“Glaciated Uplands are landscapes of erosion: glaciated lowlands are landscapes of deposition” examine the validity of this statement with reference to glaciated areas you have studied
Arran is an ideal place to look at when examining the validity of the statement. During the Devensian Glacial, the ice sheet covering Britain reached its furthest extent, totally covering Arran. This helped to shape the landscape. In around 11,000BP the Loch Lomond Readvance occurred. This time Arran was not covered by an ice sheet but its valley glaciers grew. This formed many of the features still clearly seen on the island today. They show fresh and visible signs of the glacial erosion and deposition that once occurred.
Glacial erosion is caused by ice movement combined with material within it. One type of erosion is abrasion. This occurs when pieces of rock held within the ice rub against
other pieces of rock wearing them down. Another type of erosion is plucking. This occurs when ice freezes onto a piece of rock on the valley side. When the glacier moves away it may then be broken off. For these processes to occur it helps to have a steep gradient, as this will lead to ice flow. A harsh climate is also needed, which is cold, to encourage ice formation and accumulation. These conditions are often found in upland areas.
Glacial deposition is caused by melting when material is dumped in situ. It leads to unsorted material as when it melts everything is just deposited in no particular order. The material is also unstratified and unconsolidated. It is a mix of all sizes and shapes of rocks. The a-axis of the rocks tends to be found parallel to the direction of the ice flow. Glacial deposition tends to occur in higher temperatures as this is when the ice will melt. It also tends to be found at a lower altitude as here it is warmer and the glacier may be more likely to melt. A gentler gradient means the ice is more likely to stay in situ which is necessary for deposition.
There are many erosional features that occur in upland areas like the statement suggests. A corrie is a good example:
First snow collects in a North facing hollow at a high altitude, as the conditions are cold enough for it to settle. Gradually the snow patch undergoes nivation producing a marked nivation hollow where the underlying rocks begin to disintegrate. Over time with more accumulation the snow patch will be converted into nevï¿½ and then into true glacial ice, through partial melting and refreezing. Continued accumulation will lead to the formation of a corrie glacier. The rotational slip as the ice leaves the corrie causes plucking and abrasion which erodes the hollow to create steep side walls surrounding an armchair shaped depression.
Another example of an upland erosional feature is a hanging valley, like Glen Eason in North Arran. This was formed by a smaller glacier which flowed into the main valley glacier which formed Glen Chalmadale. The smaller glacier in Glen Eason had less erosive energy so the valley has been left ‘hanging’ higher up than the main valley. The geology of the valley also played an important part in its formation, as the rock is part of the hard baked margin making it harder to erode.
There are also many depositional features that occur in lowland areas like the statement suggests. For example terminal moraine:
This is a linear ridge of glacial debris marking the maximum limit of an ice sheet or glacier. It is produced when the snout is stationary for a period of time and starts to melt. The material can no longer be held, so is deposited to form a crescent shape mound. It commonly occurs in lowland areas as this is where conditions for melting tend to be found. It is also likely to be where the glacier reached its furthest extent.
Another example of a lowland depositional feature is an outwash plain. Glen Catacol is an example that can be found in North Arran. An outwash plain is composed of gravels, sands and clays. They are a stratified and sorted deposit. In general the material gets smaller the further it is away from the snout. They are formed from materials deposited by melt water streams. Outwash plains tend to be quite flat and wide, they can reach up to 10km in length.
The previous examples have all supported the statement. There are, however, some examples of features that don’t support the statement. Striations are one such feature. They are erosional features caused by abrasion. A rock found at the base of the glacier can not be easily pressed into the ice so will scratch the rock it passes over. The scratches are very fine and narrow. They can vary in length from 1cm to 1 metre. The problem arises as they can be found wherever the ice has flowed; as this can be in both upland and lowland areas it goes against the statement.
Roche Moutonï¿½es are another example of erosional features that can be found in lowland areas. These can occur wherever there is an outcrop of slightly more resistant rock, whether it is in a lowland or upland area. The ice is forced to move over the rock. It will smooth the up slope through abrasion. This is due to the increase in pressure that occurs as it moves upwards causing melting. On the down slope it will refreeze as the pressure is released causing plucking. This makes the down slope jagged. Examples can be found in Glen Rosa in Arran.
There are also examples of depositional features in upland areas which go against the original statement. Recessional moraine can be formed further up the valley, especially at the end of a glacial phase when the glacier has retreated to an upland area. Examples of these can be found in Glen Rosa. Terminal moraines may also be found in upland areas. During the Loch Lomond readvance only corrie glaciers formed in Snowdonia. Many of these corries have examples of terminal moraine deposited at the lip.
Boulder fields cover most upland parts of Arran. They were deposited by the ice sheets that covered the island during the Devensian Glacial. Medial and lateral moraine can also be found in upland areas. These were formed by the debris that lay at the sides and at the centre of the glacier. When the glacier melted the material was deposited to form moraines. Many of these can no longer be found, however, as they have been weathered over time. There are examples that can still be seen in Glen Catacol in Arran.
Drumlins are another feature that can be found in upland areas which were created by deposition. These are smooth elongated mounds of till with their long axis parallel to the direction of ice movement. They have a steep stoss end facing the direction the ice came from and a much gentler streamlined lee slope on the opposite side. They can reach over fifty metres in height and one kilometre in length. The most widely accepted view is that they were formed when the ice became overloaded with material reducing the competence of the glacier. Once the material had been deposited it may then have been streamlined by later ice movement. There are a few examples in the Lake District.
There are actually quite a few landforms that go against the argument of the statement. When looking at how many depositional and erosional features are formed, we can see that whether they are in an upland are lowland area is often not really relevant. Often there are other factors that affect where they can be found.
Climate is an important factor to look at. It is not surprising that many of the erosional features in lowland areas have disappeared, as it is so long since the ice was found there. The Loch Lomond Readvance didn’t really affect the lowland areas and since that is the last time glaciers were present in Arran the erosional features are bound to be more prominent in upland areas. Also many of the depositional features that formed in the upland areas have been more easily weathered as the climate tends to be harsher at higher altitudes.
Although in many cases the statement is correct, there are many cases where it is not. It contrasts upland and lowland areas and suggests that erosional and depositional features can not occur in the same location. In many ways it appears true as more erosional features are probably found in upland areas and more depositional feature in upland areas. The reasons behind there location though, is often more to do with the climate.