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Coastal Processes - WindWind is one of the most important processes that affect our coast, it is responsible for creating waves, currents and producing storms. It is also significant in the creation of the sand dunes.Wind is the movement of air between two areas due to different air pressures. Air flows from areas with high air pressure, generally colder, to areas with low air pressure, generally warmer. The greater the difference in pressure the stronger the wind. Wind has many different effects on coastal processes. The strength of the wind affects the size of waves, the size and speed of a current and the amount of sand blown across the beach. Wind is measured on the Beaufort Scale, where 0 is a still day and 12 is a hurricane where wind speeds measure over 64 knots (32.7m/s). These hurricane winds can create waves of 14m in the open sea. The highest surface wind speed recorded at a Low-level site in the UK: 123 knots Fraserburgh, Aberdeenshire, 13 February 1989 The highest surface wind speed recorded at a High-level site in the UK: 150 knots Cairngorm (1,245 m AMSL), 20 March 1986 The winds affecting the Sefton Coast are predominatly westerlies which means that they blow from west to east i.e. coming off the sea onto the coast.
Tell-tale signs of wind blown sand can be seen around strandline debris where a plume of raised sand can be found behind an object in the direction the wind was blowing. Other more obvious features include sand blow onto promenades at Crosby and Southport and gardens of coastal houses. The predominant wind direction affecting the Sefton Coast is from the west, approximately 70% of wind occurring from the SE to NW sector 135-315o. Most frequent wind direction is 5-10m/s. Extreme wind conditions (>20ms-1) are most frequent from the west 65hrs/year.
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The wind creates the sand dunes by the process of saltation. This is where during low tides, when the beach is dry and the wind is strong enough, grains of sand are blown up the beach. As they blow up the beach they bounce across it. As they bounce they can dislodge other grains of sand, which can also get blown up the beach, and can themselves dislodge further grains of sand. This process can often be seen and the surface of the beach appears to be moving and slithering its way up the beach.