Did You Hear That Snow??

A look at the acoustic properties of snow




Snowy Mountain Valley View

  Snow... Snow... Snow...

A favorite line from the memorable song, "Snow" popularized in the 1954 movie, "White Christmas", sung by Bing Crosby along with movie cohorts Danny Kaye, Rosemary Clooney, and Vera Ellen. How I looked forward to watching that flick during the holiday season as a child. Made me want to ski in snow-covered mountains of Vermont myself... Well... At least it did till I discovered skiing was NOT a forte destined to lend me bragging rights!

Just the same... Though living at an elevation that enables me to enjoy distant snowflakes tightly stacked atop snow-covered mountains without having to trek through their depth myself, I still get kicks watching those clean gentle flakes trickle through the air whenever the temperature falls to a snow-producing level in my neighborhood. Always a thirll... it is... viewing the soft icy droplets that float onto my lawn and trees and surrounding areas. Always a joy... Always a wonder when this freshly falling miracle unfolds...

Those among us who truly enjoy snow's special wonder, no matter how many times we witness it falling from the clouds, continue to find stepping onto snowy fields exhilarating and inviting. Many also find ourselves wondering how such delicate miniscule flakes can manage to exert so much noise beneath our footsteps.

As it turns out, snow noise has to do with its acoustical properties. That's right... Despite its gentle, near weightlessness, snow posesses the ability to create acoustics that allow it to produce sound; and these acoustic properties play roles in snow ’s ability to escalate as well as to redirect sound. Now... Who would have thought those precious little flakes had the ability to do all of that?!

Unlike raindrops that can be quite noisy when falling on rooftops, umbrellas, and sidewalks, snowflakes produce much lighter softer sounds. As snowflakes fall from clouds and make their way to earth, they float along in unhurried fashion, swaying hither and there, as if savoring their descent. This gentle floating, in contrast to rushing raindrops, adds to reasons why falling snow acoustics lean toward quietude.

Despite the lightness of individual snowflakes, however, as flake after delicate flake falls atop one another while landing on any given surface, they form snow layers that alter their sound. The deeper the layers become, the more altered their sound becomes. Snow's ability to alter its acoustics is a major reason passersby can spur snow noise beneath their feet as they tramp across the layers. Of course... most people do not refer to snow in terms of layers; but rather, how deep it is or how their shoes sink into it.

A good way to envision snow altering its sound is to picture it in this manner: When snow falls to the ground, each snowflake that follows the one before it leaves a minute space between itself and its predecessor flake. Compare this act to dropping a deck of playing cards onto a floor, one by one. As the cards flip and fall, they likely will land near or on top of one another when dropped in the same area. However, they do not land exactly atop one another but they do leave microscopic spaces between each other that holds pockets of air.

Now imagine that the cards are snowflakes-only with different shapes... Well... Individual snowflakes do not fall directly on top of other flakes, just as playing cards do not fall directly on top of other cards-only there is a difference. The fact is that parts of snowflake “bodies ” are likely to fall on top of more than one flake; just as with dropped playing cards, however, spaces between snowflakes are likely to harbor more air pockets than playing cards.

The difference that enables snowflakes to harbor more air than playing cards is that unlike cards, snowflakes do not all have the same exact shape. For this reason, even if they did fall directly atop one another, they would not fit together perfectly such as playing cards would fit if you stacked a deck. Now... If you could capture millions of snowflakes, without disturbing their makeup, perhaps you could create a stack with like shapes... For now, simply gather that the inability to fit together increases snow layer air capturing ability.

But wait... Shapes and spaces do not determine snow acoustics on their own... In addition to spaces left between multi-shaped piles of snowflakes providing opportunities for snow to make acoustical sounds is the ice factor.

As everyone knows... Snowflakes are made from frozen water, otherwise known as ice... Likewise, everyone knows ice can be quite noisy! With these facts in mind, it should be no surprise that snow's icy makeup contributes to its ability to produce sound.

Indeed... Each snowflake's’ ability to float from clouds in quietude has to do with its appearance following its conversion from ice to flakes. Were it not for this conversion, snow would likely sound just as loud, or even louder when it hits the ground, as sleet and hail does.

Another interesting note about snow acoustics is its ability to absorb sound...

That's right... Since falling flakes do not fit perfectly atop one another when they land the spaces between layers that entrap air also acquire the capacity to absorb sound waves. When footsteps disturb ground snow, or children fall on fields of snow to make angels, contact pressure forces trapped air to squeeze from the flakes. The released air, filled with sound waves, causes ground snow to make acoustical sounds.

If you've ever made a snowball, its accoustics likely filled your ears. If you've ever made a snowman, or otherwise rolled forever-growing snowballs along the ground, you likely noticed the sound elevate with each inch the orbs grew-that is... if you were in a field of deep snow because as it turns out, the loudness level at which snow sounds when disturbed depends on the thickness its layers. This is because thicker layers trap more air and thus are likely to have louder acoustics than thinner counterparts.

One other fascinating snow acoustical fact...

In addition to creating acoustics by forming air pockets, and absorbing sound, snow also reverberates sound.

Sound reverberation, or reflection, occurs when snow gets hard. Snow gets hard simply by lying on the ground, hanging onto trees, or sprawling across rooftops. Factors that contribute to snow hardening include aging, temperature decreases, and wind.

Aging Snow

Snow hardens as it ages because it loses its suppleness.

Freezing Snow

Snow hardens as temperatures decrease because cold temperatures causes it increase its “freezing  capacity".

Winded Snow

Wind affects snow layers by smoothing out their surface areas. This smoothing out causes snow layers to become ice-like. The icy state aids snow ’s ability to reverberate sound.

Next time you encounter a showing of these delicate flakes, take a closer look at their icy makeup as you lift a million pieces from the ground or catch a few floaters from the air. Enjoy the sound they make should you decide to smash the miraculous flakes together. Yes... Listen closely... Enjoy the wonder of their acoustical sounds.... and did you know...?

Snow acoustic properties also present when snow lands, such has been shown by research when snow lands on water.

Other studies, currently underway, aim to use snow acoustics to predict when avalanches are about to occur.

Snow... Snow... Snow...

Oh! The wonders of snow...

When you DON'T have to shovel it! :}