1. Investigating how wind-blown sand moves on a beach/sand dune A beach-based fieldwork activity David Redfern Philip Allan Publishers © 2015

2. For an area such as this... David Redfern

3. Theoretical processes (a) Saltation 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. Each falling sand grain hits and dislodges other sand grains on the ground as it falls, and the process is repeated. Theory states that most sand grains carried by saltation do not move higher than 65 cm above the ground surface, with a maximum abrasive ‘sand blasting’ effect at about 25 cm. (b) Surface creep Surface creep is the process by which larger sand grains (>0.25 mm diameter) are moved. Falling sand grains carried by saltation push larger grains slightly forward along the ground. Philip Allan Publishers © 2015

4. Methodology in the field (1) Three elements of data can be collected: (a)The nature of the particles on the beach surface These can be recovered by pressing a circular plastic straight-sided 5-cm-high ring into the beach until it is completely level with the surface of the sand. A spade can then be used to remove the ring container. A plastic sheet is placed both above and below the ring before it is raised. (b) An airborne sample of wind-blown sand This can be recovered on a strip of 50-mm-wide sticky plastic tape attached vertically to a wooden stake at least 1.5 m high. The tape should be exposed for 120 seconds near the centre of the beach/exposed sand dune. The tape should be aligned normal to the wind. Philip Allan Publishers © 2015

5. Methodology in the field (2) (c) Wind speed This can be measured by use of an anemometer placed at 1.5 m above the beach level. The above [(a), (b) and (c)] can be repeated at three to five locations spaced at 100 m intervals on a perpendicular transect from the sea line inland across the beach or along the course of the sand dune. Philip Allan Publishers © 2015

6. Methodology in the laboratory/classroom In the laboratory/classroom: (a) The airborne sample tapes should be trimmed off above the highest adherent sand grain and marked off into a series of 10 equal sections, with the section furthest from the ground being given the number 10, the second one down 9 and so on. The sections should then be ranked according to the density of sand particles trapped on the tape — this is done subjectively by eye. (b) A sample of the sand particles on the sticky tape can be examined through a microscope while they are on the tape. (c) Examine the relative size of the airborne sand and the surface sand, again using a microscope. Philip Allan Publishers © 2015

7. One set of results (1) (a) In terms of density of sand particles against height, a discontinuity occurred at about 110–120 mm. It also appeared that 75% of particles were carried below 100 mm and 88% below 140 mm. The bulk of the particles remained close to the surface. Only a small percentage were above the break at 120 mm. This could mean that nearer the surface there is a bed load transport of particles (surface creep), while further up there is an airborne transport element (saltation). Philip Allan Publishers © 2015

8. One set of results (2) (b) The dominant feature of the airborne sand was that the grains were almost universally embedded on the tape ‘end-on’. The particles were aligned with their longest sides parallel to the ground and they were stuck on to the tape by their smallest side. The inference of this is that the wind’s drag must have rapidly positioned the airborne particles into an alignment of minimum drag or least resistance while they were being blown through the air. It was also found that there was little difference in the average size of the particles higher up the tape compared to lower down the tape. (c) This showed that the surface sand particles were coarser (larger) than the airborne particles, and were therefore not picked up by the wind. Philip Allan Publishers © 2015

9. Further ideas for research It would be interesting to see if the volume of wind-blown (airborne) sand increases on heavily used beaches, where the surface layer is more disturbed. The activities of humans may interfere with the sand population of the beach that has settled naturally. They could make the sand more likely to be picked up and moved by the wind. How sand movement varies inland on a transect from an open beach into an area of sand dunes could be examined. This could include examination of some areas with stronger winds (creating blow-outs) and some areas with lighter winds which experience less movement out. Philip Allan Publishers © 2015

10. Ainsdale Sands — a possible location David Redfern

11. Philip Allan Publishers © 2015 This resource is part of G EOGRAPHY R EVIEW, a magazine written for A-level students by subject experts. To subscribe to the full magazine go to: http://www.hoddereducation.co.uk/geographyreviewhttp://www.hoddereducation.co.uk/geographyreview