The summer he was 16, Sebastian Junger tried to save the boy who was trapped under the ice, but the boy wasn’t there.

Seb—that’s what everyone called him—was climbing high in the Alps with a group of kids his age, part of a summer outdoors camp typical for teenagers in France, where his family lived at the time. Seb was a good climber. He was comfortable out there, the ice thick under his crampons, his body—strong and experienced for his age—sweating in the cold mountain air. Ice ax in his hand, rope wrapped tightly around his waist, intertwined with the rest of the group.

They made their way down a particularly nasty ice chute, a slippery gully that would be the most challenging few hundred yards of the multiday trip. It was tricky for him and even for the guide. But they made it, steadily and carefully, to the bottom, where they rested on a large rock outcropping. They were taking off their crampons and drinking water when they heard voices from the top of the gully. It was a group of two dozen French boy scouts, a couple years younger, and Seb could see that they were going at it all wrong: disorganized, underequipped. Then one of the kids who was farther back slipped and slid into the others, triggering a human avalanche down the chute, a ghastly mass of arms and legs and snow and ice hurtling out of control to the bottom. Within seconds, the boys crashed just a few yards in front of Seb and his group, landing headfirst in a deep pile of heavy, wet snow, limbs sticking out at grotesque angles. Seb’s group could hear the muted screams of the boys buried underneath.

“Trois minutes,” Seb’s guide said. Three minutes. That was how long the children could breathe under there before they would die.