Erosional Landforms
- As a glacier moves it erodes everything in its way
- Glacial erosion creates different features as it flows downhill:
- Pyramidal peak
- Arête
- Corrie/cwm/cirque
- Tarn
- Truncated spur
- Hanging valley
- Ribbon lake
- Glacial trough/U-shaped valley
- Pyramidal peak
- As the name suggests, this is a three-sided, pointed mountain peak
- Formed when three or more back-to-back glaciers carve away at the top of a mountain
- This creates a sharply pointed mountain summit
- Examples include Snowdon in Wales and Buachaille Etive Mòr, Glencoe, Scotland
- Arête
- Arêtes are knife-edge, steep-sided ridges
- Formed when two glaciers flow back-to-back
- As each glacier erodes either side of the ridge, the edges become steeper and the ridge narrower
- This gives the arête it's a jagged profile
- Examples include Crib Goch in Wales, and Striding Edge in Lake District, England
- Corrie/cwm/cirque
- Corrie, cwm and cirques are all the same feature and are formed in hollows where snow can accumulate, usually on a north facing slope
- In Wales corries are called cwms and in France, they are called cirques
- Formed when the glacial ice moves through gravity, rotational slip, and sheer mass of the ice
- Ice freezes on the back wall of the hollow and as the ice moves, it plucks the rock out, which steepens the back wall
- Freeze-thaw, plucking and abrasion further erode the hollow into a rounded, steep-sided 'armchair' shape with a lip at the bottom end
- Examples include Helvellyn Corrie in the Lake District and Cwm Idwal in Snowdonia
- Tarn
- Tarn lake or corrie loch is a mountain pool or lake in a corrie after the glacier has melted
- Because of the corrie lip at the bottom end, the meltwater is held in place and a circular body of water is formed
- Examples include Red Tarn, Helvellyn in the Lake District and Cadair Idris in Snowdonia
- Truncated spur
- Truncated spurs are past interlocking spur edges of past river action that have been cut-off forming cliff-like edges on the valley side
- Found between hanging valleys and are an inverted 'V' shape
- formed when the lower valley glacier cuts off previous ridges or spurs as it passes by
- An example is Nant Ffrancon Valley in Snowdonia
- Hanging valley
- These are small tributary glaciers found 'hanging' above the main valley floor
- When melting occurs, there are waterfalls onto the valley floor
- An example is Cwm Dyli in Snowdonia
- Ribbon lake
- As a glacier flows, it travels over hard and soft rock
- Softer rock is less resistant to erosion, so a glacier will carve a deeper trough over this type of rock
- When the glacier has melted, water collects in these deeper areas
- This creates a long, thin lake called a ribbon lake
- Examples include Lake Windermere in the Lake District and Llyn Ogwen in Snowdonia
- The areas of harder rock left behind are called rock steps
- Glacial trough/U-shaped valley
- Glacial troughs are steep-sided valleys with a flat floor
- They start as V-shaped river valleys but due to the size and weight of the glacial ice, it changes to a U shape as the glacier erodes the sides and bottom, making the valley deeper and wider
- Examples are found all over the UK, but Nant Ffrancon and Nant Gwynant in Snowdonia are good examples
Examiner Tip
When explaining the formation of landforms of any kind (fluvial, coastal, glacial etc.) you should use labelled or preferably annotated diagrams to support your answer.
A well annotated diagram showing the stages of formation will gain you full marks and a labelled diagram will gain you credit.
Diagrams do not need to be flawless but a solid representation of the feature and follow the geographical rules:
- In a box, drawn in pencil and labelled/annotated in pen
- Arrows drawn with a ruler, in pencil and points to the feature (not the writing) and never cross
- Shade in colour to highlight features
- Labelling should ideally be around the outside, but can be on the feature
- If annotating, you can use numbers on the sketch and write below the diagram in sequence
