Coastal Erosion & Sea Level Change (Edexcel A Level Geography): Flashcards
Exam code: 9GE0
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Define eustatic sea level change.
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Define eustatic sea level change.
A global change in sea level caused by a change in the volume of water in the ocean basins, for example from melting ice or thermal expansion.
Define isostatic sea level change.
A local change in relative sea level caused by a change in the height of the land compared to the sea, usually acting more slowly than eustatic change.
What are the three main causes of eustatic change?
Eustatic change is mainly caused by changing amounts of ice, thermal expansion of warming water, and tectonic processes altering ocean basin capacity.
True or False?
Isostatic change usually happens faster than eustatic change.
False.
Isostatic change generally happens more slowly than eustatic change because land adjustment and sediment processes take longer than water volume changes.
During post-glacial adjustment, heavy ice sheets the land, which then when the ice melts.
During post-glacial adjustment, heavy ice sheets depress the land, which then rebounds when the ice melts.
When did contemporary sea level largely stabilise before recent change?
Global sea level largely stabilised around 3000 years ago, before rising again rapidly from the nineteenth-century industrial revolution onwards.
How much has global sea level risen since the start of the industrial revolution?
Since the nineteenth century, global sea level has risen by about 235 mm, enough to overtop some coastal defences and worsen storm-surge flooding.
By 2100, the IPCC predicts sea level will be between and higher than today.
By 2100, the IPCC predicts sea level will be between 0.26 m and 0.77 m higher than today.
Around people live on high-risk coasts, and about of the world’s cities are coastal.
Around 1 billion people live on high-risk coasts, and about 75% of the world’s cities are coastal.
Define emergent coastline landforms.
Emergent landforms are coastal features exposed by a relative fall in sea level, often due to isostatic uplift, such as raised beaches and fossil cliffs.
Define submergent coastline landforms.
Submergent landforms form when rising sea levels flood coastal areas, creating rias, fjords, and features like the Dalmatian coast.
What is the difference between a ria and a fjord?
A ria is a drowned V-shaped river valley, while a fjord is a flooded U-shaped glacial valley, typically deeper, especially inland, and often deeper than adjacent seas.
Define sub-aerial processes.
Weathering and mass movement operating on cliffs and slopes above sea level, weakening rock and increasing the rate of coastal erosion.
How does wetting and drying affect Holderness boulder clay?
Repeated wetting at high tide and drying at low tide makes boulder clay expand and contract, causing it to crack and crumble.
Explain freeze-thaw weathering on the Holderness coast.
Water enters cracks, freezes and expands overnight, then thaws. Repeated expansion and contraction weakens the boulder clay cliffs.
On the Holderness coast, a large saturated block moving downslope in one piece is called a .
On the Holderness coast, a large saturated block moving downslope in one piece is called a rotational slip.
What is the approximate rate of erosion on the Holderness coast?
The Holderness coast retreats at about 1.8 metres per year, one of the fastest coastal erosion rates in Europe.
Define dredging.
The removal of sediment from rivers, estuaries or the sea, reducing the amount of material supplied to the coast.
How do dams increase coastal erosion?
Dams trap river sediment behind the wall, so less reaches the coast. Smaller beaches mean destructive waves erode cliffs more quickly.
Dams on the River Ebro caused a % reduction in downstream sediment supply.
Dams on the River Ebro caused a 93% reduction in downstream sediment supply.
True or False?
Groynes at Hornsea can increase erosion further down the Holderness coast.
True.
Groynes trap sediment, causing terminal groyne syndrome, which starves downdrift areas like Mappleton of beach material and increases erosion.
Define prevailing wind direction.
The most frequent wind direction at a location, often linked to the longest fetch and largest waves affecting coastal erosion.
Why are spring tides important for coastal recession?
During spring tides, higher high tides allow waves to reach the backshore with more energy, increasing rates of erosion and recession.
True or False?
Rates of coastal recession are usually higher in winter than summer.
True.
Winter has more storms and destructive waves, so erosion and coastal recession are generally greater than in calmer summer conditions.
Define climate change in relation to coastal flood risk.
Long-term changes in temperature, sea level and storm patterns that can increase the likelihood and severity of coastal flooding.
What are the two main factors by which climate change increases coastal flood risk?
The two main factors are global sea level rise and increased frequency and magnitude of storms.
True or False?
The pace and magnitude of climate change impacts on flood risk are certain.
False.
The pace and magnitude of increased coastal flood risk from climate change are uncertain.
According to NOAA, how much have global sea levels risen since 1880?
Global sea levels have risen about 21–24 cm since 1880.
Since 2006, the average global sea level rise rate is per year, compared with per year during the 1900s.
Since 2006, the average global sea level rise rate is 3.6 mm per year, compared with 1.4 mm per year during the 1900s.
What is a storm surge?
A storm surge is a temporary rise in sea level caused by a storm or tropical cyclone, often leading to severe coastal flooding.
Define depression in meteorology.
An area of low atmospheric pressure where rising air cools and condenses, forming clouds, rain and often stormy weather.
In the northern hemisphere, how do depressions move?
Depressions move west to east and rotate anticlockwise in the northern hemisphere.
At what wind speed does a tropical cyclone form from a tropical storm?
When wind speeds reach 74 mph, a tropical storm is classified as a tropical cyclone.
Define subsidence in a coastal context.
Subsidence is the sinking or lowering of land, often from human activity, making coasts more vulnerable to flooding.
Globally, almost people live in coastal areas below 2m in elevation.
Globally, almost 300 million people live in coastal areas below 2m in elevation.
In the UK, salt marshes can reduce wave height by up to %, while 100m of mangroves reduces waves by – %.
In the UK, salt marshes can reduce wave height by up to 80 %, while 100m of mangroves reduces waves by 13–66 %.
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