This winter, K2 has featured both the triumphs and tragedies that often encapsulate high-altitude mountaineering. On January 16, a team of Nepali climbers made history with the first winter ascent of the world’s second tallest mountain. Just three weeks later, one climber perished after a fall while descending from Camp 3, and another three climbers went missing high on the mountain without a trace.

Atanas Skatov was a 42-year-old Bulgarian climber. He was a member of the Seven Summit Treks team, a commercial operation vying for a winter ascent of K2. Skatov made it as high as Camp 3, but was beaten back by the harsh conditions and began retreating to Basecamp. Skatov unclipped to pass an anchor on the fixed lines, lost his footing, and fell to his death. He was among the most experienced climbers on the mountain this winter, with 13 successful ascents of 8,000-meter peaks under his belt.

Skatov was the second member of the Seven Summit Treks team to lose his life on K2 this winter. Catalan climber Sergi Mingote also died after a fall while descending from Camp 1 to Advanced Basecamp.

A team made up of John Snorri from Iceland, Juan Pablo Mohr Prieto from Chile, Muhammad Sadpara from Pakistan, and Muhammad’s 22-year-old son Sajid Ali Sadpara also faced tragedy this week.

The foursome left Camp 3 for a summit bid on February 4. Muhammad and Sajid Ali were climbing without supplemental oxygen, and by the time they reached the Bottleneck at 8,200 meters, Sajid Ali was not feeling well. He tried using an oxygen regulator but it was not functioning properly. His father instructed him to descend back to Camp 3, and the other three climbers continued pushing for the summit. That was the last time anyone saw them.

The group climbed without a satellite phone or walkie talkie, and evidently their GPS tracker was not working. Without communications, it is still a mystery at this time as to what happened to the three climbers. Sajid Ali returned safely back to Basecamp and said in a statement two days later:

“I think they reached the summit. They must have had the accident on the descent because at night it started to get very windy. They have been eight-thousand meters for two days, at that height in winter I have no hope that they are alive.”

In the days following the team's disappearance, summit temperatures on K2 hovered around -80°F with windchill. At the time of this writing, they have been missing above 8,000 meters for six days. Three reconnaissance helicopter flights have gone up to 7,000 meters searching for any sign of the missing climbers but have come up empty handed. Bad weather has continually thwarted rescue attempts.

Nirmal Purja, summited K2 in winter without supplemental oxygen just a few short weeks ago, wrote on Instagram: “I feel a bit heavy hearted while writing this note as we have shared some great stories and memories with these guys. I didn’t get to know John very well but he seemed like a great guy. JP is cool, humble, and a strong climber. [Muhammad] is closest to my heart, who has always been a big brother to me… He always treated me as his younger brother and sometimes shared his words of wisdom and experiences. I cherish all the memories that we shared.”