Three quantities in this case have been disputed since 1959 and can be computed from public data: the steepness of the slope at the tent, the darkness of the night, and the temperature. The code is published with this report.
Two measurements exist, at two scales, and they answer different questions. The public Copernicus GLO-30 elevation model (30 m grid, radar-derived, snow-free) gives the average ground slope at the best-supported tent position, the cairn-marked site three independent Russian researchers agree on (61.7585 N, 59.4294 E, 899 m), as 15 to 16 degrees over windows of 60 to 300 m, with about one degree of random error; the other candidate positions (the point the prosecutors fixed in 2019, 115 m to the north; Borzenkov's GPS reading; the memorial sculpture) give 16 to 19.5 degrees. Directly upslope the ground rises at 17 degrees for the first 100 m and 14 for the next 100 m, and 200 to 300 m up it flattens to a 6-degree shoulder. A 30 m grid smooths away anything shorter than about two grid cells, so a step 4 to 6 m high and 10 to 20 m long, the feature the slab model rests on, is invisible to it whether or not it exists.
The measurement at the scale of the steps is Puzrin and Gaume's own. In September 2021 a drone photogrammetry survey of the slope around the possible tent locations produced a 9 cm terrain model. Their 2022 Comment reports that the average slope along their section is "around 20°" and that "the steps have inclinations exceeding 28 degrees, and many slopes are even steeper than 30 degrees", adding that "these slopes are not just local, they are continuous: no matter where you pitch your tent you are likely to be below one of them". The survey was made on bare ground. In winter, Galina Pigoltsina, the climatologist who modelled the site's weather for the prosecutors in 2019, reports wind transport of 600 to 1,000 m³ per metre of slope, enough, in Puzrin and Gaume's words, to "completely cover local topographic features such as the steps"; the model's mechanism depends on that: a weak layer that formed on the stepped early-winter surface at about 28 degrees and was then buried under a slab whose surface lay at the gentler average angle.
The 1959 witnesses bracket the average. Sergey Sogrin, who climbed to the tent site on 4 March with Moisey Akselrod's search party, testified that "the slope on which the tent stood is not dangerous, the steepness is 15 to 18 degrees" (sheet 334). Vadim Brusnitsyn, a student searcher, gave "approximately 20 to 25 degrees" and "reaches 20 degrees at the tent" (sheets 366, 369). Prosecutor Tempalov's tent-site protocol says 30 degrees, in a sentence that also puts the summit at 300 m when it is 760 m away (sheet 2). The 2019 prosecutors' glaciologist, Viktor Popovnin, measured 21 degrees at the point the geodesists gave him and probed «каменная гряда» under the snow where the tent stood, a stone ridge. The 2021 paper's "about 23 degrees" was the average snow slope estimated from the 1959 photographs, and its 28-degree weak layer an estimate of the step behind the tent; the 2022 survey replaced the estimate with a measurement of the steps and lowered the average to about 20.
What the two measurements settle is limited. On the average slope, the 30 m model agrees with Sogrin, with Borzenkov's 16 to 17 degrees and, within the smoothing of a radar grid and the uncertainty of the tent position, with the drone survey's 20; it is below the 23 degrees of the 2021 paper, which the authors themselves replaced with about 20 degrees in 2022. On the steps, the 30 m model says nothing, and the 9 cm model says they are there, steeper than 28 degrees and continuous across the slope. The coarse average is not evidence against the model's 28-degree layer. What no survey has measured is the snow: whether in the winter of 1958–59 a weak layer lay on such a step above the tent, and which step the tent stood under.
| 1 to 2 February 1959, local time (UTC+5) | Event |
|---|---|
| 14:40 | Tent site loses direct sun behind Kholat Syakhl (terrain horizon 13 to 17 degrees to the south-west) |
| 17:03 | Sunset on a flat horizon |
| 17:54 / 18:49 / 19:40 | End of civil, nautical and astronomical twilight |
| 19:40 to 04:15 | Full night with no moon at all; Burmantovo reports overcast until midnight, clear by 03:00 |
| 04:15 | Waning crescent (33 per cent) rises in the south-east, 7 degrees high by 06:00 |
| 08:35 / 09:26 | Civil dawn and sunrise on 2 February |
The moon was five days from new (new moon 8 February, 00:22 local). Anyone on that slope between about seven in the evening and four in the morning was in complete darkness under cloud, then starlight on snow. Ivanov's estimate that the tent was pitched "at about 17:00" was inferred from the exposure of the last frames on the cameras; since the site was already in mountain shadow from 14:40, those frames could be earlier.
The nearest weather-station records, from Ivdel, Nyaksimvol and Pechora, 100 to 200 km away, survive in the daily archive of NOAA, the US weather agency. The week before was mild for the season, with daily maxima of minus 4 to minus 7 at Ivdel and Nyaksimvol. On the night of 1 to 2 February a cold front passed: the Ivdel minimum fell from minus 11.2 to minus 20.3, Nyaksimvol from minus 13.9 to minus 30.8, Pechora from minus 23.1 to minus 35.1. A loose sheet in Maslennikov's search notebook copies the readings for that night from Burmantovo, the nearest weather post, in the Lozva valley below the mountains: minus 13 at 21:00, a warm blip to minus 5 at 23:00 as the wind veered west, minus 15 at midnight with a north-west wind, minus 21 under a clear sky at 03:00. Station winds in the lowland were light; the case file's search-organisation report says the pass "usually" has 15 to 20 m/s and up to 36 (sheet 39).
| Estimate at the tent (899 m) | Evening, 18:00 to 22:00 | Small hours, 01:00 to 05:00 |
|---|---|---|
| Air temperature, station-based (this study) | −10 to −15 °C | −20 to −26 °C |
| Air temperature, Pigoltsina 2019 microclimate model for the prosecutors | −16 to −19 °C | −26 to −31 °C |
| Wind (Pigoltsina, tent in a north-west lee) | 9 to 10 m/s | 10 to 12 m/s |
| Wind chill at 8 to 15 m/s (the standard 2001 wind-chill formula) | −22 to −29 | −34 to −45 |
Exposed skin freezes in under 30 minutes below a wind chill of about minus 28 and under 10 minutes below about minus 40. These people were in socks, shirts and one or two sweaters. The cold alone is enough to kill all nine within the night. It does not explain why they left the tent.
Tent to cedar: 1,551 m horizontal, 256 m of descent, mean gradient 9.4 degrees, bearing 62 degrees. Wind crust for the first 850 m (where the searchers found footprints standing proud as columns), then loose snow one to two metres deep to the forest edge. Walking time without boots in the dark: 35 to 85 minutes. The three bodies on the slope lie within 31 m of the straight line from the fire to the tent, at 323, 503 and 654 m from the fire; Kolmogorova, the farthest, had climbed 72 of the 256 m and still had 184 m of ascent and 900 m of walking left.