Glacial Landforms (DP IB Geography)

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

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