Coasts - A levels geography

Fetch

Distance over which the wind blew.

Wave break ratio

The ratio of the wave height to the wave length cannot be more than 1:7 as this is when a wave breaks.

Swash

When a wave breaks, water is washed up the beach and can deposit sediment.

Backwash

Water runs back down the beach and is capable of removing sediment from a beach.

Constructive Waves

Add sediment to the shallow gradient beach and have high swash and low backwash. Longer wavelength, lower height, low wave frequency, and elliptical orbit.

Destructive Waves

Take sediment from the steep beach and have high backwash and low swash. Shorter wavelength, higher height, more frequent wave frequency, and circular orbit.

Sediment Cell

A length of coastline, which is relatively self-contained as far as the movement of sand or shingle is concerned, and where interruption to such movement should not have a significant effect on adjacent ones.

Tides

Regular rising and falling movements of the surface of the sea and caused by the effects of the gravitational pull of the moon and sun on the oceans.

Spring Tides

Sun, moon and earth all in one straight line --> highest high tides and lowest low tides = largest tidal range.

Neap Tides

Sun and moon 90 degrees out of phase --> highest low tides and lowest low tides = smallest tidal range.

Biological Weathering

Weathering from organic agents

eg marine animals (secrete acids/clams burrow)

land animals (such as rabbits burrowing)

birds

plant roots

Chemical Weathering

Oxidation, carbonation, solution, acid rain.

Mass Movement

Gravity causing downhill movement of material. E.g. Soil creep, mudflows, landslide, rockfall, landslip/slump, runoff, solifluction.

Marine Erosion causes

• Waves (Waves that break at the foot of the cliff cause the most erosion) - Beaches (sandy beaches have lower gradient than shingle beaches) - Geology (types of rocks and structures of the rocks) - Human Activity (defences)

Revetments

Concrete or wooden barriers ('walls') at angles placed along the beach to take the full force of wave energy.

Rock Armour or Rip-Rap

Large boulders dumped in front of a cliff or sea wall to take the full force of the waves. Gabions work on sort of the same way but in metal cages.

Cliff Fixing

Driving iron bars into cliff face to stabilise it and absorb some wave power, sometimes metal mesh netting.

what do offshore barriers encourage

waves to break offshore to reduce their impact on the base of cliffs

Hard Enginering

Controlled disruption of natural processes by using man-made structures. E.g. Groynes, sea walls, rip rap, revetments, offshore barrier.

Soft Engineering

Use of methods to reduce erosion and achieve stabilisation/safety of coastlines, while enhancing the habitat and saving money. E.g. Beach nourishment, cliff regrading and drainage, dune stabilisation, marsh creation.

Managed Retreat

Abandoning current line of sea defences and then developing the exposed land in some way (possibly salt marshes to reduce wave energy. Newly flooded areas, limited maintenance, attractive wetlands habitats created. Loss of agricultural and residential land, interruption of communications.

Environment Agency

Responsible for around 1400km of over 13,000km of Britain's coastline.

Bays and Headlands

Form due to varying resistances of rocks.

Caves, arches, stacks and stumps

Hydraulic action and abrasion causes crack in cliff which eventually forms cave. Cave widens and deepens until it erodes through to other side of cliff forming an arch. Sub-aerial processes wear away the top of the arch, thinning it over time. Eventually arch collapses, leaving a detached stack. The stack is eroded by hydraulic action so it collapses to form a stump.

Wave-Cut Platforms

Wave-cut notch at the foot of a cliff and as it develops the overlying beds are undermined and eventually collapse.

how do offshore bars form

Strong backwash usually leads to sand running parallel to the shoreline at the low-water mark

Berms

Beneath storm ridge on a beach, may be a series of ridges. Mark the successively lower high tides as the cycle goes from spring tide to neap tide. In-between cusps.

Spits

Long, narrow piece of sand or shingle that has one end joined to the mainland and projects out into the sea or part of the way across an estuary. Longshore drift and wind directions.

Barrier beach

Changes in coast direction. If spit develops to close off an embayment it may create a lagoon which is what this is.

Saltmarshes

Behind spits, areas of mudflats exposed at low tides, vegetation will develop and in time trap more sediment causing growth.. Usually form in estuaries where there is a lot of sediment and it is on a landward side of a spit.

E.g. Hurst Castle.

Sand Dunes

Concentrations of mound-like landforms composed of sand that has blown off the beach by onshore winds. Created by processes of: saltation, LSD depositon/wind direction, and vegetation fixing (MARRAM GRASS). Need: lots of sand, wind, flat area and dry beach.

Isostatic Change

Changes in the land level causes sea level change. E.g. Land height increases --> sea levels fall.

Eustatic Change

Changes in the sea level. Usually due to change in ocean volume.

Fjords

Submergent landform. Drowning of glacial troughs and result in very deep, steep-sided inlets of the sea that typically maintain significant depth for a considerable way inland. E.g. New Zealand

Rias

Submergent landform. Formed when valleys in a dissected upland are submerged. Deep water near the mouth and shallower water inland, with irregular shorelines. Basically land around a river flooded?. E.g. Devon.

Raised Beaches

Emergent landform. Former wave-cut platforms or beach material - now vegetated. Can often see old wave cut notch and fossil sea cave. A small cliff separates raised beach and present beach. E.g. West Scotland.

Dalmatian Coasts

Submergent landform. Rising sea levels cause valleys to flood, often leaving tops of ridges exposed. E.g. Croatia.

Physical weathering

Salt crystallisation, frost shattering, thermal expansion, raindrop impact, wetting and drying.

Hydraulic action

Motion of water against a rock surface produces erosion.

Abrasion

Bits of rock and sand in waves grind down cliff surfaces like sandpaper.

Attrition

Waves smash rocks and pebbles on the shore into each other, and they break and become smoother.

Solution

Acids contained in sea water dissolves some rocks, and then this is carried along in the water.

Suspension

Fine light material is carried along in water.

Saltation

Small pebbles and stones are bounced along the river bed.

Traction

Large boulders and rocks are rolled along the river bed.

what is wave quarrying

When waves break against unconsolidated materials eg sand and scoop out loose material

Cavitation

Vapour bubbles put under pressure in the rock by breaking waves and create an extra force so that the bubble implodes, becoming liquid, giving off various forms of energy that blast apart the rock.

Longshore drift

Swash moves sediment along the beach and the backwash, under gravity, pulls the material back down the beach at right angles to the coastline.

Drift-aligned beach

Sediment is transferred along the coast by longshore drift.

Swash-aligned beach

Sediment moves up and down the beach with little lateral (left/right) transfer.

Shoreline Management Plan (SMP)

Detailed documents for a sediment cell that talks about the intervention needed. They are an approach to coastal management that involves all stake-holders in making decisions about how coastal erosion and coastal flood risk should be managed.

Hold the line

Maintaining the current position of the coastline, usually by hard-engineering methods. Cheap but requires constant maintenance.

Advance the line

Extending the coastline out to sea, can be done by beach nourishment and groyne construction. Protects natural habitats but can be expensive and look unnatural.

No active intervention

Letting nature take its course and allowing the sea to erode cliffs and flood low-lying land and allowing existing defences to collapse. Cost free but land that could have homes and farmland on it is lost.

Integrated Coastal Zone Management (ICZM)

A process for the management of the coast using an integrated approach, regarding all aspects of the coastal zone, including geographical and political boundaries, in an attempt to achieve sustainability. I.e. Lots of areas join together rather than just one area acting alone like with SMP.

Barrier islands

Where parts of a barrier beach break apart from others to leave little parts.

Tombolo

Longshore drift causes an island to become joined to the mainland. A spit grows out from the mainland, which is due to the shape of the headland changing.

UK isostatic/eustatic change

North and West rising due to isostatic recovery --> sea levels falling. South and West sinking as rivers pour water sediment into Thames and English channel --> crust sinks --> sea levels rise --> more floods.

Positive feedback

Where a flow/transfer leads to increase or growth.

Negative feedback

Where a flow/transfer leads to decrease or decline..

Landform

Individual component of a landscape.

Waves

Caused by wind. Size depends on fetch, wind strength and wind duration.

Rip currents

A rush of water that flows rapidly back to sea through a narrow opening in a sandbar. Speeds of 5 mph. 2-3 ft high waves. Calm days after storm. Need breaking waves, pier, or groynes.

Low energy coast

More deposition than erosion. Not powerful waves. Beaches and spits. E.g. Lincolnshire.

High energy coast

More erosion than deposition. Powerful waves. Headlands, cliffs and wave-cut platforms. E.g. Cornwall.

Weathering

Breakdown of rock 'in situ' or close to ground.

Recent sea level change

Last 10,000 years has been a period of global sea level rise following the end of the last glacial period. Some coastlines have experienced a rise in sea level whilst others have experienced a fall.

Beach zones

Offshore --> Nearshore --> Foreshore --> Backshore

UK ice coverage

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Predicted /recent changes

By 2100, sea levels rise by 30-100 cm