Coasts eq3 Flashcards
why does sea level changes on a daily basis?
- high and low tides
- atmospheric air pressure
- winds
Isostatic Change
def
A local rise or fall in land level, relative to the sea level.
Eustatic Change
def
A rise or fall in water level caused by a change in the volume of water. This is a global change.
submergent
Submergent coasts are those that are formed when sea level rises, flooding formerly exposed land areas.
emergent
Emergent coasts are those that are formed when sea level declines, leaving new land areas. This new land area is now attacked by waves and eroded.
isostatic
glacial cause
the weight of the ice causes the Earth’s crust to sag. When they melt, the land surface slowly rebounds upwards over thousands of years. This post-glacial adjustment slowly lifts the land surface out of the sea.
isostatic
example
England and Wales are subsiding at up to 1mm per year.
Scotland is still rebounding upward, in some places by up to 1.5mm per year.
eustatic
cause
when ice sheets form on land in high latitudes, water evaporated from the sea is locked up on land as ice leading to global fall in sea level.
melting ice sheets return water to the sea causing the sea level to rise globally.
WHat is happening to UK sea levels?
- retreat of icesheets
- Scotland is rebounding upwards by up to 1.5mm per year
- England and Wales are subsiding at up to 1mm a year.
- This process is called isostatic readjustment
Kiribati
the first country rising sea levels will swallow up as a result of climate change.
The holderness coastline
Europe’s fastest eroding coastlines
average annual rate of erosion is around 2 metres per year
The main reason for this is because the bedrock is made up of till (material deposited by glaciers 12,000 years ago)
delta
Deltas are wetlands that form as rivers empty their water and sediment into another body of water, such as an ocean, lake, or another river. eg Nile Delta
WHy is BAngladesh vullnerable?
vulnerable to storms surges and sea-level rise caused by climate change, with much of its land being less than 5 metres above sea level.
most densely populated country, located on floodplains of three major rivers.
what causes storm surges?
low pressure systems ( depressions) and tropical cyclones.
depressions
are areas of low air pressure generating surface winds that spiral into the centre of low pressure in an anti-clockwise direction. They occur in mid-latitudes, like the UK.
tropical cyclones
reas of very low surface air pressure (deeper depressions) generating very strong winds (118 kph +). They’re classified on the Saffir Simpson scale into 5 categories, where the fifth has winds of over 250 km.
The rise in sea level during the storm surge is accentuated:
- At high tide, particularly spring tide
- Shape of coastline funnels into increasingly narrow space
- Sea bed shallows towards coast
short term impacts of storm surges
- Deaths and injuries
- Destruction of infrastructure
- Damaged water pipes, electricity transmission lines and sewage systems
- Homes destroyed
- Businesses destroyed
- agricultural land contaminated
Why is Bangladesh vulnerable to storm surges?
- Low income country so limited coastal management
- Subsidence- in the past 50 years, Bangladesh has sunk by 1.5m due to isostatic readjustment.
- Most densely populated country
- Removal of mangroves ( natural flood defence)
risks of the Nile Delta
- rising sea level would destroy weak parts of the sand belt and inundatr more than 1/4 of the delta
- silt and sediment no longer reach because of the dam
- no anual flooding anymore (polluted water)
low lying
Assessing Bangladesh’s risk to coastal flooding
- 46% of the countries population lives less than 10 metres above the sea level
- Located on flood plains
- When storms strike, it doesn’t take long until the land is flooded entirely
rivers
Assessing Bangladesh’s risk to coastal flooding
- Three major rivers run through Bangladesh - Brahmaputra, Meghna and Ganges
- These converge in Bangladesh, brought together by 54 other rivers into the empty bay of Bengal
storm surges
Assessing Bangladesh’s risk to coastal flooding
- Cyclone Sidr swept in from the bay of Bengal on 15 November 2007
- Brought a storm surge that reached up to 6 metres high in some places
- Very devastating and are very common
- Changes in sea level caused by intense low pressure systems
subsidence
Assessing Bangladesh’s risk to coastal flooding
- Isostatic readjustment
- clearance and drainage of more than 50 large islands
- Used to grow rice to feed the population
- Prevented natural deposition of sediment used to protect islands height
- Islands are fast submerging
vegetation removal
Assessing Bangladesh’s risk to coastal flooding
- Mangrove forests are found along the coasts
- They provide protection and shelter to storm surge
- 71% of Bangladesh’s mangrove forest coastline is now retreating by as much as 200 metres per year
global sea level rise (eustatic)
Assessing Bangladesh’s risk to coastal flooding
- Global greenhouse gas emissions have caused sea level rise (SLR) at a global and local level since the industrial revolution, mainly through thermal expansion and ice melting
isostatic
sediment cause
Land can ‘sink’ at the coast due to the deposition of sediment (accretion), especially in large river deltas where the weight of sediment deposition leads to very slow ‘crustal sag’ and delta subsidence.
global warming
eustatic
cause
Global temperature increases cause the volume of ocean water to increase (thermal expansion) leading to sea level rise.
