Finest particles Carried by turbulent eddies Transported over large distances
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Saltation:
Coarser (sand) particles Move in long, low hops Pass momentum by grain impacts
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Creep
Larger particles slide along surface
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Sediment transport: Air vs Water
Larger particles transported in water, Saltation dominates air flow, Suspension dominates water flow
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Desert pavements / Regs
Loose particles are blown away (eroded) from the surface, Sediment sorting by selective entrainment produces a pavement, Erosion is limited by surface coarsening
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Yardangs
Wind abraded ridges oriented with the prevailing winds and separated by abraded chutes that conduct windblown sand
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Inselbergs
Isolated mountains’ of resistant rock, Rounded slowly by abrasion over long periods of time
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Sand seas / Ergs
Large regions of sand deposition, induced by changes in wind speed (due to barriers or transitions between climate zones)
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Controls on dune form:
Sand supply, wind regime, vegetation
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Barchans (or crescentic dunes):
Solitary, crescent shaped dune whose horns point downwind Form where sand supply is limited and wind is strong and constant
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Transverse dunes
Form in sand rich environments with strong steady prevailing winds Barchans merge to form long wavy ridges perpendicular to wind
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Longitudinal (seif) dunes:
Long straight ridges more or less parallel to the wind Moderate to low sand supply and strong prevailing wind with minor variations in direction
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Parabolic dunes:
Crescent shape but tips point up wind Common in costal areas with moderate to abundant (a lot) sand and winds and some vegetation cover Vegetation anchors parts of dune while other parts migrate
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Ephemeral rivers
Characterised by flashy flow regimes and unarmoured river beds, and Promotes high rates of sediment transport during floods
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Arroyos
Deep channels found in semi-arid environments, Formation driven by land use and climate change (leading to vegetation change), occurrence of intense storms, and positive feedbacks
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Mechanisms driving channel adjustment
(1) Vegetation colonises bars that are dry at high flow (2) Vegetation prevents significant floodplain flow (3) Vegetation slows bank erosion & prevents bend cutoff (these reduce channel width and force thalweg regions to link up)
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