Artificial avalanche release

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Avalanche explosion with a mortar near the Bernina Railway , 1967
Control and equipment container for a "GasEx" avalanche triggering system in Austria

An artificial avalanche triggering (also: controlled avalanche triggering , English : artificial avalanche triggering , French : déclenchement artificiel d'avalanche ) is the triggering of an avalanche with artificial means at a specified time .

An artificial or controlled avalanche release is carried out with technical devices with which the dangers of a large snow avalanche as a harmful avalanche can be reduced or avoided. The unwanted or uncontrolled avalanche release (e.g. due to the eruption of cornices ) on a large scale may be considered a natural disaster , but it can also occur on a small scale, e.g. B. trigger relevant hazards up to death in a roof avalanche . Artificial (controlled) avalanche triggering is one of the temporary avalanche protection measures that can be implemented and deployed at short notice and are tailored to the time, place and extent of the avalanche danger. Whether and when an avalanche is triggered in a controlled manner is decided on the basis of avalanche warning, situation observation, prognosis and reports (risk assessment for the triggering of an avalanche). B. a local avalanche commission or other bodies. The controlled release of avalanches can be accompanied by other measures, such as B. Blocking roads / road sections, slopes, ski areas, etc. or through temporary evacuations .

Reasons for the controlled release of avalanches

In principle, permanent avalanche protection measures (e.g. in the form of avalanche barriers, dams, galleries, tunnels, etc.) take precedence over temporary avalanche protection measures and are usually more effective. The non-application of permanent avalanche protection measures can have various reasons (examples):

  • limited financial resources for traditional protective measures
  • Avoiding major interventions in nature
  • economic and political pressure to keep certain regions and roads open,
  • Technical development has opened up alternatives to permanent avalanche protection measures through temporary avalanche protection measures.

Aims of controlled avalanche release

Temporary avalanche protection measures can be used as a substitute for permanent avalanche protection measures if the relevant principles are observed, if this is justifiable in individual cases (especially in the case of existing facilities) or if it makes sense to supplement the permanent avalanche protection measures. Even permanent avalanche protection measures do not create absolute and continuous safety everywhere according to the long-term avalanche expertise with avalanche barriers. Any residual hazards can be minimized with temporary avalanche protection measures.

The aim of the controlled release of avalanches is to prevent or reduce the dangers of an uncontrolled avalanche on people or property if other measures (stabilization of the snow cover through, for example, slope preparation , retention of the snow masses, e.g. through avalanche barriers, etc.) are not possible are or are no longer sufficient.

The target objects of the controlled release of avalanches are usually uninhabited but economically used areas (e.g. ski slopes, road sections, parking lots, etc.). In Austria, inhabited areas are secured with controlled avalanche releases only in rare exceptions, in Switzerland, however, in individual cases.

Avalanche release

Controlled avalanche release options

The controlled triggering of smaller, less dangerous avalanches is intended to prevent large avalanches, which could cause correspondingly great damage and go off in an uncontrolled manner. Various technical options are available for the controlled artificial release of avalanches (examples):

The advantage of the stationary systems is that they are largely independent of the weather and the time of day and that they are safe for the people involved, as remote triggering (e.g. by radio) and avalanche triggering above the snow cover is usually possible (which means that the triggering pressure is more efficient). The disadvantage of stationary systems for triggering avalanches is the limited scope of application and the limited possibility of reacting to changed situations and the avalanche triggering systems can be endangered or damaged by avalanches themselves. The investment costs are usually higher for stationary systems than for mobile avalanche releases, which are only used depending on the situation.

The advantages and disadvantages of mobile systems are mostly the opposite of those of stationary systems.

In the European Union , the controlled release of avalanches must usually be carried out in such a way that the greatest possible degree of safety can be ensured for the people involved when the avalanche is released ( employee protection ). Driving a person into a blanket of snow to trigger a small avalanche by the skier cutting the unstable blanket of snow at an upper, supposed break-up zone, is very risky, even if the skier is secured with a rope or an avalanche airbag, etc. not suitable for employee protection. Other methods of triggering an avalanche through direct mechanical stress are also sometimes very risky.

The suitability of the respective technical possibility for the controlled release of avalanches basically depends on the protected asset and must be determined on a case-by-case basis, as every system has advantages and disadvantages. Failure to trigger an avalanche can also have significant disadvantages.

Requirements for a positive controlled avalanche release

There is a positive, controlled avalanche release:

  • if the avalanche is successful or
  • solidification of the snow cover or
  • it can be determined that there is no unstable snowpack.

The positive success of an avalanche release depends, depending on the circumstances, on:

  • Location of the trigger point,
  • Time of release,
  • Weather conditions and solar radiation,
  • Strength of the trigger impulse (e.g. mass of the explosive charge - the larger the charge, the larger the effective radius),
  • Height of the trigger point (trigger pressure) above the snow surface (the greatest effect is a trigger pulse 0.5 to 3 meters above the snow cover).

Positive releases of avalanches during explosions can be achieved on average:

  • Over snow explosion: 70 to 90%
  • Surface cracking: 60%
  • Blasting in snow (under the snow cover): 30 to 50%.

Negative avalanche release

A negative avalanche release may exist if:

  • Secondary avalanches are triggered or previously relatively stable areas become unstable due to the trigger pressure of the main avalanche,
  • the path of the main avalanche is deflected in an uncontrolled manner,
  • Main avalanche and secondary avalanche together trigger a major avalanche with a damaging event,
  • The main avalanche was not triggered, but a spontaneous departure cannot be ruled out.

Uncontrolled avalanche release

Uncontrolled avalanche releases occur e.g. For example, by humans (eg. B. variation skiers , hikers , etc.) or animals in the area of the first opening region of a snow board , demolition of snowdrifts, self-triggering a labile snow etc.

The uncontrolled triggering of avalanches can also lead to secondary triggering of avalanches in completely different areas. B. trigger a harmful avalanche.

Trigger time

Choosing the right time to trigger an avalanche is essential for success. An avalanche is the safest way to trigger an avalanche shortly after a significant snowfall or wind movement, because the snowpack has not yet stabilized. If the avalanche were triggered too late, there is a risk of too much snow moving and a damaging avalanche. Attention must also be paid to the slope and orientation of the slope. The flatter it is, the more fresh snow is required to trigger an avalanche. An avalanche should be triggered earlier on a slope with strong sunlight than on a shadowy slope.

Release height

A 2 kg load of explosives can have the following effects:

Explosion point
height		 Radius zone of
action		 Radius
break resistance
Snowmobiles
sprengung 		100% 80 meters
Surface
demolition 		40 to 50% 40 meters
Blasting under
the blanket of snow 		10 to 20 % <20 meters

Avalanche detection

The success of the controlled avalanche release as well as the monitoring of uncontrolled avalanche releases can, if a visual inspection is not possible or reasonable, be monitored by an avalanche detection system (e.g. avalanche radar , infrasound system , seismometer , pull cords etc.) and this can also be a Trigger an alarm (e.g. traffic lights on streets).

In any case, it must be checked whether the avalanche has been triggered and to what extent.

documentation

With every controlled avalanche release, it is essential to document success, failure or secondary events that have occurred. The documentation is, for example, the basis for further controlled avalanche releases, the development and content of a safety and deployment concept, determination of local features and the size of the avalanche, avalanche release method and improvement measures, determination of future release points in the area, necessary barrier measures and plans or evacuation measures , Occurrence of secondary avalanches, possible further consequences of damage, necessary communication measures, etc.

Legal requirements and consequences of controlled avalanche release

In Austria, the basic course for blasting officers is required to carry out blasting work and advanced courses for z. B. Avalanche blasting work by hand or from a helicopter. Only the training on avalanche blasting from a helicopter has to be refreshed again and again. These courses are offered in Austria by private institutions and the exams are held. In Switzerland, the Avalanche Explosion Certificate is required to carry out avalanche blasting work , which is issued by the State Secretariat for Education, Research and Innovation (SERI, formerly: Federal Office for Professional Education and Technology, OPET) to graduates of the avalanche blasting course of the Swiss Cableways (SBS) after passing the exam becomes. In Switzerland, the training must be repeated every five years.

The controlled (artificial) triggering of avalanches requires the greatest care on the part of the people involved. A breach of the duty of care (usually when a damaging event occurs and afterwards - assessed ex post ) can

  • administrative law
  • civil and
  • criminal

Have consequences for the acting person and / or the commissioning company or the responsible authority . The controlled release of avalanches may therefore generally only be carried out by specially trained specialists who also have the necessary technical aids and have sufficient local knowledge. A particularly strict standard of care must therefore be applied to persons who are authorized and appointed to perform avalanche explosions due to their special expertise ( expert liability ).

See also

Web links

Commons : Avalanche protection  - collection of images, videos and audio files

literature

Individual proof

  1. ↑ See: Technische Regel (Austria) ONR 24805: 2010 (permanent technical avalanche protection - names and definitions as well as static and dynamic effects).
  2. ↑ According to Section 99, Paragraph 2 of the Austrian Forestry Act (Federal Law Gazette No. 440/1975), avalanche means snow masses that occur when falling rapidly on steep slopes, ditches, etc. Ä., as a result of the kinetic energy or the air pressure wave caused by them or their deposition can cause danger or damage .
  3. ↑ See e.g. For Austria, for example, the “Avalanche Decrees”, which have been revised several times by the responsible Federal Ministry in Austria (1975, 1996, 2001, 2011). See: Decree of the Federal Minister for Transport, Innovation and Technology regarding avalanche protection in the area of ​​cable cars (Avalanche Decree 2011) . In Switzerland: Practical help No. 53: Artificial avalanche release (2001, SLF Davos), legal and insurance issues in the event of artificial avalanche release (2004, FOEN), practical help for work in the avalanche service: organization, assessment of local avalanche risk, documentation (2007, SILS, SLF, FOEN), artificial release of avalanches above settlements (Praxishilfe 2009, FOEN).
  4. ↑ Mag. Marianne Fritz: Avalanche protection newly regulated Federal Ministry for Transport, Innovation and Technology (bmvit).
  5. ↑ Anja Brucker: Artificial release of avalanches to secure traffic routes in Austria - status quo and assessment from the point of view of experts, pp. 62 f, 89 f.
  6. ↑ a b Lukas Stoffel: Artificial Avalanche Release , Tec 21, Volume 131, 9/2005, p. 5.
  7. ↑ Christoph Skolaut, Florian Rudolf-Miklau: Current state of knowledge about the use of artificial avalanche triggering in Austria in State of the Art for Artificial Avalanche Triggering , July 2014.
  8. ↑ a b See e.g. E.g .: Artificial avalanche release - Implementation Aid 02 for the technical guideline for torrent and avalanche control LE.3.3.5 / 0004-IV5 / 2006 as amended, Federal Ministry of Agriculture, Forestry, Environment and Water Management, Vienna, December 16, 2015.
  9. ↑ Formerly sold by Doppelmayr under the term “avalanche organ”.
  10. ↑ Use, for example, in Switzerland and the USA , not permitted in Austria.
  11. ↑ Gebhard Walter: Artificial release of avalanches , torrent and avalanche control (Austria), p. 6.
  12. ↑ Anja Brucker: Artificial release of avalanches to secure traffic routes in Austria - status quo and assessment from the perspective of experts, p. 36.
  13. ↑ a b Lukas Stoffel: Comparison of the blasting methods: Gazex, Avalanche Guard / Mast Innauen-Schätti, Wyssen Sprengmast, Avalancheur , Davos 2013, Institute for Snow and Avalanche Research (SLF). Kogelnig / Sauermoser: Securing roads with artificial avalanches (pilot project Großtallawine) , in: Journal for torrent, avalanche, erosion and rockfall protection , 2013.
  14. ↑ a b Lukas Stoffel: Davos Artificial Avalanche Release: Explosive Effect, Methods, Benefits, Problems , WSL Institute for Snow and Avalanche Research SLF, Innsbruck 2010.
  15. ↑ Lukas Stoffel: Comparison of the blasting methods: Gazex, Avalanche Guard / Mast Inauen-Schätti, Wyssen Sprengmast, Avalancheur , Comparison of methods for artificial avalanche release, WSL Institute for Snow and Avalanche Research SLF, January 24, 2013, p. 3.
  16. ↑ According to Lukas Stoffel, every 50th positive explosion leads to a secondary avalanche ( Davos Artificial Avalanche Release: Explosive Effect, Methods, Benefits, Problems , WSL Institute for Snow and Avalanche Research SLF, Innsbruck 2010).
  17. ↑ Christoph Skolaut, Florian Rudolf-Miklau: State of knowledge about the application of artificial avalanche triggering in Austria in State of the Art for Artificial Avalanche Triggering , July 2014, p. 9.
  18. ↑ Steinkogler: Temporary Avalanche Protection - Preventive Triggering and Detection .
  19. ↑ Guideline for explosives training for artificial triggering of avalanches - Avalanche blasting (LA) , Switzerland.