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1.6 Forms of Ice

1.6.1 Pancake Ice

Predominantly circular pieces of ice 30 cm to 3 m in diameter, up to 10 cm in thickness, with raised rims due to the pieces striking against one another. It may form on a slight swell from grease ice, shuga or slush or as a result of the breaking of ice rind, nilas or, under severe conditions of swell or waves, of grey ice. It also sometimes forms at some depth at an interface between water bodies of different physical characteristics where it floats to the surface. It may rapidly form over wide areas of water.

1.6.2 Ice Cake

Any relatively flat piece of ice less than 20 m across.

Small Ice Cake
An ice cake less than 2 m across.

1.6.3 Floe

Any relatively flat piece of ice 20 m or more across. Floes are subdivided according to horizontal extent as follows:

Small
20-100 m across.

Medium
100-500 m across.

Big
500-2,000 m across.

Vast
2-10 km across.

Giant
Greater than 10 km across.

1.6.4 Floeberg

A massive piece of ice composed of a hummock or a group of hummocks, frozen together and separated from any surrounding ice. They may typically protrude up to 5 m above water level.

1.6.5 Ice Breccia

Ice pieces of different stages of development frozen together.

1.6.6 Batture Floes

Large, thick, uneven and discoloured ice floes that form on the upstream side of shoals and islets in rivers when cold weather precedes or accompanies neap tides. Composed of ice of different thicknesses formed under pressure during ebb tide, the whole mass freezing together and gradually increasing in size with each successive tide. As the range increases between the neap and spring tides, large sections of grounded ice break away and drift down river. This is a Canadian description and not part of the WMO nomenclature.

1.6.7 Brash Ice

Accumulation of floating ice made up of fragments not more than 2 m across, the wreckage of other forms of ice.

Jammed Brash Barrier
A strip or narrow belt of new, young or brash ice usually 100-5000 m across formed at the edge of either floating or fast ice or at the shore. Heavily compacted, mostly due to wind action, may extend 2 to 20 m below the surface, but does not normally have appreciable topography. Jammed brash barriers may disperse with changing winds, but can also consolidate to form a strip of unusually thick ice in comparison to the surrounding ice.

Photo of a view of Quebec City bridges

Photo 1.7: View of Quebec City bridges with nilas and grey ice mixed with thin brash moving down under the bridge. Extensive fast ice (battures) has formed on both sides of the river.

Agglomerated Brash
This term is similar to Jammed Brash Barrier but is not consolidated. This is a Canadian description and not part of the WMO nomenclature.

1.6.8. Fast Ice

Ice which forms and remains fast along the coast. It may be attached to the shore, to an ice wall, to an ice front, between shoals or grounded icebergs. Vertical fluctuations may be observed during changes of sea level. It may be formed "in-situ" from water or by freezing of floating ice of any age to shore and can extend a few metres or several hundred kilometres from the coast. It may be more than one year old in which case it may be prefixed with the appropriate age category (old, second-year or multi-year). If higher than 2 m above sea level, it is called an ice shelf.

Young Coastal Ice
The initial stage of fast ice formation consisting of nilas or young ice; its width varying from a few metres up to 100-200 m from the shoreline.

1.6.9 Icefoot

A narrow fringe of ice attached to the coast, unmoved by tides and remaining after the fast ice has moved away.

1.6.10 Anchor Ice

Submerged ice attached or anchored to the bottom, irrespective of the nature of its formation.

1.6.11 Grounded Ice

Floating ice which is aground in shoal water.

Stranded Ice
Ice which had been floating and has been deposited on the shore by retreating high water.

Grounded Hummock
A hummocked, grounded ice formation. There are single grounded hummocks and lines (or chains) of grounded hummocks.