EQ3 Coasts 16.5.19
EQ3: How do coastal erosion and sea level change alter the physical characteristics of
coastlines and increase risks?
- Short and longer term sea level changes influence the physical geography of
coastlines and increase risks for people.
- Rapid coastal recession happens some locations because of both physical and human
influences.
- Coastal flooding is a significant risk on some coastlines, worsened by global warming
but uncertain in terms of magnitude.
Sea level change
Complex as both land level (isostatic) and water level (eustatic) can change over time.
- A rise or fall in water level causes a eustatic change, which is a global change in the
volume of sea water in all the worlds seas and oceans.
- Isostatic change is a local rise or fall in land level.
Eustatic fall in sea level → during glacial periods, when ice sheets form on land in high
latitudes, water evaporated from the sea is locked up on land as ice, leading to a global fall
in sea level.
Eustatic rise in sea level→ at the end of the glacial period, melting ice sheets return water
to the sea and sea level rises globally.
Global temperature increase causes the volume of ocean water to increase (thermal
expansion) also leading to sea level rise.
Isostatic fall in sea level → during the build-up of land-based ice sheets, the colossal weight
of ice causes the Earth’s crust to sag. When the ice sheets melt, the land surface slowly
rebounds upward over thousands of years.
Isostatic rise in sea level → land can ‘sink’ at the coast because of the deposition of
sediment, especially in large river deltas where the weight of the sediment deposition leads
to very low ‘crustal sag’ and delta subsidence.
Since the end of the last ice age 12k years ago, the UK has felt the impact of continuing sea
level change.
- Scotland is still rebounding upward, up to 1.5mm/year = post glacial adjustment.
Post-glacial adjustment: refers to the uplift experienced by land following the removal of
the weight of ice sheets.
- Contrast: England and Wales are subsidising up to 1mm/year.
- The UK is ‘pivoting’ with the north rising and the south sinking.
- Sea level rise caused by global warming (EUSTATIC), isostatic adjustment is to
compound the effect of this current sea level rise in the south, but cancel it out in
the north.
Tectonic activity contributes to the shape of ocean basins, if the basins get smaller,
subsequently so does the volume of water it can hold, leading to rising or falling sea level
changes.
Tectonic activity can contribute to isostatic sea level change as the tectonic uplift on plate
boundaries force oceans to be at a higher platform.
Sea floor spreading can create a larger platform for the water to sit on.
EQ3: How do coastal erosion and sea level change alter the physical characteristics of
coastlines and increase risks?
- Short and longer term sea level changes influence the physical geography of
coastlines and increase risks for people.
- Rapid coastal recession happens some locations because of both physical and human
influences.
- Coastal flooding is a significant risk on some coastlines, worsened by global warming
but uncertain in terms of magnitude.
Sea level change
Complex as both land level (isostatic) and water level (eustatic) can change over time.
- A rise or fall in water level causes a eustatic change, which is a global change in the
volume of sea water in all the worlds seas and oceans.
- Isostatic change is a local rise or fall in land level.
Eustatic fall in sea level → during glacial periods, when ice sheets form on land in high
latitudes, water evaporated from the sea is locked up on land as ice, leading to a global fall
in sea level.
Eustatic rise in sea level→ at the end of the glacial period, melting ice sheets return water
to the sea and sea level rises globally.
Global temperature increase causes the volume of ocean water to increase (thermal
expansion) also leading to sea level rise.
Isostatic fall in sea level → during the build-up of land-based ice sheets, the colossal weight
of ice causes the Earth’s crust to sag. When the ice sheets melt, the land surface slowly
rebounds upward over thousands of years.
Isostatic rise in sea level → land can ‘sink’ at the coast because of the deposition of
sediment, especially in large river deltas where the weight of the sediment deposition leads
to very low ‘crustal sag’ and delta subsidence.
Since the end of the last ice age 12k years ago, the UK has felt the impact of continuing sea
level change.
- Scotland is still rebounding upward, up to 1.5mm/year = post glacial adjustment.
Post-glacial adjustment: refers to the uplift experienced by land following the removal of
the weight of ice sheets.
- Contrast: England and Wales are subsidising up to 1mm/year.
- The UK is ‘pivoting’ with the north rising and the south sinking.
- Sea level rise caused by global warming (EUSTATIC), isostatic adjustment is to
compound the effect of this current sea level rise in the south, but cancel it out in
the north.
Tectonic activity contributes to the shape of ocean basins, if the basins get smaller,
subsequently so does the volume of water it can hold, leading to rising or falling sea level
changes.
Tectonic activity can contribute to isostatic sea level change as the tectonic uplift on plate
boundaries force oceans to be at a higher platform.
Sea floor spreading can create a larger platform for the water to sit on.
