It may be spring in the valleys, but there is still snow in the mountains—and interesting snow at that.
Stu Heard sent me pictures from a foray that he and Holley Rubinsky made up Mt. Buchanan a week ago. They discovered that an open mountain basin was decorated with donuts of snow that had rolled down the slope.
As any skier is aware, snow is a remarkably variable substance. Its properties can vary with time and with depth in the snow pack. The conditions needed to allow snow rollers requires a thin, moist and cohesive layer sitting loosely atop a firmer layer.
The way to think about it is to picture a thin layer of cookie dough that is initially rolled flat on a floured breadboard. If an edge of the dough is lifted and pushed, it can be rolled up. For snow, the wind does the lifting and initial pushing, but on the mountain slope, gravity keeps it going.
Some snow rollers on Mt. Buchanan seen at the beginning of the second week of April
Stu Heard’s images are used with permission.
also known as pin wheels
This looks like the kind of post I would expect to see on April 1. Just sayin…
Chris, chuckle, and yet snow rollers are real, bona fide, natural phenomena. You can add them to the list of other topics, such as anchor ice, frost flowers, and the circumzenithal arc, that this blog has treated, but which even experienced naturalists would respond to with a resounding, HUH? Of course, the common feature is that, while natural, these things lack feathers, or fur.
I know them as pin wheels as well. The cook at Lake O’Hara Lodge makes some incredibles pastries by the same name…
Pinwheels are also a sign of increased avalanche danger on the slope, so one should pay attention to local conditions.