glacial deposition Flashcards
glacial deposition
-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
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
drumlins
-Drumlins are elongated, egg-shaped hills and made of glacial till
T-hey 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
low land depositional features, 3 examples
-till plain
-logement 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
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
