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ice jam

an accumulation of broken river or sea ice caught in a narrow channel.

ice keel

from the point of view of the submariner, a downward-projecting ridge on the underside of the ice canopy; the counterpart of a ridge; ice keels may extend as much as 50 meters (55 yards) below sea level.

ice lens

a dominantly horizontal, lens-shaped body of ice of any dimension.

ice limit

the average position of the ice edge in any given month or period based on observations over a number of years.

ice patrol ship

a research ship which performs ice surveys in polar regions.

ice pellet

precipitation of small balls or pieces of ice (hailstones) with a diameter ranging from 5 to 50 millimeters (0.2 to 2.0 inches), or sometimes more, falling either separately or agglomerated into irregular lumps; when the diameter is less that about 5 millimeters (0.2 inch), the balls are called ice pellets.

ice piedmont

ice covering a costal strip of low-lying land backed by mountains; the surface of an ice piedmont slopes gently seawards and may be anything from 1 to 50 kilometers (0.6 to 31 miles) wide, fringing long stretches of coastline with ice cliffs; ice piedmonts frequently merge into ice shelves; a very narrow ice piedmont may be called an ice fringe.

ice prisms

a fall of unbranched ice crystals, in the form of needles, columns, or plates, often so tiny that they seem to be suspended in the air; these are visible mainly when they glitter in the sunshine (diamond dust); they may then produce a luminous pillar or other halo phenomena; this hydrometeor, which is frequent in polar regions, occurs at very low temperatures and in stable air masses.

ice quake

a shaking of ice caused by crevasse formation or jerky motion.

ice rind

a brittle, shiny crust of floating ice, formed on a quiet surface by direct freezing or from grease ice, usually in water of low salinity; thickness less than 5 centimeters (2 inches); easily broken by wind or swell, commonly breaking into rectangular pieces.

ice rise

a mass of ice resting on rock and surrounded either by an ice shelf, or partly by an ice shelf and partly by sea; no rock is exposed and there may be none above sea level; ice rises often have a dome-shaped surface; the largest known is about 100 kilometers (62 miles) across.

ice segregation

the formation of discrete layers or lenses of segregated ice in freezing mineral or organic soils, as a result of the migration (and subsequent freezing) of pore water.

ice sheet

a dome-shaped mass of glacier ice that covers surrounding terrain and is greater than 50,000 square kilometers (12 million acres) (e.g., the Greenland and Antarctic ice sheets).

ice shelf

portion of an ice sheet that spreads out over water.

ice skylight

from the point of view of the submariner, thin places in the ice canopy, usually less than 1 meter (3.3 feet) thick and appearing from below as relatively light, translucent patches in dark surroundings; the under-surface of an ice skylight is normally flat; ice skylights are called large if big enough for a submarine to attempt to surface through them (120 meters, 131 yards), or small if not.

ice stream

(1) a current of ice in an ice sheet or ice cap that flows faster than the surrounding ice (2) sometimes refers to the confluent sections of a branched-valley glacier (3) obsolete synonym of valley glaciers.

ice vein

an ice-filled crack or fissure in the ground.

ice wall

an ice cliff forming the seaward margin of an inland ice sheet, ice piedmont or ice rise; the rock basement may be at or below sea level.

ice wedge

narrow ice mass that is 3 to 4 meters (10 to 13 feet) wide at the ground surface, and extends as much as 10 meters (33 feet) down; a decrease in temperature during the winter leads to ice wedge cracks in the ground around ice wedges; during the summer, these cracks accumulate melt-water and sediment, forming pseudomorphs.

ice worm

an oligochaete worm that lives on temperate glaciers or perennial snow; there are several species that range in color from yellowish-brown to reddish-brown or black; they are usually less than 1 millimeter (0.04 inch) in diameter and average about 3 millimeters (0.1 inch) long; some eat red algae.

ice-bearing permafrost

permafrost that contains ice.

ice-bonded permafrost

ice-bearing permafrost in which the soil particles are cemented together by ice.

ice-cemented glacier

a rock glacier that has interstitial ice a meter or so below the surface.

ice-cored glacier

a rock glacier that has a buried core of ice.

ice-cored topography

topography that is due almost solely to differences in the amount of excess ice underlying its surface.

ice-nucleation temperature

the temperature at which ice first forms during freezing of a soil/water system that does not initially contain ice.

ice-rich permafrost

permafrost containing excess ice.

ice-wedge cast

a filling of sediment in the space formerly occupied by an ice wedge.

ice-wedge polygon

a polygon outlined by ice wedges underlying its boundaries.


a piece of ice that has broken off from the end of a glacier that terminates in water.
Lamplugh Glacier, in Glacier Bay Alaska, shows the terminus of a typical tidewater glacier. The terminus of the glacier is heavily crevassed and jagged, and is calving small icebergs. For scale, note the man standing on the rocks in the foreground (near the center of the photograph). This photograph was taken in 1941. (Photo courtesy of W. O. Field, archived at the World Data Center for Glaciology, Boulder, CO.)

iceberg tongue

a major accumulation of icebergs projecting from the coast, held in place by grounding and joined together by fast ice.


a harbour, inlet, etc, is said to be icebound when navigation by ships is prevented due to ice, except possibly with the assistance of an icebreaker.


part of a glacier with rapid flow and a chaotic crevassed surface; occurs where the glacier bed steepenes or narrows.
Icefalls on three parallel glaciers. (Photo courtesy of Tom Lowell, University of Cincinnati.)


a mass of glacier ice; similar to an ice cap, and usually smaller and lacking a dome-like shape; somewhat controlled by terrain.
Kalstenius Icefield, located on Ellesmere Island, Canada, shows vast stretches of ice. The icefield produces multiple outlet glaciers that flow into a larger valley glacier. The glacier in this photograph is three miles wide. (Photo courtesy of the Royal Canadian Air Force, archived at the World Data Center for Glaciology, Boulder, CO.)


a narrow fringe of ice attached to the coast, unmoved by tides and remaining after the fast ice has broken free.

Icelandic low

the low pressure center near Iceland (mainly between Iceland and southern Greenland); on mean charts of sea-level pressure, it is a principal center of action in the atmosphere circulation of the northern hemisphere.