By DAN CRAY /LOS ANGELES

hen American explorers Lewis and Clark navigated the Columbia River in 1805, they first heard the roar of the Pacific Ocean 29 km from the coast--a distance so great that many historians have questioned its accuracy. No such doubts trouble Gordon Hempton, a 45-year-old professional sound collector who won an Emmy Award in 1992 for his Vanishing Dawn Chorus, a recording of the sounds of sunrise from around the globe. Hempton is an acoustic ecologist, a relatively new breed of environmentalist committed to preserving the world's natural sounds before they are drowned out by the din of machine noises. For the past 18 years, Hempton has forayed into some of the planet's most remote wilderness areas to record and preserve these endangered soundscapes before they vanish forever.

"Most people have the illusion that there are still quiet places on planet Earth," says Hempton, "but that's not the case." Indeed, noise pollution has become so bad that Hempton estimates intervals undisturbed by man-made noise in American national parks rarely exceed a few minutes. His long treks into the backcountry woods around Olympic National Park in the state of Washington where he lives are regularly interrupted by the roar of aircraft and the buzz of chain saws. "It's wonderful when insects begin to hum at dawn and you hear the countless wings beating from many square kilometers around you," he says. "Then you hear an insect you haven't noticed before--and of course, it turns out to be a jet."

But Hempton is fighting for the right to peace and quiet a few centimeters at a time. The Dawn Chorus Project would establish zero tolerance for human noise intrusions in 2.5 sq cm sites in 10 U.S. national parks. But since the roar of an airliner, for example, can carry 32 km, a vast area would have to be made noise-free to get those square centimeters of silence. The likely result: no more helicopter tours of the Grand Canyon, no more snowmobile rides in Yellowstone, no more boom boxes at Yosemite campsites. Officials with the U.S. Department of the Interior admit noise has become a problem and applaud Hempton's idealism, but they say his proposal is too extreme. "Gordon wants a pure sound, while we're more concerned with handling the worst noise sources," says Wes Henry, wilderness coordinator for the National Park Service. Not good enough, argues Hempton, who points out that the drive to attract tourists has increased noise levels and that airline flight patterns still routinely take planes over nature reserves. "[The Department of the Interior] is saying natural sounds are being protected," remarks Hempton, "yet there has never been a single acoustic inventory in any national park." As part of his project, Hempton intends to carry out these acoustic surveys, painstakingly cataloguing the threatened sounds of nature: the faint lisp of snowflakes in winter, the rush of wind through pines.

Hempton believes people must realize that natural soundscapes should be conserved like any other endangered species. To achieve these islands of silence, he suggests some simple solutions: Alter flight paths, use pioneer methods to maintain trails and ban some forms of tourist activity. "National parks are like natural cathedrals," Hempton says. "The acoustic environments inside these cathedrals deserve the same respect we have inside our man-made cathedrals." Hempton's only prayer is that someone in the U.S. Department of the Interior is listening.