Why does cold snow squeak?

I walked to work today. My home thermometer said it was -9 degrees. And the snow was squeaking. Why does it do this? No one has definitively studied it, but here are some possibilities.
1. When you step on really cold, stiff ice crystals, the jagged edges rub abruptly against one another. Think of it sort of like a cricket rubbing the barbed edges of its legs together. As snow warms, it may become a bit more flexible, and loose water molecules in the snow may lubricate it, so the squeak goes away.
2.Another possible explanation is that the pressure of stepping on the air-filled snowflakes rapidly expels the air and produces the characteristic squeak, sort of like a very small, high-pitched whoopie cushion.