Geography coasts

definition of erosion

 the wearing away of rocks by a force, like wind or waves

definition of corrasion

 the process of mechanical erosion where rock and soil are worn away by the scraping of rocks carried by a force 

abrasion

the wearing away of cliffs by sediment rubbing against rocks and waves picking up and hurling stones at the cliff face 

hydraulic action

breaking waves compress into pockets of air in cliffs, and the pressure may cause the crack to widen, breaking off rock 

solution

soluble particles are dissolved at sea

attrition

Erosion caused when rocks and boulders transported by waves bump into each other and break up into smaller pieces

Freeze- thaw weathering

When water gets into cracks in rock and freeze, expanding. This widens the crack. The water melts and goes deeper into the rock, where the process repeats until the rock is broken off.

onion- skin weathering

repeated heating and cooling of the rock causes the layers to peel overtime, breaking the rock into concentric layers

weathering

the weakening or the decay of rocks in their original place, on/ close to the ground. mostly caused by weather factors such as rainfall and changes in temperature

sub- aerial processes

occur above the water line, and include biological, mechanical and chemical weathering

coastline

transition zone between land and sea

marine processes

natural physical actions of the sea (erosion, deposition, and transportation) which shape/ change coastlines through the movement of waves, tides and currents

terrestrial processes

land- based natural processes like weathering, mass movement and river sediment input, that influence the shape and development of coastlines

how are waves formed?

formed by the wind breaking over the sea. the ripples caused by friction at the surface of the water develop into waves. Can also be formed dramatically when earthquakes or volcanic eruptions shake the seabed (tsunamis)

backwash

the movement of the wave back down the beach perpendicular to the coast 

swash

the wave breaking and moving up the beach (angle depends on wind direction)

destructive waves

-occur when wave energy is high and wave has travelled over long fetch

-created in strong conditions- erode coasts

-shorter wavelength+ steep

-stronger backwash than swash

mass movement

downward movement of material under the influence of gravity

rockfall

weathering weakens rock, fractures develop, breaks rock, rocks tumble down slope

landslide

fast movement of debris down a slope 

mudflow

waterlogged soil flowing downhill like a thick fluid 

rotational slip

saturated soil flowing downhill in one block 

geology influencing coastal environments

Hard rock resists erosion, forming steep cliffs and headlands, and soft rock erodes faster, creating bays and gentler coastlines

Vegetation influencing coastal environments

Plant roots bind soil and cliffs, reducing erosion, and vegetation absorbs wave energy and traps sediment

People influencing coastal environments

Coastal defences alter erosion and deposition patterns, human activities like building and tourism increase erosion 

Sea levels influencing coastal environments

Rising sea levels increase coastal erosion and flooding, sea-level change can create landforms

Concordant Coastlines

same rock along the coastline’s length 

Discordant coastlines

alternating bands of soft and hard rock along the coastline

Wave refraction

waves break in shallow water at the base of headlands and bend, changing its angle, redirecting it onto the side of the headland, causing erosion in high energy zones

Formation of wave cut platforms

see image

Formation of caves and stumps

see image

Formation of a spit

A spit forms when longshore drift transports sediment along the coast and deposits it where the coastline changes direction or at a river mouth. As wave energy decreases, material is dropped, building a narrow ridge of sand or shingle out into the sea. Over time, the spit grows longer, often with a curved end due to changing wind and wave direction, and salt marshes may develop in the sheltered water behind it.

Formation of a bar

A bar is formed when longshore drift moves sediment along the coastline and deposits it across a bay. Over time, the spit continues to grow until it extends fully across the bay, joining two headlands. This cuts off the bay from the sea, and the trapped water behind the bar forms a lagoon.

Formation of a beach

A beach is formed when constructive waves deposit sand and shingle along the coast. These waves have a strong swash and weak backwash, so more material is deposited than removed. Over time, repeated deposition builds up a gentle sloping beach, with material often sorted by size due to wave action.

Sand dunes- formation

Sand dunes form when wind blows dry sand from the beach inland. The sand is trapped by obstacles such as driftwood or vegetation and is deposited. Over time, this builds up mounds of sand, which grow and move inland as more sand is added. Marram grass helps stabilise the dunes by trapping sand with its leaves and roots.

Sand dunes- features

Embryo dunes form first near the beach. Yellow dunes grow larger with some vegetation like Marram grass. Grey dunes are more stable with more plant life. Dune slacks are low, wet areas between dune

Sand dunes- threats

Sand dunes are threatened by tourism, as trampling by people damages vegetation that holds the sand together. Development and construction can remove dunes completely, increasing erosion. Vehicle use and strong storms can also destabilise dunes, causing them to be blown away more easily.

Sand dunes- distribution

areas of coastlines- East Coast of North America and Central America, West Africa etc

Coral reefs

Underwater ecosystems made of coral polyps that build hard limestone structures 

Coral reefs- features

Animals made of calcium carbonate

Coral reefs- conditions required

• Warm water (around 23–29°C)

• Shallow water (less than 25 m) for sunlight to reach corals

• Clear water with low sediment for photosynthesis

• Salty water (marine conditions)

• Stable coastlines with low wave action to prevent damage

Coral reefs- threats

-trampled by people

-Overfishing- imbalances ecosystem

Coral reefs- impacts

Economic

• Provide fishing resources for local communities

• Support tourism (snorkelling, diving) → income and jobs

Environmental

• Protect coastlines by reducing wave energy and erosion

• Support biodiversity, home to many marine species

Social

• Provide food and livelihoods for coastal communities

• Cultural and recreational value for local people and tourists

Coral reefs- distribution

shallow waters around the tropics and equator, like australia

Mangroves

Coastal forests of salt-tolerant trees growing in intertidal, muddy areas 

Mangroves- distribution

-found between tropics

-one third found in asia

mangroves- adaptations

roots- stick out of mud- allows for gas exchange during high tide

leaves-salt glands excrete nearly all of the salt in the plant- makes them salt tolerant

seeds-grow roots attached to plant and float in water until they find shallow waters to grow in

mangroves- importance

-protect coastlines from erosion (wave action becomes gentle due to their roots/ absorb wave energy)

-attract tourism

-provide nurseries for fish (supports fishing industries)

mangroves- threats

-agricultural runoff- causes algal bloom (eutrophication)- imbalances ecosystem

Salt marshes

Low-lying coastal wetlands with salt-tolerant grasses

salt marshes- threats

• Coastal development: Building on coastlines destroys salt marsh habitats.

• Fishing: Overfishing and trawling damage the marsh ecosystem and disturb wildlife.

• Invasive species: Non-native plants and animals outcompete native species and change the habitat.

• Climate change: Rising sea levels flood salt marshes, reducing their area.

• Sewage/fertilizer: Runoff causes pollution and eutrophication, harming plants and animals.

Abiotic

non-living factors of an ecosystem

biotic

living factors of an ecosystem

Threats of coastal ecosystems by humans

Coastal ecosystems are threatened by human activities in several ways. Industrialisation causes pollution and habitat loss, damaging reefs, mangroves, and salt marshes. Agricultural practices lead to runoff of fertilizers and pesticides, harming water quality and wildlife. Tourism damages habitats through trampling, waste, and construction, while deforestation removes protective vegetation like mangroves, increasing erosion and flooding.

coastal flooding

coastal area is inundated with water

coastal flooding- causes

thermal expansion- sea absorbs heat in the atmosphere- causes water molecules to expand- rises sea levels- leads to coastal flooding

melting ice- ice that was originally on land melts, adding water to sea, increasing sea levels.

Storm surge: Sudden rise in sea level from strong winds & low pressure

Tsunami: Large sea waves from underwater earthquakes/volcanoes

Climate change: Long-term sea level rise increasing flood risk

threats from coastal flooding-

• less freshwater available

• loss of tourism

• loss of traditional way of life

• loss of soil/ land area

• erosion of beaches/ land

• disrupted fishing

• coral bleaching

Users/ uses of the coast

fishing, tourism, housing. indulstrialization, natural habitats

Prediction & Prevention of coastal flooding

• Forecasting: Using tech/data to predict storms and floods

• Building design: Raising or strengthening buildings to resist floods

• Planning: Limiting building in flood-prone areas

• Education: Teaching communities how to prepare and respond

Soft Engineering

when the natural environment is used to help reduce coastal erosion

Soft Engineering- Beach replenishment

-Adding sand/shingle to the beach to make it wider and to absorb wave energy

-Advantage: Protects coast by absorbing waves

-Disadvantage: Expensive, needs regular maintenance

Soft Engineering- Cliff regrading

Reducing cliff slope to prevent collapse

-Advantage: Reduces cliff collapse risk

-Disadvantage: Changes natural landscape

Soft Engineering-Ecosystem rehab & revegetation

Planting vegetation to stabilise coastlines

-Advantage: Stabilises coast, supports wildlife

-Disadvantage: Slow to work, vegetation can be invasive

Soft Engineering- Managed retreat

Allowing flooding to create natural barriers like salt marshes

-Advantage: Creates natural habitats, low maintenance

-Disadvantage: Loss of land or property

Hard engineering

involves the construction of man made structures to manage the coastline

Hard engineering- Groynes

• Wooden or rock barriers built perpendicular to the coast to trap sediment

• Advantage: Build up beaches, naturally protecting the coast

• Disadvantage: Starves down-drift areas of sediment, causing erosion there

Hard engineering- Sea walls

• Concrete or stone walls along the coast to reflect wave energy

• Advantage: Very effective at preventing erosion and flooding

• Disadvantage: Expensive, unnatural appearance, can increase erosion elsewhere

Hard engineering- Rip raps

• Large boulders placed at the base of cliffs to absorb wave energy

• Advantage: Relatively cheap, absorbs wave energy effectively

• Disadvantage: Can look unnatural, dangerous to people

Hard engineering- Gabions

• Wire cages filled with rocks to protect cliffs from erosion

• Advantage: Cheap, flexible, absorbs wave energy

• Disadvantage: Need maintenance, can look unattractive

Hard engineering- revetments

• Sloped wooden, concrete, or rock structures along the shore to reduce wave impact

• Advantage: Reduces wave energy and slows erosion

• Disadvantage: Expensive, can look unnatural