KATHMANDU — Nepal's Sagarmatha Pollution Control Committee opened the Khumbu Icefall climbing route on Mount Everest's south side on April 29, despite an unstable serac hanging over the key trail. The committee warned that the ice block has multiple cracks and may collapse at any time, urging all expedition operators and climbers to exercise extreme caution.

The new trail passes below the serac, which is part of the Khumbu Icefall, a constantly shifting glacier with deep crevasses and huge overhanging ice. Sections of the icefall can be as large as 10-story buildings, and it is considered one of the most difficult sections of the climb.

The massive block of ice stalled climbers from moving further up the peak for more than two weeks. Guides known as "Icefall doctors," deployed by the SPCC to lay the yearly climbing route by setting ropes and securing aluminum ladders over crevasses, usually finish route preparation by mid-April.

Around 410 climbers and an equal number of Nepali climbing guides are at the base camp, situated at an altitude of 5,300 meters, preparing for the ascent to the summit this month during the window of good weather. Climbers began gathering at the base camp last month. High travel costs and increased permit fees have not deterred hundreds from attempting the climb.

Mountain guide Lukas Furtenbach, who has 40 international climbers, 11 guides and 90 Sherpas on the mountain, said from base camp that the route was more complex and exposed than last year in one section. "Anyone who says they're not concerned is either inexperienced or not paying attention," Furtenbach said. "The Icefall is constantly changing, but right now it's not just more broken — it's also forced into a line that passes under unstable features."

Furtenbach's team is reducing loads, minimizing exposure time, carefully timing movements through the Icefall, and relying on highly experienced Sherpa and guides for risk assessment. Other expedition operators are cautioning their members about the risks and monitoring the situation.

Expedition operator Ang Tshering Sherpa advised climbers to time their movements carefully. "If you go in the morning, it might be safer because the ice is frozen, but in the afternoon it becomes dangerous as weather gets warmer, with the risk of ice melting and falling," Sherpa said.

A falling serac triggered an avalanche over the Khumbu Icefall in 2014 that killed 16 Nepali guides and workers. China has closed its route this year, leaving all climbers to attempt the ascent from Nepal on the south side.