Why does snow crunch when it’s cold?
When temperatures drop, interesting things happen in the world around us. Cold temperatures can affect everything from feel and sight to even sound. One of the more familiar sounds of bitter cold is the crunching squeak of cold. The creaking noise happens at just about every temperature, but it’s the bitter cold that makes it most audible.
Think of snow falling from the sky. Neat little flakes coast down from the sky above. The flakes themselves are made up of ice crystals and air. Then around each flake is even more air separating the flakes in the atmosphere.
As the snow accumulates on the ground, those pockets of air between the snowflakes themselves remain. Just a lot smaller than in the air. When we meteorologists measure snow, we often check the snow to water content ratio. A pretty normal number is 10-to-1, meaning for every 10 inches of snow there is just one inch of water there if it is all melted.
That’s a lot of air between snowflakes. Enough air that when you stomp on some fresh snow, it kind of goes "whoomf." No matter what the thermometer says.
But after it settles and compacts the space between flakes shrinks. The ice crystals wind up smashed against one another and even refreeze to one another.
If it is warm (teens Fahrenheit or warmer) the weight of your foot or tire of your car melts the snow beneath it as it compresses under your body weight. Because the snow melts, the compaction is silent.
As the temperatures fall into the single digits and below zero, the snow no longer melts. The weight of your foot or the tire of your car breaks the tiny bonds holding the flakes together. The friction caused by the breaking is the squeaky crunch you hear when walking on snow on a cold day.
So that sound is unique to cold weather. Too warm and the snow melts under pressure, cold enough and the snow doesn’t melt — instead the bonds break, making the satisfying squeak of a cold winter walk.
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