"A Compelling Natural Force"
Prosecutor-criminologist L. N. Ivanov, 28 May 1959 (case file vol. 1, page 384). Public domain (Russian official document, not an object of copyright under article 1259 of the Civil Code of the Russian Federation). Picture source
The 1959 case closes without naming a cause, and reviews in 2019 and 2020, then a 2021 scientific study, point to a small avalanche.
28 May 1959 to January 2021
The story
On 28 May 1959 the investigator, Lev Ivanov, closes the criminal case. He finds no other people at the scene, no signs of a fight and nothing stolen. He writes that the hikers died from a force they could not overcome. The Russian phrase has been translated as "overwhelming force" and as "a compelling natural force".
Officials at the Institute and in the city sports bodies are punished for poor organization. The case does not say what the force was, and that gap fills with theories for sixty years.
In 2015 the Investigative Committee of Russia reopens the case. In 2019 it calls a snow avalanche the most likely cause. The Prosecutor General's Office runs its own review from 2019 and, in July 2020, reaches the same answer: an avalanche, then cold, darkness and a blizzard.
In January 2021 Johan Gaume of EPFL in Lausanne and Alexander Puzrin of ETH Zürich publish a model that tries to answer the main objections: the gentle slope, the long delay and the lack of debris. Their answer is wind-blown snow loading a small slab above the cut until it fails.
What the record says
it is concluded that the cause of their demise was overwhelming force, which the hikers were not able to overcome.
Resolution to close the case, 28 May 1959, sheet 387 (dyatlovpass.com translation)
According to the 1959 Soviet criminal investigation, “a compelling natural force” led to the death of the Dyatlov group. However, the nature of this force has not been identified.
Gaume and Puzrin, Communications Earth & Environment (2021), Introduction
[The dead tourists’] injuries are characteristic for the injuries of rock climbers caught in an avalanche,
Andrei Kuryakov, Prosecutor General's Office for the Ural Federal District, quoted by TASS, 11 July 2020
The 1959 wording is in the closing resolution, sheet 387; translations differ. The 2020 avalanche conclusion was announced by Andrei Kuryakov, reported by TASS and RFE/RL. Kommersant-Ural later reported that the Prosecutor General formally warned Kuryakov for speaking at that press conference for personal purposes, so the 2020 announcement itself is disputed in Russia. Gaume and Puzrin say their work shows the plausibility of a rare kind of slab failure that could possibly explain the incident, and that they do not address the radiation, the hikers' behavior after leaving the tent or the state of the bodies; and relatives of the hikers and many researchers still challenge the official finding.