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Transcript
Sea-Level Change
Sea-levels are predicted to rise by 1m this
century (by 2100).
Why?
Sea-Level Change Key Terms
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Eustatic – global-scale sea level change
caused by a change in the volume of water in
the ocean store
Isostatic – local-scale sea level change caused
by a change in the level of the land relative to
the level of the sea.
Emergence – the impact of a relative FALL in
sea level (Marine Regression)
Submergence – the impact of a RISE in
relative sea level (Marine Transgression)
Eustatic (global) Changes
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A decrease in global temperatures leads to
more precipitation occurring in the form of
snow.
Eventually this snow turns to ice and so water
is stored on land rather than being returned
to the ocean store.
Consequently there is a global FALL in sea
level.
If global temperatures subsequently rise,
glaciers retreat and ice melts causing a RISE
in global sea level.
Isostatic (local) Changes
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During a glacial period, the weight of ice in ice
sheets and glaciers adds weight to the earth’s
crust.
This causes the crust to sink lower into the
mantle rock beneath.
This results in an apparent rise in the level of
the sea.
At the end of the glacial period the ice melts
and weight is lost from the crust causing it to
slowly rise. The sea level will then appear to
fall.
Some places on the east coast of Scotland
are rising at a rate of 7mm a year.
Landforms of Submergence
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Rias
Fjords
Fjards – submerged glacial lowlands
Dalmatian Coasts – submerged valleys
running parallel to the coast
Rias
Rias are submerged river valleys. The lowest part of the
river’s course and the floodplains alongside the river may
be completely drowned, but the higher land remains
exposed, e.g. Kingsbridge Estuary, Devon
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In cross section the ria has relatively shallow
water becoming increasingly deep towards the
centre. The exposed valley sides are quite
gently sloping.
In long section rias are quite even with a
smooth profile and water of uniform depth.
In plan view they tend to be winding,
reflecting the original route of the river and
its valley.
Fjords
Fjords are submerged glacial valleys. They have steep,
cliff-like valley sides and the water is uniformly deep
(often 1000m in depth). These were formed when glaciers
eroded below sea-level. When the ice melted the valleys
were flooded, e.g. Milford Sound fjord, New Zealand
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The u-shaped cross-section reflects the
original shape of the glacial valley.
Unlike rias, fjords are not deepest at their
mouths, but have a shallow section at the
seaward end known as the threshold.
Fjords have much straighter routes, due to
the erosive power of the glacier.
Landforms of Emergence
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Raised Beaches
Abandoned Coastlines
Raised Beaches
Raised beaches, e.g. Little Gruinard, Ullapool are areas of
former wave-cut platforms and their beaches which are
left at a higher level than the present coastline.
Abandoned cliffs, caves and stacks can also be found.
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Fjard
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Ria
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Dalmatian
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Coast
Abandoned
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Cliff
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