- Created by transfer of energy from the wind blowing over the sea surface.
- Energy aacquired by waves depends on strength of wind, length of time it is blowing and distance over which it blows (FETCH).
- When waves approach shallow water, friction with sea bed increases, base of the wave begins to slow down - increases height and steepness of the wave until upper part plunges forward and the wave 'breaks' onto the beach.
- Any rush of water up the beach is called SWASH, water running down the beach into the sea is BACKWASH.
- Waves are CONSTRUCTIVE or DESTRUCTIVE.
- Low waves, with a long wavelength (up to 100m).
- Have a low frequency of around 6 - 8 per minute.
- As they approach the beach the wave front steepens slowly - gentle spill onto beach surface.
- Swash loses volume/energy as water percolates through beach material - gives very weak backwash, insufficient force to pull sediment off the beach.
- Material is slowly moved up the beach leading to the formation of berms.
- High waves with a steep form and a high frequency of 10 - 14 per minute.
- On approach to the beach they rapidly steepen and plunge down when breaking.
- Creates powerful backwash - little forward movement of water, inhibits swash from the next wave.
- Little material is moved up the beach - leaving backwash to pull material away.
- Commonly associated with steeper beach profiles.
- Force of each way may project some shingle towards the rear of the beach - forms a large ridge (STORM BEACH).
Effects Of Waves
Effects Of Waves
- Constructive waves build beach up, result in steeper beach profile - encourages waves to become more destructive (associated with steeper profiles).
- Destructive waves move material back towards the sea, reducing beach angle/encouraging more constructive waves.
Should encourage state of equilibrium but impossible with othe factors (wind strength/direction) not being constant.
- When waves approach a coastline of irregular shape they are refracted - become increasingly paralell to coastline.
- Def: The periodic rise and fall in the level of the sea.
- Caused by gravitational pull of the sun/moon (moon has greater influence due to proximity). Moon pulls water towards it, creating a high tide - compensatory bulge on the other side of the Earth. Areas of the world between the two bulges experience the tide at its lowest.
- As moon orbits the earth, high tides follow it. When moon, sun and Earth are in a straight line (twice a lunar month), the tide-raising force is strongest.
- Produces highest monthly tidal range (SPRING TIDE).
- Twice a month the moon/sun positioned 90 degrees to each other in relation to Earth - gives lowest monthly tidal range (NEAP TIDE).