Glacial Landforms

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Glacial Landforms

Although in Britain there are no glaciers remaining, there are many landforms that can be used as evidence to show that glaciers once covered much of the Northern half of the country.

UK map

Arêtes - Where two corries formed back to back they both eroded backwards until they created a narrow knife-edge ridge between them This is called an Arête. Also see pyramid peaks.

Corries - Also known as cirques, they are the starting point of a glacier.

At the beginning of the last age snow began to accumulate in hollows on hillsides, slowly accumulating enough to turn into ice. This ice slowly gouged out a steep back wall through the processes of freeze-thaw and plucking. Large crevasses on the top of the ice, called bergschrund's allowed water to flow into the ice, where it froze to create more ice.

The bottom of the corrie was eroded by abrasion as the ice moved forward in a rotational way. Where the rate of erosion was less, at the front of the ice, a rock lip was left. As more and more ice accumulated it flowed over the lip and into the valley below, creating a glacier.

Once the ice melted the corrie was often filled by melt water to form a lake. The rock lip and moraine acted as a natural dam. These lakes are known in Britain as Tarns.

Raw materials

Glacial Trough - The other name for a U-shaped valley cut by a glacier.

Hanging Valleys - see u-shaped valleys

Pyramidal Peaks - Formed in exactly the same as an Arête only this time three corries back onto each other. Eventually the backwards erosion leaves a sharp pyramid peak. An example of this is the Matterhorn in the Alps.

Ribbon Lakes - see u-shaped valleys

Truncated Spurs - see u-shaped valleys

U-shaped Valley - Just as a river produces a distinctive V-shaped valley, so a glacier produces a U-shaped one. Usually a glacier will follow the general direction of a river valley, however it doesn't flow around areas of hard rock it cuts straight through them. This means that when the glacier melts it leaves behind a valley with very steep sides.

Glacial valleys that flowed into the main valley have been chopped off and the rivers in them now flow over huge waterfalls from hanging valleys. The interlocking spurs of the river valley have also been cut through to leave truncated spurs behind. On the valley floor a long, thin ribbon lake may well form, with the terminal or recessional moraine forming a dam to hold the water in.

Raw materials

Boulder Clay/Till - This is the mixed angular material found on the valley floor, which has been deposited by the glacier as it melts. It is made up of sand, stones and clays. The stones are angular, as they have not yet been rounded by water action. This is also called ground moraine.

Drumlins - These are smooth mounds of deposited material that are formed parallel to the direction of the movement of the glacier. They are quite large, usually between 30 and 40 metres high and up to 500 metres long.

They look similar to eggs that have been stuck lengthways into the ground, and are described as being a "swarm of drumlins" as there are usually a number in one single area.

Drumlins are formed by moraine being deposited due to an obstruction causing an increase in friction or a slowing of the glacier. Most of the material is deposited at one end of the drumlin, with the rest tapering off towards its thin end. The flow of ice over this deposited material then shapes it into the characteristic form of a drumlin.

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Erratics - These are large boulders that have been carried by the glacier and then deposited in an area of differing rock type, so that they look completely out of place. Erratics can have originated from hundreds of miles away.

Moraines - as already mentioned there is a range of moraines. Moraine is the term used for any material carried or deposited by a glacier. The five main types of moraine are:

  • Terminal Moraine: This is the material deposited at the snout of the glacier at the furthest extent of its growth. The terminal moraine may act as a dam for a ribbon lake.
  • Lateral Moraine: Runs parallel to the glacier and is the material that has been eroded from the valley sides by the actions of freeze-thaw and the glacier itself. Once the glacier melts this will be left on the valley floor.
  • Medial Moraine: Where two glaciers meet, their lateral moraines meet to form a medial moraine, which runs down the centre of the glacial surface. Once the glacier melts this will be left on the valley floor.
  • Ground Moraine: otherwise known as boulder clay or glacial till, this is the material deposited on the valley floor by the glacier. It is usually the result of plucking and abrasion.
  • Recessional Moraine: Similar to a terminal moraine they were created when the glacier retreated and then stopped, allowing it to build up a pile of deposits. A recessional moraine could act as a dam to create a ribbon lake.
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