater which transports the rock debris away, forming a nivation hollow
Why is freeze-thaw weathering important in the creation of a cirque?
Freeze thaw weathering breaks up and loosens the rock so that it can be plucked
Why is plucking important in the creation of a cirque?
Rock that has been broken by freeze-thaw weathering is plucked which steepens the back wall
Why is abrasion important in the creation of a cirque?
Abrasion by rocks picked up from the plucking deepens the corrie and allows the ice to move in a rotational manner (rotational slip)
Why is there a rock lip and what gets deposited on it?
- Rock lip forms as ice leaves the hollow
- Deposition of debris before the glacier moves out of the corrie
Why may a tarn form in the cirque?
Happens post-glacially when the cirque fills with water
Why are the largest and most frequent locations of cirques north-east facing?
- In the lee of prevailing westerly winds
- In the shadier sites protected from insolation
- Westerly winds blow snow into the hollows
What is an example of a cirque in the UK?
Easedale Tarn in Cumbria
What is an example of a cirque outside the UK?
Hodges Glacier, Georgia
What is an arete and what causes them?
A narrow, rocky steep-sided ridge formed from the intersection of two cirque headwalls
- Macro scale landform
- Happens when two cirque headwalls erode backwards towards each other
E.g. Striding Edge, Helvellyn
What is a pyramidal peak and what causes them?
A horn with steep sides and several aretes radiating from it
- Macro scale landform
- Steep, pointed peak
- Formed when three or more cirques back onto each other
E.g. The Matterhorn, Alps
What is a glacial trough?
A steep sided flat bottomed valley
- Macro scale landform
What is the appearance of a glacial trough?
- Straight
- Wide base
- Steep sides
- Stepped long profile
What causes glacial troughs to develop?
- As a valley glacier ice moves through a mountain valley, it straightens, widens and deepens the valley
- The valley changes from V-shaped to U-shaped
- Plucking and abrasion widen and deepen the valley
- Meltwater carrying sediment erodes the bed/banks (subglacial fluvial erosion when under the glacier)
- Compressional flow means that the glacier will over-deepen parts of the valley floor which forms rock basins
- Deeper areas of the U-shaped valley are caused by the confluence of glaciers, less resistant geology or well-jointed rocks
- After glaciation, the sides of the valley get weathered and mass movement moves rocks to the valley base forming less steep sides with scree slops