Have you ever noticed how, after a big snowfall, the landscape gets very quiet, and everything looks like it’s covered in that insulation you find in the walls of houses? Things that had a distinct shape before — wheelbarrows, mailboxes, parked cars — all become muffled lumps, and the ambient noise we’re all so used to is suddenly gone. Some of this has to do with the fact that heavy snow can result in folks staying inside, cutting down on traffic noise and the sounds of tag football games and such. But there’s something else: Fresh snow actually is kind of like nature’s blow-in insulation.
Snow Creates Air Pockets
Snow makes everything it falls upon look so lumpy because each snowflake is an irregular shape — a six-sided, crystalline structure that doesn’t lend itself to stacking neatly atop other snowflakes. As billions of snowflakes fall on top of one another, they don’t merge together and zip off the landscape like rain; instead they pile up on each other like a bunch of origami cranes, creating a material that has lots of tiny holes between each flake. This porous material smooths out all the sharp edges that make the things the snow falls upon distinguishable from each other. The little nooks and crannies between the snowflakes allow sound waves to enter, but then it strips them of their energy as they make their way through the fluffy material.
How Does Sound Travel?
Sound travels in mechanical waves, and in order for something to make noise, physical molecules — gas, liquid or solid — must be jiggled around in order for sound to be transmitted. Temperature also affects how quickly sound waves can move: They speed up in warmer weather and slow down when it gets cold. Not only can sound waves in cold weather be a little sluggish, falling snow can interfere with them, making sounds in a winter wonderland seem muffled.
A blanket of fresh snow also does a lot to dampen noise. Sound absorption is measured using a scale called sound absorption coefficient alpha (α), which measures how well a material absorbs sound on a scale from 0 to 1. The sound absorption rating for snow is in between 0.5 to 0.9, which means, at its most effective, a few inches of new fallen snow provides an impressive amount of acoustic insulation for a lot of different frequencies of sound. One study, published in 2016 in ScienceDaily, found that a couple inches of snow can absorb roughly 60 percent of ambient sound.
Why Doesn’t the Quiet Last Long After Snowfall?
The sound-dampening air pockets don’t last very long after snow falls. The shape of the delicate snowflakes changes pretty rapidly once they settle to the ground — as they begin to snuggle in together or melt, the space between them shrinks, leaving fewer spaces for sound to travel and get trapped. In addition to that, once the sun hits a snowy field a thin layer of ice forms on the top almost immediately, so the porous material that traps noise in its first hours becomes a soundwave reflecting surface that turns a silent landscape into a sort of amphitheater.
So next time you hear that hush of new fallen snow, enjoy it! It probably won’t last long.