The deaths of nine Russian skiers back in 1959 still remains a mystery.
The Dyatlov Pass incident was an event that took the lives of nine hikers in mysterious circumstances on the night of 2 February 1959 in the northern Ural Mountains.
The name Dyatlov Pass refers to the name of the group's leader, Igor Dyatlov.
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The incident involved a group of nine experienced ski hikers from the Ural Polytechnical Institute who had set up camp for the night on the slopes of Kholat Syakhl. Investigators later determined that the skiers had torn their tents from the inside out and fled the campsite, probably to escape an imminent threat.
Two of the bodies were found by a tree line about a mile from the camp, and were wearing nothing but their underwear, despite the freezing temperatures.
Three more bodies were found between the campsite and the tree line. One of the bodies had a fractured skull, but doctors determined these five deaths were due to hyperthermia.
When the clothes were tested, there were traces of radiation found on them, as well as around the campsite.
Experts said there was no evidence of an intruder entering the tent, and that the tent was ripped from the inside.
So what could have happened? A number of theories have emerged:
One says an avalanche buried the tent, which would explain the tent's damage and hypothermia. The undresses hikers may have undergone a phenomenon known as paradoxical undressing, where disoriented hypothermia victims remove their clothes because they feel like they're burning up. This theory does not explain the radioactivity and the woman's missing tongue.
Soviet test missile
Some say a Soviet test missile caused the deaths, which would explain the inhuman trauma, but there was no evidence of an explosion or records of a test.
Some suggested a yeti may have attacked the group, however no real evidence of this could be found.
There were reports of 'spheres' seen in the area at the time of the deaths, and lead investigator Lev Inavov even thought there was a connection between the flying spheres and the deaths. The alien theory may explain radioactivity and inhuman trauma.
Authorities determined the deaths were caused by an "unknown compelling force" and the crime was left unsolved.
Access to the region was consequently blocked for hikers and adventurers for three years after the incident.