geography coasts revision

depositional landforms

the process where a transporting agent loses energy and drops sediment

a beach as dynamic equilibium

sediment erodes from the beach during a storm and with constructive waves

sediment deposited offshore

waves forced to break out sea. energy is dissipated and reduces erosion of beach

after storm, constructive waves return / redistribute sediment from the offshore bar back to the beach

sections of the coastal zone (…shore)

inshore - between the point where waves meet on the Low Water Mark

foreshore - are between high water mark and low water mark

nearshore - are in the LWM and where waves begin to break

backshore - area beyond the HWM and landward limit of marine activity

sediment cells

a stretch of coastline within which the process of erosion, transportation and deposition operate, and the movement of sediment is largely self-contained

sources of sediment in sediment cells

• Marine organisms (coral, shells etc)  

• Weathering an mass movement  

• Rivers and estuaries  

• Offshore currents, waves, tides etc  

• Longshore currents  

• Cliff erosion 

marine process - erosion

hydraulic action - wave power hits cliffs, loosening interior of joints. cavitation is similar but involves the effervesce of rocks to create a mini explosion

wave quarrying / pounding - high ernertgy waves hit the cliff, it can remove large chunks of rock in ojne go through vibration

corrasion / abrasion - when high energy waves carry pebbles which then hit the cliff face, chipping away fragments when the wave breaks.

solution – weak carbonic acid in seawater dissolves rock at the coastline and breaks it down (particular if it contains calcium carbonate e.g. limestone and chalk) 

attrition – rocks and boulders loosened from the coastline are ground, smoothing and rounding the boulders to become pebbles, which become shingle, which become sand 

sub-aerial processes - weathering

1. salt weathering - salt evaporates living crystals which expand in rocks widening cracks

2. wetting / drying - rock asborbs and release moisture as tides rise and fall leading to a loss of interconnectedness

3. freeze-thaw action - sub zero air causes water in rocks to freeze and expand

4. chemical solution – minerals in coastal rocks are dissolved by chemicals in sea water and acid rainfall  

5. biological weathering – plant roots enlarge rock fissures, nesting marine organisms and birds that drill into the rock such as the piddock 

mass movement: rock fall

loose fragments of rock breaks of a cliff face and fall onto the beach, creating talus / scree at the base of the cliff

mass movement: landslide

blocks of rock become dethatched from the cliff face and slide down, occurs when bedding planes dip towards the sea

mass movement: mudflow

saturated soil and rock flows down a cliff face, happens after heavy rainfall on loosely consolidated cliffs

mass movement: rotational slip (slump) - mass movement

saturated soil and rocks slide down the cliff face with a rotational (curved movement)

creates a steep profile in the cliff

marine sediment transport processes:

suspension - fine material such as clay and sediment is carried by the sea

solution - dissolved minerals carried by the sea

traction - large boulders and pebbles are rolled along the sea bed

saltation: small stones, pebble and silt bounces along the sea bed

longshore drift process

• the prevailing wind (most common wind direction causes waves to approach at an angle

• when they hit thew beach, the swash it an an angle

• when the wave runs out of energy, it will slope down the beach due to gravity

• this will then continue across the coastline in the direction of the prevailing wind

arolian sediment transport processes

1. surface creep - large material rolled across the sand floor by the wind (similar to traction)

2. saltation - material bounced / hop across the sand floor

3. suspension - carrying sand particles in the air by strong wind or smaller pebbles

factors effecting erosion:

`wave strength - controlled by fetch and the wind speed . longer fetch creates more powerful waves with more erosive power

underwater topography

beaches - increase distance waves travel before it reaches cliffs and energy. headlands refract waves around them, reducing erosive power at one location while increasing another

weathering - creates weaknesses in rocks for erosion to exploit

human activity - dredging to remove material and coastal management reducing it

Fetch definition

the length of water surface over which the wind blows in a consistent direction

concordant and dicordant coastline

Concordant – contains layers of rock which run parallel to the coastline  

Discordant – coastlines where layers of rock run perpendicular to the coastline 

erosional formation: coves

• on concordant coastlines

• the more resistant band of rock is breached

• erosion speeds up when it reaches the softer, les resistant rock behind which spreads laterally

• once it reached the harder rock, erosion slows down

erosional formation: headlands and bays

• more resistant rock erodes slowly, leaving rock sticking out to sea which is a headland

• the less resistant rock erodes more quickly and retreats to form a bay

• a beach develops here because the wave a constructive as well as the eroded soft rock being broken down by attrition

• wave refraction is important as it concentrates wave energy on the headland, this encourages deposition int he bay, further developing the beach