Geography IGCSE - Coasts

Coast

The transition zone between the land and the sea or ocean

Swash

movements of waves up the beach

Backswash

movements of waves down the beach

Destructive waves

• When waves build up over a long period of time, with strong winds and a long fetch, they have a lot of power and are destructive.

• These waves have a stronger backwash and cause erosion

Constructive waves

• Waves with less energy → have a stronger swash

• They do not cause erosion.

• They are more likely to deposit their load and build beaches

3 Factors affecting wave size:

1. Wind speed

2. Wind duration - the length of time the wind has blown

3. Fetch - the distance over open water over which the wind blows

Stronger the wind → the longer its duration is

Greater the fetch → the bigger the wave

The bigger the wave → the greater its energy and therefore erosional power

Erosion

wearing away of the land by the sea

Transportation

 movement of eroded material along the coast by the sea

Deposition

when eroded material is dropped/deposited by the sea

Processes of coastal erosion

Hydraulic Action

waves hit or break against cliff face → air trapped in joints or cracks is put under pressure → increasing pressure of water and air causes rocks to crack

Abrasion

Caused by waves picking up materials such as pebbles → throwing them against a cliff face → wearing away surface (like sandpaper)

Chemical weathering

The dissolving of rocks by sea water through a chemical reaction

Attrition

Process by which material carried by waves collide into each other, breaking up and becoming rounder and smaller over time

Sea transportation

Traction → Larger, heavier materials, like pebbles rolled along riverbed

Saltation → pebbles are bounced along river bed, commonly near the source

Suspension → fine, light particles lifted by the river's turbulent flow and carried in water column

Solution → when sea water dissolves certain types of rocks

Cliffs + wave cut platforms

• piece of land sloping down to the sea - processes of weathering → weaken the rock

• section of the cliff base between the high and low watermark → hydraulic action and abrasion → continues and over time rock will break away from the cliff base and collect on the beach → material removed by destructive waves → leaving wave-cut notch

• wave-cut notch will become larger → leaving cliff above unsupported

• wave-cut notch becomes so large → overhanging cliff collapses due to gravity

• Hydraulic action, abrasion and weathering will repeat wave-cut notch formation and cliff collapse, causing the cliff to retreat

Spit

• An extended stretch of sand that extends out to sea from the shore → occurs when change in shape of coastline

Stages of formation:

• Longshore drift is process that moves sediment

• coastline changes direction → a sheltered area (bay) allows for deposition of sediment

• increased friction → more deposition occurs 

• spit slowly builds up to sea level → extends in length

• If the wind changes direction → the wave pattern alters → hooked end

• area behind the spit becomes sheltered

• Silts are deposited here to form salt marshes or mud flats

Cave, arch, stumps + stacks

• hydraulic action forcing water into a crack → puts pressure on it causing it to grow larger

• crack will grow into a notch → then form into cave due to destructive waves that are converging on headland

• wave refraction → hitting coastline at an angle, uneven distribution of energy

• over time caves will get larger through abrasion

• sea may break through the back of them → sea arch

• more hydraulic action and abrasion will widen the base of the arch

• top of the arch will be weakened → less stable → eventually collapse → stack (detached pillar of rock)

• Erosion will cause notches to form at base of stack which makes it unstable → along with weathering processes → stack topple into sea → stump which is only visible at low tide

Beach

• Form in sheltered areas (bays)

• Deposition occurs through constructive wave movement → swash is stronger than the backwash

• Beach formation usually in summer months → weather is calmer

• Sometimes sand from offshore bars can blow onto the shore by strong winds

• Blown sand can create sand dunes at the backshore of a beach

Headlands + bays

• in areas of alternating bands of resistant (hard) and less resistant (soft) rocks

• Initially, less resistant rock (e.g. clay) is eroded back→ forming bay

• A bay is an inlet of the sea where the land curves inward

• more resistant rock (e.g. limestone) is protruding out to sea as a headland

• A headland usually features:

  • Cliffs along sides

  • Projects out to sea

• A bay usually has:

  • A wide, open entrance from the sea

  • A roughly semi-circular shape extending into the coastline

  • Land that is lower than the headlands surrounding it

Sand dune

large piles of sand that form at the back of sandy beaches built by wind

Formation of sand dune (beginning)

• Windblown sand is deposited against an obstruction (driftwood)

• more sand particles are caught → dunes grow in size → forming rows at right angles to the prevailing wind

• process called succession → vegetation will eventually colonise and fix the ridges of the dunes

• The first plants (pioneer species) have to cope with:

  • Salinity

  • Lack of moisture as sand drains quickly (highly permeable)

  • Wind

  • Temporary submergence by wind-blown sand

  • Rising sea levels

Formation of sand dunes (phase 1)

• Embryo dunes

  • Deposition starts when debris traps wind-blown dried sand

  • Pioneer species (e.g. Lyme Grass and Sea Couch Grass) begin to colonise

  • little soil content and high pH levels (alkaline)

  • Embryo dunes reach a maximum height of 1 metre

Formation of sand dunes (phase 2)

• Fore dunes

  • embryo dunes give some protection against prevailing wind

  • allows other species of plant to grow (e.g. Marram Grass)

  • Marram grass begins to stabilise dune with its root system

  • plants add organic matter to the dunes → making dunes more hospitable for plants to grow

  • Maximum height is 5 metres

Formation of sand dune (phase 3 and 4)

• Yellow dunes

  • darken as organic material adds humus to the soil

  • Marram grass dominates the vegetation → more delicate flowering plants and insects found in dune slacks

  • 20% of the dune is exposed, down from 80% 

  • Height does not exceed 8 metres

• Grey dunes 

  • Grey dunes are more stable → less than 10% of exposed sand → have good range of biodiversity

  • Soil acidity and water content increase as more humus is added

  • Shrubs and bushes begin to appear

  • Height is between 8 - 10 metres

Formation of sand dune (final phase)

• Mature dunes

  • They are found several hundred metres or more from the shoreline

    • soil can support a variety of flora and fauna such as oak trees and alders (climax vegetation)

Coral reefs

• Corals are tiny animals → called polyps

• Begin life as a tiny, free swimming larva

• Polyps → clear bodies → skeletons are white

• Settle on hard area e.g. rock → never move again

• Polyp of hard corals makes a hard, protective shell of out calcium carbonate → (soft corals don’t build reef)

• Reefs constructed from million of tiny “hard” coral polyps → live together in colonies

• When polyp dies → skeleton remains → another poly will grow on top of it; adding to old coral structure

• Beautiful colours come from algae that line inside the tissue

Conditions for coral reefs growth

• Temperature → minimum of 18 → grows best 23-25 in tropic seas

• Clear water → coral needs light for algae to photosynthesize →  corals get energy → clear water with limited suspended material

• Shallow water → related to need for light → corals grow in shallow water (depths of 60m)

• Salinity → corals are marine creatures →  survive in salt water

Mangroves

• Coral reefs and mangroves → fundamentally connected ecosystems

• Mangroves protect coral reefs from sedimentation → keep water clear of particles and nutrients → important for reef health

• Mangroves provide spawning and nursery areas for many animals species that spend adult life on reefs

• Coral reefs → provide shelter for mangroves and inhabitants

• Calcium carbonate eroded from reefs → provide sediment in which mangroves grow

Conditions for mangrove growth

• Intertidal zone - coastal environments and estuarine margins

• High salinity (water and soil)

• Muddy, sediment with low oxygen content

• Tides (regularly submerged in water)

Hazards from coasts

• coastal erosion → Areas that are made of less resistant rock will erode faster than those coastlines made up of more resistant rock such as granite

• Tropical storms → Hurricanes, typhoons and cyclones are all types of tropical storms

Opportunities for people from coasts

• Development including:

  • Homes

  • Shops

  • Hotels

  • Roads

  • Schools

  • Restaurants etc. 

• Nature reserves

• Swimming and sports

• Industry

• Fishing and aquaculture

• Tourism

• Agriculture

• Ports and harbours

Reasons for coastal protection

Prevent Erosion → prevent erosion of beaches and cliffs → safeguarding land + properties from being washed away

Manage Flooding → reduce risk of flooding from storm surges + high tides → protects coastal communities + habitats

Maintain Beaches → help preserve beaches, → vital for tourism, recreation + local economies

Protect Habitats → conserve important natural habitats → e.g. mangroves + coral reefs → crucial for biodiversity + environmental health

Safeguard Infrastructure → safety of critical infrastructure → e.g ports, roads + residential areas that are vulnerable to coastal hazards

Manage impacts of coastal erosion (soft engineered defences)

• natural coastal protection → mangroves + coral reefs

Manage impacts of coastal erosion (hard engineered defences)

Beach Replenishment (soft engineered defences)

Features	Prevent Erosion
Sand + shingle are dumped onto a beach → replace material that eroded away	helps absorb + dissipate wave energy → protects coastline by widening the beach front → acts as a buffer zone against wave action

Fencing, Hedging, and Replacing Vegetation (soft engineered defences)

Features	Prevent Erosion
fences and hedges, and planting or replanting vegetation to stabilize sand dunes → reduce wind erosion on beaches	Vegetation helps stabilize soil + sand with root systems → reduces displacement by wind + water, → fences trap sand + help build up dunes

Cliff Re-grading (soft engineered defences)

Features	Prevent Erosion
slope of cliff is altered → made less steep → reduce risk of mass movements + rockfalls	reducing the angle of the cliff → decreases gravitational pull on loosened materials → slowing down processes that lead to cliff erosion + collapse.

Sea wall (hard engineered defences)

Features	Prevent Erosion
Solid barriers built parallel to the coastline → protect land behind from wave action	reflect wave energy back into the sea → reduces erosion + preventing coastal flooding

Revetments (hard engineered defences)

Features	Prevent Erosion
Sloping structures on cliffs in coastal zones → made from wood, concrete, rocks	absorb + dissipate energy of waves before they hit the shore → reduces erosion

Rock armour (riprap) (hard engineered defences)

Features	Prevent Erosion
Large boulders piled up along coast → absorb energy of incoming waves	breaks up + dissipates wave energy → protects coastline by reducing erosive force of waves on shore

Groynes (hard engineered defences)

Features	Prevent Erosion
Barriers built perpendicular to shore at regular intervals along beach → trap sand moving down beach due to longshore drift	help build up beach → trapping sediment → acts as buffer against wave energy → protects coastline from erosion

Gabion boxes (hard engineered defences)

Features	Prevent Erosion
boxes filled with rocks placed in areas → absorb wave energy	reduce impact of waves → prevent removal of soil + beach material → stabilize slopes + shoreline areas