coasts

Abrasion (corasion)

The wearing away of cliffs by sediment flung by breaking waves.

• Arch

Wave-eroded passage through a small headland. This begins as a cave formed in the headland, which is gradually widened and deepened until it cuts through.

• Attrition

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

• Bar

Where a spit grows across a bay, a bay bar can eventually enclose the bay to create a lagoon. Bars can also form offshore due to the action of breaking waves.

• Beach

The zone of deposited material that extends from the low water line to the limit of storm waves. The beach or shore can also be divided into the foreshore and backshore.

• Beach Nourishment

The addition of new material to a beach naturally, through the action of longshore drift or artificially, through the dumping of large amounts of material.

• Beach Reprofiling

The addition of new material to a beach artificially, through the dumping of large amounts of sand and shingle.

• Backwash

The return of water to the sea after waves break on a beach.

• Cave

A large hole in the cliff caused by waves forcing their way into cracks in the cliff face.

• Chemical Weathering

The decomposition (or rotting) of rock caused by a chemical change within the rock; sea water can cause chemical weathering of cliffs.

• Cliff

A steep high rock face formed by weathering and erosion along the coastline.

• Constructive Waves

Found on low-angled beaches and mainly responsible for coastal deposition. They are gently breaking, with a much stronger swash than backwash.

• Deposition

Occurs when material being transported by the sea is dropped due to the sea losing energy.

• Destructive Waves

Found on steep beaches, these are steeply breaking and mainly responsible for coastal erosion. The strong backwash pulls sand and shingle down the beach.

• Dune Regeneration

Action taken to build up dunes and increase vegetation to strengthen the dunes and prevent excessive coastal retreat. This includes the re-planting of marram grass to stabilise the dunes as well as planting trees.

• Erosion

The wearing away and removal of material by a moving force, such as a breaking wave.

• Fetch

The maximum distance of water over which winds can blow in the same direction, generating waves. In the UK, the south-west has a fetch of 5000 miles, which coincides with the direction of the prevailing wind. So, the largest waves form with south-westerly winds, particularly in Winter.

• Gabions

Steel wire mesh filled with boulders used in coastal defences.

• Groynes

A wooden barrier built out into the sea to stop the longshore drift of sand and shingle, and so cause the beach to grow. It is used to build beaches to protect against erosion and as a coastal defence against flooding. However, by stopping the longshore drift, they starve beaches further down the coastline of beach replenishment.

• Hard Engineering

The use of concrete and large artificial structures by civil engineers to defend land against natural erosion processes.

• Headlands and Bays

A rocky coastal promontory made of rock that is resistant to erosion; headlands lie between bays of less resistant rock where the land has been eroded back by the sea.

• Hydraulic Power

The process by which breaking waves compress pockets of air in cracks in a cliff. The pressure may cause the crack to widen, breaking off rock.

• Longshore Drift

The zigzag movement of sediment along a shore caused by waves going up the beach at an angle (swash) and returning at right angles (backwash). This results in the gradual movement of beach materials along the coast.

• Managed Retreat

Allowing cliff erosion to occur in some areas, where the land use is less valuable. Benefits include reduction in coastal flooding and more marshland habitats. It may involve setting back the land use and allowing the sea to flood areas that were previously protected by embankments or sea walls.

Mass Movement

The downhill movement of weathered material under the force of gravity. The speed can vary considerably.

• Mechanical Weathering

Weathering processes that cause physical disintegration or break up of exposed rock without any change in the chemical composition of the rock, for instance freeze-thaw.

• Pioneer Species

The first plant species to colonise an area that is well adapted to living in a harsh environment.

• Rock Armour

Large boulders dumped on the beach as part of the coastal defences.

• Rotational Slip

Slippage of a cliff face along a curved surface causing the cliff to retreat eventually.

• SMP (Shoreline Management Plan)

Each local authority should have one that outlines the strategies for their stretch of coastline for defensive purposes.

• Saltation

Stones and pebbles being bounced along by waves.

• Sand Dune

Coastal sand hill above the high tide mark, shaped by wind action, covered with grasses and shrubs.

• Sea Wall

A concrete wall which aims to prevent erosion of the coast by providing a barrier which reflects wave energy.

• Sediment Starvation

An area of beach where sediment has been held back by structures (e.g. groynes) and as a result the beach down drift loses sand and rocks, exposing the coastline and making processes such as marine erosion more likely.

• Sliding

Occurs after periods of heavy rain when loose surface material becomes saturated and the extra weight causes the material to become unstable and move rapidly downhill, sometimes in an almost fluid state.

• Slumping

Rapid mass movement which involves a whole segment of the cliff moving down-slope along a saturated shear-plane or line of weakness.

• Soft Engineering

Managing erosion by working with natural processes to help restore beaches and coastal ecosystems.

• Solution (or Corrosion)

Chemical erosion caused by the dissolving of rocks and minerals by sea water.

• Spit

A depositional landform formed when a finger of sediment extends from the shore into the sea, often at a river mouth. Spits form on coasts where the prevailing wind blows at an angle to the coastline, resulting in longshore drift.

• Stack

An isolated pillar of rock left when the top of an arch has collapsed, over time further erosion reduces the stack to a stump.

• Stump

Formed by continued wave action attacking a stack until it collapses into a “mini stack.”

• Suspension

Small particles carried in sea water e.g. sands, silts and clays, which can make the water look cloudy.

• Sub-Aerial Erosion

Weathering from above by the elements such as rain, wind and ice.

• Swash

Forward movement of a wave up a beach.

• Traction

Large rocks being rolled along by the waves.

• Transportation

The movement of eroded material.

• Undercutting

Marine processes eroding at the base of a cliff between high and low water marks to the extent that eventually the material on the cliff face collapses because it does not have support at the base.

• Vegetation Succession

A sequence of vegetation species colonising an environment (starts with pioneer plants).

• Wave Cut Platform

A rocky, level shelf at or around sea level representing the base of old, retreated cliffs.

• Waves

Ripples in the sea caused by the transfer of energy from the wind blowing over the surface of the sea. The largest waves are formed when winds are very strong, blow for lengthy periods and cross large expanses of water.

• Weathering

The break-down of rock by physical or chemical processes.

Characteristics of constructive waves

Strong swash

Weak backwash

Calm weather

More likely in summer

Deposit material

Characteristics of destructive waves

Weak swash

Strong backwash

Erode coast