Glacial Deposition Landforms & Landscapes (Edexcel A Level Geography)

• When debris is deposited by the ice mass and not meltwater, it is called ice contact deposition
• During the warmer summer months, glaciers begin to melt, and glacial till is deposited on the valley floor or sides of a moving glacier
• Till is unsorted, irregular debris ranging from clay to stones to boulders of any size and shape
• Features of ice contact deposition include erratics, moraines, and drumlins

Erratics

• Erratics are random boulders 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 from Scandinavia have been found in boulder clay of the North East of England coastline
• Erratics are carried deep in the ice and do not erode the same as till at the edges of the glacier
• An example is the Great Stone of Fourstones, (Big Stone) on the moors of Tatham Fells, England

The Great Stone of Fourstones - erratics are random rocks that vary in size!

Moraines

• Unsorted glacial till that is deposited in mounds are called moraines
• Moraines are termed from their position on the glacier:
  • 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
  • Recessional: They show the point of glacial retreat
  • Push: They form if the glacier advances after retreat

Main types of moraines

Drumlins

• Drumlins are elongated, egg-shaped hills and made of glacial till
• They form beneath the glacier when the glacier meets an obstruction and material is deposited as a ground moraine  
• The moraine is then shaped by the moving ice, which follows the direction of the flow of ice
• 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 with a tapered tail 
• The more elongated the drumlin the faster the ice was flowing
• Examples include The Drumlin Field below Cam Fell in the Yorkshire Dales and Conway Valley, North Wales

• Lowland ice contact depositional features include:
  • Till plain
  • Lodgement till
  • Ablation till

Till plains or ground moraine

• When the ice mass retreats during the warmer months, till is deposited over a vast area across the valley floor 
• Meltwater will also flow out of the glacier's snout forming meltwater rivers
• These rivers carry large amounts of glacial till, which will undergo further erosion through attrition to become outwash 
• This finer till is sorted and when the energy of the river reduces, the outwash is deposited in layers further down the valley on the outwash plain

Glacial till                                                                                   Glacial outwash plain

Lodgement till

• Found mainly with slow-moving glaciers which carry more debris sub-glacially
• Lodgement till is subglacial unconsolidated material that is forced, or 'lodged' into the bedrock below

Ablation till

• Ablation till includes supra and englacial material deposited as the glacier melts

Transportation of glacial till

• Landforms of glacial deposition are useful in understanding the direction and extent of ice cover - striations are deepest at initial point of contact
• It also provides a record of past glacial changes over a longer timeframe than current observational records
• Past temperatures and levels of precipitation can be measured with ice cores, indicating past glacial climates
• Orientation of the landform can indication glacial direction and upland or lowland landforms can be a good indicator of actual ice mass - crag and tail as a macro feature needing a large ice mass to deform around resistant rock rather than flow over as in the meso landform of roches moutonnées 
• Debris analysis can indicate distance travelled, as in the case of the Scandinavian erratics; or the rate of travel as in drumlin swarms, as slow moving glaciers carry more till
• Morainic ridges indicate edges of ice sheets or glacial snouts in instances of glacial retreat