Why does snow start that crunch noise at low Temps?

Since we in the North East are in the middle of a cold snap I have a question about snow. I am sure you have noticed the phenomena where snow starts making that crunchy noise other than a virtually silent squish noise when you walk on it. I always wondered what causes that change and at what temperature. My observations are at cold temperatures around 20 Fahrenheit is when this weird sound starts. Does anyone else notice this?

The top layer of snow is freezing into a thin sheet of ice. The ice acts as an insulator to prevent the cold from doing the same to the snow below it. Till you step on it of course.

There’s always a small amount of water mixed in with the snow, which acts as a lubricant when the snow crystals “bump together” when you step on them. However, the colder it is, the less water is present, the less lubricated the snow is, and the noisier it gets when you step on it. (The presence of water in the snow is also why you can make snowballs only when it’s above -5[sup]o[/sup] C or so.)

Hate to be pedantic about it, but do you have a cite for that? Here’s one for the lubrication theory.

I don’t know about where you live, but around here right now, the snow is already frozen when it arrives. It certainly has no icy coat on top of it, it’s a loose, fluffy powder in our -10 Fahrenheit environment. And it makes that squeaky crunch that the OP describes.

I believe this occurs because at low temperature the snow ratio is very high. This allows significant air space between snow flakes. When you apply pressure, the snow is compressed, the flakes rub together, and make a crunching sound.

Snow which falls at near freezing is more densely packed, with a lower snow ratio. It won’t compress under pressure.

Ahh, we seem to be talking about different “crunches.”

**racer72 **is talking about that crunch you get when the top layer of snow melts ever so slightly then is frozen again, creating a stratum not unlike a well-prepared crème brulée. This is a real crunch, where a solid surface is broken.

Everyone else appears to be talking about that sound that you hear as your footstep compresses fluffy snow, which I realized when I saw QtM say “squeaky.” It’s not so much of a crunch as an implosion.

Children from my generation know that snow squeaks underfoot 'cause of Fridgits!

Over in this thread where they were talking about boiling water instantly turning into snow, the OP happened to link to a video in which you can hear the squeaky snow, and the current temp was shown.

*** Ponder

Our snow tends to be made of small dry flakes – they ain’t joking when they call it powder. And it squeaks like crazy underfoot. I assume that the lower the water content, the noisier the snow.

We got eight inches of fluffy snow on Saturday and it made no noise as you walked on it. Now that the temperatures are in the low teens, it’s crunchy for exactly the reason racer72 said; the topmost part of it iced over and you crush the crust when you walk on it. It doesn’t matter if it was dry fluffy snow or heavy wet snow, when it gets cold enough it all crunches.

Your snow may have a crust, but ours at present certainly does not. And it still crunches and squeaks.

Believe me, I recognize crusty snow.

I’d go with MikeS’s cite/site as an explanation of the chrunch that comes with low temperatures as mentioned by the OP. It’s not due to crust or compression of previously fluffy snow. A crust* forms at a much higher temperature than the 20F transition mentioned. It’s not due to compression of fluffy snow either, because at low temperatures the snow will squeak/crunch again and again even if you step on the same patch. Of course some compression is involved, but it’s not like it starts fluffy, compresses and the springs back.

*Ice crust on snow is called “skare” in Norwegian by the way. If you can walk on it at mid summer and not break it, it’s going to be a late spring. At least according to an old saying.

:eek:
I’d say if you can walk on it at mid summer, it’s going to be a late summer! :smiley:

That’s just a consequence of the very late spring. :wink:

You can hear the same phenomenon on the beach in the summer. Walk on the dry sand & listen to it move underfoot. Then go down near the water’s edge where the sand is wetter. The sound changes.

You can discover a lot of different sounds between the area where the water is 1" deep to where the water hasn’t been for 2 minutes, two hours, or two days as you move inshore.