Slush, also called slush ice, is a

slurry A slurry is a mixture of denser solids suspended in liquid, usually water. The most common use of slurry is as a means of transporting solids or separating minerals, the liquid being a carrier that is pumped on a device such as a centrifugal pu ...

mixture of small

ice crystals Ice crystals are solid water (known as ice) in crystal structure, symmetrical shapes including hexagonal crystal family, hexagonal columns, hexagonal plates, and dendrite (crystal), dendritic crystals. Ice crystals are responsible for various at ...

(e.g.

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 ...

) and liquid

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 ...

. In the

natural environment The natural environment or natural world encompasses all life, biotic and abiotic component, abiotic things occurring nature, naturally, meaning in this case not artificiality, artificial. The term is most often applied to Earth or some parts ...

, slush forms when ice or snow melts or during mixed precipitation. This often mixes with dirt and other pollutants on the surface, resulting in a gray or muddy brown color. Often, solid ice or snow can block the drainage of fluid water from slushy areas, so slush often goes through multiple freeze/thaw cycles before being able to completely drain and disappear. In areas where

road salt Road salt (also known as de-icing salt, rock salt, or snow salt) is a salt used mainly as an anti-slip agent in winter road conditions, but also to prevent dust and snow build-up on roads. Various kinds of salts are used as road salt, but calciu ...

is used to clear roadways, slush forms at lower temperatures in salted areas than it would ordinarily. This can produce a number of different consistencies over the same geographical area with scattered salted areas covered with slush and others covered with frozen precipitation.

Hazards

Because slush behaves like a non-Newtonian fluid, which means it behaves like a mostly solid mass until its inner

shear force In solid mechanics, shearing forces are unaligned forces acting on one part of a Rigid body, body in a specific direction, and another part of the body in the opposite direction. When the forces are Collinearity, collinear (aligned with each ot ...

s rise beyond a specific threshold and beyond can very suddenly become

fluid In physics, a fluid is a liquid, gas, or other material that may continuously motion, move and Deformation (physics), deform (''flow'') under an applied shear stress, or external force. They have zero shear modulus, or, in simpler terms, are M ...

, it is very difficult to predict its behavior. This is the underlying mechanism causing slush

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 ...

s and their unpredictability and thus hidden potential to become a

natural hazard A natural disaster is the very harmful impact on a society or community brought by natural phenomenon or hazard. Some examples of natural hazards include avalanches, droughts, earthquakes, floods, heat waves, landslides - including submarin ...

without caution. Slush can also be a problem on an aircraft

runway In aviation, a runway is an elongated, rectangular surface designed for the landing and takeoff of an aircraft. Runways may be a human-made surface (often asphalt concrete, asphalt, concrete, or a mixture of both) or a natural surface (sod, ...

since the effect of excess slush acting on the aircraft's wheels can have a resisting effect during takeoff, making its projection unstable, which can cause an accident such as the

Munich air disaster The Munich air disaster occurred on 6 February 1958, when British European Airways Flight 609 crashed on its third attempt to take off at Munich-Riem Airport in Munich, West Germany. The aircraft was carrying the Manchester United F.C., Manche ...

. Slush on roads can also make roads slippery and increase the

braking distance A brake is a mechanical device that inhibits motion by absorbing energy from a moving system. It is used for slowing or stopping a moving vehicle, wheel, axle, or to prevent its motion, most often accomplished by means of friction. Background ...

s for cars and trucks, increasing the possibility of rear end crashes and other road accidents. Slush can refreeze and become hazardous to vehicles and pedestrians. In some cases though, slush can be beneficial. When snow hits the slush, it partially melts and also becomes slush on contact. This prevents roads from becoming too congested with snow or sleet.

References

{{Ice Snow or ice weather phenomena Forms of water Water ice