Eustatic & Isostatic Change
- Sea level can change as a result of isostatic and eustatic changes
- Eustatic change occurs when there is a greater volume of water in the ocean basins
- Isostatic change occurs when the height of the land changes relative to the water level
- Isostatic change happens more slowly than eustatic change
Eustatic change
- Eustatic change happens due to changes in the amount of ice, as a result of thermal expansion and tectonics
- This change will be global
- Changing amounts of ice
- At the end of the last ice age 10,000 years ago global sea level rose rapidly due to melting ice creating well-known waterways like the English Channel
- Sea levels may also decrease when ice forms, locking water away in the ice sheets and glaciers
- Thermal expansion
- Thermal expansion occurs as water warms, warmer fluids expand to take up a greater volume
- Tectonics
- Magma rising to the surface lifts the crust and reduces the capacity of the oceans causing sea levels to rise
Isostatic change
- Isostatic change is a localised change and may be due to:
- Post-glacial adjustment
- During a period of glaciation, extremely heavy icy sheets weigh land down
- When the glacial period ends and the ice melts the land will rebound to a higher level, lowering the sea level in a process known as isostatic recovery or readjustment
- Accretion
- Within the sediment cell, there are areas of net deposition causing land to build up
- Subsidence
- Caused by the lowering of the water table or increased deposition weighing down the sediment
- Tectonics
- The folding of the sedimentary rock
- Lava and ash from volcanoes increase the height of the land relative to the sea level
- Post-glacial adjustment
- The UK is still experiencing isostatic recovery from the end of the last ice age
- Land in the north in Scotland is still rebounding and rising by approximately 1.5mm a year
- Landsend in Cornwall is sinking by 1.1mm each year
Isostatic changes in the UK