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Verbatim definitions of sea ice and lake ice terminologies are compiled here int o a table, allowing easy comparison of terminologies from three different sourc es: The Manual for Great Lakes Ice Forecasting by C.R. Snider (Snider,1971), The World Meteorological Organization (WMO) Sea Ice Nomenclature Guide (WMO,1970), and Geology of the Great Lakes by Ernest Willard Marshall (Marshall,1977).
Definitions of Lake Ice Terms

ice type

Manual of Great Lakes Ice Forecasting

WMO Sea-ice Nomenclature

Geology of Great Lakes Ice


anchor ice

parts of icefoot which are frozen completely to the bottom

submerged ice attached to bottom





icing of a river's floodplain

ball ice

small ice elements grow by accretion or coalescence while entrapped in turbulent water which is at its freezing point throughout its depth, forming spheres up to 1 m in diameter


roughly spherical masses of slush, sludge, or brash which accrete in turbulent waters



a large feature of pack ice arrangement; longer than it is wide; from 1 km to more than 100 km in width

narrow band of fragments of floating ice of any concentration

black ice

closely packed crystals w/ few impurities

dark nilas - nilas which is under 5 cm in thickness and is very dark in color

simple ice sheet which crystallized slowly

brash ice

conglomerations of small cakes and chunks from other formations, coalesced and refrozen into irregularly shaped elements (2 - 10 cm diam), often w/ sharp projections

accumulations of floating ice made up of fragments of not more than 2 meters, the wreckage of other forms of ice.

small fragments of lake, river, or sea ice less than 2 m in diameter

brash patch



Teardrop shaped patch of brash ice drifting before the wind. The fronts of patches vary from blunt to rounded.

brash swamp



area of loose ice either floating or aground consisting principally of broken and abraded fragments of sheet ice less than 2 m in diameter



ice pieces of different ages frozen together



detached segment of sheet ice < 15 m diam

any relatively flat piece of sea ice <20 meters across



elongate air bubbles form in decaying ice


bond between ice grains melts and drains through the ice cover leaving an unbonded aggregate of grains

compact pack ice


pack ice in which the concentration is 10/10 and no water is visible




the ratio in tenths describing the amount of the sea surface covered by ice as a fraction of the whole area being considered

ratio of the extent of ice present to total extent of lake surface in the area under consideration

congelation ice



types of ice which result from the freezing of water and which are the low temperature, surface equivalent of magmatic rocks.

consolidated pack ice


pack ice in which the concentration is 10/10 and the floes are frozen together

ice cover formed by the packing and freezing together of floes, brash, sludge and slush



any fracture of fast ice, consolidated ice or a single floe which may have been followed by seperation ranging from a few centimeters to 1 m

break or split without complete seperation of parts such as a thermal crack in the ice

dried ice


sea ice from the surface of which meltwater has disappeared after the formation of cracks and thaw holes. During the period of drying the, the surface whitens

an ice surface from which the meltwater has drained off through thaw holes, cracks, and along individual crystal boundaries; characterized by a sharp needle-like or nubbly texture

drift ice

unattached to ice foot



extruded ice



thin ice resulting from the freezing of water that discharges onto a surface

fast ice

attached to (or compressed against) ice foot

sea ice which forms and remains fast along the coast, where it is attached to the shore, to an ice wall, to an ice front, between shoals and grounded icebergs. Vertical fluctuations may be observed during changes of sea-level. Fast ice may be formed in situ from sea water or by freezing of pack ice of any age to the shore, and it may extend a few meters or several hundred kilometers from the coast.

an ice cover which remains fast generally in the position where it originally formed; found along coasts where it is attached to the shore, or over shoals where is held in position by grounded hummocks or ridges

finger rafting


type of rafting whereby interlocking thrusts are formed, each floe thrusting fingers alternately over and under each other. Common in nilas and grey ice



detached segment of sheet ice > 15 m diam

any relatively flat piece of sea ice 20 meters or more across

a single piece of pack ice, ranging in size from 2 m to several kilometers in diameter

flooded ice

thin layer of water on ice surface

sea ice which has been flooded by melt water or river water and is heavily loaded by water and wet snow




Any break or rupture through very close pack ice, compact pack ice, consolidated pack ice, fast ice, or a single floe resulting from deformation processes. Fractures may contain brash ice and/or be covered with nilas and/or young ice. Length may vary from a few meters to many kilometers.



individual ice crystals floating freely

fine spicules or plates of ice suspended in water

fine spicules or discoids suspended in water; formed in supercooled turbulent waters

grease ice

surface completely covered by frazil (not yet frozen together)

a later stage of freezing than frazil ice when the crystals have coagulated to form a soupy layer on the surface. Grease ice reflects little, giving the sea a matt appearance.


grey ice


young ice 10-15 cm thick. Less elastic than nilas and breaks on swell. Usually rafts inder pressure.



compressional feature, floe onto floe or floe onto ice foot, edges deform and ice fragments pushed upward and downward

hillock of broken ice which has been forced upwards by pressure. May be fresh or weathered. The submerged volume of broken ice under the hummock is called a bummock.

ice piled haphazardly one piece over another

ice field

fast sheet ice

area of pack ice consisting of any size floes, which is greater than 10 kilometers across


ice foot

fringe of ice along shore, formed by frozen spray, captures and incorporates various types of drift ice

a narrow fringe of ice attached to the coast, unmoved by tides and remaining

after the fast ice has moved away.

fringe of grounded ice up to several hundred meters in width attached to the coast and unmoved by fluctuations in water level; remains several weeks after fast ice has melted

ice rind

brittle sheet < 7 cm thick

a brittle shiny crust of ice formed on a quiet surface by direct freezing or from grease ice, thickness < 5cm, easily broken by wind or swell, commonly breaking in rectangular pieces

formed by the freezing of sludge on a quiet lake surface; thickness < 5 cm


lane of open water between 2 floes, or between a floe and the ice foot

any fracture or passageway through sea ice which is navigable by surface vessels

navigable passage through the ice cover or ice floes due to wind and currents




ice cover consisting of ice pieces of different ages frozen together



a thin elastic crust of ice, easily bending on waves and swell and under pressure, thrusting in a pattern of interlocking fingers (finger rafting). Has a matt surface and is up to 10 cm in thickness. May be subdivided into dark nilas and light nilas.


pack ice


term used in a wide sense to include any area of sea ice, other than fast ice, no matter what form it takes or how it is disposed.

general term including any form of floating ice other than fast ice, regardless of form or concentration

pancake ice

small cakes (< 3 m diam) deformed by abrasion w/ each other,raised rims formed by accretion of spray

predominantly circular pieces of ice from 30 cm - 3 m in diameter, and up to 10 cm in thickness, with raised rims due to the pieces striking against one another. It may be formed 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.

approximately circular aggregates of slush, sludge and brash, .5 - 3 m diameter, with slightly raised rims due to bumping against each other


thin spots (or holes) in ice field formed by currents in underlying water

any non-linear shaped opening enclosed in ice, may contain brash ice and may be covered with new ice or nilas. submariners refer to these as skylights.





relatively small ice enclosed water area in the midst of pack ice other than a lead

pressure ridge


a line or wall of broken ice forced up by pressure. May be fresh or weathered. the submerged volume of broken ice under a ridge, forced downwards by pressure, is termed an ice keel.


rafted ice

edge of one floe on top of edge of another floe

type of deformed ice formed by one piece overiding another

one ice layer over or under-riding another; these layers may or may not be frozen together



sharp irregular ridges formed on snow surfaces by wind erosion and deposition. On mobile floating ice the ridges are parallel to the direction of the prevailing wind at the time they were formed.

wave-like and tongue-like ridges of snow formed by the scouring action of wind on a dense snow cover

shore lead


lead between pack ice and the shore or between pack ice and an ice front

lead between pack ice and shore or fast ice



accumulation of spongy white ice lumps, a few centimeters across, formed from grease ice or slush


skim ice

frazil crystals frozen together, but no tensile strength


initial thin competent layer of ice on a water surface




myriad of randomly oriented tabular and acicular, skeletal crystals only slightly frozen together


snow falls on freezing cold water (may eventually become snow ice)

snow which is saturated or mixed with
water on land or ice surfaces, or as a

viscous floating mass in water after a heavy snowfall.

formed from snowflakes falling into the water in great numbers, and from snow loading on an ice sheet which depresses the ice allowing lake waters to flow up along grain
boundaries into the overlying snows

snow ice



ice formed from the freezing of water-soaked snow



long narrow area of pack ice, about 1 km or less in width, usually composed of small fragments detached from the main mass of ice , and run together under the influence of wind, swell or current.


thermal cracks



cracks in ice cover caused by thermal contraction of the ice

vein ice



congelation ice which forms in a water filled crack or fissure, where cooling occurs primarily from the sides toward the center

white ice

large amounts of air within the crystalline structure