Slush

Slush, also called slush ice, is a mixture of snow and liquid water.

Slush on a window

In the natural environment, slush is made when ice or snow melts. This often mixes with dirt and other materials, resulting in a gray or muddy brown color. Ice and snow can often block the draining of water from slushy areas, so slush often freezes and melts multiple times before completely disappearing.

In areas where road salt is used to clear roadways, slush forms at lower temperatures than it would usually in salted areas. This can cause many differences, even in the same area.

Hazards

Melted snow in a roadway that has turned to slush in the wheel paths

Slush behaves like a non-Newtonian fluid, which means it acts solid until its inner shear forces reach a certain amount. When this happens, it can suddenly become fluid. This makes the behaviour of slush very unpredictable. This is the reason avalanches happen and are so unpredictable. This gives them potential to become a hidden natural hazard.

Too much slush can be a problem on an aircraft runway since it cause resistance on the aircraft’s wheels. This can cause accidents such as the Munich air disaster. Slush on roads can also increase the braking distances for cars and trucks, increasing the chance of rear end crashes and other accidents.

Slush can be dangerous and slippery in overnight frost.

Sometimes, slush can be helpful. When snow hits slush, it melts on contact. This stops roads from becoming too full of snow or sleet.