Geology Reference
In-Depth Information
New ice (weakly frozen
crystals—have definite
form only while they
afloat)
Frazil
Fine spicules suspended in water.
Grease
Crystals have coagulated to form a soupy layer.
Reflects little light.
Slush
Snow mixed with water on ice surface after heavy
snowfall.
Shuga
Accumulation of spongy white ice lumps formed
from grease ice.
A few centimeters
across
Nilas
Dark Nilas
Very dark in color.
<5 mm thick
Light Nilas
Lighter in color.
>5 mm thick
Young ice
Gray
Less elastic than Nilas. Breaks on swell. Usually rafts
under pressure.
0.1-0.15 m thick
Gray‐White
Under pressure, it is more likely to ridge than to raft.
0.15-0.3 m thick
First‐year (FY) ice
Thin FY
Sea ice of not more than one winter's growth,
developing from Young ice.
0.3-0.7 m thick
Medium FY
0.7-1.2 m thick
Thick FY
>1.2 m thick
Old ice
Second‐year (SY ice)
Ice survived one summer's melt; it stands higher out
of the water.
Multiyear (MY ice)
Ice survived more than one summer's melt.
Hummocks are smoother than SY ice.
Table 2.5
Sea ice types based on ice form.
Form of Ice
Subtype
Definition
Dimension
Pancake
Predominantly circular pieces with raised rims. It may
form from nilas, shuga, or slush under a slight swell or
from gray ice under severe swell or waves of gray ice.
Ice 0.3-3 m in diameter,
up to 0.1 m in thickness
Ice floe
Small
20-100 m across
Medium
100-500 m across
Big
500-2000 m across
Vast
2-10 km across
Giant
>10 km across
Ice Breccias
Ice pieces of different stages of development frozen
together.
Brash ice
Accumulation of floating ice made up of fragments;
the wreckage of other forms of ice.
Fragments <2 m across
Fast ice
Land fast
ice
Ice that forms and remains fast along the coast directly or
indirectly through an ice wall or front. It may be formed
in situ
from water or by freezing of floating ice of any
age to shore. It may be more than 1‐year old in which
case it may be prefixed with the appropriate age
category (old, second‐year, or multi‐year).
Can extend a few meters or several
hundred kilometers from the coast
Ice foot
A narrow fringe of ice attached to the coast, unmoved by
tides. It remains after the fast ice has moved away.
Ice shelf
Fast ice higher than 2 m above sea level.
Anchor ice
Submerged ice attached or anchored to the bottom,
irrespective of the nature of its formation.
Table 2.6
Sea ice types based on ice concentration.
Concentration Level
Definition
Consolidated ice
Floating ice in which the concentration is 10/10 and the floes are frozen together.
Compact ice
Floating ice in which the concentration is 10/10 and no water is visible.
Very close pack/drift
Floating ice in which the concentration is 9/10 to less than 10/10.
Close pack/drift
Floating ice in which the concentration is 7/10 to 8/10, comprising floes mostly in contact
with one another.
Open drift
Floating ice in which the concentration is 4/10 to 6/10, with many leads and polynyas. Floes
generally not in contact with one another.
Very open drift
Ice in which the concentration is 1/10 to 3/10 and water dominates over ice.
Open water (ice free)
No ice present. If ice of any kind is present, this term shall not be used.
