Coasts EQ3 - Coastal erosion and sea level change Flashcards
What is eustatic change?
A rise or fall in water level caused by a change in the volume of water - GLOBAL change
What is isostatic change?
A local rise or fall in land level
How can eustatic change cause rises and falls in sea level?
During glacial periods, ice sheets form and ‘lock up’ water from the sea, causing a fall in sea level (MARINE REGRESSION)
At the end of glacial periods, melting ice sheets return water to the sea. Global temperature rise also cause thermal expansion, causing sea level rise (MARINE TRANSGRESSION)
How can isostatic changes cause rises and falls in land level?
Post glacial-adjustment causes isostatic rebound due to the weight of ice sheets melting off of crust - lifting the land surface out of the sea (MARINE REGRESSION)
Land can sink at coasts due to accretion of sediment and a seesaw effect causes subsidence (MARINE TRANSGRESSION)
What is an emergent coastline?
Parts of the littoral zone where a fall in sea level has exposed land once part of the sea bed
What features are found on an emergent coastline?
Raised beach
Fossil cliff
What is a raised beach?
A relict beach now above high tide level, usually vegetated by plant succession
What is a fossil cliff?
A steep slope found at the back of the beach exhibiting evidence of formation through marine erosion, now above high tide level
What is a submergent coastline?
Sections of the littoral zone where sea level rise has inundated areas that were previously part of terrestial land
What features are found on a submergent coastline?
Rias, fjords and Dalmatian coastlines
What is a ria?
A drowned river valley, flooded by the sea and wider than expected (estuarine coastline)
What is a fjord?
Drowned glacial valley flooded by the sea
What is a Dalmatian coastline?
Long narrow islands running parallel to the coastline, separated from the coast by narrow sea channels called sounds
What are some of the key facts on past and future sea level rise?
Past - in the last 18,000 years sea levels have risen by 140m
Future - IPPC predicts sea level rise of 50cm by 2100, every degree rise in temperature causes a 0.8mm sea level rise
Why is sea level rise difficult to predict?
- uncertainties in science of relationship between climate change and melting ice
- thermal expansion depends on global temperature rise and is hard to predict
- uncertainty on when and how much ice sheets will melt
- uncertainty on GHG emissions and climatic warming
What is rapid coastal recession caused by?
Caused by physical factors but can be influenced by human actions
What are the physical factors contributing to rapid coastal recession?
Geological - lithology, geological structure
Marine - strong longshore drift, long fetch promoting destructive waves
What are the human actions influencing coastal recession?
Anything that disrupts the operation of the sediment cell - dams and dredging
Dams - starve coast of a sediment source
Dredging - scoops up sediment from beaches, rivers or sea
How has the Aswan High Dam impacted the Nile Delta’s sediment cell?
Reduced sediment volume from 130mil tonnes to just 15 mil tonnes per year
Erosion rates have jumped from 20/25m per year to over 200m per year
How do weathering and mass movement work together to influence the rate of coastal recession?
Weathering weakens rocks above the high tide mark, making mass movement easier by reducing the internal cohesion of the rock
Repeated mass movement causes coastal recession
What different temporal factors affect coastal recession?
- wind direction and fetch
- tides
- storms
- seasons
- weather systems
What local factors increase flood risk in low lying and estuarine coasts?
- height
- degree of subsidence
- vegetation removal
What else increases the risk of flooding in low lying countries apart from local factors?
Global sea level rise
How will sea level rise impact the Maldives?
Only 2.3m above sea level
A 50cm sea level rise by 2100 would mean the Maldives would lose 77% of it’s land area
What is a storm surge?
A temporary rise in local sea level produced when a depression, tropical cyclone or storm reaches the coast
What factors worsen the impacts of a storm surge?
- high tide
- shape of coastline funneling into a narrow shape
- sea bed shallowing towards the coast
What are the short term impacts of a storm surge?
- deaths and injury
- destruction of infrastructure
- homes destroyed
- business destroyed
- loss of agricultural land
What were the impacts of Cyclone Sidr’s storm surge in 2007?
- Drinking water was contaminated by debris and many sources were inundated with saline water from tidal surges, and sanitation infrastructure was destroyed.
- Death toll over 3,000
- Cost estimated at US $1.7 billion
- Infrastructure damage
What was in the 2014 IPCC report’s ‘high confidence’ area?
- sea level will rise between 18-59cm by 2100
However the pace and extent is uncertain due to population growth, economic development and political commitment to GHG reduction - The area of the world’s major deltas at risk from coastal flooding is likely to increase by 50%
What was in the 2014 IPCC report’s ‘medium confidence’ area?
- some evidence of increased wind speeds and larger waves
- erosion will generally increase
What was in the 2014 IPCC report’s ‘low confidence’ area?
- tropical cyclone frequency remains unchanged but severity worsens
- more storm surges and depression
What is coastal recession?
The loss or displacement of land, or the long-term removal of sediment and rocks along the coastline
