In late January 1959 a party of ten left Sverdlovsk, the industrial city in the Urals now called Yekaterinburg, for a winter ski trek across the northern Urals. Nine were students or recent graduates of the Ural Polytechnic Institute, aged 20 to 24: Igor Dyatlov, a 23-year-old engineering student with several winter expeditions behind him, who led the group; Zinaida Kolmogorova, Rustem Slobodin, Yuri Doroshenko, Georgiy Krivonischenko, Aleksander Kolevatov, Lyudmila Dubinina, Nikolay Thibeaux-Brignolle and Yuri Yudin. The tenth, Semyon Zolotaryov, was a 37-year-old ski instructor who had asked to join. Yudin fell ill and turned back at the last settlement on the route; the other nine went on.
On the afternoon of 1 February, after leaving a store of food for the return journey in the valley below, they climbed onto the open east slope of Kholat Syakhl, a treeless dome of a mountain, and dug a platform for their tent into the wind-packed snow about 150 m below the crest and 1.5 km above the forest edge. The last photographs on their cameras show them digging. Sometime that night, in the dark, with the air falling toward minus 25 °C, all nine cut their way out through the tent wall with a knife and walked downhill without boots or coats.
When the telegram that was due on the group's return did not come, a search began. On 26 February the searchers found the tent half collapsed under drifted snow, with boots, coats, food and money still inside, and a line of footprints, some of them barefoot, leading down the slope. The next day they found two of the nine under a large cedar at the forest edge, beside the remains of a fire, stripped to their underwear, and two more on the slope between the cedar and the tent, lying as if they had been climbing back toward it; a third on that line was found under the snow on 5 March. All five had died of cold. The last four were not found until May, when the snow began to melt. They lay in the bed of a stream in a ravine some 75 m from the cedar, under several metres of snow, and three of them had injuries that the forensic examiner, Boris Vozrozhdenny, said needed a great force, of the kind seen when a person is thrown by a car: two crushed chests, a crushed skull, and no wound on the skin. The investigation was closed on 28 May 1959 by Lev Ivanov, the investigator from the regional prosecutor's office who ran it, with the finding that the nine had died of «стихийная сила», an elemental force, that they were unable to overcome. The resolution does not say what the force was.
Nothing in the file explains why nine experienced people would leave their only shelter at once, in the dark, at that temperature, without stopping for boots, or how three of them came by crushing injuries a kilometre and a half from the tent. The file was closed and put away. The explanations with serious advocates fall into five camps. The first holds that snow, either a small avalanche or a collapse of the snow that had piled onto the tent, came down on the sleepers and drove them out, and that the injured were crushed either then, at the tent, or later, when the snow bank they had sheltered under in the ravine gave way. This is the view of the Russian prosecutors, who reviewed the case in 2019–20 and announced a small avalanche and hypothermia without publishing their evidence, and of Johan Gaume, a snow and avalanche scientist, and Alexander Puzrin, a geotechnical engineer, whose 2021 paper gave the avalanche version its first physical model. The critics of this view include people who have examined the slope and its snow in winter, among them the aviation engineer Vladimir Borzenkov and the 1959 searchers Vladislav Karelin and Sergey Sogrin, who say the slope is too gentle, the snow too well bonded and the tent too undisturbed for any avalanche.
The second camp holds that a violent fall wind off the mountain, of the kind that killed eight skiers in Sweden in 1978, made the tent impossible to hold; this was proposed by the Swedish archaeologist Richard Holmgren in 2019. The third holds that low-frequency sound generated by wind over the summit drove the group out in terror; this is the argument of the American writer Donnie Eichar's 2013 book Dead Mountain. The fourth holds that the group was attacked, by hunters of the Mansi, the indigenous people of that part of the Urals, by criminals, or by agents of the state in an intelligence operation gone wrong, the last argued at length by the pseudonymous Russian author Alexei Rakitin in 2013. The fifth holds that a rocket test, a secret weapon or a toxic release killed them; it is fed by reports of glowing spheres over the Urals that February and by traces of radioactivity found on some of the clothing. Each explanation accounts for some facts in the file and is contradicted by others.
The judgment rests on the 1959 case file itself, read in Russian: 392 numbered pages of protocols, interrogations, radio messages from the search, nine autopsy reports and the closing resolution, scanned and transcribed by the site dyatlovpass.com. From it 459 separate facts were extracted, each tagged with the number of the page, called a sheet, that it comes from, so that every claim on this page can be checked against the original. To that were added three things the file does not contain: the slope, the darkness and the cold of that night, computed from public elevation, astronomical and weather data; a line-by-line reconstruction of Gaume and Puzrin's avalanche model from the equations they published, to see what the model needs to be true; and the one forensic examination since 1959, of Zolotaryov's exhumed bones in 2018. Every explanation with a serious advocate was then scored against 28 documented facts, one fact at a time, and the finding is the reading that no documented fact contradicts. The result is a natural death with no other person involved, at about 90 per cent; snow on the tent as the reason they left, at about 65, with the Gaume–Puzrin avalanche the leading candidate at 45; and the crushing injuries in the ravine rather than at the tent, at about 75. Those percentages are judgments about the evidence, and the finding below says how far each one moves when the evidence is weighed differently. The measurement that would settle the largest open question, a snow profile up the step above the exact 1959 tent position, has never been taken.
The finding comes first, with its confidence and what would overturn it. The evidence sections come next: the facts the case file documents, each with its sheet number; what the nine autopsies and the 2018 examination record; the slope, darkness and cold as computed; and the replication of the avalanche model. Every published explanation is then scored against the 28 facts in one table, with the contradicting sheet named wherever a fact rules an explanation out. The most probable sequence of the night follows, step by step with its confidence, then the documented facts the finding does not explain, the measurements and documents that would move it, what this page adds to earlier work and where it falls short, and the sources and code.