The question of irregular topography however remained open. Radiotelevisione Svizzera decided to produce a documentary The Dyatlov Mystery, which focuses on our work. We assisted them in organizing two expeditions up Dyatlov Pass during winter 2021, and another at the end summer 2021. The winter expedition was not able to help us with the topography due to the snow cover. However, it proved useful later. However, the summer expedition was equipped with a drone which allowed us to create a high-resolution digital model of terrain near possible tent locations (Fig. 2). The steps have an inclination of 28 degrees or more, while many slopes are steeper than that. These slopes are not local; they are continuous. No matter where your tent is pitched, you will likely be below one.
You can find more information atDigital Elevation Models (DEMs) show the local slope angle. The DEM was created using a drone photogrammetry analysis (summer 2121 survey) with a resolution of 9cm. bAA section showing how, even though the average slope angle of steps is around 20, steeper steps may have an inclination exceeding 30, as indicated by the white dashed line.
Finally, we had the task of investigating the objection that this area is not susceptible for avalanche danger. Russian Federation Natural Hazards Handbook5The avalanche risk area of Category II was established in 1997. This means that Dyatlov Pass has at least one avalanche every kilometer for the next 10 years. January is the most dangerous month. The resolution of the hazardmap was very low, so critics were able to claim that Category II risk is only for the western slopes of mountain chains and not the eastern ones, where Dyatlov groups tents were found.
Here is where the story takes a strange twist. Dmitriy Borisov (Russian mountain guide) contacted us in October 2021. He had taken a photograph of a strange feature on the western slope a nearby mountain (Fig.3a and b), approximately 3km from the tent location. It looked like a local depression on the slope with possible avalanche traces. However, we were concerned that it could also have been a shadow from the cloud. Matteo Born, RSI’s film director, looked through the footage he had taken during his winter expedition. He accidentally found the same features in a higher resolution (Fig.3c & Supplementary Movie1) taken the next day, March 30th! It is highly unlikely that a single cloud would stay in one spot for 24 hours. It is difficult to determine the type of snow slope instability from these pictures. However, the dark shaded area below the ridge could be a Tensile Crown fracture due to one or more slab avalanches. These could be classified as a snow cornice, small wind slab avalanches, or cornice falls according to a dozen international avalanche practitioners or scientists.
aThe location of the area where avalanches have been observed. Source: Google Earth 2021 Maxar technologies Landsat/Copernicus. bPicture taken by Dmitriy Borosov at the Dyatlov Pass on the 29th March 2021. The red-colored zone is located approximately 3km from the tent. cPicture taken from a video shot by Matteo Born, RSI movie director, on the 30th of March 2021. dDmitriy Borisov took the picture of a crown-tensile fracture on this slope on 29 January 2022. ePicture of a small slab of avalanche in middle of slope taken by Dmitriy Borosov on the 29th of January, 2022.