Coasts- Sources of Energy Flashcards
Role of solar energy in the coastal system
- initial energy input for the coastal system is from the Sun
- Sun’s energy causes different air pressures (different rates of heating) which creates wind
- this wind then generates waves
How does wind strength impact wave energy?
- the stronger the wind is, the bigger the wave created will be
- because the energy in the wind will be transferred to the waves
How does the fetch impact wave energy?
- the greater the fetch, the bigger the wave will be
- the wind has more time to transfer its energy to the waves
How does the duration of the wind impact wave energy?
-the longer time the wind has to transfer energy to the waves, the greater amount of energy the wave will have
How are wind-driven waves formed?
- created by the frictional drag between the wind and surface water
- as wind blows across the surface of the ocean, the continual disturbance creates a wave crest
- as the wave approaches the shore, disturbance to the circular motion beneath the surface leads to more horizontal wave movement
- this causes the wave to break
Why are some areas of the UK subjected to more powerful waves than others?
- some areas have a much larger fetch
- eg. The SW coast has a fetch extending 3000 miles across the Atlantic Ocean to Brazil
- the large fetch gives the wind more time to transfer energy- making it more powerful
- SE has a much smaller fetch- so less powerful waves
Constructive wave characteristics
- distant weather systems generate these in open ocean
- low, surging waves
- long wavelength
- strong swash, weak backwash
- beach gain (constructive)
- associated with gentle beach profile
Destructive wave characteristics
- local storms responsible for these waves
- high, plunging waves
- short wavelength
- weak swash, strong backwash
- beach loss (destructive)
- associated with steeper beach profile
What are tides?
The periodic rise and fall in the sea level caused by the gravitational pull of the Sun and the moon (mainly the moon)
Neap tide
- moon at right angles to the Sun when in first or last quarter
- gravitational pulls act against each other to create lower high tides and higher low tides
- so there is a small tidal range
Spring tides
- Sun and moon in line at full moon or new moon
- gravitational pulls act together to create higher high tides and lower low tides
- so tidal range is large
Characteristics of a high energy coastline
- rocky coastline
- erosion exceeds deposition
- contains cliffs and headlands
- in the UK- often Atlantic facing
- many examples in Cornwall
Characteristics of a low energy coastline
- see less powerful waves
- beaches and spits found
- Sandy and estuarine coasts
- deposition exceeds erosion
- sheltered areas (eg. bays)
Wave refraction
- shape of sea bed reorients approaching waves- waves reach shallower water at different times
- as water depth decreases, wave velocity decreases
- waves are bent towards the part of the shoreline where they are moving most slowly
- wave crests roughly mirror the contours of the sea bed
- higher the sea bed relief, the slower the wave
- wave height increases as they approach the shore
- waves break and converge on headlands-increasing the energy released by breaking wave
Rip currents
- strong localised underwater currents that occur on some beaches
- commonly formed when a series of plunging waves cause a temporary build up of water at the top of the beach
- met with resistance from breaking waves- water returning down the beach is forced just below the surface (following troughs in beach profile)
- this fast flowing offshore surge of water can drag people into deep water
