DEFORMATION PROCESSES

and run together under the influence of wind,

4.4.10 Iceberg tongue: cf. 10.4.2.3.

swell or current.

4.4.6 BIGHT: An extensive crescent-shaped indenta-

5. PACK-ICE MOTION PROCESSES

tion in the ice edge, formed by either wind or

5.1 Diverging: Ice fields or floes in an area are sub-

current.

jected to diverging or dispersive motion, thus re-

4.4.7 ICE JAM: An accumulation of broken river ice or

ducing ice concentration and/or relieving stresses

sea ice caught in a narrow channel.

in the ice.

4.4.8 ICE EDGE: The demarcation at any given time

5.2 Compacting: Pieces of floating ice are said to be

between the open sea and sea ice of any kind,

compacting when they are subjected to a converg-

whether fast or drifting. It may be termed com-

ing motion, which increases ice concentration and/

pacted or diffuse (cf. ice boundary).

or produces stresses which may result in ice de-

formation.

4.4.8.1 Compacted ice edge: Close, clear-cut ice edge

compacted by wind or current; usually on the

5.3 Shearing: An area of pack ice is subject to shear

windward side of an area of pack ice.

when the ice motion varies significantly in the

direction normal to the motion, subjecting the ice

4.4.8.2 Diffuse ice edge: Poorly defined ice edge lim-

to rotational forces. These forces may result in

iting an area of dispersed ice; usually on the

phenomena similar to a flaw (q.v.).

leeward side of an area of pack ice.

4.4.8.3 Ice limit: Climatological term referring to the

6. DEFORMATION PROCESSES

extreme minimum or extreme maximum ex-

tent of the ice edge in any given month or pe-

6.1 Fracturing: Pressure process whereby ice is per-

riod based on observations over a number of

manently deformed, and rupture occurs. Most

years. Term should be preceded by minimum

commonly used to describe breaking across very

or maximum (cf. mean ice edge).

close pack ice, compact pack ice and consolidated

pack ice.

4.4.8.4 Mean ice edge: Average position of the ice

edge in any given month or period based on

6.2 Hummocking: The pressure process by which sea

observations over a number of years. Other

ice is forced into hummocks. When the floes ro-

terms which may be used are mean maximum

tate in the process it is termed screwing.

ice edge and mean minimum ice edge (cf. ice

limit).

6.3 Ridging: The pressure process by which sea ice

is forced into ridges.

4.4.8.5 Fast-ice edge: The demarcation at any given

time between fast ice and open water.

6.4 Rafting: Pressure processes whereby one piece

of ice overrides another. Most common in new

4.4.9 ICE BOUNDARY: The demarcation at any given

and young ice (cf. finger rafting).

time between fast ice and pack ice or between

6.4.1 FINGER RAFTING: Type of rafting whereby inter-

areas of pack ice of different concentrations (cf.

locking thrusts are formed, each floe thrusting

ice edge).

"fingers" alternately over and under the other.

4.4.9.1 Fast-ice boundary: The ice boundary at any

Common in nilas and grey ice.

given time between fast ice and pack ice.

6.5 Weathering: Processes of ablation and accumu-

4.4.9.2 Concentration boundary: A line approximat-

lation which gradually eliminate irregularities in

ing the transition between two areas of pack

an ice surface.

ice with distinctly different concentrations.