What is Frazil Ice?

Ice Crystals in Supercooled, Turbulent Water

If you are familiar with the famous slush-like drink known as a "Slurpee" then you have a good idea of what frazil ice looks like.

Frazil ice is a suspension of ice crystals in supercooled turbulent water. It most often forms in fast-moving, turbulent streams. In these streams the rapid motion of the water inhibits the formation of ice crystals.

A stream famous for its frazil ice is Yosemite Creek in Yosemite National Park. There the conditions necessary for frazil ice formation occasionally occur in March and April. The video at right by the National Park Service and the Yosemite Fund shows an impressive episode of frazil ice formation.

How Still Water Freezes

Still water freezes by forming a thin shell of ice at the surface where cold, subfreezing air is in contact with the ice. Water molecules have no problems arranging themselves into ice crystals in that still environment. If the air temperature remains below freezing the thin layer of ice will grow thicker and thicker.

Supercooled Water

Flowing water behaves differently. The motion makes it difficult for water molecules to assemble into the rigid crystal structure that we know as "ice". When the water is cold enough to freeze but can not freeze because of motion it is known as "supercooled" water.

Frazil Crystals and Frazil Ice

Although turbulent water can not "freeze over" like still water it can eventually become cold enough that tiny ice crystals begin to form and are carried along, suspended in the moving water. These tiny crystals are needle-shaped or disk-shaped and are known as frazil crystals.

If the supercooled temperature persists, enough ice crystals will form that the water becomes a flowing slush. This condition is known as frazil ice.

Video: Glaciers in Yosemite National Park

Frazil ice in Yosemite Creek. This video by the National Park Service and The Yosemite Fund takes you to Yosemite Creek in early spring where frazil ice completely fills the channel, surges, dams the channel and diverts flow in a new direction.

Do you know?.... Is ice a mineral?

Frazil ice overflowing the channel of Yosemite Creek in Yellowstone National Park. Image is a screenshot from the video above by the National Park Service and The Yosemite Fund.

Video on Frazil Ice

frazile ice

Frazil ice fills the channel of Yosemite Creek in Yosemite National Park. Image is a screenshot from the video above by the National Park Service and The Yosemite Fund.

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