Summary 3.8 Sea Level Change notes AQA Physical Geography

3.8 – Sea Level Change

Eustatic and Isostatic change:
Eustatic: when the sea level itself rises or falls
- changes are global
- in gold glacial periods precipitation falls as snow
- huge ice sheets form that would usually be ocean water  SEA LEVEL FALLS
- when temperatures rise again ice sheets melt and retreat  SEA LEVEL RISES
- caused by temperature – thermal expansion
- caused by tectonic movement


Isostatic when the land rises or falls (relative to the sea level)
- changes are local
- during glacial periods the weight of ice sheets makes land sink – isostatic subsidence
- as ice begins to melt at end of glacial period land readjusts and rises again – isostatic
recovery
- caused by tectonic movement
- caused by glacial uplift and depression

Reasons for sea level rise:
- thermal expansion
- melting of freshwater ice (such as Greenland and Antarctic ice sheets)
- tectonic movement
- change in shape of basin
- change in volume of water


CASE STUDY - Sea level change due to tectonic activity: Indian Ocean
Earthquake measured 9.0 and 9.3 on the Richter Scale.
Tsunami killed 330 000 people
Indian island of Sumatra was worst hit  closest land to earthquake’s epicentre
Capacity of Indian ocean was reduced following rise in seabed (permanent rise of 0.1mm)


Landforms formed by sea level change:
1.) Emergent coastal landforms
 Raised beaches – the result of isostatic recovery which raises wave-cut platforms and
their beaches above the present sea level

Emergent coastline: coastline that is exposed when the sea level falls


1.) Submergent coastal landforms -
 Rias – sheltered winding inlets with irregular shorelines
 Fjords – created when a rise in sea level floods deep glacial troughs (long and steep)