55 terms

Grade 7 Coasts

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sediment
any material, regardless of size, which has been transported by an agent of erosion
swash
the body of water rushing up a beach after a wave has broken
backwash
the movement of water back down a beach towards the sea
fetch
the distance across open sea or ocean over which the wind blows to create waves; the longer the fetch, the greater the possibility of large waves
constructive waves
low-frequency waves of low height, with a strong swash but weak backwash; the waves therefore build up material on a beach
destructive waves
high-frequency , steep waves which have little swash and so move little material up a beach; however, they have strong backwash and so drag material down the beach into the sea
biggest wave ever recorded
Caused by an earthquake off the coast of Alaska on 9 July 1958 its height was 530.5 metres
There are four categories of coastal erosion. These processes operate together to erode a coastline
abrasion, attrition, hydraulic action and solution
Specialised ecosystems
develop along coastlines, with plants and animals adapting to extreme and constantly changing habitats
Waves
created by the wind blowing across the sea's surface
stacks
pillar of rock surrounded by sea and separated from the mainland
stumps
the remains of a stack that has been eroded almost to sea level
arches
rocky opening through a headland
caves
area at the base of a cliff that has been hollowed-out by wave action
cliffs
steep rock outcrop
headlands
point along a coast where harder rock juts out into the sea
bays
indentation in coastline where wave action erodes softer rock
longshore drift
the transportation of material along a coastline
groynes
barrier of wood or stone built down a beach to stop beach materials from being washed away
spit
ridge of sand or shingle attached tot he land at only one end
bars
ridge of sand or shingle across the entrance to a bay or river estuary
lagoon
area of salt water separated from the sea by a bar or reef
Tombolo
low-lying ridges of deposited material, but they link offshore islands to the mainland. They form causeways which can give access to the island at low tide but is submerged at high tide
Abrasion
wearing away of cliffs by sediment flung by breaking waves.
Attrition
erosion caused when rocks and boulders transported by waves bump into each other and break up into smaller pieces.
Beach
the temporary deposition of sand and shingle along the coastline. Without its beach a coast is vulnerable to erosion, e.g. the cliffs at Barton on Sea were easily eroded following the construction of a groyne updrift at Bournemouth.
Beach Replenishment
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.
Biological Weathering
the breakdown of rock through the action of plants and animals.
Chemical Weathering
the decomposition (or rotting) of rock caused by a chemical change within that rock; sea water causes chemical weathering of cliffs.
Clay Cliffs
clay is a soft, impermeable rock which soaks up water to become saturated. When this happens the clay becomes unstable and begins to slump. Clay cliffs have gentle slope angles.
Cliff Collapse
steep cliffs made of hard, resistant rock, fall down when there is a loss of supporting rock underneath caused by wave attack.
Erosion
the wearing away of the land by rivers, ice sheets, waves and wind.
Estuary
the tidal mouth of a river where it meets the sea; wide banks of deposited mud are exposed at low-tide.
Freeze-Thaw Weathering
also called frost-shattering as it occurs in cold climates when temperatures are often around freezing point and where exposed rocks contain many cracks. Water enters the cracks during the warmer day and freezes during the colder night. As the water turns into ice it expands and exerts pressure on the surrounding rock, causing pieces to break off.
Gabions
steel wire mesh filled with boulders used in coastal defences.
Hydraulic Action
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.
Impermeable Rock
a rock that will not allow water to pass through it e.g. clay.
Managed Retreat
allowing cliff erosion to occur as nature taking its course: erosion in some areas, deposition in others. Benefits include less money spent and the creation of natural environments.
Mass Movement
the downhill movement of weathered material under the force of gravity. The speed can vary considerably, from soil creep, where the movement is barely noticeable, to slumps, slides and mudflows, where the movement becomes increasingly more rapid.
Mud Flows or Slides
occur 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 in an almost fluid state.
Notch
an undercut part of the cliff base where wave attack concentrates erosion. See Wave Attack Zone.
Off-shore
out at sea, away from the land.
Permeable Rock
allows water to percolate or pass through it e.g. limestone, sandstone and chalk.
Physical Weathering
the disintegration of rock into smaller pieces without any chemical change in the rock; this is most likely in areas of bare rock where there is no vegetation to protect the rock from extremes of weather e.g. freeze-thaw and exfoliation (or onion weathering).
Prevailing Wind
the direction from which the wind usually blows.
Raised Beach
beach left stranded high on a cliff face after a fall in sea level.
Revetments
wooden, steel, or concrete fence-like structures that allow sea water and sediment to pass through, but the structures absorb wave energy. A beach can build up behind the revetment and provide further protection for the cliff. These are used as part of coastal defences.
Rip-Rap
large boulders dumped on the beach as part as part of coastal defences.
Rock Strongpoints
rocks dumped into sea to form a narrow artificial headland; these have replaced wooden groynes at Barton on Sea. Their aim is to control longshore drift of sediment in a similar way to wooden groynes and have proved to be more effective as they have a stronger structure to resist storm waves.
Sea Defences
measures taken to defend the coast from erosion, cliff collapse and flooding.
Sea Walls
aim to prevent erosion of the coast by providing a barrier which reflects wave energy.
Sediment Cell
Sediment moved along the coast by longshore drift appears to form part of a circular cell which leads to it eventually returning updrift. Dredging of offshore shingle banks can therefore contribute to beach depletion.
Storm Surge
a rapid rise in sea level caused by storms forcing water into a narrowing sea area. Low air pressure at the centre of the storm also causes sea levels to rise.
Tourist Developments
resorts such as Barton on Sea wish to build their beaches to attract tourists who are an important source of income to the area. Cliff-top hotels, however, can actually contribute to erosion, creating an impermeable zone that increases saturation in the surrounding cliff area. Tourists walking on the cliff face also contribute to erosion by destroying vegetation.
Vegetation
a ground cover of bushes and grass on a cliff face helps prevent cliff erosion; their roots hold and trap (stabilise) soil and prevent it being lost by mass movement.