Geography - coasts Flashcards
Waves
Waves: Friction or drag on the surface of the sea caused by the blowing wind causes a swirl in the water. Energy of wind causes a movement across the water surface in a wave motion
What effects waves:
Fetch: Larger fetch = more time for wave to accumulate or transfer energy
Wind speed: Higher wind speed = more energy transferred - bigger wave
The time period for which wind is blowing: Longer time = more energy able to be transferred from the wind to the waves, more time to build in size
Constructive waves
Responsible for deposition Adds sediment to coast Swash is bigger then backwash Waves are low Creates gently sloping beaches
Destructive waves
Responsible for erosion Removes sediment from coast Swash is smaller than backwash Waves are high and steep Creates steeply sloping beaches
Mass movement
The downhill movement of weathered materials under the force of gravity
Erosion
the wearing away and removal of material by a breaking force such as a wave
Deposition
The dropping of sea material due to loss of energy
Weathering
The decomposition of Earth’s rocks, soils and minerals in situ through direct contact with the planet’s atmosphere
Transportation
The movement of eroded material
Abrasion
The wearing away of material via a sandpapering effect whereby pebbles grind over a rock platform
Attrition
Where rock fragments and eroded materials are hurled towards each other and made smaller and rounder
Hydraulic action
When trapped air from waves are forced into cracks and cavities in rocks, the pressure causes the rocks to break apart
Corrosion (solution)
The dissolving of rocks in the sea
Long shore drift
Waves are caused by friction that occurs when wind blows across the surface of the sea.
The waves travel and hit the coastline in the direction of the prevailing wind. Eroded materials are dropped on the coast via deposition by the swash. However due to gravity materials such as sand are moved straight back down by the backwash at 90 degrees in a straight line perpendicular to the beach. This way materials are gradually carried and moved along the coast or beach in the direction of the prevailing wind until it meets an obstruction. Longshore drift is a process of transportation. It creates coastal landforms such as bars and spits. It may also cause problems in river estuaries due to the deposition of material and sediment. Some estuaries which are used to harbour boats have to be constantly dredged because of longshore drift constantly depositing material
Physical weathering
water (from rain usually) gets into cracks in rocks and at night when temperatures drop below freezing it causes this water to expand as it freezes, this creates pressure on the surrounding rocks and will cause it to eventually break apart. This usually occurs in high land areas where temperature is above freezing in the morning and below freezing at night
Chemical weathering
rain water contains chemicals and weak acids that may react with sediment or rocks. For example when certain acids react with limestone, it causes the limestone to disintegrate or break apart
Biological weathering
When seeds fall into cracks in rocks by the action of plants and animals. If there is a little moisture, seeds can begin to grow, the roots of the plant may grow rapidly and force their way into cracks causing the rocks to slowly break apart. Burrowing animals such as rabbits (animals that dig holes) can also break apart rocks.
Headlands
area of land that protrudes out of a coastline, usually made from hard rock and is resistant to erosion
Bays
a wide coastal inlet that is open to the sea, usually comprised of soft, less resistant rock prone to erosion
Features that cause the formation of headlands and bays
discordant coastlines, destructive waves, rock material geology
Discordant coastlines
alternating layers of soft and hard rocks parallel to the sea, meaning each layer of rock is evenly eroded
Concordant coastlines
alternating layers of hard and soft rock perpendicular to the sea, creates headlands and bays, soft rock layers are eroded easily and forms bays, harder rock layers are less easily eroded and forms headlands.
Examples of soft rock
clay, sand, gravel
Examples of hard rock
chalk, limestone
How are Wave cut platforms formed
Most headlands are edged by a cliff. Erosional processes such as hydraulic action and abrasion and corrosion hit away and wear away at the of a cliff face,
eventually undercutting it at the low and high water marks and creating a wave-cut notch, the wave-cut notch after more erosion extends into a cave
after continual erosion, biological, chemical and physical weathering the rocks above the wave-cut notch collapses as well as the pressure is too much causing the cliff to retreat landward, the steep face of the cliff is sustained.
The bass of the cave or wave-cut notch remains and forms the wave-cut platform as attrition causes the collapsed material to be broken down into smaller pieces, while some cliff material may be washed into the sea. This may be deposited at the end of the platform, forming an off-shore beach
What is headland retreat
Erosional processes such as hydraulic action, abrasion and corrosion wear away at the faults and cracks of the headland widening the fault and eventually creating a cave. After continual erosion, this cave is eventually eroded through to the other side of the headland, forming an arch. After a while with waves eroding the bottom of the arch and the chemical and biological and physical weathering acting on the overbearing rocks of the arch, the arch collapse as it is overwhelmed by the pressure of its weight and gravity, leaving an isolated stack that is now separate from the retreated headland. After further erosion and weathering, this stack becomes a stump as the rock is further undercut and eroded. The stump can only be seen at low tides
How are beaches formed
Erosion and weathering processes break off rocks at cliffs and headlands leaving loose sediment and rock material in the sea. These rocks are carried by the waves towards the coast. The losing of energy or encountering of vegetation and counter-current creates constructive waves whereby the backwash of the waves are weaker than the swash leads to the depositing of these rock materials onto the coastline. The process of longshore drift helps spread these rocks and sediments across the coastline and as this material is accumulated on the coastline a beach is formed. Sandier beaches are usually created when there is lower energy waves at the coast and water is shallow. Pebbled beaches are usually found in places where there is heavy cliff erosion nearby and high wave energy.
How are spits formed
Longshore drift carries sand and other sediments across the coastline in the direction of the prevailing wind, even when the coast changes direction, the direction of longshore drift stays the same and sediments continue to be deposited along a straight line even when the direction of the coast rounds off or changes, this leads to the creation of a spit whereby one end of the spit is connected to the coastline and the other end is in open sea
