One climber died and another was seriously injured after the two-person team fell about 1,000 feet while climbing a mountain in Alaska’s Denali National Park, officials said Friday.

The fall from Mount Johnson occurred Thursday night, the National Park Service said in a statement.

The climbers were tied together and were climbing the 5,000-foot route known as “the Escalator” when they fell, park officials said.

Their names were not revealed. The second climber suffered “serious traumatic injuries,” the park service said.

Another group of climbers witnessed the fall, called in around 10:45 p.m. local time and then climbed down to help, authorities said.

They built a snow cave to help the surviving climber until a rescue helicopter and rangers reached them around 7 a.m. Friday, the park service said.

Mount Johnson is about 8,400 feet high. The route the climbers were following is a steep technical alpine climb on the southeast face of the mountain, officials said.

The injured climber was flown to Talkeetna, south of the national park, for medical care, and a helicopter recovered the dead climber’s body later Friday, the park service said.