Ogwyn, who was filming a documentary when the tragedy hit on April 18, mourns the loss of the Sherpas killed in avalanche: "It's heartbreaking"

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Joby Ogwyn was laying in his tent at Base Camp in the early morning hours of April 18, the snow-and-ice capped peak of Mount Everest looming overhead, when he heard it – the familiar “creaking and groaning” sound of nearby glaciers cracking apart.

But something about the noise made the 39-year-old adventurer sit up, poke his head out the back of his tent and what he saw horrified him.

“It was an avalanche,” recalls Ogywn, who came to Everest intending to climb it, then jump off the 29,029-foot summit in a wing suit for the Discovery Channel. “Within a couple of seconds it looked like this big white dragon, thunderously loud, moving at probably 200 miles an hour, straight toward our Sherpa, who were carrying some of our equipment up to a higher camp.”

The avalanche, which sent blocks of ice the size of houses rocketing down the mountain’s slope, ended up killing 16 Sherpas – three of whom had been hired for Ogwyn’s project – in what would become the most deadly day in the mountain’s history.

The deaths also served as a grim reminder of the risks that the Sherpa guides, prized for their incredible strength and stamina at high altitudes, are paid to undertake for foreign climbers.

“It’s heartbreaking,” says a still-shaken Ogwyn. “I’ve been climbing in the Himalayas for the past 15 years and forged a friendship with a lot of these guys. I’m shell-shocked by this. Everyone is.”

Ogwyn soon realized that his dream of leaping off the summit and gliding 11,000 feet back down to down to Base Camp would be scrapped. Instead, he grabbed his ice axe, ropes and crampons and headed up toward the avalanche with expedition leader Garrett Madison, who spent the next two days digging through the ice, retrieving bodies.

“Once this happened,” Ogwyn says, “my outlook on what I was doing there changed completely. Everyone knows each other up there. We’re like a family, but it’s a hard family to live in because every year we lose some people.”

Instead of becoming the first man to jump off Everest, Ogwyn helped work on the documentary Everest Avalanche Tragedy airing May 4 (9 p.m. ET) on the Discovery Channel.

The network will also be contributing to the American Himalayan Foundation Sherpa Family Fund to raise money for the families of the deceased.

The American Alpine Club has also started a fundraising effort to help those in Nepal who lost a family member in the avalanche.

To read more about the tragedy on Mt. Everest, pick up this week’s issue of PEOPLE, on newsstands Friday.