Crevasse rescue is a technique that occupies a lot of time in mountaineers minds. However the chances of a climber falling so completely into a crevasse that they need to be hauled out are mercifully small. In the vast majority of cases a tight rope and a breathless scramble has most folk back on the surface.
In a worst case scenario there are 3 clear stages to rescuing someone
There are a huge variety of techniques and pieces of equipment designed for crevasse rescue. At a very basic level a glacial travel kit should include the following.
Pullys and ascenders all make rescues easier but increase the weight that must be carried and the complexity of any solutions
There are two main hositing systems both with their own advantages and disadvantages
UNASSISTED HOIST (3:1 ratio)
With this system a casulaty weighing 90kg would require a pull of 30kg to rescue them (removing friction from the equation. However to raise them 1 meter would require taking in 3 meteres of rope.
ASSISTED HOIST (3:1 ratio)
A very useful variation if your casulaty is concious, able to help and typically not more than 10m below the surface. The system is identical to the Unassisted Hoist apart from the attachment point for the loop of spare rope.
6:1 RATIO HOIST
If more force is required it is possible to add a 2:1 system to both the Unassisted and Assisted hoists to increase the ratio to 6:1. This requires an additional karabiner and Prussick Loop