Avalanche control

Every year skiers are tragically killed in avalanches, but most severe accidents happen outside the secured areas. So, the question is – how are such secure areas established, how are avalanches controlled and steep mountain sides secured? Well, there are several options and we will present some of the most used technics in this article.

First of all, avalanche control can obviously only take place within a limited area due to costs, time and geographically challenges. That is why you should never go outside marked/secure areas without an experienced guide. The controlling methods are also heavily impacted by the time available – you could have heavy snowfall in the afternoon or during the night, and you still need to have the ski resort opened safely in the morning. In the old days, a resort could be closed for days while it was being cleared, but the financial impact of closing down a resort is huge and that is why we see heavy investing in modern avalanche control facilities. However, most resorts will be closed once in a while due to extreme weather and the hazards that follow, but more investments in controlling avalanches in smart ways, mean less lost skiing days – which leads to happy guests, and more importantly – returning guests.

Different types of avalanches

An avalanche is basically snow sliding from a higher point to a lower point. Given extreme speed and density this is more dangerous than what it sounds like when talking about some soft snow sliding down a hill. Avalanches can travel with speeds of up to 300 km/t and with masses of 10.000.000 tonnes. Obviously, that doesn’t just pose a danger to people, but also houses, roads and constructions like bridges and electrical masts or gondolas.

It is estimated that on average more than 50 people are killed every year in avalanches in Europe and the US.

The fastest traveling avalanches are “powder snow avalanches” – as the name suggests, they are formed by large amounts of fresh, dry powder with low density. They are usually triggered within the first 2-3 days of heavy snowfall and can be set off simply by skiers cutting through the fresh powder.

The most common fatal avalanches (up to 90% of all registered fatalities arise from those) are “slab avalanches“. They are mostly created by wind that has deposited, or redeposited, the snow. It has a characteristic appearance of a block (slab) of snow that is cut out from its surroundings. They vary in thickness from a few centimetres up to three meters or more.

Photo: Courtesy Photo, National Avalanche Center

“Wet snow avalanches” are slow moving avalanches with an enormous density – up to 500 kg/m3 which is more than twice the density of a powder avalanche. Even though they travel at speeds as low as 10-40 km/h they are the most destructive avalanches due to the masses they bring. They easily crush anything on their path, whether it be houses, trees or gondola masts. They often occur in early spring when temperatures are on the rise and when snow packs are water saturated and isothermally equilibrated to the melting point of water.

So how are avalanches controlled?

First of all, the “pisteur” will need to determine the risk of an avalanche. Sometimes this is easily done by evaluating amount of recent snowfall, temperatures and slope angels or historic knowledge of avalanches in a specific area. When the danger is not obvious, further evaluation will need to take place. This can be done by digging through the layers of snow and determine how layers of snow has packed. As seen from the photo below, different layers are visible and the exact possible break point of an avalanche can be determined.

By Clayoquot, CC BY-SA 3.0, Link

When deemed a risk to skiers, the avalanche needs to be triggered before letting people into the area. Years ago, it was a risky job for the pisteur who would ski through the avalanche risk areas cutting the snow open to manually trigger the avalanche. Even if not triggering the avalanche by his own skiing, he would still need to physically go to the risk zones and place explosives that could then be ignited from a safe distance.

More modern options include placing explosives by a system of cables that will drag the explosives into position before being triggered – the system is known as CATEX and can be seen here. Other options used in less accessible areas are explosives dropped from helicopters or the “Avalancheur” where an explosive “arrow” is shot from an air compression canon. In certain parts of Russia, real artillery fire is used to set off the avalanches.

However, probably the most modern and effective way of setting off avalanches in a controlled manner, is the so-called  GAZEX system. You have probably seen the “pipes” on mountain sides and wondered what they were.

The pipes are mounted in high risk areas and creates a blast wave based on a mix of oxygen and propane gas that is ignited in an expansion chamber. The blast is directed through the pipe and will set off the avalanche. The system has quite high preliminary expenses, but once installed it can be operated from a laptop at a safe distance and multiple times to the extent necessary. The explosive gas is kept in canisters on the mountain and only requires occasional refills throughout the season depending on the use. This is considered the least risky and most reliable control mechanism in modern avalanche combating. The explainer video below will show how the GAZEX system works.

No matter modern avalanche control mechanisms you always need to carefully adhere to resort information about the avalanche risks. The European risk scale runs from 1 to 5. 1 indicating low risk and 5 suggesting very high risk. The risk scale level will be communicated to skiers at most lift stations both up and down, and it should be taken very seriously.

Ski safely!