OK, so these girls are not naked, they're in swimwear, maybe underwear at a push. And it's hardly unbelievable that they're out in the snow dressed like that really, given that every snowboarder with an ounce of sense wears sun goggles, and you're liable to end up with a sore red nose after a day on the slopes if you forget to slap on plenty of sunscreen. No, outside of the winter season the weather up on the mountains can be pretty balmy, and all of that expensive snowboarding gear is as much about protection as it is about keeping warm.
But have you ever wondered why the sun doesn't melt the snow? It's actually down to pretty straightforward thermodynamics. Basically, snow just happens to be really good at reflecting back heat generated by the light of the sun. Fresh snow will reflect about 90 per cent of the sun's rays, which is partly why regular snowfall helps to maintain a healthy spread for longer.
When snow does finally melt, it's actually caused by warm air floating up from the sea. So if the snow is at a high enough altitude to be beyond the reach of the sea air, it doesn't have to melt at all. Except that sooner or later it'll turn to ice, which is easier to melt, although by that time more snow has fallen, so... You get the idea! It's basically what creates the classic snow cap on a mountain, and more importantly it's the reason you can ski or snowboard all year round in some places.
So if you feel like taking your snowboard out in a pair of your Granddad's old Y-fronts, it's really up to you. Of course we'd prefer it if you didn't, and please, at least wear a helmet.