Ice Crystals

It's still cold here. The sun is shining and sky is clear, except for a few wispy high-altitude clouds, and is that pale blue colour I associate with intense cold.

While digging coal from the bunker earlier this morning I noticed the snow had changed overnight. I can see where moisture has condensed direct from the air and extended the crystals, froming little whiskers, some a couple of millimetres long. It's very pretty to look at close up, and gives the snow a sort of "knobbly" appearance from a distance.

When on a walk down to the village a little later I started thinking about "why does traffic turn snow to slush?" (assuming no use of salt). There seem to be two candidate explanations:

1. The traffic gives energy to the snow, raising its temperature briefly,
2. Increased pressure decreases the freezing point of water. This is sometimes demonstrated by the "wire passing through the block of ice" experiment, and is given as the explanation for why ice skates glide over the surface of the ice so well (but there is some debate about whether this is in fact correct).

I doubt I will bother to do the sums over Christmas.