PACK ICE 
445 
bottom on shallow shores and remains fixed to the land 
during the winter, being separated by the working tide 
crack from the fast sea ice beyond. 
Pack Ice 
Pack ice, in distinction to fast ice, is not bound to the 
shore, but moves under the influence of local currents 
and wind. In the Antarctic, pack ice is evidently seldom 
formed at sea and largely consists of fast ice which has 
been broken away and carried off to sea by blizzards or 
some such transporting agent. The pack extends in 
normal years in December from about 66° to 71° S. Lat., 
a distance of 300 miles from north to south, and at times 
evidently fills the whole width of the Ross Sea. 
Pack may be heavy or light, closed or open — the latter 
conditions being entirely dependent on local winds and 
currents. Thus heavy pack if open may offer no in- 
superable bar to navigation, whereas in closed pack, 
whether heavy or light, little progress can be made by 
ships. Heavy pack is usually associated with hummocks 
or pressure ridges rising to a height of four or five feet 
above the general level of the floe. These hummocks 
and pressure ridges are called upon to furnish ice for 
cooking and other purposes in the pack, being com- 
paratively free from salt, owing, as mentioned previously, 
to the fact that the salt in the ice goes into solution and 
drains away, whenever the temperature rises above zero. 
Towards the end of February the Ross Sea becomes 
comparatively free of pack and offers no bar to navigation. 
