CGP Sea Level Changes

• Eustatic sea level change


  Caused by a change in the volume of water in the sea, or by a change in the shape of the ocean basins
• Isostatic sea level change


  Caused by vertical movements of the land relative to the sea
• The effects of eustatic sea level change are always global
• The effects of isostatic sea level change are always local
• Causes of eustatic sea level change

  • Changes in climate
  • Tectonic movements of the Earth's crust that alter the shape and volume of ocean basins
• Causes of isostatic sea level change

  • Uplift or depression of the Earth's crust due to accumulation or melting of ice sheets
  • Subsidence of land due to shrinkage after abstraction of groundwater
  • Tectonic crustal processes
• Sea level has risen in the last 10,000 years
• During the last glacial period, water was stored in ice sheets, so sea level was lower than present
• At the last glacial maximum, sea level was about 130 m lower than present
• As temperatures started to increase about 12,000 years ago, ice sheets melted and sea level rose rapidly
• Sea level reached its present level about 4,000 years ago
• Over the last 4,000 years, sea level has fluctuated around its present level
• Since about 1930, sea level has been rising
• Climate change

  Causes changes in sea level
• Global sea level is currently rising almost 2 mm each year
• If greenhouse gas emissions remain very high during the 21st century, sea level rise is predicted to increase to 10-16 mm a year by 2100
• Impacts of sea level rise on coastal areas

  • More frequent and more intense coastal flooding
  • Submergence of low-lying islands
  • Changes in the coastline
  • Contamination of water sources and farmland
  • Increased coastal erosion
• Raised beaches


  • Formed when the fall in sea level leaves beaches above the high tide mark
  • Over time, beach sediment becomes vegetated and develops into soil
• Wave-cut platforms (marine platforms)

  • Exposed when sea level falls, leaving them raised above their former level
• Relict cliffs


  • Cliffs above raised beaches that are no longer eroded by the sea, and slowly get covered by vegetation
• Rias

  • Wide and long, with a cross-profile that is deeper and narrower the further inland they reach
• Dalmatian coastlines


  • Formed where valleys parallel to the coast are flooded, leaving islands parallel to the coastline
• Fjords


  • Long and narrow, with very steep sides, and a shallow mouth caused by a raised bit of ground called the threshold formed by deposition of material by a glacier
• Coastal landscapes can be dominated by processes of erosion or deposition, but most are formed by both
• Coastal processes can create new landforms or change existing landforms, meaning coastal landscapes change over time
• A change in one factor can lead to changes in others, e.g. a change in wave direction might increase deposition and eventually change a landscape dominated by erosive landforms to one dominated by depositional landforms
• Relict landforms can still experience coastal processes, e.g. a relict cliff may be weathered by salt and freeze-thaw
• Coastal landscapes are often made up of a mixture of active and relict landforms that reflect different periods of change
• Changes in coastal landscapes can vary from short and episodic (e.g. storm waves that last for a few hours) to long and gradual (e.g. tectonic uplift over thousands of years)