Slide block

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A slip block or slip wedge is a test used to assess the risk of slab avalanches on mountain slopes. In combination with a snow profile , statements about the stability of the snow cover are obtained.

execution

Slip block : An avalanche shovel is used to uncover a 2 m long (parallel to the slope) and 1.5 m wide block of snow down to the ground, so that only its uphill side is connected to the snow cover. The snow profile can be created at the front. At the back, the slip block is cut off with an accessory cord . The snowpack stability is very weak if the sliding block comes loose when cutting with the cord, when approaching from above or when digging. Then the block is entered by an average heavy person with skis (or the sports equipment used on the slope). After a while there is light bobbing. If the block comes off like a slab of snow , the stability is weak. Weak to moderate stability is given when the block loosens in a series of jumps that are performed increasingly faster and more intensely. The last test is a jump from topless without skis - only in ski boots . If the block only now comes loose, the danger of avalanches is low. The type of fracture surface also allows important conclusions to be drawn: the more stepped it is, the safer the snowpack is; A smooth fracture point, on the other hand, indicates easier propagation of the fracture and thus greater danger.

Alternatively, a triangular segment is cut out of the snow cover in the case of the sliding wedge . For this purpose, an avalanche probe is rammed into the snow to deflect it and a cord is stretched around it. With this the wedge is sawed free. The load is applied in stages, as with the slip block. The wedge method takes less time than the square block and is also the more accurate method.

A simplified variant is the small block test : Here a 40 x 40 cm block is exposed. The strength is checked by tapping the avalanche shovel sideways from top to bottom. This method is less meaningful than the standardized sliding block or wedge, but it is easier and faster to perform.

A slide block is created at regular intervals, on different slopes, in locations typically exposed to weather (especially wind and sun) and at a point with an average slope in order to be able to make a statement about the avalanche situation in the area.

history

For a long time, the slide block was considered to be a suitable method for assessing the avalanche danger for individual skiers. However, the method is based on the assumption of a relatively homogeneous snowpack, since the strength of the snowpack at a certain location is used to determine the strength of the entire area. However, this assumption is no longer tenable due to recent avalanche knowledge, the snowpack is now considered to be extremely inhomogeneous, so that the stability at individual points can only be generalized inadequately. This realization prevailed after a tragic event in Switzerland, when two men died in an avalanche after putting on a sliding wedge: The sliding wedge had held up even under the highest load, but the entire slope around the (still standing) wedge had come loose and the men buried.

Furthermore, it is now assumed that simpler and faster methods of risk assessment are more suitable for individual winter sports enthusiasts. Although the slide block is largely discredited as a basis for individual decisions, it has retained a certain validity as a method of assessing the regional hazard potential (e.g. for preparing an avalanche report ) and as a didactic method.

literature

  • Werner Munter : 3x3 avalanches - making decisions in critical situations . Pohl & Schellhammer, Garmisch-Partenkirchen 1999, ISBN 3-00-002060-8 .
  • Jürg Schweizer: The Rutschblock Test - Procedure and Application in Switzerland . In: The Avalanche Review . tape 20 , no. 5 , 2002, p. 14–15 ( slf.ch [PDF; accessed on February 29, 2008]).

Web links

swell

  1. ^ Georg Kronthaler / Bernhard Zenke: mountaineering . Ed .: German Alpine Club / Austrian Alpine Club / Swiss Alpine Club . No. 4 . Innsbruck 2006, p. 56-64 .