how do coastal kandforms evolve over time as climate changes Flashcards
as the climate changes what happens to sea level
- as global tenps decrease more snow and ice accumulate
- this stores more water as solids which reduces liquid return to oceans –> global sea levels fall
- as water molecules cool they contract –> denser which reduces volume
- a 1 degrees fall in global mean temp = approx 2m sea level fall
key timframes
- 130,000 years ago (tyrrhenian interglacial period)
- global mean annual temps: 3 degrees higher than today
- sea level: 20m higher than today - 180,000 years ago (Riss glacial period)
- temp fell 7 degrees lower than today
- sea level fell by 100m - 83m lower than today
emergent landforms
- formed during sea level fall
- created by wave processes during high sea levels –> exposed when sea level falls
- found inland away from current coastline
raised beaches
- old shore platforms now above current sea level
- found inland along emergent coastline with abandoned cliffs, wave-cut notches, caves, arches, stacks
marine terraces
- larger scale than raised beaches
- formed by marine erosion during previsous higher sea levels
example of a raised beach
isle of portland near weymouth - dorset
- raised beach 15m above current sea level
- formed 125,000 years ago (tyrrhenian interglacial period)
- portland limestone eroded by hydraulic action
abandoned cliff above raised beach
cryoturbation
mixing and displacement of soil and rock due to permafrost freeze-thaw cycles.
modification of emergent landforms
after sea levels fall emergent features like raised beaches and cliffs are not shaped by waves but more by sub-aerial processes.
1. PHYSICAL WEATHERING - freeze-thaw through frost weakens exposed rocks, carbonation affects limestone
2. BIOLOGICAL - activity from limpets + whelks on raised beaches –> erosion, biological colonisation rises with global warming
what will happen to emergent coatlines if sea levels continue to rise
- bring emergent landforms closer to the coast or re-submerge them
- therefore they could once again be eroded by marine processes like hydraulic action and abrasion
what will have to the ocean if climate change continues
- higher global temps causes ice melting –> increases water volume –> sea levels rise
- water expands when warmed - increases volume
- same with cooling –> 1 degree increase in gl;obal temps = 2m rise in sea levels
würm glacial period
- ended 25,000 years ago
- temps were 9 degrees lower than today
- sea levels were 90m lower than today
- since then sea levels have risen - a process called Flandrian Transgression
rias - submergent coastal landforms
- drowned river valleys formed when rising seal levels flood the lower course of river and floodplain
- higher land on either risde oof valley
- winding shape following origional river channel
- shallow edges, deepes towards centre
- formed by fluvial erosion - later flooded by Flandrian Transgression
- Alluvial deposits are present in buried valleys
example of a ria
- padstow cornwall - sand washed from atlantic during sea level rise
- low tide - river channel between exposes sandbanks which are submerged at high tide
fjords - submergent coastal landforms
- formed when glacial valleys are flooded after sea level rise
- deeper and straighter than rias
- U shaped cross section
- depth 1000m + at seaward end due to reduced erosion where ice thinned
example of fjord
- Sogne Fjord Norway 200km long, 1000m deep
shingle beaches - submergent coastal landform
- ice sheets melt at end of last glacial period - large areas of land flooded and sediment reworked
- sediment deposited by rivers and low energy waves then pushed ashore by waves –> forms beaches, tombolos, bars
- shingle beaches form when coarse sediment accumulate at the coastline
- found at base of former cliffs or where wave energy is sufficcient to transport coarse material
how are fjords, shingle beaches and rias modified these days
rias and fjords modified by:
- present day wave processes
- subarerial processes, changes to climate/ sea level
- can lead to reduction in valley side steepness
shingle beaches
- change due to unconsolidated nature, LSD
