Albuquerque, N.M. ? Former Gov. Gary Johnson says he thought he was going to die when part of an icefall collapsed during his descent from the summit of Mount Everest.

“That was the scariest part of the whole thing,” he said Thursday.

Johnson, who made it to the 29,035-foot summit May 30, said he and fellow climber Dave Hahn were on top of the Khumbu Icefall when it collapsed.

“We can’t see it. We can just hear it, and it’s close. We hear the crash,” Johnson told the Albuquerque Journal in a telephone interview from Katmandu, Nepal.

“We were certain we were dead, that it was going to domino,” Johnson said. “It was petrifying.”

The icefall, which is constantly shifting, is a glacier pitched over a precipitous drop at 20,000 feet on Everest.

Former New Mexico Gov. Gary Johnson negotiates the Hillary Step on his way to the summit of 29,035-foot Mount Everest.

Johnson said he had another close call coming down from Everest — he forgot to turn back on his oxygen. He had turned it off for the half-hour he spent on top of the mountain, and estimated he was without oxygen for about two hours.

“I bonked,” the 50-year-old said.

“When we got down to the South Summit, Dave notices my oxygen is off. Dave said, ‘Not only did you not have oxygen, but you had a rubber mask over your face.”‘

It was exhilarating to stand atop Everest, Johnson said. “It was so cool. What a view. Man. Unbelievable.”