Rudi Mair and Patrick Nairz are the avalanche warning experts from the Tyrolean Avalanche Warning Service. In their bestselling avalanche book "Avalanche. Die 10 entscheidenden Gefahrenmuster erkennen", the two avalanche experts present a new, complementary approach to avoiding avalanche accidents. When analyzing hundreds of mostly tragic avalanche accidents, Rudi and Patrick discovered that most accidents occur in typical, recurring hazard patterns. They therefore developed 10 typical, particularly accident-prone and frequent hazard patterns. Recognizing these avalanche hazard patterns should help winter sports enthusiasts to behave with appropriate caution - and thus avoid accidents.
Hazard pattern (gm) 1 - the second snowfall
After the first snowfall of a winter, sliding snow avalanches, i.e. avalanches that slide down steep, smooth slopes, can pose a particular problem. After the second significant snowfall, slab avalanches occur more frequently. These are considered the typical skier avalanches and are responsible for at least 95% of fatal avalanche accidents. The second snowfall is so crucial because between the first layer of snow and the second snowfall, a pronounced weak layer can sometimes form, which is easily disturbed by winter sports enthusiasts. Problems of this kind usually occur on high (>2000 m) and high alpine (>3000 m) shady steep slopes.
An example: Avalanche Vorderer Brunnenkogel
Avalanche. Five top snowboarders leave the valley descent from the Hinterer Brunnenkogel in poor visibility. They disregarded a barrier. Two of the five snowboarders - an Australian and a Canadian - enter a slope with a gradient of up to 40°, while the rest of the group waits above the slope. In doing so, they trigger a slab avalanche that takes both people with it. The Canadian is thrown over a bulge of ice, but remains unharmed on the avalanche surface. The Australian, on the other hand, falls into a crevasse and is buried 1.5 m deep by the flowing snow. The search proved difficult, partly because the Australian had no avalanche transceiver with him. During the rescue operation, 60 people are deployed, but they are unable to save the 20-year-old Australian's life.Short analysis Two precipitation events are decisive: An early, intense onset of winter on September 22, 2002 and the snowfall from November 2, 2002. In the former, it snowed up to 100 cm along the main Alpine ridge, in the latter it was just 20 cm under the influence of wind. Between these two events, the snow from September 22nd transforms into distinct, loose cup crystals in the steep, shaded and high alpine terrain. The snowpack structure is therefore extremely unfavorable: floating snow lies on glacier ice. Above this is fresh, poorly bonded, not too thick drift snow. Other unfavorable factors: the terrain is extremely steep in places. In addition, the crevasses that are open during the summer do not have stable snow bridges at this time. Where: Vorderer Brunnenkogel / Southern Ötztal Alps / 3200 m / NE slope / 40°
Who: Who: 5 people involved / 1 person killed
When: 4. 11. 2002, 11:30 a.m.
Avalanche: Slab avalanche (dry) / L 100 m / W 35 m / Rip 0.3 m / Burial 1.5 m / 1 day
Regional danger level: no current LLB available
Headline LLB: no current LLB available
Danger pattern (gm) 2 - sliding snow
Snow prefers to slide downhill on steep, slippery rocks. In the process, gliding snow pockets form, i.e. clearly visible cracks in the snow cover, sometimes several meters deep. Contrary to an old doctrine that is unfortunately difficult to eradicate, such sliding snow pockets are not considered favorable, but rather unfavorable criteria for a possible avalanche. A sliding snow mouth indicates the possibility of a sliding snow avalanche, but says nothing about whether and when the snow mass will actually fall as a sliding snow avalanche. In terms of the time of release, sliding snow avalanches are among the most difficult to predict because they can occur at any time of day or night, on the coldest as well as the warmest day of the winter, even in generally stable snow conditions. In addition, sliding snow avalanches cannot be triggered by additional loads
An example: Avalanche Red Column
Avalanche. An East German ski tourer spends a short vacation with his wife in the Virgental Valley in East Tyrol. On December 20, 2008, he decides to walk through the Dorfertal to the Johannishütte. During the descent, he is caught by an avalanche of sliding snow, which comes loose about 500 m above his path. The avalanche sweeps him into the trench below and buries him completely. The rescue operation proved difficult due to the dangerous conditions, partly because the person was not carrying an avalanche transceiver. On the following day, December 21, the ski tourer was located and dug out. On December 22, the helicopter crew succeeded in recovering the body. Short analysis In the wrong place at the wrong time. This is how the avalanche accident can be described in a nutshell. The risk of avalanches gradually increases from December 19 because increasingly humid and warm air masses are entering the country. Accordingly, the risk of being buried by a (spontaneous) avalanche in a potentially dangerous area - including the narrow Dorfertal valley - increases. On the day of the accident, it was still snowing in large parts of Tyrol at the beginning. In the course of December 20, the snow line then rises significantly and reaches up to approx. 1700 m in the west of Tyrol and briefly up to approx. 2000 m in the east. The snowpack therefore becomes increasingly wet and consequently more susceptible to disruption. The terrain above the avalanche source is predestined for sliding snow avalanches because it is very steep, smooth meadow terrain. This is why you can also see other sliding snow mouths and cracks in the photo. Where: Rote Säule / East Tyrolean Tauern / 2200 m / SW slope / 35°
Who: 1 person involved / 1 person killed
When: 20. 12. 2008, approx. 15:00 h
Avalanche: Sliding snow avalanche (wet) / L 1000 m / W 30 m / Start 0.5-1 m / Burial 1 m / 1 day
Regional danger level: 3 (considerable)
Headline LLB: Pay attention to fresh accumulations of drifting snow! Sliding snow avalanches are still possible in the south!
Danger pattern (gm) 3 - Rain
Rain is a classic warning sign in snow and avalanche science because it adds weight to the snowpack and leads to a rapid loss of stability. Avalanches are therefore inevitable. Rain can occur in any part of the winter. The big advantage: no hazard pattern is easier to recognize than rain.
An example: Avalanches StöcklenalmAvalanches. Some hut keepers regularly have problems with their hut access routes, especially when a weekend with critical conditions is approaching. On one such day, just before the Stöcklenalm, the landlord of the Franz Senn Hut observes four Frenchmen heading towards the hut via the summer path, which was very dangerous at the time. He tries in vain to persuade them to turn back by shouting at them. As the people are permanently in the danger zone, he waits until they have crossed the stream and reached safe ground. Half an hour later, the hut warden passes the same spot again and sees numerous spontaneous avalanches, all of which have washed over the Frenchmen's tracks.Short analysis The weather during the previous week can be described succinctly as "April weather". There is a mix of mostly intense rain showers, with considerable amounts of fresh snow above around 1800-2200 m, lots of clouds and brief clearings. This has a negative effect on the snowpack build-up and consequently on the avalanche situation. On April 23, 2008, it rains with diffuse visibility. As a result, the snowpack becomes increasingly damp, below 2200 m it soaks up like a sponge and is completely wet. The conditions for wet snow avalanches could not have been better. Looking back, this was the most active period for avalanches of the entire winter season. Due to the very unfavorable conditions, the hut owner vehemently advised against going to the hut on his homepage ... Where: Stöcklenalm / Northern Stubai Alps / 1620 m / all slopes / > 30°
Who: 4 people involved
When: 23. 4. 2008, 15:20 h
Avalanche: Slab and loose snow avalanches (wet) / L 5-250 m / W 5-150 m / Approx. 0.6 m
Regional danger level: 3 (considerable)
Headline LLB: Wet snow avalanches below 2200 m, high alpine snow slab danger!
Danger pattern (gm) 4 - cold to warm / warm to cold
For too long, avalanche experts believed that a large temperature difference during the snowfall (whether cold to warm or vice versa) had a favorable effect on the avalanche situation. However, this is only true under certain conditions. For the most part, however, such a temperature difference has a negative effect because it favors the build-up transformation within the snowpack: As a rule, this results in the formation of a thin, weak layer that is consistently susceptible to disruption. This is also often found on south-facing terrain. An insidious affair, also because the weak layer is not yet present immediately after the snow has fallen and only forms over the course of the following days.
An example: Avalanche high courage
Avalanche A few days before the Hohe Mut lift in Obergurgl is due to go into operation, the operations manager of Skilift GmbH Obergurgl tasks two of his employees with repairing an explosive cable car. At this time, the cable of the lift is partially covered in snow on the ground. Starting from the drive station, which is located northwest of the Hohe Mut at approx. 2300 m, the employees traverse the approx. 35° steep N to NW slopes along the rope without skis. In the so-called 2nd Mut gully, they trigger a snow slab with a small crack thickness, which carries them about 100 m and buries them completely. Both people were not wearing avalanche transceivers and could only be found by the rescue team - for one of them this help came too late.Short analysis The decisive factor was the change from warm to cold weather, which brought fresh snow. In North Tyrol, Föhn winds are forecast until November 23, 2007. Temperatures are high and there are often strong winds. The surface of the old snow is therefore soaked up to around 2600 m, and even soaked at lower altitudes. From November 23rd, it starts to snow as the high altitude current turns and the air temperature drops. Usually 20-30 cm of snow falls. In the vicinity of the interface between the wet old snow cover and the dry new snow, a thin layer of angular snow forms in all exposures. Obvious signs of danger can be seen at the time of the accident in the form of clearly visible but not too thick packets of drifting snow. The avalanche below the drive station is only triggered by a snow groomer after the avalanche has started. Where: Hohe Mut / Southern Ötztal Alps / 2280 m / NNW / 37°
Who: 2 persons involved / 1 person killed / 1 person injured
When: 5. 12. 2007, 11:00 am
Avalanche: Snow slab avalanche (dry) / length 250m / width 15m / avalanche depth 0.2-0.3m / burial 0.5m / 40min.
Regional danger level: 3 (considerable)Headline LLB: In North Tyrol widespread considerable avalanche danger - Attention to the significant rise in temperature!
Danger pattern (gm) 5 - Snow after a long cold spell
A classic avalanche event: After a long cold spell, it starts to snow. In addition, a strong wind blows, which displaces the fresh snow. Within a very short time, a very delicate avalanche situation arises for winter sports enthusiasts. This also applies if, after a long cold spell, there is only a strong wind without snow. The problem: fresh drift snow is deposited in lee slopes, which comes to rest on a loose layer of old snow, usually consisting of floating snow. The drift snow and old snow are very poorly connected to each other. The snowpack is then just waiting to be disturbed by additional loads.
An example: Avalanche Mölser Berg
Avalanches A group of ten from the OeAV, accompanied by two mountain guides and an instructor, spend a touring weekend at the Lizumer Hütte. On February 5, they plan a leisurely day tour up the Mölser Berg in glorious weather. They decide to ascend the last section towards the summit directly via the O-slope, which is initially hilly and then becomes steeper. When seven participants are already in the safe ridge area and three others are just below a flattening, a clearly audible WUMM sound is heard. As a result, a large slab avalanche breaks loose, taking two people about 150 meters with it. They all react quickly, pull out their ABS backpacks and are only partially buried. They remain uninjured.Short analysis: It has been snowing in the Tux Alps since January 31st with cold temperatures and strong winds, with around 60 cm of snow. The old snow cover consists mainly of floating snow in the W sector via N to E, and partly of surface frost on the shaded side. Their formation was promoted on the one hand by the thin snow cover during January and on the other hand by arctic temperatures from January 22. The fresh drift snow bonds poorly with the old snowpack. Several spontaneous avalanches were observed. On February 3, a high avalanche danger is still reported above 2000 m in the accident area. On the day of the accident, the loose snow surface, which was created by the decreasing wind towards the end of the snowfall, was deceptive. Signs of wind are often covered up as a result. Characteristic is also the extensive expansion of the avalanche due to the extensive floating snow foundation.
Where: Mölser Berg / Tux Alps / 2440 m / east-facing slope / 35°
Who: 12 people involved / 2 people caught
When: 5. 2. 2005, 11:30 a.m.
Avalanche: Slab avalanche (dry) / L 300 m / W 300 m / 0.5-2.5 m inrun
Regional danger level: 3 (considerable)
LLB headline: Delicate situation for winter sports enthusiasts!
