Self-arrest
Self-arrest is a technique employed in mountaineering, in which a climber who has fallen and is sliding down a snow or ice covered slope arrests the slide by themselves without recourse to a rope or other belay system.[1]
Self-arrest can be performed by using some combination of a climber's boots, hands, feet, knees, elbows, crampons, and ice axe. Use of an ice axe greatly increases the probability of effectively stopping a fall down a snow field, ice field, or glacier.
Self-arrest techniques
Widely used self-arrest techniques involve placing one's body weight on top of an ice axe to drive the head into the slope. Lack of ice axe makes the probability of successful self-arrest much lower.
Effectiveness of self-arrest
The likelihood of being able to self-arrest a slide is estimated to be around 50%[citation needed], and this depends on three main factors:
- Angle of the slope: The greater the angle of the slope, the harder it is to arrest a slide. On very steep slopes, the chance of effective self-arrest may approach zero.
- Hardness of the slope: The harder the surface of the slope the harder it is to perform self-arrest. On icy slopes (e.g., on an icefall), the pick may fail to engage the surface, or it may bounce with great force on hitting a snag making it difficult to even maintain control of the axe. Negative or neutral angle picks are considered superior by some in this regard as they have a lower tendency to snag on the ice while others maintain that they will not penetrate ice as easily as positive angle picks.
The tip of the pick of the ice axe forms a short blade. When there is positive clearance the downhill point of this blade will engage the ice first when the axe is in arrest position. With negative clearance the uphill point of the blade will engage first. On hard ice, a negative-clearance-axe will skate across the surface when attempting arrest, resulting in very little braking force. This has often resulted in very serious injury and death. A positive- clearance point will dig in aggressively, requiring skill to avoid excessive braking force but giving the climber their best chance to survive.
- Speed in performing the maneuver: The longer the delay before the climber starts to put weight on the axe's pick the longer they will freely accelerate down the slope. If the climber is slow to perform the maneuver, by the time they get into the self-arrest position their speed may be high enough to make the arrest impossible.
Self-arrest as a safety measure
Self-arrest is a measure of last recourse. In general one should not rely on self-arrest to assure safety while engaging a slope. Instead the appropriate techniques of self-belay or roped belay should be used. Mountaineering experts have suggested that use of a dynamic rope and climbing harness without intermediate protection points, as done by roped parties during glacier travel, should be avoided when travelling on terrain with a significant incline. This technique may make self-arrest almost impossible, causing the fall of a single climber to bring down the entire party.
See also
References
- ^ Steven M. Cox and Kris Fulsaas, ed. (2003). Mountaineering: The Freedom of the Hills (7 ed.). Seattle: The Mountaineers. ISBN 0-89886-828-9.
- Pit Schubert, Sicherheit und Risiko in Fels und Eis Band 1 (7th edition), Bergverlag Rother (2005), ISBN 3-7633-6016-6