Updated December 24, 2012 at 11:07 a.m.
Steamboat Springs The Colorado Avalanche Information Center has a report of a relatively small, skier-triggered avalanche that took place Dec. 21 near the summit of 9,685-foot Iron Mountain about nine miles northeast of Clark and one mile north of Hahn’s Peak Lake in North Routt County.
The report from the scene of the avalanche stated it took place on a steep slope about 10 vertical feet below the summit and a “skier took a short ride, coming to rest with only a ski buried.”
The Avalanche Information Center has downgraded avalanche danger in the Steamboat zone to “moderate” since the slide happened in North Routt, but Monday's snowstorm was expected to change that status.
The report indicates that the slide was triggered when a skier made a kick turn followed by a sudden collapse of the snowpack.
The size of the snow fracture where it was triggered was about 12 inches but it broke into wind-loaded snow to the skier’s right, where the fracture line was about 43 inches. The slide traveled only a short distance but was about 50 yards wide.
Steamboat-based avalanche expert Art Judson said Monday morning that the description of the avalanche is typical of what might happen with current conditions in the snowpack.
He interpreted the report to be a slab avalanche involving a layer of consolidated snowpack comprising tiny bonded crystals from recent snow and wind that was sitting on depth hoar (larger crystals) that formed on an old snow layer from earlier in the winter.
“When you have depth hoar and a slab over it, it’s unstable,” Judson said.
The observer at the scene of the slide estimated the pitch of the slope to average 38 degrees with a maximum angle of 45 degrees.
Avalanche forecaster Ethan Green, of the Colorado Avalanche Information Center, cautioned Monday that the next round of snow will add more weight to the slabs sitting on the fragile layer of hoar at the base of the snowpack.
“The danger will increase this afternoon and overnight as the next winter storm brings more snow to the area,” Green wrote on a Web report just before 6:30 a.m. Monday. “Human-triggered avalanches are possible on slopes with old, weak snow near the ground. The northwest to east aspects will have the greatest risk of these human-triggered slabs.”
To reach Tom Ross, call 970-871-4205 or email tross@SteamboatToday.com