Chapter 5: Coastal change and conflict

Geology of coasts
1. Soft rock coasts
  1. clay - easily eroded by by the sea
    1. Holderness, Yorkshire
  2. cliffs
    1. May be high but less rugged and steep than hard rock coasts
      1. piles of mud + clay on cliff face
        at foot of cliff - few rocks, some sand + mud
        sea often brown
2. Hard rock coasts
  1. granite - reistant to erosion
    1. Land's End, Cornwall
  2. cliffs
    1. high, steep + rugged
      1. bare cliff face
        some rocks + boulders at foot
        erosion features e.g. caves, arches, stacks
erosion
1. Hydraulic action
  1. Waves hitting rock foces air into cracks. Trapped air, released quickly, breaks up the rock
2. Abrasion
  1. Waves pick up stones and hurl them against the cliff which wears away the rock
3. Attrition
  1. Pebbles carried by waves - rounder + smaller as they collide with eachother
Coastal landforms
1. At a headland
  1. Cave - when waves erode weakness in the rock e.g. joint/fault
    1. Arch - when 2 caves erode back from either side of a headland and meet in the middle
      1. Stack - when the arch roof weathers and arch collapses
        Stump - stack eroded by wind and water
2. wave- cut platform
  1. 1. waves cause undercutting at base of slope
    1. 2. forms a notch that gradually gets bigger
      1. 3. rock above loses support and collapses
        4. debris gradually washed away by waves
        process repeats - cliff slowly retreats backwards and becomes steeper
        e.g. seven sisters, east sussex
Coasts
1. concordant coast - alternating hard and soft rocks occur parallel to coast and are eroded at different rates
  1. formation of lulworth cove
    1. 1. waves slowly cut through weakness in resistant band of limestone - forms a small narrow entrance to cove
      1. 2. cove widens- soft clay eroded quickly
        3. a band of chalk behind the clay is more resistant so erosion is slower
2. Discordant coast - alternating hard and soft rock occur at right angles to coast and are eroded at different rates
  1. hard rock stands out as headlands and soft rocks form bays
waves
1. constructive
  1. in calm conditions waves are
    1. small, weak, low frequency
      1. don't break with much force
        add sand/ sediment to coastline by deposition
        swash is greater than backwash so sediment is pushed up beach
  2. long wavelength
    1. shallow gradient
      1. strong swash
        weak backwash
2. destructive
  1. break with lots of force + energy
    1. have the power to carry out erosion of beaches + rocks
      1. high frequency
        backwash is greater than swash so sediemnt taken away from beach into sea
  2. steep gradient
    1. tall waves
      1. short wavelength
        weak swash
        strong backwash
Longshore drift
1. 1. waves approach the coast at an angle
  1. 2. Swash pushes sand and gravel up beach at same angle
    1. 3. Backwash carries sand and gravel back down beach at 90 degrees under force of gravity
      1. 4. sand + gravel move along beach in a zigzag fashion
        5. sand is lighter so moves up the beach further than gravel or pebbles
Formation
1. spit
  1. longshore drift carrys beach sediment beyond a bend in coastline
    1. leading to an extention of the beach into the open water
      1. end of spit becomes curved when exposed to srong winds + waves
        deposition happens in the sheltered water behind then spit, and becomes a salt marsh
  2. definition: material deposited by the sea which grows across a bay/river mouth
2. Bar
  1. if longshore drift continues along the spit
    1. over time, the sand + pebble accumulation grows larger and builds builds across an estuary to form a bar / join up with coastline on the other side
      1. bar cuts off rivers from the sea so water builds up behind bar - forms a freshwater lake/ lagoon - e.g. slapton Ley, devon
Weathering
1. Mechanical
  1. salt cystal growth (left from evaporated seawater) causes stress in rock - breaks into tiny fragments
2. Chemical
  1. acid rain - reacts with weak minerals - dissloves + rock decays
3. Biological
  1. roots of vegetation - grow in rock cracks + slit rock apart
Mass movement
1. rock fall
  1. fragments of weathered rock from a cliff face fall under gravity + collect at base
2. Slumping
  1. bottom of cliff eroded by waves
    1. slope becomes steeper and cliff can slide downwards in a rotational manner
      1. triggered by saturation due to rain
        this lubricates the rock and makes it heavier
climate change on marine erosion + deposition
1. uk - rising sea levels as warmer temps. from global warming melt glaciers ans ice sheets
  1. changing storm patterns - stronger + less predictable
2. impacts on marine erosion
  1. stronger storms- bigger wave energy - more erosion
  2. abandoned cliffs - come under new attack by waves as sea level rises
  3. soft clay coasts - faster retreat
3. impact on marine depositional features
  1. rising sea levels - beaches + bars at risk of submergence and erosion
    1. e.g. Studland beach, Dorset - 1 million tourist p.a (eroded by 2-3m a year)
      1. facilities relocate + beach replenished
  2. extreme weather becomes more common - violent storms (+hurricanes)
    1. destroy beaches/ spits
      1. rising sea temp. - more storm energy - spits breached creating large gaps
        e.g. 2004 hurricane charley - coast of florida - north captiva spit breached - 450m gap due to high tides + v. strong winds
climate change
1. Sea level rise - 0.3m prediction by 2100
  1. loy-lying areas at risk e.g bangladesh + maldives
  2. Thames estuary flooding - 12X more frequent by 2100
    1. TTB - holds back v.high tides
    2. 'Thames estuary 2010' new project to build new flood walls along river
2. Storms at sea
  1. increase height of waves - cause flooding
  2. the environment agency manages + forecasts
How fast a coast retreats depend on ...
1. Rock type - hard rocks erode slower that soft
2. Number of faults + joints - with more the rocks erode faster
3. Fetch - if wind blows over a wide area of sea (fetch), the waves are stronger + will have a greater impact on cliffs
4. cliff exposure - ones exposed to strong winds + weather will erode quicker than ones sheltered
5. Storms - ones exposed to frequent storms erode quicker
6. Sea defences - those protected have a slow retreat
Cliff erosion effects
1. Houses destroyes
2. Farmland lost
3. loss of income
4. Hotels + caravan parks abandoned
5. loss of roads

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Chapter 5: Coastal change and conflict

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