Coasts

Why coasts are important

Why coasts are important

Transport and fishing industry provide jobs, leisure and tourism, residential, collect resources from the sea like oil

How coastlines are under threat

Pollution, natural disasters, climate change, flooding in low line areas, oil spills

How waves form

Waves are created by wind blowing over the surface of the sea. As the wind blows over the sea friction is created - producing a swell in the water. The energy of the wind causes water particles to rotate inside the swell, moving the wave forward

Crest

Top of the wave

Backwash

The movement of water and load back down the beach

Velocity

The speed that a wave is traveling. It is influenced by the wind, fetch and depth of water.

Wavelength

The distance between two crests or two troughs.

Trough

The low area in between two waves.

Wave height

The distance between the crest and the trough.

Swash

The movement of water and load up the beach.

Wave Frequency

The number of waves per minute.

Constructive waves

Build beaches, each wave is low, and are less frequent

Destructive waves

Destroy beaches, waves are very high and very frequent

Coastal erosion

The wearing away and breaking up of rock along the coast

Erosion processes

Attrition, Corrosion (solution), Abrasion, Hydraulic action

Attrition

Waves smash rocks and pebbles on the shore into each other, and they break apart and become smaller and rounded

Corrosion (solution)

Acids contained in sea water starts to dissolve alkaline rocks like Chalk and Limestone

Abrasion

Bits of rock and sand in carried by the waves wear down cliff surfaces

Hydraulic action

Air may get trapped in cracks in the rock, and when a wave breaks the air is compressed and weakens and erodes the cliff

Headland

A piece of land jutting out into the sea

Bay

A broad coastal inlet often with a beach

Concordant headline

A continuous layer of either soft or hard rock witch erode away to form coves

Discordant coastline

Layers of hard and soft rocks that erode away to form headlands and bays

How coves are created

Waves cut through the weakness of the soft rock and over time the gap widens where the softer clays have been easily eroded. The rock does not continue to erode much after this as it has hit the harder rock, meaning that the erosion will be a lot slower.

Wave-cut platform

A wide, gentle, sloping, rocky surface at the foot of a cliff

Wave-cut notch

A small indentation cut into a cliff roughly at the level of high tide caused by erosion

How wave cut platforms are formed

The base of the cliff is attacked by destructive waves which erode the cliff by hydraulic action and corrasion forming a wave-cut notch, this gets larger until the cliff collapses, and as the process repeats the cliff retreats

Caves

Formed when a large crack opens in the rock because of hydraulic action. As the waves wear away at the crack it opens up to form a cave.

Arch

The cave gets bigger and breaks through the headland

Stack

The arch is eroded at the base until the roof gets too heavy and collapses into the sea, leaving a stack

Stump

The stack is undercut at the base until it collapses to form a stump

Longshore drift

The movement of sediment along the coastline

Spit

An accumulation of sand with one end attached to land and the other end reaching out across and estuary or into the sea

How a spit forms

Large amounts of sediment are transported by longshore drift, and prevailing winds help to transport material along the coast. where the coastline suddenly changes direction it leaves a sheltered, marsh area of water.

Bar

A barrier (ridge) of sand stretching across a sheltered bay or river mouth

How a bar forms

Longshore drift moves sand out across the bay, and shallow water in the bay allows deposited sand to build up. The deposited sand eventually joins up with the other side of the bay and blocks off the water in the bay.

Tombolo

A thin strip of land created between a coastal island and the mainland

How a tombolo forms

A spit continues to grow through longshore drift joining land to an offshore island

Sand dune

An accumulation of wind-driven sand

Processes by which sand is transported

Saltation, traction, suspension

Saltation

Small pieces of shinge or large sand grains are bounced along the sea bed

Traction

Pebbles and larger material are rolled along the sea bed

Suspension

Small particles such as silts and clays are suspended in the flow of the water

Conditions needed for sand dunes to form

Winds blowing onshore (towards land), dry sand, wide beach with no buildings behind it, flat relief

Shape of a typical sand dune

Crescent shapes - generally wider than long

Vegetation and sand dunes

Marram grass - the leaves slow down the wind speed, causing sand to be deposited and trapped

Humus

The organic content of the soil formed from decomposing plants and animals

Changes in humus content in the soil

As the plants take root there is more humus in the soil

Changes in acidity

As the plants take root there is a low pH

How sand dunes are formed

When dry sand is blown up a beach it gets trapped in an object and accumulates around the object forming a sand dune

Transect of a sand dune

Embryo dunes, Foredunes, Yellow dunes, Grey dunes, Dune slack

Where salt marshes are found

They form in coastal areas that already have mud flats, that are well sheltered, such as creek inlets and estuaries where fine sediments can be deposited. They also form behind spits

Types of plants that grow in salt marshes

Saltgrass, Saltwort, Glasswort, Beach tea

Relief of a salt marsh compared to relief of a sand dune

Salt marshes are flat ecosystems, while sand dunes are hills of sand typically found above the the usual maximum reach of the waves

Value of salt marshes to people

Collect carbon. Provide ideal conditions for the farming of some species of shellfish. In some areas they are left as natural coastal defences as they can be safely flooded by hightide, and therefore protect housing and agricultural areas inland.

What does a coral reef start with

Coral larvae

How quickly does coral grow

15cm/year

What produces corals’ food

Algae

What does coral do at night

Take in water, expand their tentacles and feeds on algae

Conditions needed for coral reefs

Warm, saline waters, shallow seas - up to 40 metres to allow for photosynthesis, clean, clear water, few sediments in the water, plentiful supply of oxygen in the water / unpolluted, plentiful supply of plankton, a steady salt content, close to the equator

Frining reef

A submerged platform of living coral that extends from the shore to the sea.

Barrier reef

A fringing reef that is separate from the mainland or the island by a deep lagoon

Atoll

A circular barrier reef forming an island that encircles a central lagoon

Values of mangrove forests

Protect against hurricanes, tsunamis and strong waves, they reduce erosion rates, 3/4 of all tropical fish are born here, good source of wood, food supply, tourist location

Mangrove forest

An area of trees or shrubs that grow in tropical coastal swamps that are flooded at high tide.

Conditions required for the growth of mangroves

Warm, brackish, shallow waters, areas of mud exposed at low tide, wet climate with annual rainfall exceeding 1250mm a year

Where mangroves are found

In the tropics, 30°N of the equator, 30°S of the equator

Adaptations of mangroves

Salt water, no oxygen in the soil, waves and currents

Adaptations which help survive in salt water

They can excrete salt through the leaves and bark, they also stick roots up into the air which suck oxygen out of the air and water and get rid of excess salt, and then float away by the outgoing tide

Threats to mangroves

Shrimp farming, tourism

Coastal management

Mangroves, Groynes, Rip rap/armour blocks, Gabions, Revetments, Recurved sea wall, Breakwater, Beach nourishment

Groyne

Trap sediment that is carried along the coast by longshore drift, which builds up a bigger, wider beach protecting the land behind it

Rip rap/armour blocks

The waves break on the rip rap and not on the coastline - they act as a barrier for erosion

Gabions

Placed at the base of cliffs, metal cages filled with rocks and stacked together to make a wall to protect the coast

Revetments

Wooden posts with slats of wood or concrete laid on top of the beach to stop the sand being eroded

Recurved sea wall

Protects the inland area against wave action and coastal erosion

Breakwater

Are placed out in the ocean to break the wave energy earlier and converts the wave to a low energy, constructive wave

Beach nourishment

Replacing the sand and shingle that has been lost by the action of the sea