Coastal Landscapes and Changes EQ3 Flashcards
Why is sea levels vary from day to day?
- high and low tides alter lock sea level very few hours
- atmospheric air pressure has an influence in sea level (low pressure causes a slight increase)
- winds can push water towards the coast and cause variations in wave height.
What is eustatic sea level change?
Eustatic changes is the global rise or fall in water levels caused by a change in the volume of water.
What is isostatic sea levels change?
A local rise or fall in local land level.
What causes a eustatic fall in sea level?
During glacial periods
- ice sheets form on land due to the colder temperatures in high latitudes
- water evaporated from the sea falls as snow and compresses into ice sheets over time
- this means water is trapped in ice sheets and global volume of water in the sea is reduced
What causes an eustatic rise in sea level?
During interglacial periods the earths heats up causes a global use in sea water as
- ice caps/ sheets melt returning located up water to the sea
- thermal expansion were the warmer temperatures cause water molecules to expand by 9%
What causes a isostatic fall in sea levels?
Rises in local lands levels causes a fall in local sea level this happen due to
- post glacial adjustment
- accretion (sink region experiencing net deposition building land up and leading to a fall in sea level)
- tectonic activity
What causes a isostatic rise in sea level?
- post glacial adjustment
- subsidence
- tectonics
How does subsidence cause a isostatic rise in sea level?
The deposition of sediment over time e.g. large river deltas (The Nile) causes crustal sag were the weight of the sediment becomes to much. Additionally hew bay infrastructure or building can have the same effect.
How has post glacial adjustment led to a isostatic rise or fall in sea level?
During glacial periods the weight of the ice sheets on the crusts causes the lithosphere to be compress downward. At the end of the glacial period the ice sheets melted and isostatic adjustment took place were the previously compressed crust would start rebound upwards causing a fall in local sea levels. This then creates a seesaw effect were adjacent areas subsides.
What is an example of post glacial adjustment in the UK?
At the end of the last ice age the UK was partially covered in ice in the northern regions. This meant when the ice caps melted northern England experienced a isostatic fall in sea levels with the crust rebounding back up and (1.5 mm annually) and Southern Britain is experiencing as isostatic rise in sea levels due o the the seesaw effect (1mm annually).
How has tectonic activity created eustatic changes in sea level?
- rising magma at constructive plate boundary’s reduce capacity of the the ocean creating sea level rise
- uplift of crustal plates reduce ocean capacity (Indian Ocean) creating eustatic rise
How does tectonic activity led to isostatic changes in sea level?
- folding of sedimentary rock at a destructive plate margin produces an isostatic changes fall of anticlines and rise for synclines
- lava or ash form volcanic active builds up the land height creating a isostatic fall.
What creates a emergent coastline?
- eustatic fall in sea level (decreased volume of water)
- isostatic fall in sea level (increase height if land)
What creates a submergent coastline?
- eustatic rise in sea level (volume of water increased)
- isostatic rise in sea level (land height decreased)
What is an emergent coastline?
Parts of the littoral zone where a fall in sea level exposed land once apart if the sea bed, produced by post glacial adjustment.
What are the landforms founds at emergent coastlines?
- raised beaches
- fossil cliffs
What’s a raised beach?
A raised beach is formed at emergent coastlines it is a relic beach now above high tide line. Normally a flat surface covered by sand or pebbles and is usually vegetated by lament succession.
E.g. Isle of Arran has a raised beach 5 metres above current sea level
What is a fossil cliff?
This is a steep slope found at the back of a raised beach, which exhibits evidence if formation through marine erosion (wave cut notches) by now above high tide level.
What is a submergent coastline?
Sections of the littoral zone where sea level rise is inundated areas that were previously part of terrestrial land. Formed by areas subsiding due to post glacial adjustment creating a marine transgression.
E.g. Southern England
What are the landforms found at a submergent?
- rias
- fjords
- Dalmatian coastline
What is a ria?
A ria is a drowned river valley. It’s a sections of river valley flooded by the sea making in wider than it would be expected based on the size of river flow.
How are rias formed?
Sea level rise, causes the encroachment of sea water inland onto low lying coastlines ‘drowning’ river valleys.
What is an example of a ria?
Kingsbury Estuary, South Devin Coast. This is a 6 metre long ria.
What is a fjord?
Fjords are drowned U-shaped glacial valleys. They form when a glacially eroded valley is flooded by the sea.
E.g. Sognedjord, Norway is 205 km long and 1.3 metres deep.