Roughly half of the teams preparing to climb Everest have begun their descent from Base Camp following last week’s tragic avalanche that killed at least 13 sherpas.

The BBC reports that there were around 50 expedition teams at base camp, with 31 of those headed to Everest. There were around 300 foreign climbers due to climb Everest this season, but the avalanche has left this in doubt. The Nepalese government has assured those turned away that their climbing permits will be valid for the next five years.

The avalanche was the most deadly accident in modern Everest mountaineering, killing 13 sherpas who had climbed the slope early in the morning to fix ropes for climbers intending to make the climb. It struck the Khumbu Icefall area, which is a passage with ice boulders that can break off without warning.

Merrell Pack Alpha Michael Chambers was due to be climbing Everest before the disaster struck, but is now on his way back down.

Speaking to The Pack, Chambers mentioned that they were actually due to be in the avalanche region on the day, but weren’t due to pure chance: “We were supposed to be in the icefall that morning but fortunately one of our team members was sick.”

“We have cancelled the expedition out of respect for our Sherpa team who lost many friends, brothers, and cousins in the avalanche. Will be back home in a few days,” he added.