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Snowpiercer: Drought Dust Raises Avalanche Danger in Colorado Backcountry

 
We all know what a blanket of fresh snow is supposed to look like — it’s the stuff of poetry. And for skiers and snowboarders, it’s the magic carpet that carries us beyond the edge of gravity, free-falling down mountainsides immersed in a spray of frozen crystals.

But for the last 10 years, the snows falling in parts of the Colorado Rockies have been far from virgin white. From March through May, the mountainsides sometimes look more like gravy covered mashed potatoes, as regional weather patterns blow huge amounts of desert dust to the high peaks of the San Juans and beyond. Instead of skimming down the slope with wings on their feet, skiers sometimes find themselves stuck in the muck.

The dust depositions have become so frequent and intense that avalanche experts now consider the layers when they issue forecasts and warnings for the Colorado mountains, or when they gather for professional development seminars like this week’s Colorado Snow and Avalanche Workshop in Breckenridge.

Much of the seasonal dust is coming from dry lake beds in Arizona, from arid grazing lands around the Four Corners area and from intensively used recreation and energy development areas in the wider region. Satellite images clearly show the source and the deposition areas, and 10 years of detailed data from snow-study plots around the Colorado mountains show how the dust is affecting snow and water.

dust satThe recent increase in dust deposition spiked in 2012, when a single storm delivered more than 400 pounds of dust per acre to a study area in southwest Colorado’s San Juan Mountains — that’s two heaping wheelbarrows of dust spread across an area just a little smaller than a football field.

Additional studies have looked at layers of sediments at the bottom of alpine lakes, which can also show big dumps of dust. Those records show an early spike during the European settlement era, then a leveling-off until about 15 years ago. It may only be circumstantial evidence, but the timing coincides with a general and long-term warming and drying trend in the Southwest.

Snowpack dynamics

Global warming may not be causing the problem per se, says Center for Snow & Avalanche Studies director Chris Landry, but it’s not helping matters, either. Some climate studies suggest the Southwest will dry up as average global temperatures rise. That will make disturbed soil even more susceptible to transport and reduce vegetation that helps hold soil in place.

Along with creating a huge puzzle for water managers by shifting the timing and quantity of snowmelt runoff, the dust layers — sometimes 10 per year — have also increased the risk of certain types of avalanches in the Rocky Mountain backcountry, where thousands of skiers, snowboarders, climbers and snowmobilers play in the snow. The dust is even affecting operations at ski areas that rely on late-season business. In 2010, Arapahoe Basin used its snow-grooming equipment to push the discolored snow off the trails the resort was using for late season skiing.

Depending on their exact depth and density, the dark layers dramatically alter the interaction of the sun’s energy with the snowpack. Instead of reflecting solar rays back to the atmosphere, the contaminated layers absorb huge amounts of heat. Avalanche watchers more frequently are seeing slides break loose atop on of the dust layers, and forecasters in regional avalanche centers add the dust storm into their risk assessments.

“There are dramatic fluxes of energy going on in near-surface snowpack,” Landry said several years ago, addressing a panel of avalanche experts. “You have to be concerned about the massive amounts of extra energy going into this snowpack … Extreme conditions produce extreme avalanches,” he said, adding that he suspects dust layers can also cause massive cornice failures.

snowpitA snow pit shows a layer of dust that accumulated during a spring storm. PHOTO COURTESY COLORADO AVALANCHE INFORMATION CENTER.

Even if it doesn’t cause an avalanche, the dust has a direct impact on the quality and even the length of the spring ski season — not a small thing in a region where the snowpack is generally sketchy all winter. In the Rockies, mountaineers look forward to the formation of a relatively stable spring snow layer, but the recent series of dust storms has changed that dynamic.

“It clobbers the snowpack,” says Colorado-based avalanche expert Dale Atkins, explaining how, on a sunny slope, the dust can rot the snowpack from the inside-out, creating weak layers more prone to sliding.

“When you put dust on snow, it’s less slippery. You … can really feel the difference,” says Atkins.

With decades of ski patrolling and avalanche forecasting experience, Atkins says it’s clear that the dust storms have become more frequent, and that’s what other observers are reporting anecdotally, Atkins says, describing a recent dust storm in Cortez.

“We just watched this wall of dirt and dust blow in in the afternoon and the evening … You could feel it in your eyes, taste it in your mouth. Talking to the locals, it’s become a common occurrence,” Atkins says.

The dust may also be going farther. Two or three years ago, there was significant dust deposition in Boulder, the first such event in recent memory, although Atkins acknowledges there may have been similar events during historic dry spells like the Dust Bowl Era.

“Until the Southwest turns wet, which is probably pretty unlikely, we seem to be stuck with this, Atkins says.

dustciclesIcicles forming in Frisco, Colorado show the telltale red hue of desert dust that has become a hallmark of spring weather in the Colorado Rockies.

In the short-term, weather watchers have been hoping for some relief from El Niño, known to sometimes bring above-average precipitation to the Southwest.

A series of wet years, with plentiful spring snow, could help further explain the story. If dust depositions in the Rockies were to decrease during such a period, it would be easier to draw the link between cause and effect, and perhaps plan and design management actions to mitigate the effects (less ground disturbance, revegetation projects during wet years, etc). And even without the heat-trapping effect of greenhouse gases, the region has, according to well-established tree ring records, seen periods of extreme drought on par or worse than the past 15 years.

The long-term future is a different story. From everything we know now, the Southwest is likely to become warmer and drier, part of a global shift and expansion of subtropical deserts into temperate zones. Already, large parts of California have seen a Baja-like climate the past couple of years.

“It’s a global thing, and that really does have to do with climate, if, like they say, that desert band is expanding,” says Scott Toepfer, a forecaster with the Colorado Avalanche Information Center. Weather and snow observers in the European Alps have also reported more frequent dust storms from the Sahara, with similar effects on the snowpack.

After decades of Colorado skiing, Toepfer says the topic of dust-on-snow is definitely a recent thing. Starting the early 1980s, there might have been a dust event every few years.

“Occasionally people would say, ‘what is this stuff?’ Then it was every few years and now it’s multiple times every year,” Toepfer says. “It has affected the quality of the skiing. It’s like putting a layer of sandpaper on the snow. It makes it grabby,” he says. “It is very easy to trigger avalanches in the newer snow resting on the dust, and even if it’s buried 12-18 inches deep, it eventually comes back to the surface. It is a persistent weak layer.”

Biking season?

There may be an overall effect on the seasonal recreation experience in the Rocky Mountains, bringing an earlier end to the ski season and a shift to other activities earlier in the year.

“When you get into a pattern when there’s a lot of dust on the surface, it makes you want go from skiing to biking right away,” says Colorado Avalanche Information Center director Ethan Greene.

“You tend to see the dust kind of collected in the snow, in little pockets where it drops … You’re sliding across this uneven surface, some of it’s slushy, some grabby … It’s not that 2,000-foot smooth run you’re looking for,” Greene says.

“At the same time, the lower elevation slopes are probably melting out earlier because of the dust, which means longer hikes to mixed conditions, while boating and biking conditions get better sooner. It really affects the quality of the ski experience in an adverse way,” he says. “In the past six or seven years, the spring ski season was pretty short, in my mind. When there’s a lot of dust, it becomes the prevalent factor,” he concludes.

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