A grain flow is a type of
sediment-gravity flow in which the fluid can be either air or water, acts only as a lubricant, and grains within the flow remain in suspension due to grain-to-grain collisions that generate a dispersive pressure to prevent further settling. Grain flows are very common in
aeolian settings as grain avalanches on the slip faces of
sand dunes
A dune is a landform composed of wind- or water-driven sand. It typically takes the form of a mound, ridge, or hill. An area with dunes is called a dune system or a dune complex. A large dune complex is called a dune field, while broad, fl ...
. By contrast, pure grain flows are rare in subaqueous settings, where the grains in a flow are generally held in suspension dominantly by
traction,
saltation, fluid
turbulence
In fluid dynamics, turbulence or turbulent flow is fluid motion characterized by chaotic changes in pressure and flow velocity. It is in contrast to a laminar flow, which occurs when a fluid flows in parallel layers, with no disruption between ...
and/or grain
buoyancy
Buoyancy (), or upthrust, is an upward force exerted by a fluid that opposes the weight of a partially or fully immersed object. In a column of fluid, pressure increases with depth as a result of the weight of the overlying fluid. Thus the p ...
when the grains are floating in the clay matrix of a
mud flow
A mudflow or mud flow is a form of mass wasting involving fast-moving flow of debris that has become liquified by the addition of water. Such flows can move at speeds ranging from 3 meters/minute to 5 meters/second. Mudflows contain a significa ...
. However, grain-to-grain collisions are very important as a contributing process of sediment support in subaqueous, sand-rich,
high-density turbidity currents. The high concentrations of sand that develop at the base of high-density flows brings grains close enough together that frequent grain-to grain collisions are inevitable and result in layers of sediment that are
inverse graded as the smaller grains are able to fall in between larger grains and settle out beneath them.
[Lowe, D.R. (1982), ''Sediment gravity flows: II. Depositional models with special reference to the deposits of high-density turbidity currents,'' Journal of Sedimentology, Society of Economic Paleonotlogists and Mineralogists, v. 52, p. 279-297.]
In metallurgy
In
metallurgy
Metallurgy is a domain of materials science and engineering that studies the physical and chemical behavior of metallic elements, their inter-metallic compounds, and their mixtures, which are known as alloys.
Metallurgy encompasses both the sc ...
, the grain flow refers to the
plastic deformation
In engineering, deformation refers to the change in size or shape of an object. ''Displacements'' are the ''absolute'' change in position of a point on the object. Deflection is the relative change in external displacements on an object. Strain ...
of
crystallite
A crystallite is a small or even microscopic crystal which forms, for example, during the cooling of many materials. Crystallites are also referred to as grains.
Bacillite is a type of crystallite. It is rodlike with parallel longulites.
Stru ...
s during
rolling
Rolling is a type of motion that combines rotation (commonly, of an axially symmetric object) and translation of that object with respect to a surface (either one or the other moves), such that, if ideal conditions exist, the two are in contact ...
or
forging
Forging is a manufacturing process involving the shaping of metal using localized compressive forces. The blows are delivered with a hammer (often a power hammer) or a die. Forging is often classified according to the temperature at which i ...
.
Notes and references
Sedimentology
{{geology-stub