Research Project on Landforms
Describe the landforms produced by glacier ice and meltwater and explain how these landforms reflect variations in glacier energy.
Glaciers and ice sheets are seen as powerful agents of erosion than can radically alter landscapes and carve distinctive landforms. Distinctive landforms can also be formed by the process of meltwater.
To enable these unique landforms to be formed, many factors have to be taken into consideration so we can understand how these landforms were made. The most important processes are that of erosion and how the landscape can effect glacier energy. The main processes of erosion are Quarrying (plucking) and Abrasion.
Quarrying is where ice at the base of a glacier or ice cap is melted by friction and pressure, and this often refreezes in cracks in the rock that it comes into contact with. Freeze thaw weathering weakens the rock, and fragments of it are plucked out by the ice that flows over it. This is the process of quarrying.
Abrasion is where frozen that contains fragments of rock (Often as a result of quarrying) can be very effective at grinding the surface it moves over, particulary under great pressure from the weight of ice above. This grinding process has two main consequences-rough surfaces can be polished quite smooth, and smooth surfaces can be sratched by abrasion to create striations aligned in the direction of ice movement. Striations are very useful in reconsructing directions of ice movements in the past.
Three of the unique landforms produced by Glaciers are Cirques, Aretes and-shaped valleys. Cirques are bowl "shaped depressions caused by quarring processes at the head of valleys in which glaciers form. As the ice moves down a valley it is the process of abrasion on the rock floor and quarrying that form the cirque (See figure 1). A typical cirque is semi-circular in shape when viewed from above, with a steep headwall and side walls, and a much flatter floor ( Chris Park "The environment" ). Many of the cirques have been deepened by other processes of erosion, and after the ice inside the cirque has melted they usually leave lakes called tarns. When Cirques are being formed and ice is present in them, a wide deep gap often develops between the ice and the headwall, called a bergshrund, as the ice is pulled away from the headwall and moves downslope.
Aretes are formed where a glacier erodes adjacent cirques on opposite sides of a moutain ridge. The knife edged ridge between the two cirques is called an arrete. For example Striding edge in the Lake district.
U-shaped valleys are usually formed by erosional processes taking place in a bpr-exixting V-shaped valley more than likely formed by a pre-glacial river. They are usually straight or gently meandering. These valleys are formed as a glacier extends and advances down-valley. U-shaped valleys are often excavated quite deep, ao that the mouths of tribtary valleys are left hanging high above the new valley as hanging valleys.
Even though Cirques, Aretes and U-shaped valleys are the most charachteristic landforms created by glaciers, there are many other landforms created. Two nother widespread forms created by glaciers are Roches Moutonnees and Crag-and-tails.
Roches Moutonnees, are formed where glacier ice has moved down a valley and have created outcrops of bare, resistant rock. The upstream side ( called the stoss), shaped by abrasion, is usually smoothed, rounded and steamlined. The down stream side ( the lee) is usually steep and angular because it is formed by quarrying processes.
A Crag-and-tail can also be formed around resistant rock underneath moving ice. Quarrying gives a rocky, angular appearance to the upsteam side ( the crag), while the downsteam side ( the tail) has a gentlee direction of ice movement and is covered by glacial deposits.
The five Landforms just mentioned were all created by the power within the glacier. The following landforms were all created by the deposition left by the glacier. Much of the sediment carried by the glacier is from the process of quarrying itself, this sediment is then deposited in different ways to form different land forms.
Sediment that is deposited directly by a Glacier or ice sheet is called Till. Till is usually composed of a mixture of rocks, sand and clay but this varies from are to area.
Usually in till sheets we find depressions called Kettle Hoples, these form where blocfks of ice buried in the till melt and the underlying material slumps down to nform a hollow after the glacier or ice sheet has retreated.
Drumlins are created by the deposition of material (till) beneath a Glacier. They can be up to several kilometers long and they are allingned more or less parallel to one another, the upstream(stoss) slope is sometimes much steeper than the downstream (lee) slope. If there are a group of Drumlins they are often known as "a basket of eggs".
Moraines are deposits of glacial till in the form of hammocky hills or hill-like features. There are various types of morraine, which aree deposited at different parts of the glacier:
- Lateral morraines: These are deposited at the side of a valley Glacier.
- Ground morraines: This is Till.
- Medial morraines: These form in the centre of a glacier downstream from the confluence of neighbouring valleys as adjacent lateral moraines join together.
- Terminal morraines: These are deposited at the end of the lower end of a melting glacier and are composed of sediments that have been carried in, on and under the ice as it advanced. As a valley glaciers retreats then halts, often a number of times in succession. Each halt can be marked by a terminal morraine across the valley, so these are valuable in reconstructing the glacial history of an area.
Altough many of the landforms which are created in glaciated environments are formed by the movement of ice, meltwater also has an important role in reshaping the land scape. As the meltwater flows from glacier margins towards the sea, the water shapes the land, carving out gorges and depositing broad spreads of gravel, sand and silt. Meltwater can be formed by the friction on the bedrock beneath the Glacier. The meltwater transports sediment downsteam, and its deposits are called Fluvioglacial deposits.
Eskers and Kames are two particulary distinctinctive fluvioglacial features. Eskers are long, narrow, sinous ridges formed from fluvioglacial sediments deposited by meltwater streams flowing in or beneath a glacier or ice sheet. Kames are similar in respect that they are long ridges of fluvioglacial sediments, but the flow of water is now over the surface of the glacier. The deposit remains along the valley side after the glacier ice has melted, from this we can estimate the relative height of the ice margin.
When a large valley glacier or ice cap melts, particularly if this happens quickly e.g rapid climate change, it can produce large amounts of meltwater. This high level of meltwater can cause extensive erosion on the landscape, for example erosion on glacial walls.
The landforms produced can have an effect on glacier energy. The relief of the landscape is vey important, the movement of ice is effected by gravity, so in theory the steeper the slope the more energy a ice sheet will have. However there are other factors which have to be taken into consideration, the first being the type of material/rock. If the Glacier is traveling through a hard rock, there is going to be more resistance slowing the energy of the glacier.
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