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Bullet River and Sea Erosion
Home » Hydro Meteorological Disasters » River and Sea Erosion

Erosion Process
Sea Erosion
Waves start by attacking the main points of weakness in the rock such as the joints and any faults that there may be in the rock. The point of weakness is increased until it becomes a cave. The waves continue to attack the cave, which finally results in an arch being formed through the headland. The arch is then attacked by both coastal and sub - aerial erosion and finally the roof of the arch falls into the sea. This then leaves behind a stack, which is then slowly eroded down to become a stump.

Low outcrop of rock formed by the erosion of a coastal stack. Unlike a stack, which is exposed at all times, a stump is exposed only at low tide. Eventually it is worn away completely.

The easiest way of describing the overall effect of coastal erosion is that, if left unchecked, all the coastlines would be, low wave cut platforms. Most erosion takes place around high tide and will be carried out in one of three ways. The first is Hydraulic erosion which has an effect of a small explosive charge. The sudden impact of a wave on to the cliff face forces air into any cracks that they might be or along the bedding planes, compressing the air briefly then releasing the pressure. the changes in pressure causes the cracks to widen and go further into the cliff, material breaks away and washed out of the cliff by following waves. The material washed away becomes means for further erosion. The debris is washed against the base of the cliff in a process known as corrosion and acts in a grinding motion. In this process, not only does erosion take place at the foot of the cliff but the sediment itself is worn down and rounded in a process known as attrition. The third type of erosion is chemical, particularly in limestone and chalk cliffs where chemicals within the sea water attack the rocks eroding the weaker sections and gradually causing the cliff to collapse.

Sea Erosion

Coastal lands may experience long-term erosion under some conditions. For instance, if sea level is rising, the beach may eventually migrate landward or drown. This causes coastal land behind the beach to erode. Also, if the amount of sand from the seaward side is reduced, a beach will erode the land behind it to maintain a constant sand supply. This creates a condition called coastal erosion.

Beaches on eroding coasts undergo seasonal profile adjustments, but they slowly shift their position landward as the land erodes. Hardening a shoreline can interfere with necessary profile adjustments because the dune can no longer share its sand with the beach. As a retreating beach encounters a seawall or revetment it can no longer draw upon a landward sand supply and it begins to erode.

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