Sea-Level Change

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  • Change in relative sea water levels.
    • Isostatic change
      • this refers to the change in sea level which happens on a local scale.
        • fall in sea level - during the build up of ice sheets across the land, the land level subsides. after this ice melts, the land rebounds over thousands of years. (the elastic rebound theory).
        • rise in sea level - land can sink at the coast due to deposition of sediment (accretion). this can happen especially at river deltas where so much deposition causes the land to 'sag'
      • Scotland is emerging at approx. 1.5mm a year, but England and Wales is subsiding at approx. 1mm a year.
    • Eustatic change
      • this refers to the sea level change which happens on a global scale. (change in volume of water).
        • rise in sea level - post-glacial period, the ice sheets return to water in the sea, increasing the volume of water globally. Also, global increase in temperatures means the volume of water increases due to thermal expansion (the volume of water expands).
        • fall in sea level - during glacial periods, water from the sea forms on land as glaciers and causes a global fall in sea levels.
    • Emergent coastlines
      • occurs due to post-glacial isostatic adjustment.
        • raised beaches and fossil cliffs form as a result of emerging coastlines.
      • Earlsferry, Fife (Scotland) has a raised beach.
      • Lendalfoot, Ayrshire (western Scotland), the A77 runs along a raised beach.
    • Submergent coasts
      • The post glacial Eustatic change of sea level rise has resulted in 'drowned' coastlines.
        • The south of England is experiencing this due to the rise in global sea level post-glacial period.
      • Ria's form as a result of submerging coasts. When an estuary has filled with water that has been pushed inland, drowning valleys that were eroded by rivers.
        • Useful, as they are sheltered ports, and stretch for miles inland. Kingsbridge estuary, Devon.
      • a Fjord is a drowned river valley, that is U-shaped, and a glacial eroded valley. they can also reach up to 1000m deep, deeper than the adjacent sea. (Norway)
    • Barrier islands
      • can form by the original coastal sand dunes later being flooded by rising sea levels, forming a lagoon. they are a natural form of defence.


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