2B.7 ab

• eustatic change: change in sea level due to changes in water mass
• isostatic change: change in sea level due to the movement of land
• last glacial maximum: period when glaciers were at their highest level
• 4 reasons for eustatic changes:

  • thermal expansion/contraction
  • a fall in temps
  • melting glacier ice/ ice sheets
  • tectonic activity
• thermal expansion/contraction: as water becomes warmer, it occupies a larger volume and expands --> factor that's most responsible for sea level change in the last 300 years
• fall in temperatures: e.g. due to glacial period = more precipitation falls as snow. water remains stored in glaciers as it's too cold to evaporate, so is unable to return to the sea --> causes the hydrological cycle to slow down. as water freezes, ice becomes more compacted
• melting glacier ice/ ice sheets: water is redistributed from polar ice sheets and continental glaciers as they melt from landmasses e.g. Greenland Ice sheet or glaciers (land ice not sea ice)
• tectonic activity (eustatic): rising magma at a divergent plate margin/hot spots lift the overlying crust, which displaces water, reducing the capacity of the ocean, causing sea level to rise. e.g. uplift of crustal plate reduced Indian Ocean's capacity causing 0.1mm eustatic rise in global sea level
• post glacial isostatic adjustment: the crust is weighted by an ice sheet causing it to be depressed into the mantle resulting in a relative rise in sea level

  If the weight is lifted (when an ice sheet melts) the crust rebounds and rises causing a relative fall in sea level
• subsidence: excessive pumping of aquifer systems has resulted in permanent subsidence and related ground failures. When water is pumped out, the soil compacts, reduces in size and the number of pore spaces which causes the land to sink
• tectonic activity (isostatic): earthquakes cause land to be shifted upwards or downwards, this causes a localised rapid change in sea level. the overlying plate becomes distorted (bulge from uplift) temporarily --> plate then settles back to as it was
• accretion: sediment is added to a landform e.g. a river delta by deposition, which causes the land to sink. It tends to be balanced by subsidence , caused by the weight of newly deposited sediment, leads to very slow crustal sag and delta subsidence. Most deltas are already undergoing natural subsidence that results in accelerated rates of relative sea level rise
• 4 reasons for isostatic change:

  • post glacial adjustment
  • subsidence
  • tectonic activity
  • accretion
• flandrian transgression: period of time from 20,000 years ago that has seen the fastest and largest change in sea level
• the isostatic and eustatic changes in the UK:

  • Scotland is rebounding due to melting glaciers
  • The SE sinks due to submergent features such as rias + amplified by rise in sea level
  • --> equilibrium
• emergent coastline: produced by post-glacial adjustment. parts of the littoral zone where a fall in sea level exposed land once part of the sea bed
• raised beaches:

  • beaches which are above high tide line
  • flat and covered by sand/ pebbles
  • experiences succession (vegetation)
  • e.g. Scottish Islands of Islay, Jura and Mull
• what are the 2 emergent coastline landforms?

  raised beaches and fossil cliffs
• relic/ fossil cliffs:

  • steep slope at the back of a raised beach
  • wave-cut notches, caves, arches occur here
• submergent coastlines: sea level rise allows the sea to submerge low-lying land masses --> more common in river valleys and glacier valleys
• what are the 2 types of submergent coastlines?

  rias and fjords
• rias:

  • formed when river valleys are submerged by rising sea level
  • they share the same long and cross profiles of a river
  • e.g. Poole Harbour in Dorset
• fjords:

  • drowned U-shaped valleys
  • formed when rising sea level submerge a glacial valley (glacial trough)
  • straight and narrow with very steep sides
  • have a shallower part near the mouth where the glacier left the valley and deposited material
  • e.g. western coast of Norway
• dalmatian coastlines: form in the same way as rias but the rivers run parallel to the coast - leaving islands as they were submerged e.g. in Croatia