Watch a video of McNamara and Mamala surfing the glacial wave.
"There were incredible waves with 30-to-40-foot faces," says surfer Garrett McNamara of the swells he and fellow Hawaiian Kealii Mamala towed each other into this past August. The massive freshwater rollers in Alaska's Copper River were generated by ice blocks calving off the Childs Glacier. "They barrel unbelievably," he says. They also come loaded with ice chunks, silt, and more than a few logs. The veteran big-wave riders came back from the first-of-its-kind expedition unscathed, but don't expect anyone to repeat their conquest soon. "Imagine catching a wave while you're waiting for the Empire State Building to fall on you," says McNamara. "I wouldn't advise it. At all."
Childs's 1.5-mile-wide, 300-foot-tall face calves 20 to 30 times a day. Most BLOCKS are the size of a car, but every so often a 100-foot-thick sheet breaks loose, crashing down with enough force to launch debris (and the occasional salmon) 100 yards.
Falling ice plunges into a 40-foot-deep TRENCH carved in the river bottom by previous impacts, creating supersize "ripples."
As swells move outward from the impact zone, they cross shallow GRAVEL BARS, which jack the rollers up into breaking waves as tall as 40 feet.
McNamara and Mamala positioned themselves roughly 100 yards from the glacier. At the sound of cracking ice, the jet-ski driver would accelerate up to 50 miles per hour toward the explosion, then arc away, SLINGSHOTTING the surfer onto the wave.
The rides were thrilling but ugly: a trashy MINEFIELD of silt-masked logs, rocks, and ice. "For the first five days I was just hanging on, trying not to fall down," says Mamala.
The most, uh, pressing danger wasn't the calving; it was the basketball-size ICE MISSILES from the resulting explosion. McNamara and Mamala wore helmets and flak-jacket-like reinforced wetsuits.
A RESCUE jet ski manned by medic/cameraman Chris Bauman was always ready to swoop in to pick up a surfer after a wipeout and—they hoped—before the next wave.