Explain how long term sea level changes occur as a result of both eustatic and isostatic change (6 marks)
Isostatic readjustment - isostatic realignment following the land subsidence as a result of the weight of ice during an ice age. During inter glacial periods the ice melts causing some areas to rebound and others to sink as the land rebalances. E.g SE UK is sinking at 1.5 mm a year while N is still rising
Eustatic - increase in volume of ocean water caused by thermal expansion and melting of land ice melt - 31 mm per year (1993 -2003). Sea level rise of 120 m since the last ice age. (occurs much faster than isostatic change and is a global process). If Antarctic melted sea levels would rise by 50m
Tectonic causes - fault line - push land upwards or create land depressions. 2004 Indian Ocean Earthquake involved fault line slipping and seabed rose several metres, reducing capacity of indian ocean and producing permanent rise in sea level.
What are emergent coastal landforms?
As land rose due to isostatic recovery (Readjustment), former shorelines, platforms and their beaches were raised above the present sea level.
What are raised beaches?
Emergent coastal landform. Areas of former wave-cut platforms and their beaches which are at a higher level than the present sea level. On the Isle of Arran (West Coast of Scotland) three distinct raised beaches represent separate changes in sea level
What are fossil cliffs?
Emergent coastal landform. Raised beaches (flat areas) and fossil cliffs (slopes) were formed during the last 10,000 years in Fife Scotland. Relic/ fossil cliffs refer to the eroded cliff lines behind raised beaches. Each fossil cliff is approximately 10 metres high at Fife
What is a submergent coastline?
Where a rise in sea level floods the coast creating rias, fjords and Dalmatian coasts
What are rias?
Submergent coastal landforms. Drowned river valleys. Formed when valleys in a dissected upland area are flooded. They are common in south-west England, where sea levels rose after the last Ice Age - drowning the lower parts of many rivers and their estuaries. e.g The Kingsbridge Estuary in Devon is now a natural harbour
What are Dalmatian coasts?
Submergent coastal landforms. Similar to rias but the rivers flow almost parallel to the coast rather than at right angles. The Dalmatian coast in croatia gives it is name.
What is a Fjord?
Submergent coastal landform. A drowned glacial valley. As sea levels rise, U-shaped valleys left by glaciers are submerged. They are deeper inland than near the coast. Shallower entrance marks where the glacier left the valley. Scotland (Loch Torridon), Norway, New Zealand are good examples.
What is marine transgression?
Where the coastline is flooded and produces a submergent coast. Caused by eustatic rise in sea level and isostatic rise in sea level.
What is marine regression?
Where the sea level drops and produces an emergent coast. Caused by eustatic fall in sea level and an isostatic fall in sea level.
What physical factors will increase the rate of coastal retreat?
Long wave fetch
Soft Geology and unconsolidated sediment (vulnerable to subaerial processes - mass movement and weathering)
Spring tides when waves reach backshore
Storm (depressions) strong winds
Large, Destructive waves
Strong Longshore drift; eroded material is quickly removed exposing the cliff base to further erosion
Cliffs with structural weaknesses e.g seaward dip and faults
What are the human factors that will increase the rate of coastal retreat?
- The building of damns on rivers which traps river sediment, starving the coast of sediment source
- Dredging removes sand and gravel for building purposes
- The building of coastal defences which will stop or limit sediment supply to a store
Which areas are vulnerable to coastal flooding?
By 2060, 12% of the world’s population will live in low elevation coastal zones (those 10 m above sea level)
Which areas are vulnerable to coastal flooding?
- Large river deltas and estuaries e.g Ganges, Nile, Mississippi
- Low lying land that is already defended e.g The Netherlands, East England
- Small low lying islands in the Pacific and Indian Oceans
By 2060 how much of the worlds population will live in low elevation coastal zones (those below 10m above sea level)
12%
Why are the mega-deltas of Asia at particular risk of flooding?
- Rapidly growing populations
- Lack of coastal defence
- Sea Level Rise
- Dams constructed upstream which traps sediment
- Over extraction of ground water causing subsidence and accelerating sinking
- Increased storm surges from typhoons
- Delta subsidence caused by weight of sediment deposition
- River straightening for navigation increases flow and sediment not deposited at shore
- Destruction of mangroves for tourism and wood
CASE STUDY: Bangladesh - Sea Level Rise and Storm Surges Stats.
Bangladesh is the country most at risk of sea level rise (between 6- 20 mm a year)
70% of country consists of flood plains.
Since 1700 1.3m people have been killed in storm surges
CASE STUDY: What are the consequences of increased coastal flooding in Bangladesh?
- Wetter environments from sea and rivers become breeding grounds for diseases such as cholera and malaria
- Loss of farmland due to flooding and salt contamination will reduce the country’s GDP
- Shortages of rice and vegetables will lead to famine and malnutrition
- Salt water incursion is affecting the drinking water of 20 million people
How many people were displaced in 1995 when Bhola Island was submerged?
1/2 million people
What makes the Pacific Islands particularly vulnerable to coastal flooding?
- 100% of people live within 1km of the coastline
- Hazard hotspots
- Very remote and isolated
- Small physical size
- Environmental degradation
- Low elevation only
What makes the Pacific Islands particularly vulnerable to coastal flooding?
- 100% of people live within 1km of the coastline
- Hazard hotspots
- Very remote and isolated
- Small physical size
- Environmental degradation
- Low elevation only 4m above sea level
- Dense populations
- Groundwater salinisation by sea water
CASE STUDY: Impacts of flooding on Kiribati
- Most of population live on Tarawa, where the maximum height above sea level is just 3 metres
- Sea level rise and storm surges due to climate change have increased flooding, beach erosion and the contamination of limited fresh water supplies
- This also causes bleaching of coral reefs
By what % is the risk of flooding in Kiribati supposed to increase?
By 200 times between 2000 and 2080
Explain how local factors can increase the risk of coastal flooding (8)
- Height above sea level, already low
- Subsidence (land sinking) as sediment is held back behind dams, or irrigation reduces flow
- Mangrove destruction and removal of coral rocks for sea defences
- Inadequate flood defences
- Increased frequency and intensity of tropical cyclones
