Desert dust from Southwest contaminates the Colorado mountain snowpack
By Bob Berwyn
SUMMIT COUNTY — The Colorado high country has experienced its first significant dust event of the season, as southwest winds in March 23 coated the mountain snowpack with a distinct layer of desert dirt.
The dust was most apparent in the southwestern part of the state, but spread as far north as Winter Park and even the Steamboat area, said Brian McCall, a forecaster with the Colorado Avalanche Information Center. The dust layer was clearly visible in snow pits around the region. McCall said the dust doesn’t present an immediate avalanche concern, but bears watching as new snow layers pile up.
Dust storms in previous years have been implicated as factors in avalanches, including a slide in the Tenmile Range last year that injured a snowboarder and required an extensive and technical rescue effort that ended with a helicopter evacuation. The dust changes the reflectivity of the snow. If a dust layer is exposed to the sun, it can melt more quickly, then refreeze as an icy crust. Subsequent layers of snow may not bond well with the crust, leading to a weakness in the snowpack.
Earlier dust storms this spring didn’t leave much of a record in the snowpack, but the March 23 storm was intense in parts of the San Juans, said Chris Landry, director of the Center for Snow & Avalanche Studies.
“The dust season has begun, only time will tell how severe it’s going to be,” he said.
The Silverton-based research team has extensive study plots to measure the effects of the airborne pollution, which has been traced to sources in Arizona and Utah. In some cases, the dust may be linked with soil-disturbing activities like grazing, agriculture and off-road motorized recreation.
Along with factoring into avalanches, recent studies suggest that the dust speeds up the snowmelt season and reduces flows in the Colorado River. Changes in the timing pace of snowmelt may also be affecting alpine vegetation.
State air quality officials say the dust storms have also resulted in air quality issues in parts of Colorado.
Anecdotally, 2009 and 2010 saw some of the worst dust depositions in recent memory, according to long-time residents of the southwestern mountains. Empirically, the research record only goes back a few years, so it’s not possible to say conclusively whether the dust storms have become more numerous and intense, Landry said.