Bedload erosion can also be a major factor in bedrock erosion. It is caused by saltating grains or traction. Saltating is where the grains are lifted up by the water and then tossed back down. Most of the time this is with gravels and if the stream power is big enough pebbles.
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These smaller particles are carried by the fluid in suspension, and advected downstream. The smaller the particle, the less important the downward pull of gravity, and the longer the particle is likely to stay in suspension. Saltating dune sand in a wind tunnel. A recent study finds that saltating sand particles induces a static electric field by friction.
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Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating. This process has been found to double the number of particles predicted by previous theory.Electric Sand Findings, University of Michigan Jan. 6, 2008 This is significant in meteorology because it is primarily the saltation of sand particles which dislodges smaller dust particles into the atmosphere.
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A study from 2008 finds that the initial saltation of sand particles induces a static electric field by friction. Saltating sand acquires a negative charge relative to the ground which in turn loosens more sand particles which then begin saltating. This process has been found to double the number of particles predicted by previous theories. Particles become loosely held mainly due to a prolonged drought or arid conditions, and high wind speeds.
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Saltation normally lifts sand-size particles no more than one centimeter above the ground and proceeds at one-half to one-third the speed of the wind. A saltating grain may hit other grains that jump up to continue the saltation. The grain may also hit larger grains that are too heavy to hop, but that slowly creep forward as they are pushed by saltating grains. Surface creep accounts for as much as 25 percent of grain movement in a desert.
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Saltating sand deflated loess on the uplands where not blocked upwind by a topographic barrier such as steep- walled stream valleys or vertical bedrock outcrops. As a consequence, paha are found where downwind of impediments that protected loess deposit from saltating sand. As paha grew, the rise in elevation due to loess aggregation would have altered local wind patterns by causing eddies in the hill's wake reducing the wind's effective strength. Downwind of a forming paha, less sand would have been carried or mobilized, resulting in more loess.
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The process of geological saltation is quite important on Mars as a mechanism for adding particulates to the atmosphere. Saltating sand particles have been observed on the MER Spirit rover.G. Landis, et al., "Dust and Sand Deposition on the MER Solar Arrays as Viewed by the Microscopic Imager," 37th Lunar and Planetary Science Conference, Houston TX, March 13–17, 2006.
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Grey dunes are formed when pioneer species inhabit embryo dunes and begin a successional process toward dune stabilization and soil formation. Pioneer plants capture saltating sand grains carried by the wind and deposit them to continue build up the dune. Grey dunes are then formed after the root structures of pioneering plants stabilize foredunes. Sand stabilization allows for dead plant material to be decomposed within the soil, adding nutrients and water-retention abilities to the soil.
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Thus underwater visibility rarely exceeds 10 metres (30ft) and frequently may be less than 3 metres (10ft). The reefs in the bay, though numerous in the centre and east, are mostly discontinuous, forming a patchwork of low rocky outcrops surrounded by sediment. This means that they tend to be covered by thin veneers of sediment as tide and wave action lifts and sweeps saltating sand across them. The amount of sand will vary, depending on the size of the reef area, how high the reef rises above the surrounding sediment plain, the strength of tidal streams in that part of the bay and how strong the wind has been recently (and thus how big the waves). The flip side of this is that the marine life communities on these reefs tend to be rather different from those inhabiting areas with perhaps more visually spectacular ‘clean’ reefs further west.
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