2b.8c Flashcards
Describe the long term factors that influence rate of recession
wind direction/fetch, tides, seasons, weather systems and occurence of storms
What is the basic principle of rates of recession
The rate of cliff retreat depends on the amount of contact time between the sea and the rock
What kind of wind causes the largest waves
Largest waves from prevailing wind direction (South West in South Wales)
What is fetch
Distance that waves travel uninterrupted
Longer fetch = faster retreat (because they gather more energy)
What are depressions
Low-pressure weather systems
More intense, faster wind speeds
Large destructive waves
-Depressions form in the North Atlantic and take several days to pass across the UK from the SW to NE. As they pass the spiralling inflow air produces changes in wind direction
What are anticyclones
High pressure
Calmer conditions
Smaller waves
Explain the concept of a tidal bulge
1) The earth rotates on its axis once every 24 hours
2) The moon has a gravitational attraction – water is pulled towards the moon creating a ‘bulge’.
3) ‘Inertia’ always tries to counteract this – so on the far side, water tries to move away, also creating a ‘bulge’ on the far side of the Earth, away from the gravitational pull.
4) In the rest of the world, gravity and inertia are balance.
5) The bulges always stay aligned with the moon as the Earth’s rotates – so you get high and low tide, transitioning between the two.
Describe what happens to the tide when the sun and moon align
1) Once a month (every 2 weeks / 14 days)
2) Spring high tides happen when the Sun/Moon are aligned, so gravitation pull is at its strongest.
3) The sun/moon are also aligned every other 2 weeks, although the earth is between the sun and moon.
4) Then… lowest high tides are neap tides – Sun/Moon at right angles – weakest gravitational pull.
What are perigean spring tides
- The moon takes 1 month (27 days) to rotate around the Earth, which is slightly less than 28…
- The rotation is elliptical, which means its sometimes closer to the Earth than others, and when closer the gravitational effect is stronger.
- 4 times a year, this proximity coincides with the spring high-tide, so you get an even higher spring high tide (perigean spring tides)
What influence do tides have on rates of coastal recession
- Rates of recession more rapid during high tide when deeper water in the foreshore zone allows waves to maintain a higher energy when they reach the backshore. (And they reach the backshore in the first place)
- Greater energy of impact on backshore increases erosion and rates of recession
-Higher sea level produces deeper water near the backshore and faster recession
How often do high tides occur
High tides occur twice each day, about 12 hours apart
How do storms affect rates of coastal recession
- Storm events are deep (very low pressure) depressions
- They produce large, high energy destructive waves and fast rates of recession
How will global warming influence storms
-Global warming is predicted to increase intensity of atmospheric circulation - more frequent storm events - higher intensity of storm events - increased rates of recession
How do seasons affect rates of coastal recession
- Storm events are more likely to occur in the winter when the contrast in temperature and pressure between the tropical and polar air masses is the greates
- rates of recession are faster in winter than summer
- Number and intensity of storms affecting the UK each winter varies
Describe weather systems in the UK
- UK located at the polar front between the boundary of warm tropical air of the Ferrel cell and the cold polar air of the Polar cell
- Interaction between warm and cold produces high air pressure anticyclone and low air pressure depression weather system
