Coasts - A Level Geography Edexcel

Littoral Zone

The wider coastal zone including adjacent land areas and shallow parts of the sea just offshore

What can the littoral zone be divided into?

Backshore, foreshore, nearshore, offshore, breakerline, beach

Weathering

Chemical and mechanical processes by which objects are exposed to weather or worn down

Erosion

Wearing away of land by wave action

transportation

Movement of material in the sea and long the coast by the waves

Concordant coastline

Rock strata runs parallel to the coastline

Discordant coastline

Different rock strata intersect the coast at an angle, so geology varies

Concordant coastline - Lulworth Cove

Concordant coasts are generated when rocks run parallel to the coastline. A point of weakness can be formed from a stream. The stream meets the sea where hydraulic action widens the stream, building up pressure which breaches the hard rock. Once the hard rock has been eroded, the waves erode the soft rock which is much easier as it less resistant. Waves are destructive so the backwash is stronger than the swash so water and material is dragged out the cove. This can cause small beaches. Waves continue to erode the hard rock. Attrition and abrasion are responsible for the erosion and the cove is widened more and more.

Discordant coastline - Dorset Coastline

The waves erode the soft rock which eventually forms a bay, where wave energy is low. Hard rock is resistant to erosion, so sticks out and forms a headland, where the wave energy is high. As the waves approach the headland, it absorbs wave power and refracts - meaning they change motion and direction around the headland. After the wave hits the headland, it is likely to become a constructive wave. These waves carry material and deposit it as swash is more powerful than backwash. The bay will eventually come forwards and become a beach, whilst the headlands are slowly eroded by hydraulic action. The coastline eventually becomes smooth until the process repeats.

Cliff profile

The height and angle of a cliff face as well as its features, such as wave-cut notches or changes in slope angle.

Cliffed Coast

High energy coast.

Rate of erosion exceeds deposition.

Headlands and wave cut platforms

sandy coasts

Low energy.

Beaches and dunes.

Estuarine coastline

Low energy.

Deposition exceeds rate of erosion.

River water meets sea water so cancels out power and deposits load.

Creates spits, tombolos and salt marshes

Longshore drift

The movement of water and sediment down a beach caused by waves coming in to shore at an angle

mass movement

Material downslope under influence of gravity e.g Dorset 2015

Resistance

Hardness of a rock

dynamic equilibrium

Balanced state of a system where inputs and outputs balance over time

spit

Sand beach ridge extending beyond a turn in the coastline. At the turn, longshore drift currents spread out and lose energy so deposit it's load.

Tombolo

a bar of sand or shingle joining an island to the mainland, due to wave refraction

Bar

Sand or shingle beach connecting two areas of land with a shallow lagoon behind it. Occurs when a spit grows so long that it extends across a bay, closing it off.

Cuspate foreland

Is a triangular accumulation of sand and or gravel located along the coastline.This feature is formed by longshore drift from opposing directions which neutralise eachother.

Fetch

Uninterrupted distance across water over which a wind blows, and therefore the distance waves have grown in size

Constructive wave

Low and long spilling waves with a powerful swash

Destructive wave

High and steep plunging waves with a strong backwash associated with erosion

Wave size depends on

Strength of wind, duration or wind, water depth and wave fetch

Beach morphology

The shape of a beach, including its width and slope (the beach profile) and features such as berms, ridges and runnels. It also includes the type of sediment (shingle, sand, mud) found at different locations on the beach.

Abrasion

Sediment picked up by waves is thrown against cliff face, breaking bits off.

Attrition

Wearing down of rocks

Solution

Dissolving of rocks e.g limestone

Hydraulic action

Air in cracks in cliffs is compressed when waves crash in. The pressure exerted by the compressed air breaks off rock pieces.

traction

Large rocks rolled along the sea bed

Saltation

Smaller rocks bounce along sea bed

Suspension

Lighter sediment carried in suspended load

Solution

Dissolved sediment

Sediment cell

Self contained, physical barriers where sediment is eroded and transported

Sediment Cell Sources

Where sediment is eroded from cliffs

Sediment cell transfer zone

Sediment moved along a coast e.g beach

Sediment cell sink

Dominant process of deposition e.g spits

igneous rock

Very slow erosion rate as it's resistant. E.g. granite

metamorphic rock

Resistant to erosion, folded and fractured so are sometimes vulnerable

sedimentary rock

Weak and easily erodible e.g. sandstone or limestone

rotational slide

Bedding plane between impermeable clay and sand dips seaward

Cracks develop in dry weather - routes for rainfall

Heavy rainfall saturated permeable sand

Water percolates through permeable sand but is forced to move along clay/sand boundary as clay is impermeable - high water pressure in sand

Toe erosion by marine processes undercut the cliff

Gravity causes slumping

Fault

Fractured rock

Fold

Tectonic forced that distort rock strata

joint

Divides rock strata into blocks with regular shape

Fissure

Small cracks in rocks

Dip

Angle of rock strata in relation to the horizontal

Horizontal dip

Vertical or near vertical profile with notches reflecting strata that are more easily eroded

Seaward dip low angle

Sloping, low angle profile with one rock layer facing the sea; vulnerable to rock slides down the dip slope

Seaward dip low angle

Profile may exceed 90 degrees producing areas of overhanging rock, very vulnerable to rock falls.

Landward dip

Steep profiles of 70-80 degrees producing a very stable cliff with reduced rock falls

Salt marsh

Area of flat, silty sediment that accumulates around estuaries and lagoons. They develop in sheltered areas where fresh and salt water meet causing deposition

Halophytes

salt tolerant plants

plant succession

The changing structure of a plant community over time as an area of initially bare sediment is colonised

Climatic climax vegetation

The final stage in succession, the richest community for a climate

Processes of saltmarsh succession

Algae: binds mud together

Glasswort roots: stabilise the mud allowing further mud accretion - slows ride flow, increases deposition so land level increases

permeable

water can pass through e.g. limestone

Unpermeable

water cannot pass through e.g. clay

Saltmarsh - Hesketh Outmarsh

Hesketh out marsh is a new nature reserve set up by RSPB and Environmental agency.

Acts as a sea defence as it absorbs sea energy

Plants: seeds float in water which will become a new eco system of plants

Wildlife: avocets and redshanks are among the birds already nested

Threats: changes to natural hydrology, pollution

Sand dunes

Form when sand is blown off the beach by onshore winds (aeolian processes) and is trapped by the debris towards the back of the beach

Exerophytes

Can cope with lack of water

Processes of sand dune succession

Marram grass: stabilise mobile sand with roots

Reduce wind speeds slowing increased deposition

Adds dead organic matter to sand

Marram grass

type of grass that is adapted to windy, exposed conditions and is used in coastal management to stabilise sand dunes - can cope in gale wind forces and tolerates 60* due to its tough long flexible leaves

Sand dune climatic climax

Woodland

Changes in the eco system which can be measured with increasing distance from the shore

•pH decline

•age of dune increase

•available water increase

Sand dunes formby

Vegetation: marram grass and pine trees

Wildlife : red squirrels and natter jack toad

Threats and management: erosion (4m per year). National Trust Organisation is trying to prevent this

Beach morphology

The shape of a beach, including its width and slope (the beach profile) and features such as berms, ridges and runnels. It also includes the type of sediment (shingle, sand, mud) found at different locations on the beach.

emergent coastline

As sea levels fall, coastline land is exposed which was previously covered by the sea

Submerging coastline

As sea levels rise, the land is covered

accretion

Sediment added to a landform

Isostatic change

Local rise or fall in land level

Eustatic change

Rise or fall in sea level caused by change in volume of water (global change)

Isositatic fall

During the build up of land based ice sheets, the colossal weight of the ice causes the Earth's crust to sag. When the ice sheets melt, the land surface slowly rebounds upward over thousands of years. The plots-glacial adjustment slowly lifts land surface out of the sea

Isostatic Fall Scotland

Scotland is still rebounding from the last glacial period around 12,000 years ago, in some places by 1.5mm per year.

Formations: raised beaches, fossil cliffs

Isostatic rise

Land can 'sink' at the coast due to the deposition of sediment, especially in large river deltas where the weight of sediment deposition leads to very slow crystal slag and delta subsidence e.g. Egypt Delta

Aswan Dam, Egypt Isostatic Rise

Nile constantly deposits material making the land heavier. This results in flooding meaning that low-lying communities in Egypt are vulnerable. In the Aswan dam, sediment is trapped and deposited in the reservoir behind the dam. This means less sediment is moved down the lower stretches of the Nile - depriving it of sediment. Consequently the rate of erosion increases making the delta become smaller

Eustatic fall

During glacial periods, when ice sheets form on land in high latitudes, water evaporated from the sea is locked up on land as ice leading to a global fall in sea level

Eustatic rise in sea level

At the end of a glacial period, melting ice sheets return water to the sea causing the sea level to rise globally.

Global temperature increase cause the volume of ocean water to increase (thermal expansion) leading to sea level rise

Isostatic and eustatic change - sediment sell

Change in sea level can disrupt a sediment cell by decreasing its sediment budget, ultimately disrupting the dynamic equilibrium.

Natural Disasters changing sea level

Tectonic activity - New Zealand has lifted the shoreline by several metres due to the repeated earthquakes. (LOCAL)

Storm surges - air pressure drops, weight of air pressing down on the sea surface drops so the sea surface rises E.g. cyclone Xaver

Mangrove Forrests (Sundarbans, Bangladesh)

Mangrove forest complex stabilises coastal erosion and provides protection from extreme weather.

Under threat: 75% retreating up to 200m per year - increasing erosion and deforestation.

Ria

A drowned river valley in an unglaciated area caused by sea level rises flooding the river valley, making it much wider than would be expected based on the river flowing into it.

Haff coast

Long shallow lagoon separated from the open sea by a narrow sand bar or barrier beach

Fjord

Drowned glacial valley, U-shaped, deep water level e.g. New Zealand

Dalmatian Coast

Form in places where river valleys run parallel to the coast so that when they rise, a series of elongated islands remain offshore

Dredging

making a river deeper or wider by digging up sand and mud from the bottom

Hallsands, Devon (dredging)

January 1912, the Devon fishing village of Hallsands collapsed into the sea. In the 1890's the Admiralty decided to expand the naval dock yard 30 miles away. The Board of Trade fave permission for an engineering company to dredge shingle from along the coast between Hallsands and Beesands. The villagers weren't consulted but protested to their local MP. This led to a huge increase in erosion and the beach was lowered. All that remains today is the ruins of a chapel on the edge of a cliff top.

Dozens of families lost their homes and were forced to relocate.

They were given £6,000 but believe they never got the full compensation they deserved.

Physical factors affecting erosion

•long wave fetch

•destructive waves

•soft geology

•cliffs vulnerable to mass movement and weathering

•strong longshore drift

Erosion variants

Time, locations seasons

Storm surges

Short-term changes in sea level caused by low air pressure, such as tropical cyclones. As air pressure drops, weight of air pressing down on sea surface drops so sea level rises

Storm Z (1953)

Air pressure - 966 millibars

Surge height - 8

Areas affected: UK, Netherlands, Iceland

Social - 2,000 drowned

Economic - 100m sea wall collapsed, 1k homes destroyed

Environmental - 200,000 hectares flooded in Netherlands, vegetation and agriculture destroyed

Cyclone Xaver (2013)

Air pressure: 963 millibars

Storm surge: 5.8m

Countries: UK, Netherlands, Belgium, Holland, Denmark, Germany

Social: 2,500 died

Economic: 100,000 Scottish homes lost, £1 billion damage

Environmental: erosion resulted in many homes in the sea

Typhoon Haiyan (Philippines LEDC)

Philippines is a MHZ

6m wave

6000 dead

14million affected

$20 billion repair cost (5% of its GNP)

Stagnant water attracted mosquitoes - malaria outbreak

Responses:

1600 evacuation centres set up

Cash grants from the Red Cross

Hurricane Katrina

Occurred on 29th August 2005 in South Eastern USA. Tracked over Gulf of Mexico and hit New Orleans, a coastal city protected by levees.

80% city flooded

1,500 deaths

$300 billion cost repair

Lack of governance: failure of evacuations, hurricane warning was delayed until 19 hours before rather than 56 hours before so the evacuation was much slower

Louisiana and the Federal emergency management agency were very poor which slowed the response down

Netherlands Response to Storm Z

The Deltawerken is a hard engineering mega project. It's aims were to reduce the risk of flooding in low-lying eastern Sheldt area, where much land was under the sea. Also, to short on the length of the coastline exposed by 700km, in order to maintain safe access to North Sea for shipping import

Flood defences designed from a 1:2000 year coastal flood and 1:250 year river flood return period. This took place 1958-1997.

A series of dams were constructed that make up the eastern Scheldt area to control water flow

Embankments built to act as flood walls along the coast costing £5 billion.

Holderness Coast

fastest eroding coastline in Europe.

Geology contributes to this as it consists of boulder clay, one of the softest rocks, therefore it is easily erodible.

Narrow beaches also facilitate the erosion because the cliff is not protected so he waves erode the cliff faster.

The residents of holderness were forced to relocate, but their insurance companies refused to pay so they've lost a lot of money.

Environmental injustice can be practiced for the residents because further up the coast, engineering processes were put in place to mitigate impacts but ultimately disrupted further down shore, creating worse impacts for holderness

Environmental refugees

Communities forced to abandon their homes due to natural processes including sudden ones, such as landslides, or gradual ones, such as erosion or rising sea levels.

Tuvalu

Most land is 1/2m above sea level.

80% live or work on the coast.

Fringed by coral reefs acting as a natural coastal defence against erosion, but rising ocean temperature risks reef destruction.

Water supply is limited and at risk from salt water incursion due to overuse of groundwater.

Small economy based on tourism and fishing, no opportunity for relocation...

Hard engineering

Building artificial structures such as sea walls aimed at controlling natural processes

Advantages of hard engineering

Obvious to "at risk" people that something is being done.