Back to the same topic: Avalanches.
First, some introductory remarks. G&P's avalanche theory was touted as Breaking New Science. This is nonsense. Their theory consisted of very old knowledge about avalanches, spiced up with a mathematical argumentation claiming that one avalanche could have occurred.
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Their "theory" about snow layering, with a weak layer between two solid layers, is not “new science” but established old knowledge and common sense, based on observations. I received a thorough introduction to this knowledge while working on avalanche protection outside my hometown more than 30 years ago. Their mathematical argumentation is based on what I would call unstable variables. Snow does not have a specific friction angle, and therefore does not have a specific friction coefficient. The friction angle depends on the consistency and temperature of the snow, and the age of the snow after falling, and by transport along the surface by wind.
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I base my argumentation on my own practical experience from engineering work with avalanche protection, and on open publications from the Norwegian Geotechnical Institute (NGI). First, some more background information. In the region of Norway where I come from, there are between 8,000 and 10,000 large and small avalanches each year. In the last 20 years, 46 people have died in avalanches there. On average, 2 to 3 people die each year in avalanches. Many of these avalanches are documented and measured. Therefore, NGI has a completely unique base of experience to draw on when investigating avalanche danger. Those who perish are tourists from France, the Czech Republic, Austria, Germany, to name a few. In two cases, locals have been caught in avalanches and survived, and they were young people practicing risk sports on the snow-covered mountainsides. People living in this region have avalanche danger as part of their collective consciousness. If you were to show pictures from the Dyatlov Pass to some of those living in this region and claim that the Dyatlov group was killed by an avalanche, they would ask you what you've been smoking.
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The steepness of the slope is the main thing we look at to see if there might be an avalanche. Some people say, "Sure, but there are other things involved in an avalanche." To that, I say, "Come join our talk." It's the steepness of the slope that matters for all kinds of avalanches. Pressure, pulling, and sideways forces happen because of the slope angle, and is only some spice on top of the established knowledge. When the snow moves down the slope super slow, the tension at the upper part gets big enough and the avalanche starts. Yep, when the slope is at a certain angle, the snow moves really slowly downhill. That's what makes those forces happen. If the pressure from below isn't strong enough to balance the tension at the upper part, the avalanche starts.
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A loose (weak) layer of snow forms during weather changes. For instance, it might be cold with strong winds for a while, then the wind dies down and snow falls to a certain extent. After that, the wind picks up again, and the fresh layer of snow gets covered with snow that has blown from afar and has a higher density. If the top layer becomes thick and heavy enough, the weak layer may collapse, triggering an avalanche. Another, more dangerous weak layer can form without significant weather changes but requires continuous severe cold with little wind. This layer consists of frost rime on top of the snowpack and can be more than 1 cm thick. The layer is known as facet crystals stacked on top of each other, resembling small shot glasses. If new snow built up on top and the weight becomes significant enough, these crystals shatter, acting like a ball bearing layer for the top layer to slide out. Such a weak layer is persistent and very difficult to identify without digging in the snow, unlike a layer of loose snow, which consolidates after a certain time. I find it quite surprising that G&P are putting all their efforts into supporting their theory with a thick layer of loose snow covered by a heavier, harder top layer, considering the temperatures in the Ural region during January and February. In the end, all these specific assumptions are built into the statistics for terrain slopes that trigger avalanches. So the dangerous slopes cover all kind of preconditions.
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Back to the slope angle of the top layer. According to the data I have, the critical threshold for triggering avalanches is approximately 25 degrees. At 25 degrees, about 1% of all avalanches are triggered. Using the beta distribution on the figures I have, the probability is reduced to 1 per mil at a slope angle of 23 degrees. At a slope angle of 20 degrees, the statistical probability is virtually zero. (Probability is a number between 0 and 1, but in everyday language, we talk about 0 to 100%.)
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However, this isn't really the most interesting part. What should be of interest is that avalanches on slopes less than 30 degrees require very specific conditions. It's not useful to search for a slope angle between 20 and 30 degrees to determine if an avalanche can release. For an avalanche to release at 20 to 25 degrees, the slope must converge to a steeper incline below. Only then does the tension at 20-25 degrees become significant. On a mountainside where the incline doesn't converge but remains consistently less than 18 degrees, no avalanche releases, regardless of weak layers, and regardless of whether someone has dug a pit in the snow. The slope where the tent was pitched is between 15 and 16 degrees. No avalanche runs there. There were no avalanche. The authentic picture from the scene proves it. If an avalanche had hit the tent, it would have been completely flattened. Neither ski poles nor skis, used as anchors for the tent guy ropes, would have remained standing. The picture tells everything. Igor Dyatlov and his friends' tent was not hit by an avalanche.
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G&P have presented their theory in two publications. In their first publication, they state that they obtained digital terrain data from multiple sources. The issue with their references is that digital terrain data with elevation references from this area is only available from the NASA product SRTM3. Towards the end of my comment, I will thoroughly revisit this and other points I have mentioned here. In their second publication, they claim to have laser scanned the area with a resolution of 9 cm. I have requested their point cloud, which forms the basis of their model, without success. If one claims science, it is common courtesy in academia to release all models used in an analysis so that others can test the hypotheses independently. The point cloud G&P claim to have used should be made available to this forum for further study immediately. The points must be located in UTM zone 41. (As Cartesian coordinates)
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So, let's take a slightly deeper dive into G&P's theory. They argue that the slope above the tent was much steeper than 20 degrees, implicitly suggesting that an avalanche could have been triggered. However, they then abandon this line of reasoning and claim that a layer of snow built up over the tent, slid off, and fell down, trapping the Dyatlov group beneath the canvas. Willing minds support this and add that the Dyatlov group cut their way out of the tent to escape. Such argumentative techniques do not belong in academia. But let's take them at their words.
They have an illustration showing a wind blowing across the tent and leaving snow above it. This does not align well with weather observations. The tent was oriented in a north-south direction, and the wind came from the northwest. The wind would have hit the side wall/roof of the tent at an angle between 35 and 75 degrees. This can be assumed even if the orientation of the tent is not precisely specified and even if the wind passing over the shoulder above may have veered more to the east. The canvas would have deflected the wind, creating a wind flux along the tent, not across it. The illustration they used is only credible if there is a wind blowing at an ideal angle to the tent, with ideal wind speed, for very many hours. The wind speed was about 8-10 meters per second. The illustration also shows an extremely thick "weak layer." Where did it come from, and when was it formed under the weather conditions prevailing for several days before the disaster?
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It is impossible that a small avalanche could have caused the injuries the victims had. A larger avalanche would have swept away everything in its path. So, what is the purpose of G&P's theory? It does not prove that a small avalanche occurred, nor does it prove with high enough confidence that an avalanche could occur. The risk of avalanches increases with weather changes from colder to warmer conditions, combined with strong winds, regardless of the layering of the snow on the mountainside. When temperatures rise sharply from -5 to -10 degrees Celsius or colder and approach 0 degrees Celsius and above, alarm bells ring for those living in avalanche-prone areas. The opposite occurred in Dyatlov Pass in February 1959. Temperatures dropped significantly, reaching as low as -30 degrees Celsius.
The G&P theory should be removed from the table and filed under the title " For educational purposes.”
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In their first publication, G&P stated that they had downloaded terrain data, citing several sources. However, only the NASA product SRTM3 is available from this source. I have downloaded data from there and built a terrain model. It is too coarse to definitively characterize the terrain but can serve as an illustration. The image "SLOPE" depicts the slope of the terrain in the area. Approximately 180 meters south of the tent, the terrain slope can reach up to 30 degrees at a few points, which could be shown in a finer mesh model. Above the tent, the slope can reach up to 25-26 degrees, but if an avalanche were to occur there, it would have a reach that would sweep away anything protruding from the snow and flatten the tent.
The images mod1 to mod3 show the model from different angles. Image mod5 is created after the coarse model is broken down into squares of 25 cm, and all dimensions of the tent are incorporated into the model. Nothing is drawn by hand. With a fine mesh model, one would be able to create a completely realistic depiction of the situation, both before and after the collapse of the tent.
The images "standard" and "lag" illustrate the forces at play in an avalanche.
The image STREKK shows the stetch in the toplayer right before avalanche.
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Regarding G&P's theory, I have two more things to say. A theory claiming to be based on science must be both valid and reliable, and it must be supported by observations. Secondly, all models used in the study must be open to scrutiny by others, so they can be tested by independent individuals. For it to be considered scientific, the calculation model itself must be thoroughly explained, and the detailed terrain model they claim as a basis must be released. Without this happening, their publications cannot be regarded as serious.
Topic: Avalanche theory (Read 21005 times)
