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)
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)
