Coasts revision Flashcards
(40 cards)
2.1a) The littoral zone
Inputs into the coastal system - Precipitation and sediment carried by rivers
Outputs - Evaporation, eroded material that is taken out to sea
Stores - Beaches, cliffs and dunes
Transfers - Longshore drift, mass movement, Aeolian transport
Negative feedback loop at the coast - As the shore is eroded the material makes the wave cut platform wider, this wave cut platform can then absorb more wave energy reducing the impact on the base of the cliff.
Littoral zone is the area of the coast that can be affected by wave action. Its a dynamic zone which means that its constantly changing.
The coast is divided into 4 zones:
Backshore - not influenced by wave action but can be influenced by storm action - Here human action is walking or sunbathing.
Foreshore - Human activity here is surfing or swimming
Nearshore - Scuba diving and snorkelling occurs in the nearshore.
Offshore - waves do not impact the nearshore and there is little human activity.
2.1 b) Coasts can be classified using long term criteria such as geology and changes in sea level or short term criteria like inputs from rivers and tides
Concordant coastlines - Found parallel to the coasts, an example is Lulworth.
Discordant coastlines - Rocks are at 90 degrees to the coastline, example is Swanage bay.
Long term criteria like changes in sea level can lead to emergent or submergent coastlines: Emergent coastlines are caused by isostatic rebound where the land rises or falls - this can lead to an area of land that was previously underwater, become exposed.
Submergent coastlines - this is when areas flood due to a eustatic change in sea level - this is leading to increase in sea levels - can be seen on the dalmatian coast.
SHORT TERM PROCESSES THAT OCCUR AT THE COAST:
> waves, tides, weather events and rivers
Weather events can influence wave action - for example, extreme storm events will increase the amount of destructive waves. These waves are high energy and have a strong backswash which means that more material is transported away from the beach. This means that the beach is loosing sediment.
Warm weather increases the amount of constructive waves, which can be used to build the beach because they have stronger swash and weaker backswash.
2.1c) Rocky coasts come from geology that is resistant to erosion so are mainly found in high energy environments. Coastal plain landscapes are found in areas of low relief, these are normally found in low energy environments.
Rocky coasts can be found in the North and west of the UK and can be categorised with more resistant geology. On these coastlines erosion exceeds deposition due to strong winds and destructive waves which target the base of the cliffs, forming wave-cut platforms, stacks, stumps and caves.
Coastal plain landscapes occur where the land slopes down to the sea. These are normally low energy coastal environments that form due to coastal accretion - This is where deposition exceeds erosion because the sheltered location and constructive waves build up the beach due to their weak backwash. The increase in deposition helps to stabilise the coast and reduce erosion; the addition of vegetation can also stabilise the coast as it dissipates wave energy coming onshore and the roots help to bind sediment together, making it less easily eroded.
What are negative and positive feedback loops?
Negative feedback loops slow a process down this can be positive or negative - an example is when eroded material makes a wave-cut platform wider which can therefore be used to dissipate wave energy and reduce rates of erosion on the base of the cliff, increasing stability.
A positive feedback loop speeds up a process - For example coastal plain landscapes can be categorised by large beaches and high levels of vegetation because they are found in low energy environments. Climate change can create a positive feedback loop because it can increase the occurrence of destructive waves rather than constructive waves, these waves have a stronger backswash and will therefore lead to erosion becoming more prominent than deposition.
what are emergent coastlines?
Emergent coastlines are caused by isostatic rebound - this is where the land either rises or falls, not the sea level.
What is a submergent coastline?
A submergent coastline is caused by a eustatic rise or fall in the sea level - this can be caused by thermal expansion as it increases the volume of water.
2.2a) Geological structure is responsible for the formation of concordant and discordant coasts
Geological structure is the characteristics or arrangements of rock units.
Concordant coasts - These occur where the rock strata run parallel to the coast. Dalmatian and Haff coastlines are examples of concordant coastlines.
Discordant coastlines - these are found where rock strata meets the coast at an angle, its found perpendicular to oncoming waves - the alternating rock type creates headlands and bays because they erode at different rates.
2.2 b) Geologial structure influences coastal morphology; Dalmation and Haff coastlines are concordant whereas Headlands and bays are found on discordant coasts.
Dalmation concordant coastline - The dalmation coast in croatia was formed as a result of sea level rise and tectonic activity. Tectonic activity formed anticlines and synclines which run paralell to the sea. Sea level rise after the devensian glacial flooded the synclines leaving the anticlynes above water. This has led to a series of islands forming that run paralell to the coast.
Haff concordant coastline - During the devensian glacial large amounts of sand and gravel were deposited offshore. After the glacial period had ended material was deposited near to the land by constructive waves, these constructive waves build beaches.
The deposited sediment builds bars and the river mouths trapped water behind to form a lagoon - these features only occur on low-energy coastlines.
Discordant coastlines - An example of a discordant coastline can be found in Lulworth cove in Dorset. The rock meets the coast at an angle which forms a discordant coastline. Wave refraction is an important process that acts on discordant coasts because the different resistance of geology means the coast erodes at different rates. Waves loose energy when they come towards land as they reach resistance at the headland, the energy therefore causes the waves to bunch up and most of the wave energy is dissipated onto the headland. This causes the headland to erode and you get stacks and stumps.
2.2c) Geological structure is an important influence on coastal morphology because it influences erosion rates and the formation of cliff profiles.
Joints - these are vertical cracks caused by tectonic movements. Jointing increases erosion rates by creating fissures that hydraulic action can exploit. Folding in stair hole lead to heavy jointing which made the Purbeck limestone erode faster than the Portland limestone.
Fissures - these are much smaller cracks in the rocks that are weaknesses that erosion can exploit.
Dips - Sea-ward dip is when the profile of the cliff exceeds 90 degrees - this produces areas of overhanging rock which makes it very vulnerable to rock or block falls.
What are concordant coasts and examples?
Concordant coasts can be found when rock strata runs parallel to the coastline. Dalmation and Haff coastlines are examples of concordant coasts.
What are discordant coasts and an example?
Discordant coasts occur where rock strata meet the coast an an angle, they run perpendicular to the coast - an example of a discordant coast is Lulworth cove in Dorset.
How are Dalmation Coasts formed?
Dalmation coasts in Croatia was formed by sea level rise and tectonic activity; Tectonic activity formed anticlines and synclines which run paralell to the sea. Sea level rise after the devensian glacial flooded the synclines which left the anticlines above the water. This led to a series of islands forming which run parallel to the coast.
How are Haff coastlines formed?
Haff coastlines - During the devensian glacial large amounts of sand and gravel were deposited offshore.
After the Glacial material was deposited near the land by constructive waves- these waves build up the beaches. The deposited sediment built bars and river mouths blocked sediment, forming lagoons, these features only occur on low energy environments.
Examples of Discordant coasts?
Discordant coasts occur when rock strata is found at an angle to the coast, it runs perpendicular and the alternating strata is a weakness that erosion exploits. An example of a discordant coast can be seen at Lulworth coast in Dorset. Wave refraction acts on discordant coasts and the waves bunch up when the reach resistance on the headland, increasing erosion rates which leads to the formation of stacks and stumps.
2.3a) RATES OF COASTAL RECESSION - Bedrock lithology and unconsolidated material are important in understanding the rates of coastal recession.
COASTAL RECESSION - This is the retreat of the coast inland due to erosion, sea level rise and submergence.
- Bedrock lithology can influence rates of recession at the coast - Sedimentary rocks form as a result of compaction and cemention of sediment, examples include limestone and sandstone. Sedimentary rocks are the youngest rocks and have weak bedding planes, that erosion can exploit.
Igneous rocks form when molten rock from the earths mantle cools and hardens. An example of an igneous rock is granite.
> Erosion rates of igneous rocks are really slow because they have interlocking crystals that make it a hard resistant rock because there are little weaknesses that erosion can exploit.
- Unconsolidated material like clay has a fast erosion rate because its loose material so easily eroded. Weather can also influence this because an increase in rain increases the chance of landslides.
2.3b) Differental erosion of alternating strata in cliffs produces complex cliff profiles that influences recession rates.
Differental erosion - This is the changing rates of erosion of different roc types.
On discordant coastlines differental erosion leads to headlands and bays forming; This is because the alternating strata means that the less resistant rock erodes faster - An example of less resistant rock includes permeable or porus rocks. These rocks allow water to flow through them. This leads to rates of erosion, especially in winter because water enters the rocks and then freezes and expands, cracking the rocks. Where permeable rock overlies impermeable rock mass movements is common because the additional weight of the water and lubrication increases instability of the cliff, potentially leading to rotational slumping.
2.3 c) Vegetation is important in stabilising sandy coastlines through dune successional development and SALT MARSH development in estuarine areas.
Vegetation helps to stabilise the coast because:
> The plant roots help to bind the sand together reducing the rate of erosion.
> Wind speeds are reduced by vegetation which increases deposition and decreases erosion rates.
However, Vegetation is often sparse in coastal environments because there is a lack of nutrients, high wind speeds and a lack of shade which prevents growth.
Vegetation can either stabilise sand dunes or salt marsh.
SAND DUNE SUCESSION:
The succession of vegetation in sand environments is known as PSAMMOSERE
> Sand dunes are dynamic environments which means that everything is constantly changing. Sand dunes are create when wind blown sediment is deposited against an obstruction. As more particles are caught the dune grows in size. Overtime, the ridges of the dunes are fixed by vegetation in a process called succession. Pioneer species (the first plants to arrive) have to deal with the salinity, lack of moisture and wind but pave a way for other species which then further increases the rate of vegetation growth.
There are 5 types of sand dunes, these include embryo, fore, yellow, grey and mature dunes.
Aeolian transport is the term used to describe particles transported by the wind. Aeolian transport is the first process of dune formation as sediment is transported through saltation, surface creep and suspension.
> Embryo dunes are the first dunes that grow. They occur when wind blown sediment is trapped by debris and deposition of sediment occurs. Pioneer species like Lyme grass begin to colonise, as these plants can tolerate the high salt levels. Embryo dunes are very fragile as vegetation growth is very limited so not enough to bind the sediment with the roots - they only normally reach a height of 1 metre.
> Mature dunes - These are the oldest and most stable dunes, this means that they cannot be damaged by the wind or the sea. The further away from the sea that the dunes are you get more vegetation growth, which increases stability of the dune. Mature dunes support a wide range of vegetation but growth of oak trees can especially help to stabilise the dune due to the roots that bind sediment together.
SALT MARSH SUCCESSION:
A succession in salty water is called a Halosere.
Salt marshes often develop in Estuarine areas because there is a constant supply of sediment from rivers and its a sheltered area away from strong winds and waves.
In the Estuarine environment salt water and freshwater mix which leads to flocculation. This is when clay particles stick together, leading to sediment accumulation. The deposited sediment is then colonised by algae which binds sediment together and increases the rate of organic matter. As the accumulation of sediment rises, water depth is decreased and this keeps occurring until a climax community is reached.
Paragraph ideas for coastal recession 6 or 8 marker?
If its a 6 marker talk about bedrock lithology and then 2 nd paragraph can be on the role of vegetation , this could be on sand dunes or salt marshes.
If its an 8 marker:
P1 - Bedrock lithology
P2 - Differental erosion of alternating cliff strata
P3- Sand dune or salt marsh succession from vegetation.
How can Bedrock Lithology influence rates of recession at the coast?
Bedrock lithology is the type of rocks.
Sedimentary rocks are geologically the youngest rocks - this makes them weaker and weak bedding planes provide an area of weakness that erosion can exploit.
On the other hand igneous are other types of rocks - igneous rocks are formed when molten rock from the earths mantle cools and hardens. These rocks have a really slow eroison rate because interlocking crystals make it a hard resistant rock and there is little faults that erosion can therefore not exploit.
Bedrock Lithology can influence rates of recession because the rocks erode at different rates. This creates instability and increases the chance of mass movements like rock falls, further increasing rates of recession.
How can differential erosion influence rates of coastal recession?
Differential erosion can influence rates of coastal recession because the alternating strata means that the less resistant rock erodes faster which leads to the formation of headlands and bays on discordant coasts. An example of a vulnerable rock are permeable or porus rocks because they allow water to percolate through. This leads to recession because water enters cracks in the rocks and expands and freezes in cold weather, leading to the rock breaking. Where permeable rock overlies impermeable rock mass movement is common because the water lubricates and adds additional weight, increasing the chance of rotational slumping.
How can vegetation stabilise the coast from recession?
Vegetation can help stabilise the coast by dissipating wave energy, reducing wind speeds and plant roots bind sediment together, increasing stabilisation.
Vegetation can help to stabilise coastlines through dune successional development or salt marsh successional development.
Sand dunes form through Aeolian transport when sediment reaches a barrier and is therefore deposited; Wind transports more sediment which is then trapped behind the barrier. Overtime ridges of the dune are stabilised by pioneer species which bind sediment together. These pioneer species can withstand the high winds, salty conditions and lack of moisture which paves a way for other vegetation. Overtime, more sediment is accumulated due to less of the dune being exposed and you eventually get a mature dune. Mature dunes are the oldest and mature off all the dunes and can be stabilised by a variety of vegetation like Oak trees, in which their roots bind sediment together.
SALT MARSH SUCCESSION: Salt marshes develop in Estuarine areas because there is a constant supply of sediment from a river and the area is sheltered from strong winds, reducing erosion.
In the Estuarine environment sea water and freshwater mix which leads to flocculation; Flocculation is the process of clay particles sticking together which causes sediment to build up. This deposited sediment is then colonised by algae which binds the sediment together and increases the rate of organic matter. As sediment thickens water depth is reduced and this process continues to happen until a climax community is reached.
2.4 Marine erosion creates distinctive coastal landforms
2.4a) Different wave types influence beach morphology and beach sediment profiles, which vary at different timescales
There are 2 types of waves - these include constructive and destructive waves
Constructive waves: Constructive waves build up the beach because they have a strong swash which deposits sediment and a weak backswash so the sediment is not then taken away. Constructive waves create berms which are ridges of sand or shingle.
Destructive waves: Destructive waves break down and destroy a beach due to their weak swash and strong backswash which erodes any existing deposited sediment.
Beach morphology is the shape of the beach.
Constructive waves influence beach morphology because they create flat beaches with berms due to the deposited sediment. Destructive waves erode berms and a steep beach is created.
- Short term changes can be influenced by the weather - Sunny weather reduces the amount of destructive waves so sediment accumulation on the beach is increased - this can increase beach amenity value as its more suitable for human use - obviously flips the other way with wet weather
2.4b) The importance of erosional processes and how they influence coastal landforms
Erosional processes include:
Abrasion, attrition, corrosion and hydraulic action.
> Abrasion - Sediment is picked by waves and eroded away by the cliff or the headland.
> Attrition - As rocks bash in to each other they become smaller - sedimentary rock erode the fastest.
> Corrosion - Corrosion involves water dissolving rock minerals - this process occurs at high tide because water floods wavecut platforms and then the water stays there, the acid dissolves away the rock.
> Hydraulic action - Waves force air at high pressure into cracks in the rocks, this weakens the rocks.
Lithology influences rates of erosion because geologically younger rocks erode more quickly as they are weaker and more likely to have more cracks.
2.4 c) Erosional processes ( Abrasion, attrition, corrasion, hydraulic action) causes distinctive coastal landforms like wave cut platforms, wave cut notches, cliffs and the cave arch stack and stump sequence.
Wave cut notches are formed by erosional processes; At high tide destructive waves reach the base of the cliff. Processes of abrasion and hydraulic action erode rock at the base of the cliff, this is because the shear force of the waves force air into cracks in the cliff which weakens the rock. This leads to distincitve coastal landforms forming like wave cut notches due to the base of the cliff being eroded away. Sea caves may form along weaker points of the wave cut notch.
Wave cut platforms: On high energy coastlines, destructive waves attack the base of the cliff at high tide. Erosional processes like abrasion and hydraulic action lead to the formation of a wave cut notch that is increased in size through undercutting. Eventually the undercutting creates an overhang that collapses due to weathering and mass movement. The cliff retreats leaving a wave cut platform that is exposed at low tide.
Cave, arch, stack, stump sequence: Rocks have joints and faults in their geological structure which is then eroded by hydraulic action and abrasion leading to the formation of a cave. This process is further sped up by wave refraction which concentrates energy on to the side of the headland which creates more destructive waves. Marine erosion of the cave causes an arch to form and then hydraulic action of the arch causes a wave cut notch to form. Eventually, the roof of the arch will collapse and detach leaving a stack and then marine erosion of the stack will form a notch on both sides and eventually lead to a stump forming.
