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
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