NOAA National Weather Service
North Central River Forecast Center
A Glossary of Ice Terminology for the River Ice Network
- 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 ice
jam.
- Candled Ice:
- Decayed sheet ice which takes the appearance of
thin vertical crystals shaped like candles.
- Frazil Ice:
- Fine, small needlelike 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.
- 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
(lake ice) or by the arrest and juxtaposition of ice floes in a single
layer.
- Slope Change:
- A change in the slope of the river. Typical
examples are where two rivers meet, and upstream of a dam or reservoir.
- Slush Ice:
- A floating agglomerate of loosely packed frazil ice
which remains separate or only slightly frozen together.