Tuesday, December 18, 2007

Hoary tale.

We're back to rain and more rain. Inspired by Wanderin' Weeta's pictures of more interesting winter weather I am posting this:

The pictures here were taken about a year ago, on a walk in the bog. It was a beautiful, sunny day, preceded by a cold, clear night. I was on a mission, a search for signs of a mammal known to have occurred in Richmond, but whose present status is uncertain, the washingtoni subspecies of the Snowshoe Hare. I trekked through the Nature Park and the adjacent Defence lands. In recent years, small, brown rabbits or hares had been seen on those properties, but not positively identified. Based on the fleeting observations, including my own, they may have been Snowshoe Hares, but more likely were Eastern Cottontail Rabbits, an introduced species that has become established in the Lower Fraser River Valley. Snow-covered ground provided a chance to determine which bunny was there. As the name suggests, Snowshoe Hares have relatively large hind feet, about thirteen centimetres long. The hind feet of the cottontail are daintier, only about eight centimetres. One could measure the footprints. For this reason I carried a plastic ruler in my backpack.

Hoar frost on snow.

Because it was a sunny day after a spell of bleak weather, other people had also decided to walk the trails. I should have gone earlier. Any animal tracks there had been obliterated by human boots. The untrodden Defence Lands were more promising, quickly revealing tracks of Douglas' Squirrel and Coyote, but nothing that would suggest hare. After an hour or so, I gave up the search, but, as is almost always the case, this walk in nature turned out to be worthwhile. All around, glinting atop the snow, was a thick coat of frost. The bog looked as though draped in a furry white blanket. It was a version of hoar frost, which forms on cold, clear nights, when heat is lost to an open sky. Water vapour near the ground, or in the ground, or in this case, within wet snow, contacts a cold surface and sublimates into ice. Crystals accumulate, creating frost, which can take many forms. In these parts, hoar frost most frequently is seen on cold autumn mornings, when it appears as a thin, greasy layer on roofs, lawns, and the windows of parked cars. When it forms in the presence of new-fallen snow with a high moisture content, it can become thick and feathery.

Frost on ice.

I followed Coyote tracks back to the road, winding among a series of partially frozen pools that were ringed with dead rushes standing in frigid water. At the base of the stalks, where the water changed to ice, the hoar frost had formed as a jumbled white collar. Beyond, on the surface of the ice itself, the frost had grown into peculiar star bursts, in a way somewhat random but at the same time ordered — the way so much of nature is. I’m not sure how this happened, whether the star bursts were the leading edge of a growing formation, or if the ice below had caused the crystals to grow in a particular pattern. No matter, on a small scale, it was magnificent. And again, like so much of nature, part of what made it magnificent was its impermanence.


Wanderin' Weeta said...

Great explanation, great photos!

Now I know a bit more about a photo we took some years ago at Deer Lake; little "ice stars" at the edge of the water. A bad copy (digital photo of old snapshot)is here, on Flickr.

And thanks for the link!

A Local Naturalist said...

You're most welcome (the link), and thanks for returning the favour!