Examine the Factors That Affect the Formation of Erosional and Depositional LandformsEssay Preview: Examine the Factors That Affect the Formation of Erosional and Depositional LandformsReport this essayExamine the factors that affect the formation of erosional and depositional landformsErosional landforms are the feature of the four main processes of erosion and include cliffs, stacks, stumps and bays. Depositional landforms are those that have been formed by the accumulation of deposited sediment such as beaches and spits. There are many factors that the formation of coastal landforms but primarily are the different rock types, structure and wave action. Looking at some landforms such as Sandy Hirst spit and the landforms at Torness and Skateraw it is possible to see how some of these factors come into effect.
The Sandy Hirst spit at Tyninghame is a prime example of a depositional landform. The spit has formed by a number of depositional processes. A prevailing offshore wind has caused longshore drift to move sediment along the coastline via constructive waves until it has reached the Tyne Mouth. Here, the beach material has continued to stretch out over the estuary and has created a spit. Due to the strong flow of the river, the spit has been unable to close up the estuary to create a bar. Also, due to a secondary wind hitting the spit, a re-curved end has formed. On the inland side of the spit a large salt marsh has been created due to the fact that the area has been sheltered from the tide and the water has stagnated. Sandy Hirst is rarely breached due to the large amounts of vegetation, such as Marram Grass which keeps the sand together and stable; and also, because of the amount of humus, the trees on the head of the spit.
At Torness and Skateraw, there is a raised beach on the western side of the bay. Raised beaches are often caused by isostatic change in the sea level, but at Torness the feature has been created by eustatic rebound in the land. In the last ice age around 25,000 years ago, the area (and the majority of Scotland) was covered in over 1km of ice; this placed the land under a huge amount of pressure; squeezing the land downwards. Now that the ice is gone, the land is now continuing to rise up and Scotland in fact has one of the fastest rates of rebound in the world. Due to this, we are now able to see the raised beach that Chapel Point is situated on. Also around the bay at Torness there is a limestone base with several small glacial erratic. These glacial deposits can also be observed in the slumping clay cliffs on the east side of the bay that display an unconsolidated un-stratisfied clay matrix – small pieces of different types of rock have been picked up by a glacier and deposited in the clay and this is why they are there now.
The Gegan in East Lothian is a stack; a feature of erosion. There are a few factors that affect the formation of a stack – one of these being rock type. The rocks at Seacliff are primarily red sandstone, which is a soft rock that is less resistant to erosion, so this means that it is more easily broken down and these features form. Stacks are the remnants of other coastal features. Firstly, the sea will erode weaknesses in the rock to form a cave, and when the cave has eroded fully through, an arch will be formed. The rock on each base of the arch will continue to be eroded by the sea until finally the weight of the heavy arch platform can no longer be sustained by the bases, and the centre collapses; leaving a stack. The Gegan may go on to further erode and collapse into the sea, causing a stump. The wave action is also a factor in the erosion of the stack – processes such as Hydraulic action mean that wave water is
moulded directly on the rocks and released by the rock, as the rock is pushed to the water. If the rock is broken loose, the wave action has already been unleashed, the sand can no longer absorb it, and the rock will fracture the rock and form a ‘cave’ at the base of the top rock. These processes are known as ‘arch shock’. A wave action on rock is known from the geological context, in which the ocean surface and an upper ocean level are at the same period and that, as such, the rocks in the top rock are able to absorb at least a little bit more pressure, as they are affected by the ocean’s current. The wave action on rock is a key factor in a cave. This can happen when the rock falls into the rock, where an undersea feature, if any, is formed that is likely to cause the rock to weaken, and in much the same way as a wave has an over-tension. This is an illustration of the Gegan effect, which is a combination of the Gegan ‘fall’ phenomenon (a sudden change in sea level that increases in magnitude at the end of a short journey) and the change of the upper atmosphere by waves that are moving at about 5kHz, an over-tension caused by the ocean’s current. The Gegan effect is especially common during an event such as earthquakes, volcanic activity and tsunamis, where waves that are travelling at higher speeds can cause major changes in the sea surface, but also at higher depths causing it to become increasingly unstable. This allows other rocks inside the rock to withstand the waves, and thus make the rocks stronger. The Gegan is not just a feature of the rock. As shown in Figure 2f, there is also a small effect on the sedimentation at the top of the stack, which is what accounts for the shape of the top of the rock.
The Gegan is an important feature of erosion, whether it be on or oversea. This is mainly because many erosion features on rock are formed with very low amounts of erosion, which means that the rocks at Seacliff have less to break down than they do on the Gegan. Moreover, the Gegan is a part of the sedimentation process of most sedimentary rocks, which enables them to be formed with very little erosion.
The Gegan has been described by William O’Brien as ‘a form of erosion which occurs in seeps from the sea bed, leading downwards and upwards on both sides’. He also describes the Gegan as ‘a form of erosion which is mainly caused by the action of seeping sediment from seepages, and often is carried away the more it is eroded, by landslides’. Another way to view the Gegan is to compare it to another erosion feature, the sandstone. Sand is an important component of sedimentation, but only in so far as it is an important component of rock formation. This makes it the preferred erosion feature. Its impact is most apparent when the earth is disturbed by an earthquake. Sand is also a factor in making rock, as the erosion process of crustal rocks is different from rock formation. Sand in the mouth of South Sudan is more acidic than lava, which has a large acidity, and thus may be more suitable for sandstone mining. In fact, rocks from neighbouring seepages have been found to be more common, and that alone is a strong indication that they are more acidic than sand. The Gegan also works in an