Southport Offshore Gale Force Winde an der Mersey Mündung an der Nord-West sefton Küste heute Morgen. Die Küste hier ist Erosion und die Gezeiten zeigen oft prähistorische Schlammschichten, von denen einige menschliche und tierische Fußabdrücke enthalten. Mann, der große Fläche von welligen festen Düne, die Arten-reich und stark Kaninchen-weidet ist.
3600 x 2400 px | 30,5 x 20,3 cm | 12 x 8 inches | 300dpi
Aufnahmedatum:
10. Januar 2015
Ort:
Southport, Merseyside, UK
Weitere Informationen:
Dieses Bild kann kleinere Mängel aufweisen, da es sich um ein historisches Bild oder ein Reportagebild handel
Around 75% of all sand movement by wind is by saltation. Once the wind reaches a minimum speed, it picks up loose sand grains from the surface and carries them forward a short distance. The falling sand grain hits and dislodges other sand grains on the ground as it falls, and the process is repeated. Most sand grains carried by saltation do not move higher than 65cm above the ground surface, with a maximum abrasive ‘sand blasting’ effect at 23cm. The ‘bouncing’ motion of saltation outlined above, where a falling sand grain bounces off the ground and back into the air, is more common on hard surfaces such as pebbles. On a softer ground surface (like dry sand), the falling sand grain hits the ground and buries itself. The impact ejects a second grain into the air, which is then carried by the wind. ‘Bouncing’ on hard surfaces results in faster sand movement than ‘splashing’ on sand. Sand is deposited by the wind when the wind speed drops. Sand grains are continually being transported between the beach and the dunes nearest to the sea (known as the foredunes). Obstacles, such as driftwood or dead seaweed, can interrupt the flow of wind, and cause sand to accumulate downwind. Sand can also build up in the absence of obstacles. Since saltation over sandy surfaces is slower than saltation over hard surfaces, sand will tend to accumulate on surfaces which are already sandy. Friction is another important factor. Saltating sand grains increase friction, and this slows down wind speeds near the ground surface (known as ‘saltation drag’). As wind speeds increase, the energy gained may even begin to be exceeded by the energy lost to friction, leading to net sand deposition.
