geology Geology () is a branch of natural science concerned with Earth and other Astronomical object, astronomical objects, the features or rock (geology), rocks of which it is composed, and the processes by which they change over time. Modern geology ...

, saltation () is a specific type of

particle In the physical sciences, a particle (or corpuscule in older texts) is a small localized object which can be described by several physical or chemical properties, such as volume, density, or mass. They vary greatly in size or quantity, from ...

transport by fluids such as

wind Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ...

water Water (chemical formula ) is an inorganic, transparent, tasteless, odorless, and nearly colorless chemical substance, which is the main constituent of Earth's hydrosphere and the fluids of all known living organisms (in which it acts as ...

. It occurs when loose materials are removed from a bed and carried by the fluid, before being transported back to the surface. Examples include pebble transport by rivers,

sand Sand is a granular material composed of finely divided mineral particles. Sand has various compositions but is defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural class ...

drift over desert surfaces,

soil Soil, also commonly referred to as earth or dirt, is a mixture of organic matter, minerals, gases, liquids, and organisms that together support life. Some scientific definitions distinguish ''dirt'' from ''soil'' by restricting the former ...

blowing over fields, and

snow Snow comprises individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water throughou ...

drift over smooth surfaces such as those in the

Arctic The Arctic ( or ) is a polar regions of Earth, polar region located at the northernmost part of Earth. The Arctic consists of the Arctic Ocean, adjacent seas, and parts of Canada (Yukon, Northwest Territories, Nunavut), Danish Realm (Greenla ...

or Canadian Prairies.

Process

At low fluid velocities, loose material rolls downstream, staying in contact with the surface. This is called ''creep'' or ''reptation''. Here the forces exerted by the fluid on the particle are only enough to roll the particle around the point of contact with the surface. Once the wind speed reaches a certain critical value, termed the ''impact'' or ''fluid threshold'', the drag and lift forces exerted by the fluid are sufficient to lift some particles from the surface. These particles are accelerated by the fluid, and pulled downward by gravity, causing them to travel in roughly ballistic trajectories. If a particle has obtained sufficient speed from the acceleration by the fluid, it can eject, or ''splash'', other particles in saltation, which propagates the process. Depending on the surface, the particle could also disintegrate on impact, or eject much finer sediment from the surface. In air, this process of ''saltation bombardment'' creates most of the dust in dust storms. In rivers, this process repeats continually, gradually eroding away the river bed, but also transporting-in fresh material from upstream. The speed at which the flow can move particles by saltation is given by the Bagnold formula. '' Suspension'' generally affects small particles ('small' means ~70 micrometres or less for particles in air). For these particles, vertical drag forces due to turbulent fluctuations in the fluid are similar in magnitude to the weight of the particle. 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. A fence designed with holes can mitigate saltation by reducing particle speed, and sand accumulates on the leeward side of the fence.
A 2008 study found that saltating 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 theory.Electric Sand Findings, University of Michigan Jan. 6, 2008
/ref> This is significant in meteorology because it is primarily the saltation of sand particles which dislodges smaller dust particles into the atmosphere. Dust particles and other aerosols such as soot affect the amount of sunlight received by the atmosphere and earth, and are nuclei for condensation of the water vapour. Saltation on sand dune

Avalanches

Saltation layers can also form in

avalanche An avalanche is a rapid flow of snow down a slope, such as a hill or mountain. Avalanches can be set off spontaneously, by such factors as increased precipitation or snowpack weakening, or by external means such as humans, animals, and ea ...

References

External links

Dune sand saltation video, Kansas State UniversityClose up of dune sand saltation, Kansas State University
* * {{Rivers, streams and springs Geological processes

Process

Avalanches

See also

References

External links