Coasts

Geology

Cornwall’s rocky coast lines can withstand winter storms without suffering rapid erosion. Cornwall consists of older rocks that are resistant to erosive power of the sea including igneous rock, sedimentary rock, metamorphic rock.

High energy coastlines

Rocky coasts are generally found in high energy in the uk these tend to be: stretches of Atlantic-facing coast with powerful waves, where the rate of erosion exceeds the rate of deposition, erosional landforms are found in these environments.

Low-energy coastlines

Sandy and estuary coasts are generally found in low energy environments these tend to be stretches if the coast where waves are less powerful or where it is sheltered, where the rate of deposition exceeds the rate of erosion, depositional landforms are found in this area.

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Sediment Supply

The process of weathering and erosion produce sediment which is transport and deposited to produce coastal landforms.

In the wash sediment origins form:

  • Cliffs eroding between West Runton and Weybourne
  • Tidal currents, which picks up glacial depots from the shallow sea floor
  • Erosion of the Holderness cliffs
  • Sediment is carried southwards in suspension
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The coasts as a system

Inputs

  • Marine
  • waves
  • tides
  • storm surges
  • Atmospheric- weather/climate,
  • climate change,
  • solar energy
  •  Land-rock type and structure
  • tectonic activity 
  • People- human activity

Processes

  •  Weathering -
  • Mass movement 
  • Erosion -
  • Transport -
  • Deposition

Outputs -

  • Erosional landforms 
  • Depositional landforms
  • Different types of coats 
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The Littoral Zone

  • The littoral zone stretches into the sea and onto the shore. It is constantly changing because of the dynamic interactions between the processes operating in the seas and oceans and on land varies because of short-term factors and long-term factors 
  • The littoral zone consists of sections. The backshore and foreshore are where most human activity occurs and where most physical processes (erosion, deposition, transport and mass movement) operate
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Coasts and geological structure

Coastal morphology (the shape and form of coastal landscapes and their features)is not only the underlying geology or rock type, but also to its geology structure and cliff profiles

Concordant coastlines

Along the south coast of the isle of Purbeck the bands of more and less resistant rocks run parraele to the coast, forming a concordant coast

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Discordant Coastline

Along the eastern coast of the isle of Purpeck the bands of the more and less resistant rock run at right angles to the coast. A discordant coastline occurs where bands of different rock type run perpendicular to the coast. The differing resistance to erosion leads to the formation of headlands and bays.

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Headlands and bays

Headlands go out into the sea with bays lying between them. Headlands and bays commonly form when rocks of different strengths are exposed at the coast. More resistant rock such as chalk and limestone tend to be headlands, whilst weaker rocks are eroded to form bays

  •  as waves approach a headlands the depth of the water decreases. Velocity reduces due to friction, so that waves compress become higher, steeper and closer together. Their erosiver power increase
  •  When waves entrer the bay the water is deeper and closer together. The waves lose velocity less rapidly and are less steep than those off the headland. This sllows deposition to take place
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Waves and beaches

Swell waves Some waves originate in mid-ocean. The distance of water over which they move is the fetch. On the UK, mid-ocean swell waves appear as larger waves amongst smaller locally generated waves. Beach morphology and profiles Beaches consist of mainly loose material, so their morphology alters as waves change. The material along the beach profile varies in size and type depending on the distance from shore line. Beach profiles are steeper in the summer

  •  the swash of constructive waves deposits larger material at the top of the beach creating a berm
  •  As the berm builds, the backwash becomes weaker, so beach material becomes smaller towards the shoreline In winter berms are erodes by plunging destructive waves
  • Strong backwash transports sediment offshore deposition it as offshore bars
  •  the backwash can exert an undertow dragging sediment back as the next wave arrives over the top
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Cliff-foot erosion

Abrasion- also known as coarrion. The size and amount of sediment picked up by waves, along with the wave type, determines the relative importance of abrasion and it is advancing waves pick up sand and pebbles from the seabed, waves breaks at the base of the cliff, throwing sediment at it known as abrasion or corrasion Hydraulic action-

a). Air is trapped under high pressure as waves advance

b). As waves retreat air explodes outwards overtime this causes the joint to widen and rocks fracture

Landforms created by coastal erosion Wave-cut notches and shoreline platforms When waves break against the foot of the cliff erosion is concentrated close to the high tide line creating wave-cut notch which begins to undercut the cliff.

  • As the notch gets bigger, the rock above becomes unstable and eventually the upper part of the cliff collapse
  •  As the process is repeated the notch migrates inland and the cliff retreats leaving a remnant behind as a shoreline platform
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Coastal erosion- processes and landforms

Cliffs

The steepness of the cliffs are found where rock strata are vertical and horizontal or have almost vertical joints. the gentlest are found where rock dips towards or away from the sea Constant waves action and erosion against the base of the cliff ensures that it maintains its profile as it retreats inland Caves, arches, stacks and stumps

  •  The erosion of the rocks like limestone exploits lines of weakness to form distinctive features
  • When the joints and faults are eroded by hydraulic action and abrasion this can create two caves
  •  If two caves on both sides of a headland join or a single cave is eroded through a headland an arch is formed. The gap is further enlarged by erosion and weathering becoming wider at the base
  • Eventually the arch will become unstable and collapse leaving an isolated pillar of rock called a stack. The stack will continue to be eroded by the sea. As it collapse and it is eroded it may only appear and low tide called a stump
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Coastal transport and deposition ​

Longshore drift 

1. Waves approach beach at an angle from the direction like that of the prevailing wind 

2. Swash carries some material obliquely up beach 

3. backwash carries material directly down the beach under gravity 

4. Direction of longshore drift and sediment transport 

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marine transport, tides and currents, spits

Marine transport

  • Traction 
  • Saltation 
  • Suspension 
  • Solution

Tides and currents

  • Tides are caused by the gravitation pull from the moon and lesser the sun . The UK coastline has two low tides and two low tides a day
  • The relative difference in height between high and low tides is the tidal range. A high tidal range creates relatively powerful tidal currents, important in transporting sediment

Spits

1. Sediment is moved by longshore drift (prevailing winds and fetch

2. if the coastline changes direction, sediment will build up and start to create a spit

3. river current prevents spit extending across the estuary

4. wave refraction carries material into sheltered water to form a recurved spit

5. where finer sediment is deposited salt-tolerant plants colonise forming a salt marsh

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Beaches, offshore bars ,barrier beaches, tombolo a

Beaches

Beaches are commonly found in bays. Wave refraction creates a low-energy environment leading to deposition. Beaches can be sand or shingle depending on the nature of the sediment and the power of the waves. beaches can be swashaligned or drift-aligned

Offshore bars

Offshore bars or sand bars are submerged partly exposed ridges of sand. Destructive waves erode sand from the beach and deposit it offshore in bars

Barrier beaches

Where a beach or spit extends across a bay to join two headlands it forms a barrier beach or bar. They can trap water behind them forming lagoons

Tombolo

A tombolo is a beach or ridge of sand and shingle that forms between a small island and the mainland. They may be covered at high tide

Cuspate forelands

A cuspate foreland is a tranglarshaped headland extending out from the coastline. It occurs where a coast is exposed to longshore drift from opposite directions. Sediment is deposited where the two meet, forming a triangular shape. As vegetation begins to grow it stabiles the sediment

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Stabilising deposition land forms and sediment cel

Stabilizing depositional landforms

Many depositional landforms consist of sediments that can be easily eroded and transported

  •  Dunes can develop where sand trapped by debris towards the back of the beach
  • Salt marshes are areas of silty sediment that accumulates around estuaries or lagoons
  •  Vegetation helps to stabiles dunes and salt marshes as a result of plant succession 

Sediment cells

Sediment moves along the coast in sediment cells between beaches ,cliffs and sea through the process of erosion, transport and deposition. The coastline of England and Waves is divide into 11 major sediment cells, through smaller ones can operate within them Sediment cells act as systems with sources, transfers and sinks. The amount of sediment available within a cell is the sediment budget. Within each cell, depositional features build up which are the equilibrium with the amount of sediment available

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Sub-aerial processes

Sub-aerial processes Weathering is the gradual breakdown of rock at or close to the ground surface. There are three types.

Weathering creates sediment, which the sea uses to help erode the coast Mass movement is the movement of weathered material downslope under gravity. It can reshape the coastline Chemical weathering Carbonation-rainwater absorbs carbon dioxide from the air forming weak carbonic acid. This reacts with calcium carbonate in rocks to form calcium bicarbonate which is easily dissolved

Mechanical weathering

Freeze-thaw weathering- occurs when water enters cracks in the rock as the water freezes the water expands at about 10%, exerting pressure, forcing cracks to widen then this repeats freezing and thawing causes fragments of rock to break off

Salt-weathering- when salt water evaporates it leaves salt crystals behind. These can grow and extert stresses in the rock causing it to break up, salt can also corrode rock

Wetting and drying-rocks rich in clay expand when they get wet and contract as they dry this causes them to break Biological weathering This occurs in several ways

  • Plant roots grow into cracks in the cliff face, cracks widen as the roots groq,
  • breaking up the rock
  • Water running throguh decaying vegetation becomes acidic, leading to increased chemical weathering 
  • Birds and animals dig burrows into cliffs 
  • Marine organisms can burrow into rocks or secrete acids
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Mass movement

Soil creep

  • Very slow downhill movment of soil particles 
  • This is the slowest form of mass movemwnt

Solifuction

  • Occurs mainly in tundra areas.
  • When the top layer of soil thaws and becomes sacturated it flows over the frozen layer beneath
  •  Averages 5cm to 1 metre a year Rock fall
  • Most likeley to occur when strong,jointed, steep rock faces/cliffa are exposed to mechanical weathering
  •  Material falls to form scree at the foot of the cliff
  • Block falls are simialr.
  • A large block of roack falls form the cliff as the single oeice due to the jointing of the block

Rock/debris slides

  • Rocks that are jointed or have bedding planes roughly parallel to the slope or cliff surface are suscptible to landslides
  • An increase in the amount of water can reduce friction, casuing sliding 
  • Slabs of rock/blocks can slide along a slide or slip plane

Slumps

  • Often occur in sacturated comnditions on moderate to steep slopes 
  • There si rotaional movement 
  • Common where softer materils overlie more-resisitant or Impemable rock
  • Slumping causes rational scars or terraced cliff profiles
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Holderness Coast

The Holderness coast is on the east coast of England, it extends 61km from flam borough in the north of spurn point in the south. The Holderness coast is one of Europe’s fastest eroding coastline. On average the coast retreats 2 metres per year.

Erosion

Rates of erosion vary due to human and physical factorswhich can change. The Holderness coastline is retreating rapidly because of the geology, fetch, longshore drift and beach material. Msot of the coast conits og boulder clay. It was little resistance to erosion and produces shallow sloping cliffs The boluder clay is surrounded by chalk which has created a headland to Flamborough Head. Erosion has created cliffs, arches and stacks there. One of the main factors affecting he rate of erosion is wave energy. This depends on the fetch, the Holderness coast is exposed too winds and waves from the north-east with a small fetch of about 500-800kmacross the North Sea.

  • Currents or swell, circulate around the UK from the Atlantic Ocean into the north sea, there are often powerful destructive waves at work along this coastline 
  • Low pressure weather systems and winter storms passing over the North Sea are often intense producing locally strong winds and waves. Low air pressure weights less, raising sea levels, which produces much higher tides than normal 
  • Small almost enclosed seas often generated huge waves during storms, waves move within the sea but cannot disabuse their energy 
  • The sea floor is relatively deep along the Holderness coast, so waves reach the cliffs without first being weakened by friction with shallow beaches The seabed consists of glacial mud, sand and boulders, as do the cliffs.

There are dynamic sandbanks that move along the coast and mark the most rapid areas of erosion at the base of the cliff. The coastline is in a S shape which is only brockn where sea defences have reduced erosion at the protected point and increased southwards, the coast has been cut back up to 200m in the last centry

Management of the holderness coast

Central government agencies- The enviromental agency is responsible for coastal management. Its budget from the central government has been cut since 2010.

Local Enviroment- the local authorities are jointly responsible for coastal management with the enviroment agency. However, in 2010 local government funding was cut by central government, which resticted local coucils to minimal increases in Concil tax.

Stakeholders in the local economy

  • The tourists industry wants greater spending on coastal protection.
  • Farmers want money spent to protect their farmland, which lower value than urban space. 
  • Residents at for example,hornsea and mappleton want to garentee coastal protecton for their homes and buisnesses 
  • Insurance companies are increasinly refusing to insure vulnerable propetires
  • Enviromental stakeholders- english nature and the RSPB want to protect Spurn Head one of the UK’s largest coastal spits so a contiing flow of dand southwards by longshore drift is essential.one of the most important assesr of the spit is the protection that it gves to the mudflats of the Humber Estuatary
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