February 25, 2005


Freshly fallen snow is really nature's white noise machine.

That's right. It really is quiet after a snowfall, and not just because everyone is hiding indoors.

Scientists have discovered that in the first hours after a snowfall, the flakes have a rare acoustic quality to absorb sound waves.

Sometimes it lasts for just a few hours - as in a slushy snowfall. Other times, when it's covered by freezing rain, it heads to the opposite end of the acoustical spectrum and echoes like concrete.

Researchers worldwide, particularly where they get lots of winter weather, say they study the sound of snow in hopes of figuring out everything from avalanche triggers to noise insulation.

"After a fresh snowfall, it's very quiet and then once it's blown by wind and sunshine, it hardens and loses its effectiveness," said Gilles Daigle, who researches sound acoustics for the National Research Council, a governmental research agency in Ottawa, Canada.

"It's a quality-of-life issue here," he said, adding that he started studying snow acoustics in the 1970s, as part of an effort to reduce noise pollution. "We take into account where we should construct the roads and what kind of zoning to allow around it - it's all about land-use planning."

The reason snow works so well as a sound insulator is because all the crystals are shaped differently. So when they fall on each other, they stack like differently shaped blocks, leaving lots of air between the flakes. The air works like the holes in a sponge, trapping sound waves and dampening vibrations.

"The grains themselves aren't very spherical, so when it first falls, it's very fluffy," said Douglas Durian, who studies the physics of granular materials at the University of Pennsylvania. "It's the fragility of the packing that gives rise to the tremendous ability to dampen vibration."

All of which is more easily done with fallen snow. Falling snow, however, is much harder to study.

Snowflakes are tiny hard crystals and may scatter sound more than absorb it. But they're hard to study - they don't stay still and aren't predictable, say scientists.

It may seem like the study of snow acoustics is silly, when it just lasts for a day or so. But to Jerome Johnson, it was a matter of saving lives.

Johnson works for the U.S. Army Corps of Engineers Cold Region Research and Engineering Lab in Fairbanks, Alaska. A few years ago, he studied snow acoustics for Washington state.

"The goal was to develop ways to trigger avalanches artificially as a safety mechanism without using traditional means, such as artillery rounds," he said.

Most scientists say there needs to be more studies about snow - if only it weren't so hard to study.

"The thing with snow is that it's so variable," said Daigle, in Canada. "It changes hour by hour and it's quite challenging to keep up."

Dawn Fallik/Knight-Ridder Tribune

Blond breakthrough

Quick Takes

Blondes, it seems, don't have more fun when it comes to getting rid of unwanted hair.

Doctors have long struggled to find a laser treatment that effectively removes blond, gray, red or other lightly pigmented hair.

That's a problem in a country that reports 8.3 million nonsurgical cosmetic procedures a year - with laser hair removal right up there behind botox injections.

Well, worry, no more.

An Israeli company, Syneron Medical Ltd., unveiled this month its FDA-approved Comet laser, proven effective on light hair. It uses a patented technology that combines radio frequency and light energy to destroy pesky hair follicles.

Don't look for the Comet everywhere, though. It's a medical device so it's only available in physicians' offices. Treatments will be pricey - about $300 to remove light peach fuzz above an upper lip, for example.

Bottom line: The Comet's application may seem trivial, but don't discount the technology. It's likely to be useful in the future for serious health ailments. - Mary Beth Regan

Did you know ...

Hydroplaning, the nerve-racking wet-weather driving phenomenon, can cause your car to skid or even go off the road. To avoid hydroplaning, keep your tires properly inflated, maintain good tire tread, slow down when roads are wet and stay away from puddles.

- National Safety Council

In Brief

Burst of energy from star is `once-in-a-lifetime event'

A massive burst of energy exploded from a far-off neutron star in December, the brightest flash of light ever detected from beyond the solar system.

The Dec. 27 flare was by far the largest of three such giant outbursts of gamma rays detected in the past 35 years from neutron stars, the densely packed and supercharged remnants of a collapsed star.

"This is a once-in-a-lifetime event," said David Palmer, a scientist at the Los Alamos National Laboratory in New Mexico and lead author of a paper on the flare.

Cholera vaccine may work in people with AIDS virus

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