“Fresh snow is more like a pile of feathers,” Patel said. “There are many air pockets between the snowflakes, and that’s why the snow’s so fluffy and soft.”
When you walk on fluffy snow, it probably sounds swooshy or squeaky.
But then the sun comes out.
The sun’s warmth melts the top layer of fluffy snow. That makes liquid water that oozes into the air pockets between the snowflakes in the deeper layers of snow.
If the temperature drops again, like when the sun goes down, the snow refreezes. The liquid water between snowflakes freezes, too. Now the snow is dense and packed together. The air pockets are full of ice.
“Imagine you have a glass of crushed ice,” Patel said. “Then you pour in some water to fill the spaces between ice cubes. If you refreeze it, it makes a block of ice. That’s what happens outside, too.”
Outside, the snow can melt and refreeze over and over as the daily temperatures rise and fall. Each time it freezes, the ice becomes denser. That can make a thick layer of ice.
When you walk on that ice, it’s slippery and brittle. The ice crystals break and rub together. That makes a crunchy sound. The level of crunch depends on how cold it is. At lower temps, the ice crystal are harder and more brittle, which means crunchier snow.
As you walk, your steps create pressure and a tiny bit of heat. That, plus the sun’s warmth, melts the snow even more. It becomes less crisp and more sloshy.
You could say that, after a fresh snowfall, the texture is a slippery slope — from fluffy to crunchy to mushy to … gone.
Sincerely,
Dr. Universe
Ask Dr. Universe is a science education project based out of University Marketing & Communications at Washington State University.