River Ice Guide and Glossary

from the Army's Cold Regions Research and Engineering Laboratory

Frazil Ice

Frazil Ice	Frazil Pans	Anchor Ice
Sheet Ice
Border Ice	Sheet Ice Cover	Candled Ice
Ice Jams
Freezeup Jam	Breakup Jam	Shear Walls (after ice jam)

Glossary

Anchor Ice
Submerged ice attached or anchored to the river bed, irrespective of the nature of its formation.

Border Ice
Ice formed along and fastened to the shore. Border ice does not extend the entire width across the river. Also called shore ice.

Breakup Jam
Accumulation of broken ice pieces that restricts the flow of water; may contain frazil ice or remnants of freezeup jam.

Candled Ice
Decayed sheet ice that takes the appearance of thin vertical crystals shaped like candles.

Frazil Ice
Fine, small, needle-like structures or thin, flat, circular plates of ice suspended in water. In rivers and lakes it is formed in supercooled, turbulent water.

Freezeup Jam
Accumulation of frazil that restricts the flow of water; may contain some broken border ice pieces.

Frazil Pans
Sometimes referred to as pancake ice. Circular flat accumulations composed of frazil and slush ice with a raised rim; the shape and rim are due to repeated collisions.

Pancake Ice
Circular flat pieces of ice with a raised rim; the shape and rim are due to repeated collisions, composed of frazil and slush.

Shear Walls
Ice left along shoreline when a freezeup or breakup jam fails and moves downstream.

Sheet Ice
A smooth, continuous ice cover formed by freezing in the case of lake ice, or by the arrest and juxtaposition of ice floes in a single layer in the case of river ice.