Large avalanches occurred every day this week in the mountains around Aspen, and throughout Colorado’s hill country, and are expected to remain a danger to backcountry denizens well into the spring, a state forecaster said Friday.
Various factors in the weather and snowpack this winter have made avalanche behavior “somewhat unusual,” said Brian McCall of the Colorado Avalanche Information Center.
The Roaring Fork Valley is again experiencing a dry winter — drought conditions still exist in the state and much of the nation — and the snowpack on Independence Pass is thus far well below the yearly average. It’s also slightly below last year’s snowfall totals.
Dry winters tend to result in more problems with persistently weak snow layers, and that was a contributing factor in the March 8 avalanche that four people triggered on Independence Pass as they skinned up, McCall said in an email.
All four were caught. Three managed to grab trees, but one man was injured as he was carried farther down, McCall reported a few days after the incident. The avalanche path is about a half-mile downvalley from the Independence ghost town.
The man said this week that he broke a bone in his leg. But he didn’t want to discuss the incident, partly because he didn’t want to distract from the efforts to find Jeff Walker. Walker, 55, of Aspen, has not been seen since March 7 and is believed to have gone missing on Aspen Highlands.
McCall said the avalanche occurred on a northeast aspect above treeline, with the crown starting at 12,200 feet and the trigger point just near treeline at about 11,600 feet. It traveled just over 1,000 vertical feet down the path, he said. It failed in a weak layer in the lower snowpack, probably just above the ground.
Because of the dearth of snow, most areas of the Roaring Fork Valley this winter have had a very weak layer of snow near the ground, McCall said.
“Our shallow snowpack depths make it easier to trigger this weak, lower snowpack layer,” he said.
Light but consistent snowfall in February started to add stress to weak layers in the snowpack, McCall said.
Strong southwest winds from March 4-8, and a quick-moving storm on March 5, pushed the snowpack past its tipping point late last week and over the past weekend.
The Aspen area had a cycle of large natural avalanches, including the Independence Pass slide, as a result, he said.
“Isolated, large, deep slab avalanches have occurred throughout the Aspen zone and the rest of the state every day this week as well,” McCall said.
Such slides will remain a possibility in the backcountry well into the spring season, especially on wind-loaded slopes near and above treeline. Slopes facing north through southeast at higher elevations will be the most dangerous, he said.
“People traveling in the backcountry this spring will need to approach steep terrain very cautiously, especially for the next few weeks,” McCall said. “Warm conditions this week have increased the avalanche danger slightly on lower-elevation slopes and south-facing terrain.”
The warm conditions of late, however, are generally only affecting the upper snowpack. Weak layers in the middle and lower snowpack have not changed all that much and should still be treated as if it was still midwinter, he said.
“It will take some time for the melt-freeze process to affect the whole snowpack, especially at higher elevations,” McCall said.
For more information, visit https://avalanche.state.co.us/index.php .