geology Geology (). is a branch of natural science concerned with the Earth and other astronomical objects, the rocks of which they are composed, and the processes by which they change over time. Modern geology significantly overlaps all other Earth ...

, saltation () is a specific type of particle transport by fluids such as

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

water Water is an inorganic compound with the chemical formula . It is a transparent, tasteless, odorless, and Color of water, nearly colorless chemical substance. It is the main constituent of Earth's hydrosphere and the fluids of all known liv ...

. 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 usually defined by its grain size. Sand grains are smaller than gravel and coarser than silt. Sand can also refer to a textural ...

drift over desert surfaces,

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

blowing over fields, and

snow Snow consists of 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 througho ...

drift over smooth surfaces such as those in the

Arctic The Arctic (; . ) is the polar regions of Earth, polar region of Earth that surrounds the North Pole, lying within the Arctic Circle. The Arctic region, from the IERS Reference Meridian travelling east, consists of parts of northern Norway ( ...

Canadian Prairies The Canadian Prairies (usually referred to as simply the Prairies in Canada) is a region in Western Canada. It includes the Canadian portion of the Great Plains and the Prairie provinces, namely Alberta, Saskatchewan, and Manitoba. These provin ...

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. 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 Grade (slope), slope, such as a hill or mountain. Avalanches can be triggered spontaneously, by factors such as increased precipitation or snowpack weakening, or by external means such as humans, othe ...

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