Why does snow squeak when you walk on it?

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Why does snow squeak when you walk on it?
snow frozen to faces of prospectors
62 degrees below zero! From Wikimedia

Snow can make both ‘squeaky’ and ‘crunchy’ sounds. Snow is a mixture of ice crystals, liquid water and air, and the sound it makes when you walk on it depends on the proportions of this mixture.

When you walk on snow, your boots apply pressure that can break its ice crystals. When the snow is warmer than about minus 35 degrees F, its ice crystals are surrounded by a film of liquid water that lubricates them so they can slide past one another without breaking.

The more water around the crystals, the less likely the breakage, so if the snow is colder than 14 degrees F, your boot will crush the ice crystals, making that squeaking, or creaking, sound. Snow above approximately 14 degrees F contains enough liquid water for the crystals to “flow” silently under your boot. You’ll never get a squeak striding through slush!

The crunchy sound, on the other hand, is made by cold, packed snow. Snowpack is made of ice grains. Where they touch, they bond or weld together like a matrix. These bonds are weak in fluffy snow and strongest in cold, dense snow. The crunchy sound occurs when the bonds between the ice grains in the snowpack break apart when you step on them.

You’ll never hear the crunch walking in fluffy snow!

Steven A. Ackerman and Jonathan Martin are professors in the Department of Atmospheric and Oceanic Sciences at UW-Madison, are guests on the Larry Meiller‘s WHA-AM radio show the last Monday of each month at 11:45 a.m.