causes and effects of rapid coastal recession and flooding (2B.8)

Question 1

causes of rapid coastal recession

Answer 1

caused by physical factors (geological and marine) but can be influenced by human factors (dredging or coastal management)

1. physical: when geological and marine characteristics combine to promote erosion
   - geological factors include: lithology (eg soft rock type, weak bonds) and structure (jointed rocks, heavily faulted rocks etc)
   - marine factors include: long wave fetch (destructuve erosive waves) and strong longshore drift (can quickly remove collapsed sediment allowing erosion to restart)
2. human: can increase recession by interrupting the operation of the sediment cell (eg contruction of major dams can trap sediment which starves the coast of a sediment source) EG Aswan Dam on River Nile: erosion rates jumped from 20m per year to over 200m per year.
   ! see also the impacts of dredging !

Question 2

how do subaerial processes work together

Answer 2

• weathering weakens rock above high tide mark making mass movement easier by reducing internal cohesion.
• repeated mass movement= rapid recession.
• hard engineering strategies are often put in place to reduce marine erosion. although marine erosion will be stopped, coast may still retreat due to the affects of subaerial processes.

Question 3

variation in recession

Answer 3

! rates of recession are not constant and are influenced by different factors, both short- and longer-term (wind direction/fetch, tides, seasons, weather systems and occurrence of storms !

1. wind direction and fetch
   - wind direction changes daily: rates of recession= higher when wind is blowing offshore
2. tides
   - rate of recession= more rapid during high tide
   - deeper water in foreshore allows waves to maintain a higher energy when they reach the backshore: greater energy on backshore= increase erosion rates
3. storms
   - produce high energy destructive waves, global warming is predicted to increase the intensity of atmospheric circulation= more frequent/ intense storm events
4. seasons
   - more storm events: rates of recession are faster in winter in the UK than summer
5. weather systems
   - UK in between boundaries of warm air and cold air which produces high pressure anticyclone and low air pressure depression weather systems.
   - anticyclones= gentle winds, small waves (little- no recession)
   - depressions= strong winds and form in N. Atlantic taking several days to pass from UK changing wind direction