Khamar-Daban incident

On 5 August 1993, six Kazakhstani hikers died in the Khamar-Daban mountain range under uncertain circumstances. The event has been likened to the Dyatlov Pass incident, earning it the name "Buryatia's Dyatlov Pass".
The six hikers who died were members of a seven-person hiking group led by Lyudmila Korovina; Valentina Utochenko was the group's sole survivor. Despite the police receiving a report, no formal search was carried out until 24 August. It took two days for helicopters to locate the remains, because Utochenko had not yet been able to recount her version of what had happened. According to an autopsy report, all of the victims died of hypothermia, except Korovina, who died from a heart attack.
Khamar-Daban, a mountain range in southern Siberia, in the Republic of Buryatia, Russia, was a popular tourist hiking spot. In the summer of 1993, Lyudmila Korovina of the Petropavl "Azimut" tourist club, an experienced hiking instructor and a Master of Sports in hiking, planned a hiking trip to the Khamar-Daban mountains. She was joined by six of her students: Aleksander "Sacha" Krysin, Tatyana Filipenko, Denis Shvachkin, Valentina "Valya" Utochenko, Viktoriya Zalesova and Timur Bapanov. Korovina had previous experience hiking in the Khamar-Daban area, and the students trained with her for the trip.
The group of seven hikers, led by Korovina, arrived in Irkutsk by train in August 1993. Korovina's hiking group was one of three in the area, one of which was being led by her daughter, Natalia. Starting on 2 August 1993, their trip led from the village of Murino [ru], along the Langutai river, through the Langutai Gates pass, along the Barun-Yunkatsuk river, up the Khanulu mountain and along its ridge, ending on the watershed plateau of the Anigta and Baiga rivers. Korovina's group was meant to cross paths with her daughter's on 5 August.
The first two days of the hike turned out to have gone better than the group had planned, with them making good time up Retranslyator peak, however, on 4 August, as they were beginning their descent, they were hit with an unexpected rainstorm. Korovina decided to make camp in an exposed location, with the group failing at an attempt to build a fire that night. They managed to build a fire in the morning of 5 August and ate breakfast together before continuing their path.
According to Valentina Utochenko, the sole survivor, while descending down the mountain, at the altitude of 2,396 metres (7,861 ft), Krysin, who was at the back of the group, started screaming. He was bleeding from his eyes and ears, frothing at the mouth. He fell to the ground convulsing and then went still. Korovina ran up to him, trying to get him to gain consciousness. A moment later, she cried out, having the same symptoms as Krysin. She convulsed and then collapsed on top of Krysin. Filipenko, who had gotten to Korovina first, was the next to collapse, grabbing at her throat as though she couldn't breathe. She crawled over to a nearby rock and bashed her head against it until she went limp. Zalesova and Bapanov started to run. While running, they collapsed and died throwing up blood and clawing at their own throats, tearing their clothes off. Utochenko and Shvachkin hurried away, but shortly after Shvachkin also collapsed convulsing.
Utochenko ran down the mountain, set up a tent for the night under tree cover and fell asleep. On the next day, she returned to the site of her friends' death to retrieve supplies she needed from their bodies. For four days, she followed power lines down the mountain in hopes that someone would find her. She found a river and started following it. On 9 August, she was found by a group of Ukrainian kayakers, who took her to the nearest police station where a report was filed.
Utochenko did not speak for several days. The official search was conducted on 24 August, led by Yuri Golius. Because Utochenko had not been able to recount her version of events yet, it took two days to find the bodies using helicopters. The hikers' bodies were noted to have been partially undressed.
All of the dead hikers were found to have signs of bruised lungs. An autopsy, carried out in Ulan-Ude, concluded that Krysin, Filipenko, Bapanov, Zalesova and Shvachkin died of hypothermia, and Korovina had a heart attack. Protein deficiency due to malnutrition was listed as a contributing factor to their deaths.
Multiple theories have been proposed to explain what caused the hikers' deaths. Rescuers Valery Tatarnikov and Vladimir Zinov, who took part in the search operation for the bodies, claimed that it was impossible for the hikers to die of cold. Zinov suggested that they might have died of altitude sickness. Tourist Vladimir Borzenkov and member of the search operation Nikolai Fedorov suggested that the hikers went mad due to infrasounds. Yuri Golius, the leader of the search operation, blamed their deaths on Korovina's negligence, claiming she was starving her students, which caused them to have vitamin deficiency. In a 2018 interview for Komsomolskaya Pravda, Utochenko denied the theory that Korovina might have been responsible for the deaths. She believes that the cause of the hikers' deaths was pulmonary edema.
The first explanation proposes that the hikers died in the exact way the autopsy report concluded they did: by succumbing to hypothermia after not being properly sheltered that night. In severe hypothermia, there may be hallucinations and paradoxical undressing, in which a person removes their clothing, which would explain why the hikers were found partially undressed.
Certain parts of Utochenko's story could have been unintentionally exaggerated by her, due to the fact that people who undergo a traumatic experience often misremember details of it.
One theory suggests that the hikers might have stumbled upon a Russian military experiment conducted in the mountains and were killed so that the experiment would remain a secret. This theory was deemed uncredible due to the Khamar-Daban mountain range being a public area with many people traveling through it during tourist season, making it an unlikely place and time for conducting secret experiments.
Symptoms described by Utochenko bear resemblance to death by nerve agents. In particular, the frothing at the mouth and convulsing match death by a strong nerve agent. The bruising of the lungs could also be a sign of death by nerve gas, as contact with it might cause respiratory distress. Cardiac arrest is also caused by it, matching Korovina's cause of death.
Novichok, a family of nerve agents developed by the Soviet Union and Russia up to 1993 and considered to be the deadliest nerve agents to exist, were reportedly tested in areas near Khamar-Daban.
The nearby Lake Baikal is known to be a "toxic waste dumping ground". If the waste was washed downstream, the hikers might have drunk the toxins in their water. Some toxins might not have been visible in a standard toxicology report.
Another theory suggests that the hikers might have hallucinated and got sick due to a mushroom poisoning. Korovina was known to be a forager and she taught the art to her students. One of the hikers might have accidentally added poisonous mushrooms to their breakfast. They could also have been hallucinogenic mushrooms. In very rare cases, an overdose of muscarine and ibotenic acid, most common in Amanita mushrooms (brown/red/yellow with white dots on top, also known as mario/santa mushrooms) might cause psychosis, convulsions, cardiac arrest, and send a person into a coma. Amanita phalloides, the destroying angel, and death cap mushrooms can look similar to other edible mushrooms when they are not fully matured, such as young paddy straw and button mushrooms.