snow is weird stuff. I spent a lot of time in France when I was younger being a ski instructor, and working in a French research establishment in the Alps. Some snow is really sticky, some snow makes great snowballs, some snow won’t stick together at all and some snow slides in great slabs – avalanches. There is still a lot to learn about snow.
There is a theory that says that when you put pressure on ice (or snow) it melts, and if you have ice-skates on the force from your body weight is over a very small area and creates a very high pressure leading to the ice turning to water and you sliding – this is probably true. However this ISN’T how skis work, because in general the longer the ski, the faster you go – thats why the downhilll skiers have huge skis. So you are putting the force over a greater are than you feet, and the pressure is lower than when you just stand there. So its not the water layer theory.
I believe this is certainly true of ice-skating – the pressure from the blade of the skates is enough to melt the ice underneath providing a slippery layer of water that allows you to glide gracefully.
For skis and snow, I’m not so sure. Snow is just another form of ice (loosely packed crystals) but the pressure exerted by skis will be much less than the pressure exerted by ice skates since the skiers weight is distributed over a much greater area.
OK – I did a little hunting (isn’t the internet great?) and it looks like skis may also work by temporarily melting the snow underneath. Perhaps it is easier to melt snow since it is made of little crystals rather than a solid block? An interesting observation that supports this view is that skis are no longer slippery below about -40°C. Below this temperature, it is probably too cold for the skis to generate the layer of water needed to slide.
I’m not an expert on the physics of snow and skiing but it rings true. The friction between the skis and the snow would be enough to melt the ice crystals in the snow, which would make the surface very slippery. because it’s made up of little crystals which can move against one another, I don’t think snow would be very slippery if it weren’t for the melting.