EQ3 Flashcards
LT sea level change - Eustatic
Global - due 2 change in volume of ocean water
Cause by CC - anthropogenic + Milankovitch cycles
Decreasing water volume produces lower sea levels - inc water volume produces higher sea levels
Interglacial periods see a spike = eustatic change. Rising meltwater tricking down rivers + streams - seas inc water volume as well as a rising water temp = leads 2 thermal expansion
Sea levels rise = 21cm b/ 1870-2010
Leads 2 marine transgression - rising sea levels + flooding of low land areas
Eustatic fall = SL
During glacial periods when ice sheets form on land in high latitudes
Water evaporated from = sea is locked up on land as ice - leads 2 global fall in sea level
Eustatic rise = SL
End = glacial period melting ice sheets return water 2 the sea + sea levels rise globally.
Global temps inc + causes the volume of ocean water 2 inc (thermal expansion) leading 2 SLR
LT Sea level change
Isostatic change (local)
Local land level change
Rises in local land level causes a fall in local sea level due 2 post-glacial adjustment, accretion (deposition building up land level) + tectonics
Fall in local land level produces a rise = local sea level
May be due 2 post glacial adjustment
Subsidence (deposition can weigh down the landscape + cause sinking effect + tectonics)
Emergent coastlines
Produced by post-glacial adjustment (movement of land after being burdened by ice coverage)
EC are enlarging due 2 a fall = sea levels - exposes more of the seabed + shoreline (littoral zone larger)
Submergent coastline
Coastlines where the littoral zone is inundated w/ rising SL (SE England)
Reduces the size of the overall littoral zone now covered in sea water - previously part of the terrestrial land
Climatic warming leads 2 eustatic SLR
Warming leads 2 melting of mountain glaciers (Alps, Himalaya) + polar ice sheets increasing the amount of water in the ocean store
Melting = sea ice has no effect on SL as the ice was already displacing the equivalent water volume 2 that produced by melting
IPCC attributes 50% of SLE 1990-2010 to ice sheets melting
Warming leads 2 thermal expansion of existing ocean water as its temps rise
94% of increased heat energy in the climate system is transferred 2 oceans
IPCC attributes 40% of SLR 1990-2010 to this
Tectonic activity
TA caused the other 10% of SLR
Emission = geothermal heat into oceans by underwater volcanic activity causes thermal expansion = ocean water
TA at destructive margins
Folding of plates inc ocean basin volume lowering SL
Earthquakes along boundary can allow rebound of non-subduction margin - uplift of sea floor reduces ocean volume raising sea levels
2004 Boxing Day Tsunami w/ moment magnitude = 9.3 lifted sections of the Indian Ocean bed raising sea levels = 0.1mm
TA causes isostatic change
Faulting can uplift sections of crust lowering SL sometimes up to 2m
Sea floor spreading transports volcanic islands away from the uplifted crystal zone along constructive boundaries/hotspots 2 places where the ocean flood = colder, denser, lower lying = islands sink
Physical factors causing erosion = Holderness Coast
Rapid coastal erosion is caused by physical factors when geological + marine characteristics combine 2 promote erosion
Geological factors include:
- lithology- soft rock type, weak, cohesive bonds, porous rock
- geological structure - well jointed rocks, rocks with seaward dipping beds, heavily faulted rocks
Marine factors include:
- long wave fetch promoting large, destructive waves
- strong longshore drift that quickly removes collapsed sediment allowing erosion 2 restart
Human factors causing erosion = Nile Delta
Human activity can inc rates = coastal recession by interrupting the operation of the sediment cell. Construction of major dams of rivers can trap sediment behind the dam wall. Starves the coast of a sediment source - serious conseq
Construction = Aswan High Dam = River Nike reduced sediment volume from 130 million tonnes - 15 million tonnes per yr. Erosion rates jumped = 20-25m per yr to over 200 meters per year as the delta was starved of sediment
Dredging
Removal of sediment from a beach, sea, river
Sands or gravel = scooped up for use by construction industry
Dredging of river mouths + estuaries often 2 maintain navigable channel for ship transport
Holderness coast - weathering + mass movement
Holderness coastline made up of soft boulder clays (tills) left after the retreat of the Devensian ice sheets = 12,000 yrs ago.
Being rapidly eroded by the sea
Boulder clay = structurally weak + has little resistance 2 erosion
Produces sloping cliffs b/ 5-20 meters high
Chalk surrounds the boulder ckay. Much stronger rock has eroded along fault lines + bedding planes forming structures like cliffs, caves, arches, stacks
Mechanical weathering = hydraulic action, abrasion, freeze-thaw weathering occur
Over time mass movement including rotational slip occurs
