Eustatic and isostatic change

Short term sea level changes

• tidal changes

• Atmospheric air (low = rise in sea level)

• Winds can increase wave height

Bristol Channel has the highest tidal range in the UK with 15m

what is thermal expansion?

• ocean water warms and expands

• 1/3 of sea level rise is due to thermal expansion

• Depth, salinity and temperature effect how much it can expand

What is eustatic change?

• a rise or fall in sea level caused by a change in the overall volume of water in oceans/seas

• It is a global change

What is eustatic fall?

• during glacial periods water is stored on land as ice

What is eustatic rise?

• end of glacial periods water is stored on land as ice

What is isostatic change?

• gain or loss of land

• Linked to ice ages

• Glaciers and land ice weigh on the crust and pushes it downwards

• As the mantle is soft and viscous it pushes mantle to other areas and causes it to uplift

• Can also be caused by volcanoes creating new islands, increasing land level

What is isostatic fall?

• land based ice causes earth to sag, once it melts it rebounds

What is isostatic rise?

• land can sink at the coast because of the mass of deposited sediment sags the earth

• Hawaii formed from a mantle plume that created multiple islands as the plate (Pacific) moved

Examples of isostatic gain/fall earthquakes

Japanese Tsunami 2011

• Converging plate margin caused the coastline to drop by 2 feet

• 9.1 earthquake

Which part of the Uk is emerging and where is submerging?

• Scotland is rising (1.5mm Isle of Arran)

• South England is sinking (Cornwall -1.1 mm)