<p>Does anyone happen to know why a pile of snow slowly shrinks even on days when the temperature never rises above the freezing point of water? </p>
<p>I know there are 2 variables that combine to control the phase of a substance: temperature & pressure.
But in this case, I don’t think there is any immediate change in pressure, and the question already stated the temperature doesn’t change. </p>
<p>So…anyone know why?</p>
<p>sunlight hitting the snow- light energy becoming heat energy would be my guess</p>
<p>yes… ^that…</p>
<p>Snow is also slightly white and slightly transparent, so some light is reflected and some light is transmitted. That means some light can be transmitted through snow into the middle of the pile and be reflected and transmitted within the pile. So the pile can act a bit like a greenhouse.</p>
<p>There’s also the reason why skates can slide on ice. At first it was thought to be the pressure of the blade on the ice causing the surface to melt, but it isn’t actually. Skates can glide because of “surface melting,” because molecules in a solid lose some of their structure at the top surface, since the molecules at the top can have maybe half the number of attractions between them and other molecules since they have no upper neighbors. The molecules on top can therefore become loose and liquid-like. There’s also friction, which generates heat. What can I say, I found a website, because I read about it in my chemistry book and needed to recall the details. So my point is that if there is surface melting, which is probably more common in a snow pile than in a sheet of ice since the molecules are less tightly packed on the whole, once some of the snow is melted on the surface, the liquid can evaporate more easily. I’d guess this effect is pretty small, but who knows.</p>
<p>Thank you very much :)</p>