Sub - aerial proccesses vs marine PDF

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Sub-aerial processes are far more important in creating distinctive coastal landforms than marine processes.’ TWE do you agree with this statement? Sub – aerial processes can include weathering processes such as chemical weathering, mechanical and biological weathering. Mass movement is also a form of sub – aerial processes. Marine Processes include erosion like hydraulic action and deposition in forms such as longshore drift. Aeolian deposition is also a form of marine processes. One landform formed through both sub – aerial processes and marine processes is a beach / bay. Initially on the coastline there may not be a distinct headland and bay but just one straight coastline. To form the bay chemical and biological weathering occurs. Biological weathering is when roots of plants widen the cracks. Chemical weathering occurs when carbon dioxide is mixed with rainwater to form carbonic acid, which reacts with the carbonate in limestone to form calcium bicarbonate. The bicarbonate is soluble in water and the limestone gets weathered. This all initially weakens the headland and coastline making it much easier to erode later. With the power of the high energy waves eroding the coastline the coastline, this can lead to rock fall – a process of mass movement which weakens the geology and causes rocks to fall of the cliff. This starts to build up the beach as sediment is fallen on to the ground. The formation of a bay is mainly done by marine processes. The less resistant geology such as clay, found at Swanage bay, will erode more quickly than the more resistant geology such as chalk which erodes relatively slower. This forms the bay as a part of the coastline is retreating as the softer geology is eroding faster. The sediment on the beach may be initially from the rockfall but the main process comes from the deposition from constructive waves. Constructive waves have a strong swash and a weak backwash, so sediment from the ocean accumulates on the beach, increasing the size and depth of it. Sub – aerial processes are important in initially weakening the coastline and causing some sediment to build on the beach but marine processes are more important in accumulating the beach and forming the bay through erosive processes. Caves, Arches, Stacks and Stumps are another landform. Initially caves are formed through erosion, a marine process. Fault lines in a coastlines geology allows the high energy waves to cause pressure within them, extending the fault lines and weakening. The hydraulic action from the waves causes air to be trapped in the cracks in a cliff face, the trapped air is compressed which weakens the cliff and causes erosion which then forms a cave. The process where a cave forms an arch is mostly marine. The energy from the waves, and abrasion causes the other side of the cave to gradually grind down by the hydraulic action and rocks from the wave eroding the cliff surface to join to the cave which forms the arch. The process from which the arch turns into a stack is a mixture of sub – aerial processes and marine. Biological weathering occurs on top of the arch. Long roots from plants and saturation of water in the ground weakens the geology as it creates stress and pressure in the rocks. However, this a slow process and need the help of the marine processes of erosion. As the top of the arch is very hard to reach by regular waves, storm waves are required to break down the rock, which was already weaken by the long plant roots. The high energy waves of destructive waves can carry large boulders grinding down the rock in the arch. This can relatively make the arch into a stack quicker than relying entirely on weathering processes. The formation of a stump is mostly erosive. The waves at high tide erode the foot of the stop from the high energy of the waves and rocks smashing against it

breaking the structure forming a wave cut notch. The indent of the foot of the stack makes the structure much weaker and cannot hold the top of the stack therefore making it collapse which forms a stump. The creation of these features is mainly marine as it requires the energy of the waves and the sediment that comes with it, but sub – aerial processes are used in the initial weakening of the cliff, which aids the erosion. A blowhole is another landform. At the start, a cave is formed at the line of weakness due to the high energy waves eroding through the fault lines. Erosion extends into the cliff surface. As the geology has more limestone and less clay it causes slower erosion preventing a geo to be formed. Eventually a pocket of clay is eroded inwards and upwards to create a hole to the surface. Sub – aerial processes then take place. Biological weathering from the roots of the plants, causes erosion at the cliff surface, which then meets the extended cave which forms the blow hole. An example of this is Pigeon Crater in Flamborough Head, here there is slumping of clay at the surface where the whole is – this is a form of mass movement. For this landform. I believe sub – aerial and marine processes are both as important as the other. Sub – aerial processes are important in the collapsing of the blow hole and caves and marine processes are important in eroding the cave. Lastly wave cut platforms is another landform. As cliffs of solid rock erode overtime from their original shore position it exposes the chalk geology, uncovered at low tide and submerged at high tide. The waves have energy which allows the rock to erode through hydraulic action. This leaves an overhang in the cliff. Because of the heavy weight and a weak structure, the overhang collapses, creating a wave cut platform, this process is repeated. As well as the hydraulic action creating a wave cut platform biological weathering occurs on the cliff which weakens the top of the cliff as well the weakening from the structure from the waves. Landslides can occur – this is when the cliff becomes detached and slides down. This contributes to the wave cut platform as the rocks and boulders are separated and fall below. In conclusion, I believe that marine processes are most important in the formation of landforms as the erosive powers or deposition are much faster and efficient way of forming landforms than entirely relying on weathering processes and mass movement. Sub – aerial processes are important in the weakening of geologies and weak surfaces and it can be argued that sub – aerial processes are important in aiding marine processes and initially starting the processes. Overall marine processes are most important but does not act alone....