Snow Donuts aka Snow Doughnuts aka Snow Rollers
From The Seattle Times report with Mike Stanford, an avalanche-control expert with the Washington State Department of Transportation (WSDOT).:
Stanford found frozen doughnuts of snow on the top of Washington Pass in the North Cascades this week when he was doing avalanche-control work. At first he couldn't believe his eyes: Perfectly shaped doughnuts had rolled down the mountainside and frozen in place.
He said it's only the second time in his 30 years of working in the snow that he's seen anything like it. The larger of the snow rollers, as they are commonly called, was about 24 inches tall, he said, large enough for him to put his head through the hole.
Stanford said snow rollers form when there is a hard layer on the snow, covered by several more inches of dense snow. "Then you add a steep slope and a trigger such as a clump of snow falling out of a tree or off of a rock face."
As gravity pulls a clump down, it usually rolls down the hill and collapses, creating what the WSDOT calls a pinwheel. Or it will not roll at all, and come down in an avalanche of snow. But if the snow is the perfect density and temperature, it rolls down leaving a hole in the center, Stanford said.
Back in February 2003 Central Illinois experienced widespread snow rollers. From the National Weather Service report:
Snowfall of 1 to 4 inches occurred across central Illinois the morning of February 11. That evening, as a strong cold front pushed through the area, wind gusts of 40 to 60 mph were noted in many areas.
Once the initial "seed" of the roller is started, it begins to roll. It collects additional snow from the ground as it rolls along, leaving trails behind it. The appearance is similar to building snowmen, except the snowball is more log-shaped rather than spherical, and many times they are hollow. They can be as small as a golf ball, or as large as a 30 gallon drum, but typically they are about 10 to 12 inches in diameter.
Here's just one of the many great photos from that outbreak:
(via Dvorak Uncensored)
Comments