SEA LEVEL CHANGES

Coastal Flooding = more likely due to rising sea level.

Sea level varies on a daily basis, with the tidal cycle.

Onshore winds & low atmospheric pressure systems also cause a temporary rise in the sea's surface.

On a much longer time scale, global sea level is rising at nearly 2mm per yr & this is forecast to increase to 4/5mm per yr by 2100.
This will increase the frequency & severity of flooding in low-lying coastal areas.

• Caused by change in the volume of water in the sea.
  
  

  This can be due to:
  

• CLIMATE CHANGE: different changes affect the sea level in different ways
  e.g. a rise in temperature = melting ice sheets
  = increase in sea level.
  a rise in temperature also = thermal expansion
  = increase in sea level.
  
  

  a fall in temperature = more precipitation to fall as snow
  = increase in volume of water stored in glaciers
  = increased volume of sea
  = increase in sea level.

• Caused by vertical movements of land relative to the sea.
• Any downward movement of land = local rise in sea level.
• Any uplift of land = local fall in sea level.
  
  

  Main Causes:
  

• TECTONIC (CRUSTAL) UPLIFT/DEPRESSION: occuring mostly at plate boundaries.
  e.g. compression of the Earth's crust = accumulation of ice sheets & accumulation of sediment (deltas) mostly at the mouth.
  decompression of crust = melting of ice sheets.
  
• SUBSIDENCE OF LAND: due to shrinkage after abstraction of groundwater e.g. marshland drainage.

• MORE FREQUENT & SEVERE COASTAL FLOODING
  rising sea level leads to continued flooding of low-lying areas.
  e.g. beginning of 20th century: St. Mark's Square, Venice flooded less than 10 times a year.
  1996: flooded almost 100 times.
  
• SUBMERGENCE OF LOW-LYING ISLANDS
  lots have disappeared as sea level has risen & more are at risk.
  e.g. if sea level rises by just 0.5m, most of the Maldives will be submerged.
  
• CHANGES IN COASTLINE
  as the sea level rises, the coastline changes.
  islands are created & area of land is decreased.
  e.g. overly the last 100,000 yrs, the sea level has separates Britain from mainland Europe.
  if the sea level rises 0.3m more, 8000km2 land in Bangladesh will be lost.
  
• DAMAGED INFRASTRUCTURE
  decreased tourism & agriculture
  loss of homes/businesses

When the sea level rises relative to the coast, the sea submerges the coastline.
LANDFORMS CREATED:

RIAS (drowned river valleys):

• landforms formed where river valleys are partially submerged.
  e.g. Kingsbridge Estuary, Devon.
• Rias have a gentle & long cross profile.
• Rias are wide & deep at their mouth, becoming narrower & shallower the further inland they reach.

FJORDS (drowned glacial valleys):

• landforms formed where glacial valleys are partially submerged.
• Fjords are relatively straight & narrow with steep sides.
• Shallow mouth, caused by raised bit of ground (threshold), formed by the deposition of material by glacier.
• Fjords are very deep further inland
  e.g. Sognefjorden, Norway: 1000+m deep in places.

DALMATION COASTLINE:

• Dalmation coastlines are formed because of the rising sea level in areas where valleys lie parallel to the coast.
• The valleys become flooded, leaving islands parallel to the coastline.
• Named after Dalmation Coast in Croatia.

When the sea level falls relative to the coast, the sea emerges the coastline.
LANDFORMS CREATED:

RAISED BEACHES:

• Raised beaches are formed when the falling sea level exposes wave-cut platforms & their beaches.
• Over time, the beach sediment becomes vegetated & develops int osoil.
  e.g. Isle of Arran: subaerial weathering & lack of marine erosion
  = weathered debris collects at cliff foot
  = gentler slopes.
• Cliffs above the raised beahes are no longer eroded by the sea & slowly become covered by vegetation: RELICT CLIFFS.
• Its not uncommon to see wave-cut notches, caves, arches & stacks within relict cliffs.
• These raised features are gradually degraded over time.