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'''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 [[Belaying|belay]] system.<ref name=freedom>{{cite book|edition=7|editor=Steven M. Cox and Kris Fulsaas|title=[[Mountaineering: The Freedom of the Hills]]|publisher=The Mountaineers|isbn=0-89886-828-9|location=Seattle|year=2003}}</ref> |
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Self-arrest can be performed by using some combination of a climber's boots, hands, feet, knees, elbows, [[crampons]], and |
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]]. |
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==Self-arrest techniques== |
==Self-arrest techniques== |
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{{unreferencedsection|date=March 2013}} |
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''Cautionary note:'' |
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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. |
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''This article is not intended to provide instruction on how to perform a successful self-arrest. Its scope is merely descriptive in nature. Do not expect to be successful performing a self-arrest just by following the description in this article. Self-arrest should be learned from a qualified instructor and requires repeated practice in order to become proficient at it.'' |
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'''With an ice axe:''' |
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The most important part of the maneuver is to get into the correct self-arrest position. In this position the climber is in the [[prone position]] with feet oriented downslope, legs bent at the knees, and elbows tucked tightly against the torso. The axe is held diagonally across the chest and abdomen, with one hand tightly gripping the head of the axe and the other positioned at the base of the shaft, just above the [[Ice_axe#Components|spike]]. The head of the axe is close to the shoulder and the [[Ice_axe#Components|pick]] is buried as deeply into the slope as possible. Once in this position the climber arcs his body so that three critical points are in contact with the slope — the pick and the knees, with as much of the climber's weight as possible on the pick. |
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This maneuver is easiest when the climber falls face down and is sliding feet first down the slope. If he falls in any other position — face up, feet oriented upslope, etc. — he must first rotate his body, using the pick of the axe as a pivot point, until he is in the optimal position as described above. Self-arrest may be much more difficult to perform in such cases. |
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'''Self-arrest grip:''' |
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To be able to perform the self-arrest maneuver the pick of the ice axe should project away from the body when the hand on top of it is brought to the shoulder. To ensure that this is accomplished as fast as possible, climbers often adopt the so-called self-arrest grip. In this grip, the axe is held in the upslope hand with the tips of the fingers oriented towards the spike at the base of the shaft. The thumb is positioned over the [[Ice_axe#Components|adze]], and the pick projects out beyond the little finger. When walking or climbing with the axe held in this manner, the pick points backwards while the adze points in the direction of travel. If the axe is held pick forward, it needs to be reversed in the hand to bring it to bear against the slope. This delays the implementation of the maneuver, and can cause the climber to lose control of his axe. |
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''' While wearing crampons:''' |
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While sliding down a slope, a climber wearing crampons should keep the feet away from the slope, using the knees instead as points of contact. Putting weight on the feet while wearing crampons will cause their points to snag in the ice or snow, potentially causing significant injury to the climber's ankles and sending him/her into an uncontrolled and possibly fatal tumble down the slope. |
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'''Without an ice axe:''' |
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Without recourse to an ice axe, a skilled climber will attempt to orient his body it is in the optimal position as described above, and to put as much pressure as possible on the hands and knees, and (if not wearing crampons) toes. |
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==Effectiveness of self-arrest== |
==Effectiveness of self-arrest== |
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The likelihood of being able to self-arrest a slide is estimated to be around 50%{{cn|date=May 2014}}, and this depends on three main factors: |
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* 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. |
* 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. |
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* 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. |
* 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. |
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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 |
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. |
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* Speed in performing the maneuver: The longer the delay |
* 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. |
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==Self-arrest as a safety measure== |
==Self-arrest as a safety measure== |
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Revision as of 08:15, 21 September 2015
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