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

High energy coastline example: Holderness coast

coastline located in East Yorkshire, spanning 50 miles from Flamborough in the noth to spurn pount in the town:

1. stakeholders - residents, farmers, business owners (gas terminal, seaside resort)

2. retrieved 40 metres in some areas

3. a.8 metres a year

4. fetch of 400km

5. ringborough farm - 1939 = 145 acres 2010 = 70 acres

6. geology - high energy coastlines have rocky coasts whcih cause the waves to dispurse, Flamborough however, has a soft geology coastline, made up of boulder clay and a glacial till , maiign it more likely to by rapdily eroded overtime due to it being more easily saturated, counter with it being a more fertile source.

coasts as a system

the system is in a constant state of dynamic equilibrium and can be seen as both an open system and a closed system

coasts as a system - positive and negative feedback

positive feedback:

1. waves eroding a cliff, releasing material which can abrade against the cliff, leading to more cliff erosion

negative feedback:

2. as the shore is eroded, material makes the wave cut platform wider, absorbing wave energy and reducing the impact at the base of the cliff

factors effecting the strength of wind on waves

fetch - the distance of open water the wind blows over

strength - how forceful the wind is

duration - how long it has been blowing

storm surges - intense increase in wavelength and speed

human - impermeable surfaces and energy from boats

tidal range and the characteristics of a coast

all tides have the same amount of time to reach their tidal range:

high tidal range - large difference in high and low tide e.g. Bristol Channel

Low tidal range - small difference e.g. the Mediterranean

types of waves - constructive wave

• formed - calm local weather, short fetch

• long wavelength, spilling waves

• strong swash weak backshash

• build up a gentle beach profile

types of waves - destructive

1. formed - local storms, strong winds, high fetch

2. short wavelength, plunging waves

3. weak swash, strong backwash

4. beach is lost and a steeper beach profile is likely in short term

wave refraction

changing the amount of energy reacing the shore on a small scale, concentrating energy at the headland and increases rates of erosion

sediment cell

a section of coastline in which sediment is recycled but not added or lost. s

sources of sediment - rivers and cliff erosion

rivers:

• hold the vast majority of coastal sediment, especially in high-rainfall environments

• sediment is often deposited in river mouths and estuaries, where it is reworked by waves and tides

cliff erosion:

• important in local areas of soft rock

• sand and clay cliff erosion rates can be as high as 10m a year

sources of sediment - longshore drift and wind

longshore drift:

• sediment is transported from one stretch of coastline (output) to another

• this can change depening on sediment rates and wind speeds e.g. big or small pieces

Wind:

1. sand can be deposited in coastal region by wind, creating sand dunes at the coast

2. this depends on wind speed as well as proximity to sand

sources of sediment - glaciers and offshore sediment

glaciers

1. ice shelves carve (big chunks of ice breaking of a glacier) into the sea, depositing sediment trapped in ice

2. areas near the poles gain sediment from climate change

offshore

1. sediment offshore can be transferred into different coastal zones by waves and tides

2. in the UK at the end of the glacial perioid, sea levels rose, which led to sediment at southern coastlines to form landforms such as barriter beaches

sediment budget

the balance between the inputs and outputs of sediment in the system / sediment cell

the 3 main types of weathering

mechanical / physical - when rocks break up with no chemical changes

biological - rock breakdown due to organic activity

chemical - rock breakdown due to a chemical reaction

mechanical weathering - Freeze-thaw

when temperatures freeze below 0

1. water goes into the small cracks of rock

2. when the temperature is below 0, the water in the cracks become ice

3. the water expands as it freezes, creating forces on the surrounding rock, increasing crack size

4. this cycle continues until the fragment of rock breaks away completely

mechanical weathering - wetting and drying

similar to freeze-thaw

1. in warm climates, water doesn’t freeze, it just wets and dry’s which works the same way just without ice

2. often occurs in the inter-tidal zone

3. rocks expand when wet and contract when dry

mechanical weathering - salt crystallisation

• this occues because the salt crystals are larger than the water molecules

• this exerts pressure on the rock, causing it to break down

• water collects in the cracks in the rock when it rains

• when it is sunny, the water evaporates, salt crystals are left behind in the cracks

• salt crystals grow over time and creates stress, causing the rock to break