Thoughts On Winter Frosts

[Progenitor A]

Last night there was a hard frost (I do like that adjective, it is so succinct and so accurate - severe frosts actually do make things harder, be it water or the ground)

So this morning as I walked the dog, the grass and branches were silvered and sparkling in the morning sun. The previous day's muddied tracks now crunched satisfyingly as the frozen earth crumbled underfoot and my dog stared in astonishment as he tried to drink from frozen pools of water

English weather at its best

But, looking at the frozen puddles that rejected my dog's slopping tongue, I noticed something that everyone has seen before a thousand times, yet I did not know why it was so!

For underneath the frozen surface of the puddle were air pockets!

How on earth do they get there?

[alancalverd]

The top layer of water freezes from the edge, so its height is fixed. It may subsequently accrue dew (slick ice) and frost crystals on top. Meanwhile the water below continues to diffuse into the soil and is not replenished by dew, so air is sucked in around the edges. If the air remains cold for several days you will find thin sheets of ice with no water underneath.

[Progenitor A]

Jan 6, 2017 1:59:38 GMT 1 alancalverd said:

The top layer of water freezes from the edge, so its height is fixed. It may subsequently accrue dew (slick ice) and frost crystals on top. Meanwhile the water below continues to diffuse into the soil and is not replenished by dew, so air is sucked in around the edges. If the air remains cold for several days you will find thin sheets of ice with no water underneath.

Thanks, similar to my thoughts. The ice remains at a fixed level whilst the water below shrinks. In situations where the water level remains constant (such as my garden cast-iron water feature), no air appears below the ice

[jonjel]

In similar vein I recall going fishing many winters ago with a friend. He knew a shortcut across a field. About half way across we fell through the ice. It was a field of sprouts which had flooded, then frozen and the floodwater had then receded. After around 20 minutes of much cursing and exhaustion we managed to smash our way to the edge of the field as there was no way we could climb back onto the ice.

Happy days.