ICE TERMS
The following glossary provides definitions in general use for
the many kinds of ice encountered at sea. The terms are based on
the nomenclature established by the World Meteorological
Organization (WMO)
Anchor ice
Submerged ice attached or anchored to the bottom, irrespective
of its formation
Bare ice
Ice without snow cover
Brash ice
Accumulations of floating ice made up of fragments not more than
2m wide
Close pack ice
Pack ice in which the concentration is seven-tenths to
eight-tenths, composed of floes mostly in contact
Compacted ice edge
Close, clear-cut ice edge compacted by wind or current, usually
on the windward side of an area of pack ice
Compact pack ice
Pack ice in which the concentration is ten-tenths and no water
is visible
Consolidated pack ice
Pack ice in which the concentration is ten-tenths and the floes
are frozen together
Crack
Any fracture of fast ice, consolidated ice, or a single floe
that has been followed by a separation ranging from a few
centimeters to 1m
Deformed ice
A general term for ice that has been squeezed together and in
places forced upwards (and downwards). Subdivisions are rafted ice,
ridged ice and hummocked ice
Diffused ice edge
Poorly defined ice edge limiting an area of dispersed ice,
usually on the leeward side of ice
Dried ice
Sea ice from the surface of which melt water has disappeared
after the formation of cracks and thaw holes. During the period of
drying, the surface whitens
Fast ice
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 or grounded icebergs. Vertical fluctuations may be observed
during changes of sea level. Fast ice may be formed in situ (in its
original place) from seawater or by freezing of drift ice of any
stage to the shore. It may extend a few meters or several hundred
kilometers from the coast. Fast ice may be more than one year old
and may then be prefixed with the appropriate age category
(second-year or multi-year). If it is thicker than about 2m above
sea level, it is called an ice shelf
Fast ice boundary
The ice boundary at any given time between fast ice and drift
ice
Fast ice edge
The demarcation at any given time between fast ice and open
water
Finger rafted ice
Type of rafted ice in which floes thrust ‘fingers’ alternately
over and under the other
First-year ice
Sea ice of not more than one winter’s growth developing from
young ice. It has a thickness of from 30 centimeters to 2m and may
be subdivided into thin first-year ice/white ice, medium first-year
ice, or thick first-year ice
Floating ice
Any form of ice found floating in water. The principal kinds of
floating ice are lake ice, river ice and sea ice, which form by the
freezing of water at the surface, and the glacier ice (ice of land
origin), which is formed on land or on in an ice shelf. The concept
includes ice that is stranded or grounded
Floe
Any relatively flat piece of sea ice 20m or wider. Floes are
subdivided according to horizontal extent. Giant, over 10km wide;
vast, 2 to 10km wide; big, 500 to 2,000m wide; medium, 100 to 500m
wide; and small, 20 to 100m wide
Flooded ice
Sea ice that has been flooded by melt water or river water and
is heavily loaded by water and wet snow
Frazil ice
Fine spicules or plates of ice suspended in water
Friendly ice
From the point of view of the submariner, an ice canopy
containing many large skylights or other features which permit a
submarine to surface. There must be more than ten such features per
30 nautical miles (56km) along the submarine’s track
Glacier ice
Ice in, or originating from, a glacier, whether on land or
floating in the sea as icebergs, berg bits or growlers
Grease ice
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 light, giving the sea a matte appearance
Grey (gray) ice
Young ice 10 to 15 centimeters thick. Less elastic than nilas
and breaks on swell. Usually rafts under pressure
Grey (gray)-white ice
Young ice 15 to 30 centimeters thick. Under pressure more likely
to ridge than to raft
Grounded ice
Floating ice which is aground in shoal water (see ‘stranded
ice’)
Hostile ice
From the point of view of the submariner, an ice canopy
containing no large skylights or other features which permit a
submarine to surface
Hummocked ice
Sea ice piled haphazardly one piece over another to form an
uneven surface. When weathered, it has the appearance of smooth
hillocks
Iceberg
A massive piece of ice of greatly varying shape, protruding more
than 5m above sea level, which has broken away from a glacier. May
be afloat or aground. Icebergs may be described as tabular,
dome-shaped, sloping, pinnacled, weathered or glacier bergs
Ice blink
A whitish glare on low clouds above an accumulation of distant
ice
Ice bound
A harbor, inlet, etc., is said to be ice-bound when navigations
by ships is prevented on account of ice, except possibly with the
assistance of an icebreaker
Ice boundary
The demarcation at any given time between fast ice and drift ice
or between areas of drift ice of different concentrations (see ‘ice
edge’)
Ice breccia
Ice of different stages of development frozen together
Ice cake
Any relatively flat piece of sea ice less than 20m wide
Ice canopy
Drift ice from the point of view of the submariner
Ice cover
The ratio of an area of ice of any large concentration to the
total area of sea surface within some large geographic locale; this
locale may be global, hemispheric or prescribed by a specific
oceanographic entity such as Baffin Bay, or the Barents Sea
Ice edge
The demarcation at any given time between the open sea and sea
ice of any kind, whether fast or drifting. It may be termed
compacted or diffuse (see ‘ice patch’)
Ice field
Area of floating ice that is greater than 10km wide and which
consists of any size of floes (see ‘ice patch’)
Ice foot
A narrow fringe of ice attached to the coast, unmoved by tides
and remaining after the fast ice has moved away
Ice-free
No sea is present. There may be some ice of land origin present
(see ‘open water’)
Ice front
The vertical cliff forming the seaward face of an ice shelf or
other floating glacier varying in height from 2 to 50m or more
above sea level (see ‘ice wall’)
Ice island
A large piece of floating ice protruding about 5m above the sea
level which has broken away from an Antarctic ice shelf, having a
thickness of from 30 to 50m, and an area of from a few thousand
square meters to 500 square kilometers or more. Usually
characterized by a regularly undulating surface which gives it a
ribbed appearance from the air
Ice jam
An accumulation of broken river ice or sea ice caught in a
narrow channel
Ice keel
From the point of view of the submariner, a downward projecting
ridge. Ice keels may extend as much as 50m below the sea level
Ice limit
Climatological term referring to the extreme minimum or maximum
extent of the ice edge in any given month or period based on
observations over a number of years. Term should be preceded by
minimum and maximum (see ‘mean ice edge’)
Ice massif
A variable accumulation of close or very close drift ice (pack
ice) covering hundreds of square kilometers which is found in the
same regions every summer
Ice of land origin
Ice formed on land or in an ice shelf, found floating in water.
The concept includes ice that is stranded or grounded
Ice patch
An area of pack ice less than 10 kilometers wide
Ice port
An embayment (indentation) in an ice front, often of a temporary
nature, where ships can moor alongside and unload directly onto the
ice shelf
Ice rind
A brittle shiny crust of ice formed on a quiet surface by direct
freezing or formation of grease ice, usually in water of low
salinity. Thickness to about 5cm. Easily broken by wind or swell,
commonly breaking in rectangular pieces
Ice shelf
A floating ice sheet of considerable thickness showing 2 to 50m
or more above sea level, attached to the coast. Usually of great
horizontal extent and with a level or gently undulating surface.
Nourished by annual snow accumulation and often also by the seaward
extension of land glaciers. Limited areas may be aground. The
seaward edge is termed an ice front
Ice stream
Part of an inland ice sheet in which the ice flows more rapidly
and not necessarily in the same direction as the surrounding ice.
The margins are sometimes clearly marked by a change in the
direction of the surface slope, but may be indistinct
Ice under pressure
Ice in which deformation processes are actively occurring and
therefore a potential impediment or danger to shipping
Ice wall
An ice cliff forming the seaward margin of a glacier that is not
afloat. An ice wall is aground, the rock basement being at or below
sea level (see ‘ice front’)
Lake ice
Ice formed on lake, regardless of observed location
Level ice
Sea ice which is unaffected by deformation
Mean ice edge
Average position of the ice edge in any given month or period
based on observation over a number of years. Other terms that may
be used are the mean maximum ice edge and mean minimum ice edge
(see ‘ice limit’)
Medium first-year ice
First-year ice 70 to 120 centimeters thick
Medium ice field
An ice field 15 to 20 kilometers wide
Multi-year ice
Old ice up to 3m or more thick that has survived at least two
summers’ melt. Hummocks even smoother than in second-year ice, and
the ice is almost salt-free. Color, where bare, is usually blue.
Melt pattern consists of large interconnecting irregular puddles
and a well-developed drainage system
New ice
A general term for recently formed ice which includes frazil
ice, grease ice, slush and shuga. These types of ice are composed
of ice crystals which are only weakly frozen together (if at all)
and have a definite form only while they are afloat
Old ice
Sea ice which has survived at least one summer’s melt, thickness
up to 3m or more. Most topographic features are smoother than on
first-year ice. May be subdivided into second-year ice and
multi-year ice
Open ice
Floating ice in which the concentration is four-tenths to
six-tenths with many leads and polynyas, and the floes are
generally not in contact with each other
Pack ice
Concentration of seven-tenths or more of drift ice (see ‘drift
ice’). (The term was formally used for all ranges of
concentration
Pancake ice
Predominantly circular pieces of ice from 30 centimeters to 3m
in diameter. Up to about 10m in thickness with raised rims due to
the pieces striking up 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, or grey ice. It also sometimes forms at some depth, at an
interface between water bodies of physical characteristic, from
where it floats to the surface. Its appearance may rapidly cover
wide areas of water
Puddle
An accumulation of melt water on ice, mainly due to the melting
of snow, but in more advanced stages also to the melting of ice.
Initial stage consists of patches of melted snow
Rafted ice
Type of deformed ice formed by one piece of ice overriding
another (see ‘finger-rafting’)
Ridged ice
Ice piled haphazardly one piece over another in the form of
ridges or walls. Usually found in first-year ice (see
‘ridging’)
River ice
Ice formed on a river, regardless of observed location
Rotten ice
Sea ice which has become honeycombed and which is in advances
stages of disintegration
Sea ice
Any form of ice found at sea which has originated from the
freezing sea water
Shore ice ride-up
A process by which ice is pushed ashore as a slab
Shuga
An accumulation of spongy white ice lumps, a few centimeters
wide; they are formed from grease ice or slush and sometimes from
anchor ice rising to the surface
Skylight
From the point of view of the submariner, thin places in the ice
canopy, usually less than 1m thick and appearing from below as
relatively light, translucent patches in dark surroundings. The
under face of a skylight is normally flat. Skylights are called
large if big enough for a submarine to attempt to surface through
them (120m), or small if not
Slush
Snow that is saturated and mixed with water on land or ice
surfaces, or as a viscous floating mass in water after a heavy
snowfall
Stranded ice
Ice which has been floating and has been deposited on the shore
by retreating high water
Water sky
Dark streaks on the underside of low clouds, indicating the
presence of water features in the vicinity of sea ice
White ice
(See ‘thin first-year ice’/‘white ice’)
Young ice
Ice in the transition stage between nilas and first-year ice, 10
to 30 centimeters thick. May be subdivided into gray ice and
gray-white ice
Source: Sailing Directions (Planning Guide & Enroute)
Antarctica, 2002, National Imagery and Mapping Agency (NIMA),
Bethesda, Maryland, ISBN: 1-57785-358-X
*
Antarctica A Voyage Towards South
Pole