does anyone know what eustatic and isostatic changes are (geography)? i know they're something to do with glaciation but my teacher hasn't explained it very well and my exam is tomorrow!
please help if you can tell me in simple terms!
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- Thread Starter
- 26-01-2004 13:43
- 26-01-2004 14:00
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This is what it says
These are variations in sea level resulting from alterations in the volume of the world's oceans due to:
Melting of land ice, e.g. Melting of the Antarctic & Greenland glaciers would raise sea level by 70m. However, it should be noted that due to the reduce mass of ice on the continent isostatic rebound would reduce this see level rise to 40-50m (Jones, 1994).
Steric effect. In the last century oceans have warmed by 0.4oC leading to a 10-15cm rise in sea level due to thermal expansion alone.
Changes in ocean depth due to tectonic activity, sedimentation or volcanic activity. Sea-floor spreading tends to increase the volume of the ocean basins whilst subduction has the opposite effect. Under-sea volcanoes can add large quantities of lava to the ocean floor thus reducing the ocean basin volume. Rivers add a large amount of sediment. These sediments are in the main deposited on the continental shelves and contribute little to global sea level rise. Higgins (1965) estimates that sedimentation contributes 4mm of global sea level rise per century.
Changes due to modifications of local wind fields and ocean currents.
Changes in the hydrological cycle (evaporation, precipitation and river run-off).
These are seal level changes that result from variations in land level. These arise due to:
Tectonic activity e.g. NW U.S.A.
Man’s influence - Consolidation due to the withdrawal of water, minerals and hydrocarbons, e.g. N. Holland.
Loading, e.g. Louisiana - loosing 100km2/yr due to sediment loading (subsidence=1m/yr). Also is Finland rising by 3-9mm/yr as a result of glacial rebound.
Milankovich cycles: These relate to the tilt and wobble of the earth's axis of rotation and the eccentricity of the earth's orbit. These cyclically affect the earth's climate with a period of: i) Tilt (40kyr), ii) Wobble (21kyr) and iii) Eccentricity (100kyr).