In reply to RyanOsborne:
> Would a better option be to tie the knots at a closer distance (say 1-1.5m) so that the person in the crevasse could use them to climb back out to the surface, instead of using prussiks? i.e. clip a sling to the knot tied above you, step up into the sling, clip your harness to the knot, then repeat.
It doesn't sound entirely unreasonable although the only person I know who has really fallen into a crevasse (incidentally expect, he says, to fall about 8m in even with a tight rope etc.) found that the rope cut in a long way at the lip. I suspect this might make climbing out on loops tricky.
jon, who may appear shortly, mentioned an interesting system a while ago where you tie on with knots on one strand of the rope spaced say 15m while the other strand is longer, say 30m, with no knots. Each climber carries coils of the longer strand to keep it out of the way. The knotted strand helps stop any fall while the unknotted one can be used for hoisting etc. Makes sense to me.