COURTESY OF ART JUDSON
The path of a hard slab, Jan. 29 avalanche that tumbled down Cornice Bowl on Sand Mountain, west of Steamboat Lake, are shown in morning sun Thursday.
Updated February 6, 2009 at 11:01 a.m.
Steamboat Springs Steamboat Springs avalanche expert Art Judson rose early on Thursday to photograph a recent North Routt avalanche in favorable light.
The hard slab avalanche ran Jan. 29 in east facing Cornice Bowl on the flank of Sand Mountain, just west of Steamboat Lake.
Judson, a retired avalanche forecaster for the U.S. Forest Service, has many years of practice judging the size of avalanche paths from a distance. He estimates the fracture at 4 feet deep and 150 feet wide. The path is about 600 feet long to the toe of the debris, below the shadow line.
The Colorado Avalanche Information Center describes hard slabs as cohesive layers of dense snow often deposited by strong winds. They may also simply result from bonded older snow.
This is not the first avalanche path Judson has viewed in the bowl this winter. He made the photograph standing on Routt County Road 62 looking west. The summit of Sand Mountain is about one mile up and to the right of the cornice ridge visible in the photograph.
The fracture line itself has a noticeable peak in the center. Judson said hard slab avalanches show a great variety of fracture forms.
"Most fractures are curvilinear, but a straight line is not uncommon," he said. "Also, zigzag (fracture lines) show up from time to time, and sawtooth as well. Sometimes the propagating fracture shoots (often traveling at the speed of sound) until it hits an object like a rock or tree, then zings off in another direction."
The Avalanche Information Center cautions that there remain older, weak layers in the snowpack. The center advises that human triggered avalanches are possible, particularly near or above tree line in the Steamboat backcountry. However, avalanche danger below tree line is rated low on west to southeast aspects. The danger increases to moderate at all elevations on northwest to east aspects.