Saturday, December 25, 2010
Snow drift study
Last weekend, right after snowfall I went out to study snow patterns. I was a delightful walk, that gave me much to think about. Of course I was not the first one - many observers went before me. And they saw and deduced things that escaped me. But I'm happy to rediscover and present their observations. As far as I know, the observations by Marcel Minnaert have never been translated into English before.
John Ruskin - Frondes Agrestes - I have not had the time yet to dive into the works of John Ruskin, but he is cited many times by Marcel Minnaert, so he must be inspiring.
54. In the range of inorganic nature I doubt if any object can be found more perfectly beautiful, than a fresh, deep snow-drift, seen under warm light. Its curves are of inconceivable perfection and changefulness; its surface and transparency alike exquisite; its light and shade of inexhaustible variety and inimitable finish,--the shadows sharp, pale, and of heavenly colour, the reflected lights intense and multitudinous, and mingled with the sweet occurrences of transmitted light....
Marcel Minnaert - The physics of open space - And of course Marcel Minnaert both observes and analyses.
On the beach, we can often note the beautiful shapes created by the sand carried by the wind as this sand falls down around obstacles. Such observations
can also be made after a snowfall, but here the drift figures are more variable. This depends on the snow being fine and powdery, or being composed of heavy flakes.
If the obstacle blocks the wind completely, but has relatively small dimensions, then:
- both deposits and erodes sand in front of the obstacle:
- the wind is slowed at some distance in front of the obstacle, this leads to deposition,
- the wind creates an eddy right in front of the obstacle, this leads to erosion,
- the wind removes sand at the sides of the obstacle,
- the wind deposits the sand in the leeward side of the obstacle as a kind of sand-tail.
The wind also sorts the grains, the coarse grains lie on the windward side, the fine grains on the leeward side.