Aspen-area snowmelt bites the dust
June 9, 2013
The dust is back, and it's confounding skiers, boaters and water managers around Colorado.
Western Slope residents are becoming more accustomed to spring snow with a reddish-brown tinge that seems to deepen and darken as the season progresses and the snow melts. Most of these grains have blown in from the Four Corners area of southwest Colorado, northwest New Mexico, northeast Arizona and southeast Utah. Visually, the dust spoils the bright white snow of most Colorado postcards, but the look is only, as they say, the tip of the iceberg.
For one thing, dust-speckled snow makes a lousy, gritty running surface for a ski, so backcountry skiers tend to dislike it. Beyond that, the presence of heat-absorbing dust particles tends to accelerate snowmelt and speed the spring runoff. A faster and shorter runoff season has implications for recreational boaters, farmers and the water managers who decide when water is stored in reservoirs and when it gets released downstream.
"Dust is definitely an accelerant, it accelerates melt," said Jim Pokrandt, a spokesman for the Colorado River Water Conservation District. "In terms of water use, it quickens the runoff and irrigators are not able to use the water as efficiently. So much more water goes by than they can use at the moment, and that depletes the amount that would be left for use later in the irrigation season."
A slow, steady runoff in a year with healthy snowpack enables water managers to allocate water to various uses, from farmers and municipalities to instream flows for endangered fish, and there's enough fluid in the Colorado and its major tributaries for recreational boaters to enjoy a long and lucrative season as well.
But when drought conditions have already placed water managers in a squeeze, a dust-accelerated runoff adds insult to injury.
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Chris Landry, of the Center for Snow and Avalanche Studies in Silverton, is the acknowledged pioneer in dust-on-snow research, and his study area near Red Mountain Pass in the San Juan Mountains indicates that 2013 is one of the worst years yet.
"When it comes to this season in our study area, this was certainly the heaviest single season we've observed since we started observing in '03-'04," Landry said. "On top of that, we also experienced a single event that deposited more dust than any other complete year, except perhaps 2009."
That single event on April 8 was particularly intense in southwestern Colorado and not as heavy in other parts of the state. Still, Landry said, another longer-duration windstorm on April 15-17 deposited dust as far away as Rabbit Ears Pass near Steamboat Springs, Rocky Mountain National Park on the northern Front Range, and even Cheyenne, Wyo.
It's clear that the soil is traveling to the Rockies from the Desert Southwest, Landry said, but the root causes are unclear. Drought conditions and vegetation loss across the Colorado Plateau region have something to do with it, but soil disturbance also plays a major role. Livestock grazing, oil and gas development and rubber-tire recreation may all bear some of the blame, but Landry said "it's a huge piece of geography and there's a lot to learn."
Some have suggested the dust is being carried from Asia, but Landry said both the size of the particles and their chemical composition traces them back to the Four Corners.
"We're pretty clear that the vast majority of material landing in the Colorado snowpack is coming from the Colorado Plateau," he said. "That's not to say some of the weather systems stirring up dust in the Colorado Plateau didn't also stir up dust in the Gobi Desert, but that's a tiny fraction."
Huge relocations of soil from one land mass to another aren't necessarily new, Landry added, and they do have positive effects. Calcium-rich dust has benefited the acidic, volcanic soils of the San Juans, Landry noted, but the long-term impact of desert dust deposition in the Rockies remains to be seen.