Sea Level Changes

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Sea Level Changes
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• Eustatic change
• A global sea level change, caused by climatic
  change which causes then size of ice caps to
  increase or decrease
• During a period of glaciation sea level is much
  lower because water is stored as ice (during last
  ice age sea level was 150m below levels today)

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Sea level changes in S. England
Synoptic links with glaciation topic
Flandrian Interglacial (last 10,000 yrs)
The Devensian glacial advance
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• Isostatic change
• The change in the level of the land compared with
  the sea
• During glaciation the ice puts pressure on the
  earths crust, causing the land to lower
• When ice sheets melt the land rises
  (readjustment)

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How fast is isostatic change?
Land rising in NW Scotland by 1mm/yr
Land sinking in SE England by 1.5 mm/yr
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Sequence of sea level change
Temperatures decrease. Ice sheets grow. Sea level
falls
Ice thickness increases. Land is lowered
Temperatures rise. Ice melts. Sea levels rise
Ice continues to melt. Pressure on land released.
Land rises
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But how do we know all this?

• Accurate measurements can be made of past sea
  levels and rates of sea advance and retreat by .
• Shoreline deposits such as shells, wood and peat
  found in marine cores.
• Exposed rock outcrops containing marine fossils.
• Vegetated tidal flats above the high water mark.
• Exposed coral reefs.
• Marine rocks displaying evidence of wind-borne
  erosion.
• Radiocarbon and Uranium series dating

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Landforms resulting from net sea level rise
submerged coasts

• Rias
• Drowned river valleys caused by rising sea levels
  during Flandarin Transgression (ice melt)
• Eg Rivers Fal Camel in Cornwall
• Fjords
• Drowned U shaped glacial valleys
• Eg Loch Torridan in Scotland, Oslo Fjord
• Fjards
• Drowned glacial lowlands

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Landforms resulting from net fall in sea level
emerged coastlines

• Raised beach
• e.g Portland raised beach
• Relict cliffs
• Previous coastal cliffs that are raised above
  current sea level
• Raised mudflats
• e.g Carselands of River Forth

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What will the effects of sea level rise be in the
future?
More than 60 of the worlds population lives on
or within 60km of the coast.
Synoptic link to AS climate change find your
notes!! You need to know causes, effects and
responses.
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Effects in the UK

• Environmental
• The threat of nuclear accidents will be higher at
  Sizewell and Dungeness as they are built on low
  lying land. Dungeness is built on a shingle spit
  which is moving eastwards.
• 62 coastal SSSIs will be at risk from sea level
  rise.
• Habitats will be lost - 10 of saline lagoons
  and 8 of salt marsh is at risk.
• Coastal squeeze may result in more coastal
  ecosystems lost as they cannot migrate inland as
  the sea level rises.
• Migratory birds such as the Grey Plover and
  Avocet over-wintering in The Wash, Thames and
  Humber estuaries will lose their habitat.
• Of the 106 internationally important sites for
  wintering wildfowl, 16 are at risk and 11 are
  vulnerable.

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• Social
• 26 million people live in major urban areas in
  the coastal zones.
• People continue to build on low lying coastline
  despite the threat of increased flooding.

• Economic
• 40 of manufacturing and 57 of productive
  agricultural land is in the coastal zone.
• Coastal zone along the South coast is valued at
  5745 million.
• Cost of protecting these areas will be high.
• Cost of insurance claims and repairs if storms to
  breach sea walls. Towyn in 1990 cost 35
  million.
• Loss of tourist areas would result in a loss of
  income. Norfolk Broads are estimated to earn
  15.5 million per year.
• Homes will be uninsurable.

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Effects on the Maldives

• The islands of Tebua Tarawa and Abanuea (both
  uninhabited) have disappeared underwater.
• Most of the 29 atolls are suffering from
  increased erosion.
• Severe flooding both storms and high tides have
  occurred.
• Salt is poisoning the soil.
• Beaches of a third of the 200 Maldives islands
  are being washed away affecting both erosion
  rates and tourism.