When roping up for the glacier there are two options available:
- The standard dynamic mountaineering rope.
- Static auxiliary ropes, e.g. rad line (which are sold for glacier use as well)
There is an article in the German magazine bergundsteigen that compares both types of ropes. That concludes having a static element is not necessarily a problem as dynamic ropes have a spring or jojo effect:
Bei maximaler Seildehnung hat der Sichernde, das Gefühl den Sturz gehalten zuhaben - nur um plötzlich wie von einer Feder erneut Richtung Spalte gezogen zu werden
(At maximum rope stretch the belayer has the feeling that he was holding the fall just to get pulled towards the crevasse like pulled by a spring)
Being pulled towards the crevasse a bit however is not necessarily a bad thing. The rope will cut into the lip of the crevasse and make it easier to hold the fall.
A shock absorber as used in an absorber quick draw (e.g. ice climbing, trad climbing) will typically activate at ~2 kN and has a peak load of 3-4 kN. Unfortunately I have not been able to find any numbers for the forces involved in a crevasse fall but we can try to estimate it. Assuming a person falls with little slack on a relatively flat glacier, this is probably in the 3-4 kN range. A shock absorber probably is not reducing the load in a relevant manner. Even if it was slightly reducing the peak force...3 kN pulling at your hip unexpectedly will surely send you to hit the floor.
What can be done to protect the team?
To protect the whole team from falling into a crevasse we have some options:
- Get a big enough team. In a 2 person team the risk of the second being pulled into a crevasse is far higher than in a 4 person team.
- Keep slack to a minimum. To my observations most teams have more slack in the system than necessary.
- Use brake knots.
The rope cutting through the lip of the crevasse is a significant factor in braking a fall. [...] On a snow lip, the presence of knots in the rope is a valuable braking aid. (source: Petzl)
- Use an ice axe when walking. Using poles may be nicer to walk but only an ice axe will allow you to self-arrest
- Let the heavy guys walk at the top end. It is much easier to stop an upward pull than a downward pull.
- Use running belays if the terrain gets steeper. Basically all accidents where a whole bigger team falls into a crevasse happen on steep terrain. It is much harder to arrest a fall on steep snow than on flat snow. If the risk of pulling the whole team off the face (not only by a crevasse fall but also by a stumble) exceeds the risk of a crevasse fall, a running belay on ice screws should be used. If this is not possible, the climb should either be abandoned or everybody should go ropeless to minimize the possible damage (very frightening experience!).