Firn anchor
A snow protection or snow anchor (in some constructions also Firnhaken ) is a device that when mountain climbing for producing a fixed point , in particular in steep corn snow is used. It essentially consists of a metal anchor and a cable, at the end of which is secured .
Construction methods
Firn anchors are mostly made of light metal (e.g. aluminum). For soft snow, wide, shovel-like angled sheets (approx. 200 grams) with a large surface are used. However, their holding power is often judged to be insufficient.
For harder, firm firn, T or V profiles are used, and more rarely also U profiles, which can be hammered or hammered deeply through layers of ice with a hammer or ice ax . Such models are also known as firn hooks . They are usually about 60 to 80 centimeters long and weigh 300 to 400 grams. To increase the holding force, they are sometimes equipped with barbs that make it difficult to slide out. The disadvantage that such devices have to be unpacked to remove them is less significant here, as they are mainly used for anchoring fixed ropes during expedition mountaineering .
After the steel cable has been attached, a distinction is made between top clip (cable at the top ) and mid clip (cable in the middle of the anchor). The top clip attachment has the advantage of being easy to attach, as the cable does not have to be buried in the snow. The mid-clip design is safer, however, as this results in an even distribution of force and the anchor is less likely to tear out of the snow under load. On the contrary, if correctly attached, a mid-clip firn anchor will even be pulled deeper into the snow under load.
use
Firn anchors can be used both as standing position and as intermediate securing.
Compared to a T-anchor , firn anchors often have the advantage of saving a lot of time, and no ice ax that is otherwise required is buried. The holding forces of the firn anchor can correspond to those of a T-anchor with optimal attachment. Compared to the pick ax , an ice ax rammed vertically into the snow cover, the firn anchor has far greater holding forces due to its larger area.
A firn anchor must be created specifically for a specific direction of loading. Correct driving into the snow (as deep as possible, correct angle) is essential so that the anchor can hold under load. If the angle is too large, i.e. close to 90 ° to the snow surface, the anchor can be pulled out upwards; if the angle is too small, the load point is not deep enough and the anchor can be pulled out downwards. Usually an angle of around 65 ° is recommended. With mid-clip anchors and a sufficiently long cable, there is a resultant force that drives the anchor even deeper into the snow.
As with all other fixed points in snow and firn, the reliability can be increased by loading with the body weight (sitting or standing on the device), as this also prevents sliding out. The holding force can also be improved by placing the snow in a depression or step and solidifying it.
literature
- Gottlieb Braun-Elwert: Snow Stake . In: German Alpine Association , Austrian Alpine Association , Alpine Association South Tyrol , Swiss Alpine Club (publisher): bergundstieg . tape 08 , no. 2 . Innsbruck 2008.
- Gottlieb Braun-Elwert: Belays on snow . In: Craven Mountaineering Club (ed.): CMC News . tape 6 , no. June 3 , 1985 ( alpinerecreation.com [PDF; accessed January 5, 2009]).
- Walter Würtl: Firn stand construction site . In: German Alpine Club , Austrian Alpine Club , Alpine Club South Tyrol , Swiss Alpine Club (ed.): Bergundsteiger . tape 05 , no. 1 . Innsbruck 2005 ( bergundstieg.at [PDF; accessed on January 5, 2005]).
- Pit Schubert , Pepi Stückl: Safety on the mountain . Equipment, fuse. In: German Alpine Association, Association of German Mountain and Ski Guides (ed.): Alpine curriculum . tape 5 . BLV, Munich 1999, ISBN 3-405-14825-1 , p. 105 .