Glacial Landforms (DP IB Geography)
Revision Note
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
Depositional Landforms
Moraines
Unsorted glacial till that is deposited in mounds are called moraines
There are four types of moraines:
Terminal: Material deposited at the snout of the glacier
Lateral: Material is deposited along both sides of the glacier
Medial: Ridge of deposited material in the middle where two glaciers meet and continue to flow downhill together
Ground: Material dragged under the base of the glacier and deposited over a wide area on the valley floor
Drumlins
Drumlins are elongated, egg-shaped hills made of glacial till
They form beneath the glacier when the glacier meets an obstruction and material is deposited as ground moraine
The moving ice then follows the direction of the flow of ice to shape the moraine
The largest ones can be over 1km in length, 0.5km wide and 50m high
Multiple drumlins are known as swarms or baskets of eggs
As the material is deposited, it builds up to have a round, blunt and steep front (stoss) end
The flow of ice over the top of the drumlin drags the material along and down, creating the lee slope
The lee is gently sloped, elongated and has a tapered tail
Examples include The Drumlin Field below Cam Fell in the Yorkshire Dales and Conway Valley, North Wales
Erratics
Erratics are random rocks of different sizes and types from the area where they are found
There is no pattern to their deposition, and they look completely out of place on the landscape
Glaciers pick up large rocks and carry them hundreds, sometimes thousands, of kilometres from where they originate
Erratics are carried deep in the ice and do not erode as much as rocks at the edges of the glacier
An example is the Great Stone of Fourstones, (Big Stone)' on the moors of Tatham Fells, England
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