Chapter 5: Coastal change and conflict

Chapter 5: Coastal change and conflict

1. Geology of coasts

   • Soft rock coasts
     • clay - easily eroded by by the sea
       • Holderness, Yorkshire
     • cliffs
       • May be high but less rugged and steep than hard rock coasts
         • piles of mud + clay on cliff face
           • at foot of cliff - few rocks, some sand + mud
             • sea often brown
   • Hard rock coasts
     • granite - reistant to erosion
       • Land's End, Cornwall
     • cliffs
       • high, steep + rugged
         • bare cliff face
           • some rocks + boulders at foot
             • erosion features e.g. caves, arches, stacks

2. erosion

   • Hydraulic action
     • Waves hitting rock foces air into cracks. Trapped air, released quickly, breaks up the rock
   • Abrasion
     • Waves pick up stones and hurl them against the cliff which wears away the rock
   • Attrition
     • Pebbles carried by waves - rounder + smaller as they collide with eachother

3. Coastal landforms

   • At a headland
     • Cave - when waves erode weakness in the rock e.g. joint/fault
       • Arch - when 2 caves erode back from either side of a headland and meet in the middle
         • Stack - when the arch roof weathers and arch collapses
           • Stump - stack eroded by wind and water
   • wave- cut platform
     • 1. waves cause undercutting at base of slope
       • 2. forms a notch that gradually gets bigger
         • 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

4. Coasts

   • concordant coast - alternating hard and soft rocks occur parallel to coast and are eroded at different rates
     • formation of lulworth cove
       • 1. waves slowly cut through weakness in resistant band of limestone - forms a small narrow entrance to cove
         • 2. cove widens- soft clay eroded quickly
           • 3. a band of chalk behind the clay is more resistant so erosion is slower
   • Discordant coast - alternating hard and soft rock occur at right angles to coast and are eroded at different rates
     • hard rock stands out as headlands and soft rocks form bays

5. waves

   • constructive
     • in calm conditions waves are
       • small, weak, low frequency
         • don't break with much force
           • add sand/ sediment to coastline by deposition
             • swash is greater than backwash so sediment is pushed up beach
     • long wavelength
       • shallow gradient
         • strong swash
           • weak backwash
   • destructive
     • break with lots of force + energy
       • have the power to carry out erosion of beaches + rocks
         • high frequency
           • backwash is greater than swash so sediemnt taken away from beach into sea
     • steep gradient
       • tall waves
         • short wavelength
           • weak swash
             • strong backwash

6. Longshore drift

   • 1. waves approach the coast at an angle
     • 2. Swash pushes sand and gravel up beach at same angle
       • 3. Backwash carries sand and gravel back down beach at 90 degrees under force of gravity
         • 4. sand + gravel move along beach in a zigzag fashion
           • 5. sand is lighter so moves up the beach further than gravel or pebbles

7. Formation

   • spit
     • longshore drift carrys beach sediment beyond a bend in coastline
       • leading to an extention of the beach into the open water
         • 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
     • definition: material deposited by the sea which grows across a bay/river mouth
   • Bar
     • if longshore drift continues along the spit
       • 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
         • bar cuts off rivers from the sea so water builds up behind bar - forms a freshwater lake/ lagoon - e.g. slapton Ley, devon

8. Weathering

   • Mechanical
     • salt cystal growth (left from evaporated seawater) causes stress in rock - breaks into tiny fragments
   • Chemical
     • acid rain - reacts with weak minerals - dissloves + rock decays
   • Biological
     • roots of vegetation - grow in rock cracks + slit rock apart

9. Mass movement

   • rock fall
     • fragments of weathered rock from a cliff face fall under gravity + collect at base
   • Slumping
     • bottom of cliff eroded by waves
       • slope becomes steeper and cliff can slide downwards in a rotational manner
         • triggered by saturation due to rain
           • this lubricates the rock and makes it heavier

10. climate change on marine erosion + deposition

    • uk - rising sea levels as warmer temps. from global warming melt glaciers ans ice sheets
      • changing storm patterns - stronger + less predictable
    • impacts on marine erosion
      • stronger storms- bigger wave energy - more erosion
      • abandoned cliffs - come under new attack by waves as sea level rises
      • soft clay coasts - faster retreat
    • impact on marine depositional features
      • rising sea levels - beaches + bars at risk of submergence and erosion
        • e.g. Studland beach, Dorset - 1 million tourist p.a (eroded by 2-3m a year)
          • facilities relocate + beach replenished
      • extreme weather becomes more common - violent storms (+hurricanes)
        • destroy beaches/ spits
          • 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

11. climate change

    • Sea level rise - 0.3m prediction by 2100
      • loy-lying areas at risk e.g bangladesh + maldives
      • Thames estuary flooding - 12X more frequent by 2100
        • TTB - holds back v.high tides
        • 'Thames estuary 2010' new project to build new flood walls along river
    • Storms at sea
      • increase height of waves - cause flooding
      • the environment agency manages + forecasts

12. How fast a coast retreats depend on ...

    • Rock type - hard rocks erode slower that soft
    • Number of faults + joints - with more the rocks erode faster
    • Fetch - if wind blows over a wide area of sea (fetch), the waves are stronger + will have a greater impact on cliffs
    • cliff exposure - ones exposed to strong winds + weather will erode quicker than ones sheltered
    • Storms - ones exposed to frequent storms erode quicker
    • Sea defences - those protected have a slow retreat

13. Cliff erosion effects

    • Houses destroyes
    • Farmland lost
    • loss of income
    • Hotels + caravan parks abandoned
    • loss of roads