Coasts EQ3 Flashcards
What is Isostatic Change?
A local rise or fall in land level relative to the sea.
(post-glacial rebound) or (tectonic activity)
What is Eustatic Change?
A rise or fall in water level caused by a change in the volume of water, this is global.
Caused by melting ice sheets and thermal expansion of seawater due to climate change.
How do sea levels change on a daily basis?
High and Low Tides
During a storm, winds can push water towards a coast causing a storm surge, increasing wave height.
Also, atmoshperic air pressure has an influence on sea levels. Low air pressure causes a slight rise in sea level. A decrease in air pressure of 1hPa raises the water level by 1cm and vice versa.
What are the three causes of longer term sea level rise?
Eustatic Change
Isostatic Change
Tectonic Activity
What is a really in depth explanation of Eustatic Sea Level Change?
Two components:
Atmosphere warms -> thermal expansion of sea water -> increased volume -> sea level rises.
Land ice mass loss from glaciers, ice caps, and the Greenland and Antartic ice sheets. Since the last ice age, it is estimated sea levels have risen by 120m. If antartica completley melted, sea levels could rise by another 50m.
What are some stats regarding the effects of global warming on sea level change factors?
In the 20th century - The melting of glaciers were the highest contributer of sea level change at 0.5mm per year.
Now, due to mass global warming, Thermal expansion takes the number 1 spot with 1.6mm per year.
Why are sea levels difficult to measure?
Natural variation due to tides, waves, storm surges and seasonal temprature effects.
What is a more detailed explanation of isostatic change?
Occurs much much slower that Eustatic change and is caused by the weight of ice during the last ice age.
When ice is KMs thick, it is heavy and pushes land downwards because the upper mantle is soft, viscous liquid.
When the ice melts, the land begins to rise, this is called isostatic readjustment.
What is marine regression
Where the sea level drops and produces an EMERGENT coastline.
What is marine trangression
Where the coastline is flooded and produces a SUBMERGENT coastline.
How does Tectonic Activity affect sea level change?
Tectonic depression or uplift. Uplift of the ocean floor will result in sea level rise. Depression of the ocean floor will result in sea level floor.
These changes are refered to ass Tectono - Eustatic.
The best example is if two plates collide, then one could be pushed upwards.
How much lower was the sea during the Ice Age?
120M - the UK was connected to Europe.
What forms at a submergent coastline
A rise in sea level floods the coast creating:
Ria - A flooded river valley, I.e Plymouth Sound.
Fjord - A drowned glacier valley, U Shaped valleys left by glaciers are flooded, i.e Scotland.
Dalmatian Coast - After ice sheets melted, wide valleys flooded forming wide, sediment rich mouths. Rivers flood almost parallel to the coast. I.e - Croatia.
What forms at emergent coastlines?
A fall in sea level exposes land that was previously covered by the sea, this creates:
Raised Beach - As land rose as a result of isostatic recovery (readjustment), former shorelines platforms and their beaches are raised above present sea level.
Relic Cliffs - An old cliff exposing feautures such as CASS.
What are the physical factors that increase the rate of coastal retreat?
- Long Wave Fetch
- Cliffs vulnerable to subaerial processes
- Large, Destructive Waves
- Cliffs with structural weaknesses
- Soft geology and unconsolidated sediment
- Strong LSD
- Storms
What are the human factors that increase the rate of coastal retreat?
Construction of dams on rivers traps sediment, starving the coastline of a sediment source.
Dredging removes sand and gravel for building purposes.
Building of other coastal defences which will stop or limit sediment supply to a cell.
What is Dredging
Dredging is the removal of sediments and debris from the bottom of lakes, rivers, harbors, and other water bodies.
What are subaerial processes?
“under the air” processes are the combination of weathering and mass movement.
Which areas are at increasing risk from localised flooding?
- Low lying esturaries or delta regions
- Small Pacific and Indian ocean islands
What and why are Deltas sinking?
Deltas are where the mouth of a river flows into an ocean, or even into a desert. It is formed by sediment carried by the river being deposited in the wider mouth. This happens because the water moves less quickly there.
They are sinking because of damming and diverting meaning they have way less sediment supply. They are also at risk beacuse of mangrove removal (mangroves dissape wave energy) and sediments are compacting causing subsidence (sinking).
How do mangroves prevent flooding?
Mangroves protect coasts from flooding by acting as a natural buffer, dissipating wave energy and storm surgesm trapping sediments and stabilizing shorelines.
Nearly, 50% of the global mangrove biome has been lost since the 1950s.
Since 2001, Trinidad and Tobago has had in place a National Policy and Programmes on Wetland Conservation. This includes the concept of “no net loss” of wetlands
What are the consequences of coastal flooding?
Wetter enviroments become breeding grounds for diseases such as cholera and malaria.
Loss of farmland reduces GDP
Shortages of food
Saltwater incursion affects drinking water
Displacement.
Why are small pacific and Indian ocean islands at increasing risk of flooding?
Low elevation (Less than 4m)
Small, cannot retreat to higher land.
Loss of coral reefs from temp rise = bleaching and ocean acidification = less dissapation of wave energy.
Low income = less coastal defenses.
What is a storm surge?
A short term rise in sea level caused by low air pressure or storms.
Strong winds push heightened waves onshore.
Why is there uncertainty over future sea level rise?
Will our population continue to grow
Will we form and stick to global agreements (COP26) - Trump
Will industrialisation continue to happen at the same rate
What are the human impacts of projected climate change for coastal areas?
Migration from at risk areas
Loss of argiultural land and food security
Increasing dependence on international aid
Social and economic losses
Conflicts over land and water
What are the physical impacts of projected climate change for coastal areas?
Loss of biodiversity
Salt water incursion
Coral bleaching and loss of reefs
Increase freqency and magnitude of storms
Increase in the height of high tides
How can we mitigate climate change?
+ costs
Reduce the severity - COP21 - Afforestation - Renewable energy - Reduce population growth - changes in diets.
Costs to invest into renewable energy, taxes on carbon emissions are unpopular and is more long term.
How can we adapt to climate change?
+ costs
Reduce or limit the impacts of Climate Change. Implement coastal defenses, create barriers (thames barrier), replant mangrove forests, migration, grow salt tolerant crops (rice on nile delta), EWS.
Increased costs of food, cost of migration (socially and economically), increased water costs, increased aid costs, cost of defences, higher insurance premiums.
