To a seasoned skier, nothing could be more alluring than a descent into a high-country valley carpeted with fresh-fallen snow. And nothing could be more treacherous. The same pristine slopes that offer powder hounds the thrill of carving first tracks can conceal thrills of a more perilous kind: avalanches, known to mountaineers as the "white death." Avalanches have already claimed 19 lives in the U.S. this winter. And last week five Coloradans, who lost their way in a subzero Aspen blizzard, were almost added to that number, raising awareness of the hazard.
"We never doubted we would make it," declared 50-year-old...