EQ 3: how do coastal landforms evolve over time as climate changes?

what are two types of sea level change?

eustatic and isostatic

what are eustatic sea level changes?

a global change in sea level, influenced by changes in global temperatures

what are two causes of sea level change?

milankovitch cycles - variations in earth’s orbit around the sun (every 400,000 years)
sun spots - variations in the amount of energy produced by the sun (solar maximum every 11 years)

how does climate change link to sea level fall?

decrease in global temperature → rainfall stored as snow + ice
estimated that a 1 degree fall in mean global temperature → 2m fall in sea level

what are two named changes in global sea level?

werm era - sea levels 100m lower than today
flandrian transgression - sea levels rose by an estimated 7m in 200 years in NW England

what are two causes of eustatic sea level rise?

thermal expansion
ice melting

what are isostatic sea level changes?

local scale changes caused by a change in the level of the land relative to the level of the sea

what are two causes of isostatic sea level change?

tectonics - localised subsidence of land (downward movement of earth’s surface) occurs when tectonic compressions are reduced (e.g. mediterranean basin is subsiding as african and eurasian plates no longer converging)
post glacial adjustment - when ice melts after glacial periods, previously depressed crust rebounds upwards due to reduced weight

what are two types of landforms caused by sea level change?

emergent - landforms exposed when sea levels fall, found inland
submergent - landforms caused by eustatic sea level rise

what are two examples of emergent landforms?

raised beaches and abandoned cliffs

how are raised beaches formed?

areas of former shore platforms left at a higher level than present sea level
global sea level rises, forming new beaches and drops in sea level leave beaches stranded above current shoreline
ice melts from glacial periods and the land slowly rises - isostatic rebound
e.g. on southern tip of Isle of Portland, raised beach of height 15m above sea level

how are abandoned cliffs formed?

a cliff forms through processes like coastal wave action
sea level falls causing erosion to reduce, cliff is abandoned as nothing is shaping it
e.g. hadleigh cliff, essex, england 45m high

what are two examples of submergent landforms?

fjords and rias

how are fjords formed?

drowned glacial U shaped valleys with much straighter planforms than rias
threshold - shallow section at end of glacial rock basin caused by lower rates of erosion at seaward end of valley
e.g. Sogne Fjord, Norway 4km deep

how are rias formed?

submerged river valleys that are the lowest part of a river’s course
drowned tributaries due to sea level rise, with a dendritic pattern
e.g. found on south coasts of Devon and Cornwall (formed during Flandrian Transgression)