Coastal Landscapes - Sea Level Change

  • Long-term sea-level change occurs on a timescale
Climate Change Affecting Sea Level:
  • Ice age build up and the climate begins to change.
  • Less water in the sea and the sea-level falls.
  • New land can also form by the release can still happen. T
  • his means that sea level falls because waster goes over land which is built on snow so it builds up and stays there.
What Causes Sea-Level Change:
  1. Ice age/glacial periods (long term)
  2. Global warming (short term)
  3. Other physical processes e.g tectonics and subsidence
Two Types Of Sea Level Change:
  1. Eustatic: Volume of water changes e.g more water floating leads to a raised height
  2. Isostatic: Height of the coastal land changes so the land rises out or sinks into coastal water.
Eustatic:
  1. Ocean water warms on coasts so it changes volume. If the water is warmer it will expand slightly so the sea level will very slightly rise.
  2. Amount in the ocean increases from ice on land e.g glaciers therefore more water flows in the ocean raising the sea level
  3. Thermal Expansion: Water is heated and it expands, oceans are 4-8 thousand deep so a slight expansion adds some millimetres which can be significant.
  4. Ice Melt: Land ice melts and flows into the sea = more water in sea. Opposite can also occur.
Isostatic Change:
  1. Weight of the ice is compressed, and rock is pushed into the mantle,
  2. sea levels fall because of thermal contraction and water is stored as ice.
  3. Thermal expansion occurs = raised sea level.
  4. The land rebounds slowly as the weight of ice has increased which causes local sea levels to fall.
Sea Level Change Landforms:
Submergent:
  • Landforms that form due to being under water (submergent) e.g Fjords, Rias and the Dalmatian Coast.
Fjords:
  • Mainly in Norway
  • Very large, deep, steep-sided valley that have flooded
How Do They Form:
  1. Huge amount of snow and ice build-up in northern latitudes
  2. V-shaped valleys on the coast because rivers erode the land
  3. Glaciers flow out of ice sheets eroding the valley to make them U-shaped
  4. Ice melts and sea levels rises eustatically which is, submerged to form a fjord.
Rias:
  • River valley that is v-shaped and flooded when sea levels rise, not been eroded
  • Due to the eustatic sea level rising from the last ice age, rising sea level forms rias
  • Example: Southern Ireland Coast near Cork.
Dalmatian Coast, Croatia:
  1. Long parallel mountains formed via tectonic forces
  2. Sea levels rise because the ice ages have ended
  3. Eustatic sea level rise has flooded the coast
  4. Top of the mountain stick out as long parallel islands.
Emergent Landforms:
  • Landforms that form due to land coming out of the water e.g Raised beaches and fossil cliffs
  1. Marine erosion creates cliffs and a wave cut notch
  2. Ice age ends and all the weight of the ice sheets and glacial are removed from land
  3. Isostatic rebound occurs: Land rising back out of the mantle
  4. Raises the beaches and cliffs up so they are away from the coast
  5. Eustatic sea level fall can also produce the same features
Global Sea Level Rise Due To Climate Change:
  • If the sea level rises due to climate change, it will raise 60m and will flood the following areas: Amsterdam, London, Berlin, Venice and Baghdad
Bangladesh:
  • One of the most at risk countries from climate change and global sea level rise
  • Large river delta from the Ganges
  • Delta: Very flat and low-lying areas of sediment deposited by rivers into coastal waters
Tectonic Sea Level Change:
  • Earthquakes and tectonics can also change sea levels isostatically. An earthquake in 2016 in New Zealand uplifted a long area of coast raising the sea floor out permanently.
Summary:
  • Sea level rise and fall by many metres on a long-term timescale e.g mainly due to the ice ages
  • Eustatic change is the volume of water changing from land ice melting and thermal expansion.
  • Isostatic change means land levels rises or falls
  • Submergent landforms include: fjords, rias and Dalmatian Coastline
  • Emergent landforms include: raised beaches and fossil cliffs
  • Global sea level rise is occurring at a rapid rate due to climate change and causing risk to low lying coastlines e.g Netherlands, Bangladesh and the Holderness Coastline in Yorkshire.
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