An avalanche spilled onto U.S. Highway 550 between Silverton and Ouray on Sunday, temporarily closing the road.
Colorado Department of Transportation spokeswoman Lisa Schwantes said the slide happened in the Mother Cline path, a few miles south of the town of Ouray.
The slide path, which is south of Ouray County Road 18 (Forest Service Road 878) and north of the snowshed, is regularly treated for avalanche mitigation. Schwantes said this particular slide happened unexpectedly.
Schwantes said up to 4 feet of snow covered the highway. No vehicles were involved, she said. A CDOT snowplow responded to clear the road, and the highway was closed for about 30 minutes.
Silverton resident Jimmy S. Keene II said he came upon the scene around 4:45 p.m. on his way back to Silverton. He said the avalanche was big enough to push a car over the edge of the highway.
According to the Colorado Avalanche Information Center, avalanche danger was listed as moderate in the San Juan Mountains as of Monday.
“Today’s main avalanche concern is triggering a fresh wind slab that formed (Sunday) afternoon on north and east aspects,” the CAIC wrote in its daily report.
“Northwest- and southeast-facing slopes will also have cross-loaded terrain features with fresh wind drifts. If you see signs of instabilities like shooting cracks, avoid consequential terrain above cliffs, terrain traps and steep sustained slopes,” the report said.
On Friday, a backcountry a skier in the San Juan Mountains triggered an avalanche near the Camp Bird Mine near Red Mountain Pass on a northeast-facing slope near tree line.
An incident report says the slab originally released about 18 inches of snow. A second skier on slope triggered the slide and was able to ski out.
“The other remaining members in party skied down further ... without incident. The first skier down had warned the party of wind board in the small feature they were skiing in and advised party members to stay further right from where he had skied.”
The CAIC said it’s possible the weak layer for this avalanche was either wetted by melt at the surface or made weak from temperature fluctuations.
“We don’t know for sure,” the CAIC wrote. “What we do know is that you can still trigger slab avalanches in some terrain features. Snowmobiles and skiers triggered slab avalanches each of the last few days in each of the north, central and southern mountains.
The CAIC said that generally these are slopes with below-average snow cover, triggered from areas of shallow snow.
“We know at least one of these avalanches occurred on the faceted bed surface of a previous avalanche that ran in February,” the center reported. “The upshot is don’t discount that you might trigger a slab avalanche in the wrong spot.”
The CAIC said if backcountry users choose to ski in steep terrain, they should consider whether there might be buried layers of weak faceted snow below the snowpack.
“While the odds of triggering a large avalanche are decreasing, we’re not out of the woods yet,” the center said. “Dig down, consider how deep an avalanche might break, and choose your terrain considering what might happen if you get unlucky.”