Coastal features Flashcards
Formation of a Stack
A stack is formed by firstly hydraulic action, when the pounding waves compress trapped air in the rocks creating an explosive blast which weakens and loosens rock fragments. Abrasion then occurs when rock fragments are thrown against the headland breaking down the cliff, face wearing away the rock. Corrosion then happens when acidic salt spray dissolves the rock. And as the rock has weak points it is more easily eroded and over time the lines of weakness are enlarged and develop into small caves. And in some cases a blowhole can form in the roof of the cave as compressed air is pushed upwards by the power of the waves causing vertical erosion. There may be erosion on both sides of the headland due to wave refraction until eventually the sea cuts through the back walls of the caves, forming an arch. And continued erosion enlarges the arch. The base of the arch is also undercut by the erosion, causing the arch to become unsupported. Eventually the arch collapses due to gravity to form a stack. For example, Old Harry is a Stack at Handfast point.
Formation of a spit
Sand spits are formed by the process of longshore drift. When swash, waves driven by prevailing wind push material up the beach at an angle. The returning backwash is dragged back by gravity down the beach at right angles. And then when there is a change in direction on a coastline, allowing a sheltered area for deposition. The material then slowly builds up to appear above the water. The spit develops as long as the supply of deposits is greater than the amount of erosion. The shape can become hooked or curved at the end in response to changes in wind direction. And a salt marsh may form in a sheltered are behind a sand spit, for example Spurn Head.
Hydraulic pressure
Hydraulic pressure is when the pressure from the water causes cracks in the rock to widen.
Wave pounding
Wave pounding is when waves wear away soft rock at the base at the base of a cliff.
Corrasion
Corrasion is when rocks are hurled at the cliff and become smaller and more rounded.
Corrosion
Corrosion is also when rocks are dissolved by acidic salt spray.
Formation of Tombolo
Formation of a spit and then a spit joins a headland to an island it is called an tombolo. It is a barrier of sand stretching at to sea where it meets land. For example Chesil Beach on Dorset.
Formation of a Bar
Spit Formation and then a spit grows across the entrance to a bay, connecting 2 headlands, enclosing a small sheltered lagoon behind it. This happens when there is no strong flow of water from a river into the sea, and through time, this stagent lagoon water is infilled by deposition. Bars form when there is a change in direction on a coastline, which allows a sheltered area for deposition. For example Slapton Sands in Devon
Formation of a cave
Caves occur where the coastline consists of hard rock and is attacked by waves along a line of weakness such as a joint or fault in the rock. The waves will attack the line of weakness by abrasion, hydraulic action and solution.
Formation of an arch
Caves occur where the coastline consists of hard rock and is attacked by waves along a line of weakness such as a joint or fault in the rock. The waves will attack the line of weakness by abrasion, hydraulic action and solution. Over time, horizontal erosion of the cave may cut through the headland to the other side an form an arch.
Formation of an stump
A stack is formed by firstly hydraulic action, when the pounding waves compress trapped air in the rocks creating an explosive blast which weakens and loosens rock fragments. Abrasion then occurs when rock fragments are thrown against the headland breaking down the cliff, face wearing away the rock. Corrosion then happens when salts in sea water dissolves rock. And as the rock has weak points it is more easily eroded and over time the lines of weakness are enlarged and develop into small caves. And in some cases a blowhole can form in the roof of the cave as compressed air is pushed upwards by the power of the waves causing vertical erosion. There may be erosion on both sides of the headland due to wave refraction until eventually the sea cuts through the back walls of the caves, forming an arch. And continued erosion enlarges the arch. The base of the arch is also undercut by the erosion, causing the arch to become unsupported. Eventually the arch collapses due to gravity to form a stack. Often the stack falls over due to continued erosion at its base. This in turn will be eroded further to leave a stump. For example, Old Harrys wife on Handfast Point.
Formation of Headlands and Bays
Headlands and bays are found along coastlines where there are alternating bands of hard and soft rock. Waves erode the areas of softer rock more rapidly to form bays. Erosion occurs via hydraulic action, this is the sheer force of the waves hitting the rocks and compressing the air in the cracks and breaking off particles. Abrasion also happens when sediment in the waves hits off the rock, scraping it away. However, the waves cannot wear away the hard rock as easily and as quickly so headlands are left protruding out into the sea. Repetitive and long-term abrasion at the foot of a cliff can erode a wave-cut notch causing rock above to collapse into the sea. Headlands are left exposed and protect the sheltered bays
that form between them.
Formation of a wave-cut platform
Cliffs are formed in places where high, steep land meets the sea. The sea constantly crashes against cliffs and erodes their base due to hydraulic action, the sheer force of the waves hitting the rocks and compressing the air in the cracks and breaking off particles & corrasion, when sediment in the waves hits off the headland, scraping it away. Here, a wave cut notch forms. Over time, this notch enlarges due to corrosion, until the cliff becomes unsupported and collapses due to gravity. As a result the cliff appears to retreat backwards over a period of time. Where the material falls into the sea, a wave cut platform is created and marks out
the old coastline. Wave-cut platforms are exposed at low tide but covered at high tide.
