The artificial triggering of snow avalanches is a common measure to mitigate the risk of avalanches. The main objective is to reduce or stabilize the unstable snowpack in avalanche starting zones. By doing so, the probability of large avalanches that could endanger transportation routes, towns, and ski resorts is decreased.
Controlling snow avalanches is certainly an exciting challenge. In fact, we recently dedicated an article to avalanche control in Canada, a country renowned for its expertise in this field. But today, we will unveil how we carry out these activities at Arantec. Would you like to take a journey through the Aragonese Pyrenees?
Where are we controlling snow avalanches?
Currently, we are working in four areas of the Aragonese Pyrenees, in the province of Huesca, reducing the avalanche risk on three roads:
- A-139, access to Llanos del Hospital in the Benasque Valley (Maintenance responsibility: Government of Aragon).
- A-2606, access to Baños de Panticosa (Maintenance responsibility: Government of Aragon).
- N-330a, at the Somport pass (Maintenance responsibility: Ministry of Transport, Mobility and Urban Agenda – current denomination of the Ministry of Public Works).
- A-135 road from Torla to the Pradera de Ordesa (Maintenance responsibility: Government of Aragon).
Tourism is the main economic driver in these four areas. Therefore, keeping the transportation routes open to hotels, ski resorts, and national parks is crucial. Likewise, our work ensures the safety of users and workers involved in maintenance and operation tasks.
PIDA, the procedure that sets the basis for our work
The artificial triggering of avalanches in a specific operation requires a Plan for Avalanche Release Intervention (PIDA). This procedure ensures safety during the actions taken to trigger snow avalanches. These documents specify the following points:
- The hierarchical chain of command for the different teams involved in the operation and their functions.
- Detailed inventory of avalanche-prone areas and trigger points.
- Triggering system, location of installations if applicable, and personnel and resources involved.
- Location of explosive storage points and access to them.
- Designation of safe routes to the firing points, both manual and remote.
- When and how the area is closed to ensure the safety of individuals during the operation, and who is responsible for the closure.
- Assessment and decision-making regarding whether to maintain the closure or reopen the area after the operation.
- Responsibilities and personnel involved in the reopening after a shooting campaign.
Our PIDAs are specific to each road where we work. These plans serve as a reference document for our team of snow scientists (nivologists) during the operations. Detailed terrain and climate analysis, worker safety, applicable legislation, and cost-benefit considerations are some of the key factors in designing the operations, for which we also provide technical assistance.
What artificial snow avalanche triggering systems do we use?
Triggering systems generally vary based on the type of explosive and the need for fixed installations. Here are the main systems used in the Pyrenees:
- Systems using gaseous explosives with fixed installations (Gazex, Gazflex, and O’bellx).
- Gaseous explosives without installations (Daisybell).
- Control mechanisms using liquid explosives with fixed installations (Avalancheur).
- Systems using liquid explosives without installations (manual triggering with Secubex).
- Systems using solid explosives with fixed installations (Catex).
- Control via solid explosives without installations (manual triggering with rubber or penthrite).
In this image gallery, for example, you can see some of these systems.
Now that we have mentioned the areas where we are working, the preparatory work required for these operations, and the main systems we use, let’s provide you with detailed information on how we control snow avalanches in each area.
First of all, it is worth mentioning that we do not use solid explosives neither in Somport nor in the Panticosa/Benasque/Ordesa area. This allows us to reduce the complications associated with the storage and handling of the explosives and also increases the safety of the workers involved in the triggering operations.
In Somport, for example, we use the GAZEX system in the La Raca and Secras areas.
It consists of a fixed installation with 3 and 8 exploders, respectively, connected to a control center. These exploder cannons store gas reserves and equipment to produce the spark that triggers the explosion. The detonations can be remotely activated by mixing oxygen and propane.
This system allows for the safe control of avalanches in all weather conditions. However, at times, it may be difficult to assess the results due to limited visibility. Additionally, there is no intervention in the dangerous zones or areas close to them, as the triggering is remotely operated from the Casa de Somport using an electrical system protected by a safety key.
Panticosa, Benasque, and Ordesa
Firstly, it is worth mentioning that the return period of avalanches affecting the Ordesa road is much higher than in the other areas where we work. In fact, the last avalanche that reached the road was recorded in 1996. So far, since we have been managing this road section, there have been no preventive closures or artificial triggering operations necessary.
In the other two areas, Panticosa and Benasque, we use the DaisyBell system.
This mechanism consists of a bell-shaped device with two tanks of hydrogen and oxygen, which is transported by helicopter. Its main advantage is that it allows for multiple shots in the starting zones during a single flight, and its implementation does not require any fixed installations.
The detonations are triggered from the helicopter and carried out with the device hovering about 3-10 meters above the snow. This system allows for targeting the detonations based on the snow distribution on the terrain, thereby increasing the percentage of successful shots. However, its use is limited by weather conditions. It is not always possible to fly when desired due to weather constraints!
In conclusion, managing safety during different snowfall episodes is a team effort involving the government, the road maintenance and operation company, Arantec’s snow scientists (nivologists), and the civil guard.
The ultimate goal of this collaboration is to keep the roads open and safe for as long as possible. It is not an easy task, and the level of responsibility associated with the decisions is high. Therefore, for us, it remains a challenge every winter, but also an opportunity to showcase our knowledge and experience.
Canadian Avalanche Association. (2016). Technical Aspects of Snow Avalanche Risk Management─Resources and Guidelines for Avalanche Practitioners in Canada (C. Campbell, S. Conger, B. Gould, P. Haegeli, B. Jamieson, & G. Statham Eds.). Revelstoke, BC, Canada: Canadian Avalanche Association