Sea Level Changes

• What is Eustatic Sea Level Change?

  A change in the volume of water in the sea or by a change in the shape of ocean basins - global effects.

  Caused by:

  > Changes in climate - increase in temp causes melting of ice-sheets and thermal expansion, decrease in temp causes snow precipitation increasing the volume of water stored in glaciers decreasing sea level.

  > Tectonic movements of the Earth's crust that alter the shape and volume of ocean basins - e.g. sea floor spreading increases the volume of the basin therefore decreasing sea level.
• What is Isostatic Sea Level Change?

  A change caused by vertical movements of the land relative to the sea. Any downward movement of land causes sea level to rise locally, while uplift of the land causes sea level to fall - local effects.

  Caused by:

  > Uplift or depression of the earth's crust due to accumulation of melting ice sheets, can continue slowly for thousands of years after the weight of a retreating glacier.

  > Subsidence of land due to shrinkage after abstraction of groundwater e.g. drainage of marshland.

  > Tectonic plate margins - destructive.
• How does sea level vary on a daily basis?

  The tidal cycle.

  Onshore winds and low atmospheric pressure systems can also cause the sea level surface to rise temporarily.
• What is a Ria?

  Rias are formed when river valleys are partially submerged e.g. Milford Haven in South Wales.

  They have a gentle long and cross-profile. They're wide and deep at their mouth, becoming narrower and shallower the further inland they reach.
• What is a fjord?

  Fjords are drowned glacial valleys (rather than drowned river valleys).

  They are relatively straight and narrow with very steep sides.

  They have a shallow mouth caused by raised ground called the threshold formed by deposition of the glacier.

  They are very deep further inland e.g. Sognefjord in Norway is over 1000m deep in places.
• What is a Dalmatian Coastline?

  In areas where valleys lie parallel to the coast, an increase in sea level can cause a dalmatian coastline.

  Valleys are flooded, leaving small islands parallel to the coastline separated by narrow sea level channels.

  E.g Dalmatian Coast in the Croatian Adriatic Sea.
• How much has sea level risen since 1900?

  About 21cm and another 20cm is expected by 2200.
• How much has average temperature risen between 1900 and 2016?

  There's been a sharp rise and it has risen by 1.08 degrees since 1900.
• How much is sea level currently rising per year?

  2mm
• How will sea level rise impact coastal areas?

  > Storms are likely to become more frequent and intense - causing damage to ecosystems and settlements e.g. Odisha Cyclones.

  > More frequent and more severe coastal flooding

  > Submergence of low-lying islands - Maldives expected to have sunk by 80% in 2050

  > Changes in coastline - islands are created/submerged, rias, fjords, dalmation coasts e.g. if sea level rises by 0.3m from its current level, Bangladesh will lose 8000km squared of its land.

  > Contamination of water sources and farmland.
• How can sea level fall result in coastlines of emergence?

  > Raised beaches occur when sea level leaves beaches above the high tide mark, over time sediment becomes vegetized and becomes soil.

  > Leaves WCP exposed.

  > Cliffs are no longer under attack and get covered by vegetation - relict cliffs.