Eustatic and Isostatic change

Eustatic change is the global rise or fall of sea levels. This change is a GLOBAL change

A factor that can affect this is global warming. This happens because the increased heat changes the amount of ice stored on land as water, thus changing the sea levels. A rise in temperature will cause the ice caps to melt, and sea levels will rise, and vice versa.

The second factor that can affect this is the Steric effect. This is where the density of the water increases or decreases as the temperature rises or falls. If the temperature rises the water expands and if it falls the water contracts. It is estimated that sea levels can rise up to 0.4mm per year.

Isostatic change is the adjustment of land levels. This change is LOCAL.

3 main physical factors affect this:

• ice
• uplift
• seismic activity

Ice is the first way that can adjust the land. This can happen when the land is covered by ice in one place. For example in the last ice-age, North Western Britain was covered in 1.5 km of ice. This immense pressure causes this area land to subside, whilst any other land (South Britain) will rise, like a see-saw. When the glacier ice melts, the weight is taken off the land, and so the land will begin to rise again, whilst the other area will sink. This happens very slowly, and is known as glacial rebound.

Uplift: Underlying tectonic forces, including uplift through folding and faulting can result in isostatic uplift (rise in land level) The land may rise as a result of tectonic plates pushing each other or removal of weight.

Seismic activity: earthquakes can cause both uplift and depression of land as a result of movement along fault planes.

Isostatic change can also happen due to human interference. The extraction of resources from low lying coastal areas may lead to campaction of land followed by subsidence (sinking).