At one point we stopped at an arbitrary overlook to take in the view of the lake's still-frozen East Arm. We turned the engine off, shut the car doors behind us with a familiar muffled *whump* and stepped into the most profound silence I've ever known.
It was like being submerged. We could feel the silence pushing up against us from all sides, viscous and smooth. Our ears rang with the afterglow of life's daily din and howl -- the sounds of engines, of people, of heavy machinery and flowing air -- now absent for the first time in who knows how long. We stared at each other, mouths agape, stunned by the stillness.
I forget who spoke first, but I remember what was said -- a single word, whispered:
That moment on the lake's frozen shore was like an aural trip in time, back to an era before humans left their indelible mark on the landscape. And it's an experience that the National Park Service wants more of us to have. To that end, the Park Service made a highly-detailed map last year of what the United States would sound like if you were to remove all traces of human activity from the picture. Here's what that looks like:
This map, along with the Park Service's map of the human soundscape that came before it, is the product of a massive project involving 1.5 million hours of audio recordings taken at 479 locations in the United States. Those recordings were fed into sophisticated computer models able to produce estimates of the aural landscape throughout the U.S. with a frankly amazing level of detail and accuracy.
To arrive at estimates of what the world would sound like without people, "a natural scenario was synthesized by systematically minimizing human factors, leaving only physiographical sources of sound like wind, flowing water, precipitation, animals, and geological events," according to the National Park Service.
As you can see in the map above, the most naturally quiet areas occur in the arid regions of the west. The noisiest regions tend to be along the coasts and waterways, particularly the Everglades in southern Florida and the lower reaches of the Mississippi River.
In short, where there's water, there's noise. This is partly because water itself is noisy -- think the pattering of raindrops, the burbling of creeks and the crashing of waves. But where there's water there's life, and life is pretty noisy too. "The trend is higher sound levels in wetter areas with more vegetation," the National Park Service writes. "This is due to the sounds of wind blowing through vegetation, flowing water, and more animals (especially birds and frogs) vocalizing in more fertile locations."
The map also shows the impressive range of the natural soundscape, running from an average of fewer than 20 decibels in the high desert regions to 40 or so natural decibels in the wetter, more biologically raucous reaches of the country. An increase of 10 decibels is equivalent to a tenfold difference in the power of the soundwaves producing the sound. So a change from 20 to 40 decibels is equal to a one hundred-fold difference in the magnitude of sound typically experienced in the nation's most naturally quiet and noisy areas.
I'm not sure what decibel level we were experiencing that day on Lake Itasca. Absolute silence is basically unheard of in the natural world, and after a few minutes of acclimation we began to appreciate the existence of a whole new soundscape of subtle noises and cadences usually buried under the regular sounds of daily life -- a leaf skitting across the ice, a whisper of wind across a tree's uppermost reaches, a grumble of ice settling in on the lake.
Before long however another car came trundling down the road, driving out the stillness ahead of it.
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