EQ3-sea level change Flashcards
change globally
Eustatic fall in sea level
-glacial periods=90,000yrs colder phases=form ice sheets
-During glacial periods, when ice sheets form on land in high latitudes, water evaporated from the sea is locked up on land as ice, leading to global fall in sea level.
-sea bed =exposed as land=marine regression
-EG devensian-global SL were 120m lower than they are today. english channel+irish sea was dry land
change globally
Eustatic rise in sea level
-At end of a glacial period, melting ice sheets return water to the sea + SL ^ globally.
-Global temps ^ + causes the volume of ocean water to ^ (thermal expansion) leading to SL ^.
-interglacials=10,000yrs warmer phases=shrink ice sheets
-EG since 1750, humans r accelerating IG warming via greenhouse emissions=Anthropogenic forcing
-SL ^21 cm from 1870 - 2010.
-melting of Antarctic predicted to ^ SL by 50m
change local land+level
isostatic rise in local land level
-causes fall in local sea level
-bc: post-glacial adjustment+accretion(sink regions in sediment cell having net deposition,land^)+tectonics
change local land+level
isostatic fall in local land level
-makes ^in local SL
-due to post glacial adjustment, subsidence+tectonics
subsidence
-subsidence of land =^SL
- deposition of sediment, especially fluvial deposits in large river deltas, weight of sediment deposition overcomes the threshold + leads to slow ‘crustal sag’ + delta subsidence,
- e.g. Nile, Mississippi, Amazon
-can also be caused by the lowering of water table (from ^ evaporation from CC or human abstraction) can lead to settling of overlying sediment+land subsidence as pore water pressure is removed or by heavy buildings
the world now
-end of last ice age 12,000 years ago, UK = covered in ice down to Birmingham.
-N Britain =isostatic fall in SL as land is uplifted by 1.5 mm per annum.
-S Britain= isostatic ^SL as land is lowered by 1 mm per annum.
- UK is pivoting, with the S sinking and the N rising.
- N=SL fall bc isostatic rebound exceeds eustatic rise in global sea levels
- S=isostatic subsidence is accelerating a ^SL produced by global warming (eustatic)
- EG Land’s End in Cornwall is sinking isostatically by 1.1 mm p.a., + theres a 2.8 mm eustatic ^SL due to CC, producing a sea level rise of 3.9 mm p.a.
tectonics
eustatic
- ^ magma at constructive plate margin/hot spots lifts overlying crust, reducing capacity of ocean +producing eustatic SL^
- Uplift of crustal plate reduced Indian Ocean capacity
causing 0.1 mm eustatic rise in global SL
tectonics
isostatic
-
Folding of sedimentary rock by compressive forces at destructive plate margin =isostatic fall in SL for anticlines + a fall for synclines.
-EG Alpine folding at the Eurasian-African destructive plate boundary =isostatic fall of 60 cm in the Bakar-Vindol area of Croatia. - Lava/ash from volcanic activity produces an isostatic fall,
-EG Hawaiian hot spot island chain or **Caribbean island arc. ** -
Sea floor spreading - carries volcanic islands away from the uplifted crust at mid-ocean ridge. Colder, more dense crust subsides + SL^,
-EG Tonga, Fiji, Kiribati. -
FAULTING = uplift HORST blocks of crust =
isostatic ^ in land & fall in local SL - Subsidence of crust blocks by faulting form GRABEN
experiencing isostatic fall in land level & ^ local SL - During 2004 Boxing Day Tsunami in Indian Ocean
extension of crustal plate caused isostatic fall in land on
island of Sumatra by 20 cm in Banda Aceh region.
emergent coastline
-when a fall in SL exposes land previously covered by sea
-at end of ice age + occur when isostatic rebound takes place faster than a eustatic ^SL
-produced by post-glacial adjustment
-have landforms reflecting the previous sea levels
submergent coastline
-when ^in SL floods a previsouly exposed coast
-found in S england+ east coast of US
emergent
raised beach
-isostatic uplift
-beach deposits+raise shore platform+create terrace thats backed by relict cliffs
-relict beach now above high tide level
-flat surface covered by sand or rounded pebbles/boulders.
-Usually vegetated by plant succession (though further succession prevented due to grazing)
emergent
fossil cliff
-isostatic
-found at back of raised beach
-steep angle above SL, on raised shore platform
-can be less steep when subariel processes take beach away
-can consist of caves,archs,stacks+wave cut notches
-EG. Isle of Arran = raised beach 5 m above current SL N of Drumadoon.
Arran has 3 levels of raised beaches produced at different stages of post-glacial adjustment.
-EG. at Lendalfoot in Ayrshire, W Scotland, flat raised beach surface is used as route forA77 main road
40 m raised cliff at the back of the now now 200 m inland from the present-day beach.
submergent
rias
-isostatic or eustatic
-common in perigalcial areas
-drowned river valleys that have been submerged during period of marine transgression
-have a branching pattern reflect marendering river course+ v shaped cross section
-on discordant coastlines
-EG. Kingsbury Estuary on S Devon coast is a 6 m long ria. Main channel =1 m wide near its mouth at Salcombe.
2 large drowned tributaries extend from E side of the ria, w Frogmore Creek 2 km long and 500 m wide.
submergent
fjords
-isostatic
-drowned glacial valley
-common in glaciated areas durinhg the devensian eg norway
-deep troughs+straight profile
-often deeper then adjcent sea
-have a shallow entrance=threshold. where theres a submerged ‘lip’ formed by the ridge of a terminal moraine.
-EG Sognefjord in western Norway is 205 km long, 1.3deep and the main branch is 4.5 km wide.
submergent
dalmatian coastlines
-isostatic
-composed of long, narrow islands running parallel to the coastline + separated from coast by narrow sea channels called sounds.
-cause by SL^ flood coastline w geological structure of folds aligned parallel to coast
-Sea overtops low points forming straits linking straits linking sounds + separating sections of anticline ridge into narrow islands parallel to the coast.
-EG Croatia has a limestone coastline stretching 520 km NW-SE with 1,240 islands running parallel to the coast.
