AQA AS Geography Coasts: Sea Level Change

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Sea Level Changes
World sea level changes over time as a result of two major influences:
Eustatic fall
Isostatic uplift
Eustatic Isostatic
Eustatic sea level change is caused by a Isostatic sea level change is caused by
change in the volume of water in the sea, vertical movements of the land relative
or by a change in the shape of the ocean to the sea.
Any downward movement of the land
causes sea levels to rise locally, while
uplift of land causes sea level to fall.
The effects are always global and the The effects are always local and the main
main causes are: causes are:
Tectonic Movements Tectonic uplift or depression
Of the earth's crust that alter the shape, Occurs mostly at plate boundaries
and so the volume, of the ocean basins.
E.g. sea floor spreading increases the
volume of the basin and decreases sea Compression or decompression
Of the earth's crust due to accumulation
Changes in climate or melting of ice sheets.
An increase in temperature causes Slow uplift of land can continue for
melting of ice sheets, which increases sea thousands of years after the weight of a
level. retreating glacier has gone.
It also causes water to expand, which
increases sea level further. Accumulation sediment, mostly at the
mouths of major rivers, can also cause
A decrease in temperature causes more compression.
precipitation to fall as snow.
This increases the volume of water stored
in glaciers and so reduces the volume of Subsidence
the sea, which decreases sea level.
Of land due to shrinking after abstraction
of ground water

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A simple sequence of sea level changes may be summarised as follows:
Formation of glaciers and ice sheets produces a Eustatic fall in sea level and a
lowering of the world sea level
Continued growth of ice sheets depresses the land surface under the ice and
produces a relative Isostatic rise in sea level which may moderate the Eustatic fall
in some areas
As ice sheets begin to melt, a rapid Eustatic rise in sea level occurs, with a positive
change in base level
As…read more

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Impacts of Sea Level Rise
More frequent and more severe coastal flooding
Flooding of low-lying areas has increased with sea level rise and it will increase more with
further rises.
For example: at the beginning of the 20th century St Mark's Square in Venice flooded less
than 10 times per year, and in 1996 it was flooded almost 100 time.
Submergence of low-lying islands
Lots of low-lying islands have disappeared as sea level has risen, and loads more are at risk
of disappearing.…read more

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Submergent Features
When sea level rises relative to the coast, the sea submerges the existing coastline.
This creates different landforms.
Rias are usually created by the flooding of a river valley
where a river meets the ocean.
Rias have a gentle long and cross-profile.
They're wide and deep at their mouth, becoming narrower
and shallower the further inland they reach.
Rias can occur anywhere, although some areas have more than others, due to coastal
geography.…read more

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Emergent Features
When sea level falls relative to the coast, new coastline emerges from the sea.
This creates different landforms.
Raised Beaches
Raised beaches are formed when the fall in sea level exposes wave-cut platforms and their
Over time, beach sediment becomes vegetated and develops into soil.
Relict Cliffs
The cliffs above raised beaches are no longer eroded by the sea, and slowly get covered by
They're called relict cliffs.…read more


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