Coasts 1.3

• Natural causes of climate change

  • Milankovitch Cycles
  • Sunspots
  • Volcanic Eruptions
• Milankovitch Cycles

  • Eccentricity - Change in the size of Earth's orbit, completes full cycle every 400,000 years
  • Obliquity - Earth tilts on its axis from 22 to 24.5 degrees and back every 40,000 years
  • Precession - Earth gyrates a full circle on its axis every 22,000 years
• If all three Milankovitch Cycles are in a certain phase at the same time

  An ice age can begin and sea levels will fall
• Sunspots

  Variations in amount of energy produced by the sun with a solar maximum every 11 years
• Volcanic Eruptions

  Changes in the composition of the atmosphere due to major volcanic eruptions
• Eustatic Change

  Sea level change of the volume of Earth's oceans, change in total volume of sea water, like when ice sheets or glaciers melt
• Isostatic Change

  Result of an increase or decrease in the height of the land, when the height of the land decreases sea levels rise, during ice age the weight of ice causes land to sink hence sea levels rise (known as compression), isostatic rebound is where the land is alleviated from the weight of the ice and rebounds in height
• Glacial Period

  Riss glacial period (108,000 years ago) - Temperature 7 degrees lower than today, sea levels dropped by 100 metres, 83 metres lower than today, decrease in global temperatures leads to more precipitation in the form of snow, eventually snow turns into ice and is stored on land in cryosphere, reducing the volume of water in the ocean store and worldwide sea level fall, as temperatures fall water molecules contract leading to an increased density and reduced volume, 1 degree fall in temperature could cause 2m fall in sea level
• Inter glacial Period

  Tyrrhenian Inter-glacial (130,000 years ago) - Temperature 3 degrees higher than today, sea levels 20 metres higher than today, weight of the ice puts pressure on the land, when the ice melts during the interglacial period the land rebounds and increases in height, known as isostatic rebound, sea levels are further increased by a high input from rivers and expansion of water molecules
• Submergent Coastal landscapes (sea level rise)

  Formation of Submergent Coastal landscape - At the end of the Wurm glacial period 250,000 years ago the temperatures were 9 degrees lower than today and sea levels 90m lower, since then temperatures and sea level have risen to their present level during the period of sea level rise known as the flandrian transgression, resulting in the formation of submergent coastlines
• Rias

  Submerged river valleys initially formed by fluvial erosion, the lowest part of the rivers course and its nearby floodplains are completely drowned but the higher land forming the tops of the valley sides remain exposed, in the cross section rias have relatively shallow water, becoming deeper nearer the centre, several rias can be found on the south coasts of Devon and Cornwall including those at Salcombe and Kingsbridge
• During interglacial periods where sea levels rise

  Increased deposition occurs as rivers had less energy for erosion, results in the formation of exposed sand banks at low tide
• Fjord

  Submerged U shape glacial valleys with steep cliff like valley sides with uniformly deep water of up to 1000m, tend to have a much straighter profile than Rias as the glacier would have removed any interlocking spurs present, a threshold is formed towards the shallower, warmer, seaward end of the fjord due to lower rates of glacial erosion
• Due to the depth of water that occupied fjords during flandrian transgression

  Marine erosion rates remained high and the fjords were further deepened, in some areas there has been an infilling of sediment, deposited by meltwater from glaciers that are still present
• Shingle Beach

  How is it formed - Sea levels fall and land based ice grows, large areas of 'new' land emerges from the sea, sediment accumulates on this surface deposited by rivers and meltwater streams, as sea levels rose at the end of the last glacial period wave action pushed these sediments onshore, the tombolo at Chesil beach is thought to have been formed this way during the flandrian transgression, as sea levels rose the sediment in the english channel was carried 50km northeast by the southwesterly prevailing winds becoming attached to the Isle of portland at one end and mainland at the other
• Increasing sea level

  Will push shingle beaches further towards the coastline, Chesil beach is moving 17cm northeast per year
• Raised Beaches

  Raised beaches are areas of former shore platforms left at a higher level than current sea level, often found a distance inland from present coastline, behind the beaches it is common to find abandoned cliffs and wave cut notches, land rises as a result of isostatic rebound during interglacial periods, former beaches and wave cut platforms are now raised above the present sea level due to isostatic change, common in areas like Western Scotland and the Isle of Portland, Isle of Portland in Dorset has a raised beach formed 125,000 years ago from isostatic rebound, 15m above the present day sea level
• Abandoned Cliffs

  Cliffs that have been left above the erosional zone by falling sea levels, normally found behind raised beaches, a compilation of arches, caves and stacks etc, formed through marine erosion when it could be accessed by marine processes, containing a range of features like wave cut notches, caves and arches a significant distance behind the coastline due to rapid drop in sea level, for example Isle of Arran has a raised beach 5m above sea level including abandoned cliffs
• No longer affected by wave processes

  Emergent landforms can be affected by weathering and mass movement
• Mechanical Weathering

  Cliff tops are affected by frost shattering processes and cryoturbation in the last glacial period, results in the shattering and contortion of limestone cliff tops
• Biological Weathering

  Warmer and wetter conditions lead to the development of vegetation cover on abandoned cliffs increasing the impacts of biological weathering
• Chemical Weathering

  Further warming of the climate predicted, chemical weathering will perhaps become more influential, like carbonation of limestone cliffs