Coasts 4 - Sea level changes Flashcards
What scale are the affects of eustatic change on
Global
What is eustatic sea level change caused by?
A change in the volume of water in the sea or by a change in the shape of ocean basins (worldwide level change)
What causes these global affects?
Changes in climate and tectonic movement of crust
How does an increase in temperature change sea levels
Causes ice sheets to melt increasing sea level. Also causes water to expand increasing sea levels
How does a decrease in temperature change sea levels
Causes more precipitation to fall as snow, increasing the volume of water stored in glaciers and reduces the volume of sea decreasing sea levels
What does tectonic movements of crust do
After the shape and volume of ocean basins eg - sea floor spreads increases the volume of the basin and decreases sea level
What is isostatic sea level change caused by
Vertical movements of the land relative to the sea
What does downward and upward land cause
Downward - Sea level to rise locally
Upward - Sea level to fall locally
What are the 3 causes of isostatic sea level change
1) Tectonic processes - eg - 1 plate is forced beneath another at a plate margin
2) Subsidence of land due to shrinkage after abstraction of ground water like drainage or marshland
3) Uplift or depression of the earths crust due to accumulation or melting. If its slow it continues for 1000s of years after the retreating glacier has gone
Where and what does accumulation of sediment cause?
The mouths of major rivers causing depression
What does sea level vary with
The tidal cycle
What else causes the sea surface to rise temporarily
Onshore winds and low atmospheric pressure systems
Give 4 ways global sea level has changed
1) Last glacial period, water was ice sheets, so sea level was lower. At the last glacial maximum sea level was 130m lower than now
2) As temp increases, ice sheets ,melt and sea level rose rapidly. It reached its present level around 4000 years ago
3) Over the last 4000 years sea level has fluctuated above and below current level
4) Since 1930, sea levels have been rising
What is global warming?
Temperatures increasing rapidly over the last century
Whyat do scientists think is the cause of climate change
Human activity - deforestation and burning fossil fuels
What do these activities do
Increase the concentration of greenhouse gases in the atmosphere
What do greenhouse gases do
Absorb outgoing long-wave radiation, so less is lost in space. As their concentration increases more energy is trapped and the planet warms up
Why is an increase in temp likely to cause an increase in sea levels
Through melting of ice sheets and thermal and expansion of water in oceans
How is global sea levels currently rising
2mm a year
What will happen if greenhouse gas emissions remain high?
It’s predicted to increase 8 to 16mm a year by 2100
Why are storms likely to9 become more frequent and intense
Changes in ocean circulation and wind pattens
What would this do
Damage ecosystems and settlements
What are 4 major impacts will sea level rise have on coastal areas
1) More frequent and severe flooding
2) Submergence of low-lying islands
3) Changes in coastline
4) Contamination if water sources and farmland
How does more frequent and serve coastal flooding happen
Flooding of low lying areas has increased with sea level rise and it will increase more with further rises
What is an example of more frequent and serve coastal flooding
From 1995 - 2004, Kings Point in New York flooded 80 times but from 2005 - 2014 it was nearly 160
What is submergence of low-lying islands?
Lots of low-lying islands are at risk of disappearing
Give an example of submergence of low - lying islands
If the sea levels rise by 0.5m from its current level most of the Maldives will be submerged
How are coastlines changing
Islands are created and the area of land is decreased
Give an example of changes in coastline
If sea levels rise by 0.3m from its current level, 8000km of land in Bangladesh will be lost
How does contamination of water sources and farmland happen
Salt water enters freshwater near the coast and damages ecosystems and makes the water unsuitable
How does this affect farmland?
Damages crops and makes land impossible to farm
What does increased sea level rise and storminess cause?
Increased coastal erosion and puts ecosystems, homes and businesses at risk
What happens when sea level falls relative to the coast
New coastline emerges from the sea creating different landforms
What landforms does this create (3)
- Raised Beaches
- Cut platforms
- Relicit Cliffs
When are raised beaches formed
Fall in sea levels leave beaches above the high tide mark. Over time, beach sediment becomes vegetated and develops into soil
How are wave-cut platforms formed
Sea level fall exposes wave-cut platforms, leaving them raised above their former level
How are relicit cliffs formed
Cliffs above raised beaches aren’t eroded by the sea and slowly gets covered by vegetation
What landforms are created when sea level rises relative to the coast (3)
- Rias
- Fjords
- Dalmation coats
When are rias formed?
When river valleys are partially submerged
Describe a ria
They have gentle long and cross-profile, they’[re wide and deep at the mouth, becoming narrower and shallower the further inland they reach
What are fjords
Drained glacial valleys
Describe fjords
Relatively straight and narrow, with steep sides. They have a shallow mouth caused by a raised bit of ground formed by deposition of material by the glacier. They’re very deep further inland
When is a Dalmatian coastline formed
In areas where valleys lie parallel to the coast, an increase in sea level forms this. Valleys are flooded, leaving islands parallel to the coastline
How are landscapes formed
Individual landforms combine
How are coastal landscapes dominated
By processes of erosion or deposition, but most are formed by both
What 2 ways do coastal landscapes change over time
- A change in 1 factor leads to a change in others, eg - a change in wave direction may increase deposition and change a landscape dominated by erosive landforms to a new one dominated by depositional landforms
- Relicit landforms experience coastal processes, eg - a relict cliff maybe weathered vey salt and freeze-thaw
What are coastal landscaped made up of
Mixture of active and elicit landforms reflecting different periods of change
Where do these changes occur
On a range of spatial and temporal scales
