Ice diving...
Is a type of penetration diving where the dive takes place under ice.
Because diving under ice places the diver in an overhead environment
typically with only a single entry/exit point, it is considered an advanced
type of diving requiring special training (although whether it constitutes
technical diving is part of a wider debate within the diving community).
Ice divers are generally tethered for safety. This means that the diver
wears a special harness under the scuba unit. A line is secured to this
harness, and the other end of the line is secured above the surface by
one of a number of methods.
The diver also can use a weight harness, integrated weight buoyancy
control device, or a weight belt with two buckles on it so the weights can
not be accidentally released which would cause a run-away ascent into
the ice sheet.
Ice diving is a team diving activity because the divers line requires a
line tender. This person is responsible for paying out and taking in line
so that the diver does not get tangled. Communication to the diver, or to
the surface, is accomplished by pulling on the line. Each series of tugs
means a different thing. There is a diver suited up and ready to enter the
water at a moment's notice. This diver is a safety diver, and has his own
tender. His purpose is to assist the primary diver in the event of a
problem.
Divers who do not use a tether require extra training and full
redundant scuba systems.