Desert dirt causing earlier snowmelt
When Tom Painter and his father set out to climb South Maroon Peak one day in late June 1998, snow remained along the trail. The snow looked dirty, and somewhat idly, the younger Painter scraped off a section of snow to find much whiter snow. Then they set out again.They climbed the peak, ate their lunches, and in the late afternoon returned down the trail, coming to the place where Painter, already a scientist working toward his Ph.D., had unconsciously conducted an experiment.The darker, dust-covered snow had melted significantly. The white snow had melted far less. Why is that, asked his father, Richard J. Painter, then a mathematics professor at Colorado State University. Where does the dust come from?
Tom Painter, the scientist, couldn’t answer. He didn’t really try until, after his dissertation was complete, he began fishing for a location to conduct a more formal experiment. His interests were purely academic. Only later, by then a scientist associated with the National Snow and Ice Center Data in Boulder, did he realize the implications of his work.Results of that study were published last weekend in a scientific journal called Geophysical Research Letters. Using field measurements from Colorado’s San Juan Mountains, he reported that dust, most of it carried aloft from the deserts of Arizona and New Mexico, seem to have caused the snowpack to recede roughly a month before it would have otherwise.So what? Snow has to melt sometime, doesn’t it?Yes, but Painter’s argument – relying on the work of others – is that this dust is not necessarily natural. In fact, he says, disturbances in deserts of the Southwest have increased substantially in the last 140 years.The study has potentially large implications for the 35 million people dependent upon waters from the San Juan Mountains and other drainages in the Colorado River Basin. It is a river system driven by snowmelt, with 75 percent of all water arriving in the form of snow.Much of the water, some 16 times the total annual flow of the river, is held back in reservoirs, from Ruedi near Basalt to Fontenelle in Wyoming and, of course, the big buckets of Powell and Mead. But the most efficient reservoirs are the alpine snowbanks that, even into July, continue to melt in the high country. Lower-elevation reservoirs lose a lot of water to evaporation; Lake Powell loses 6 feet per year to evaporation.Already, the Colorado River Basin is fully used, with virtually none getting into the Sea of Cortez (most of what gets to Mexico is brackish, of poor quality). Even so, with global warming almost certain to turn up the heat in the Southwest, climatologists are now in general agreement that droughts are likely to become more common. Some have even gone so far as to say that today’s droughtlike conditions will, in the future, become the norm.If the deserts, their soils already disturbed, become more dry, they could yield even more dust on the snowpacks of the San Juans and, to lesser extents, across the Colorado Rockies.Jeff Dozier, a professor of snow hydrology at the University of Santa Barbara, says the study is important far beyond Colorado. Similarly conditions to those of the San Juans exist in other areas of the nation and world. Altogether, about a billion people in the world depend on melt from snow or glaciers for water supply.”In considering future climate changes, we often focus on warmer temperatures,” he says. “In the high-alpine zone, however, snow is more sensitive to the amount of solar radiation absorbed than it is to the air temperature.”We all know that white reflects solar radiation, something called the albedo effect, while dark material absorbs solar radiation. So even a modest change in the reflectivity of the snow caused by dust translates into a larger change in absorption of the solar radiation, Dozier explains.”For this reason, a change in the amount of dust from the desert [perhaps cause by drier conditions there] is probably more important to the San Juan snow than a change in temperature,” he says.
The work is being done in the San Juans because it is most proximate to the Colorado Plateau desert. Even so, there’s an Aspen connection. Doing the fieldwork for the experiment, and several others, is an organization called the Center for Snow and Avalanche Studies.The director – actually, most of the sweat and smarts, too – is Chris Landry, a longtime resident of the Roaring Fork Valley.The son of a 10th Mountain Division veteran, Landry grew up first at Whitefish, Mont., where his parents managed the Big Mountain ski area. He competed in both alpine and nordic events while attending Rocky Mountain School in Carbondale. Landry lived in Aspen during the 1970s and early 1980s, a time when he “more or less pioneered extreme skiing,” according to http://www.themountainworld.com. Among other notable achievements, Landry pioneered a ski descent on the east face of Pyramid Peak, a feat not repeated until this past spring.Growing up in Fort Collins, a passionate skier even then, Painter remembers reading about Landry’s latest exploits in the ski magazines.This would not be the last time Landry would follow Painter’s path. The dust on snow that Painter and his father observed at Maroon Peak in 1998 was similar to that noticed by Landry at year later, when he was in Carbondale plotting avalanche safety for marble-mining operations at the Marble quarry.That dust came from a March 1 storm. “It was bright red and out of the southwest. Visibility in Carbondale was only two miles,” says Landry. “You could hardly see the edge of the valley. That one caught my attention.”The dust on the snow created a weak layer in the snowpack. About a month after the storm, an avalanche occurred in the Aspen area when the snow above that dust layer failed.Landry later got a master’s degree in snow studies at Montana State University, moving to Silverton in 2002 to establish the Center for Snow and Avalanche Studies. He is assisting in several scientific experiments that need pristine alpine and montane settings.To that end, he has a permit from the U.S. Forest Service for a study site in Senator Beck Basin, adjacent to Red Mountain Pass, between Silverton and Ouray. Telluride is just over the ridge.
Storms can deposit dust on snow in Colorado at any time. Mostly, however, they occur from February through May, sometimes into June. The dust sometimes comes from the deserts of Asia. Scientists know this because of two tracking mechanism. First, satellite images allow them to see giant plumes rising and then lifting across the ocean. Second, scientists can analyze the chemistry of the dust specimens, looking for the chemical isotopes that can then be traced to the isotopes found in the bedrock of regions.These same tracking tools have pinpointed the Colorado Plateau – the deserts of northern Arizona and New Mexico – as the source of most of the dust that blankets the San Juan Mountains maybe a half-dozen times a year.An expert in identifying the fingerprints of dust is Jason Neff, a biogeochemist with the Geological Science Department at the University of Colorado-Boulder. The isotopes clearly tell the story of the dust, he says.”With that information, we can say very definitely it’s not local. It’s not from wood-burning, it’s not road dust, and it’s not stuff flying off ridges from near the sample sites,” he says. “It’s traveling into the state and being deposited on the snowpack.”It’s not possible, given current tools, to precisely pinpoint the source of the dust – say, for example, a locale 20 miles from Flagstaff. But Neff and other scientists believe that relatively little of this dust is natural. Some areas, such as the playas, or dry riverbeds and lakes, are natural sources of dust. But most of the dust is because of soil disturbances.Neff says he participated in a study in Canyonlands National Park, sort of an inverse study to Painter’s snow-on-dust work in the San Juans. He found a progressive loss of surface soil in areas that have been grazed by domestic livestock, as compared to untouched areas.”One-hundred years of grazing in the American Southwest, at least in that particular place in Utah, has led to a pretty large loss of soils,” he says.Neff is now doing a project in the San Juans, also with the aid of Landry’s Center for Snow and Avalanche Studies. In that study he is looking at core sediments taken from above-timberline lakes – including the dust that has been deposited. The goal is to determine whether there has been a big human effect in the last 200 years, during the time of Euroamerican settlement.”We actually had a lot more grazing 100 years ago than we do now, although we now have more cars, home construction and recreational use” in the desert Southwest, he said.Neff hopes to publish his study results later this year.
From Moab, Jayne Belnap has also been studying changes in the deserts of the Colorado Plateau. She’s a soil scientist with the U.S. Geological Survey; among her projects, she has placed big wind generators in the desert to see what sticks and what flies.While some deserts are naturally dusty, they are few. In the American Southwest, she says, the story largely is of disturbances – from livestock grazing, from recreational vehicles and from home construction. “Anything that has a compressional force. It doesn’t matter whether it’s a hoof, a bike, or an ATV or a tank – anything will disturb that surface,” she says.This is, she repeats, not normal. Desert soils will mostly stay put if they haven’t been disturbed in the face of big winds.But the larger story here, she says, is of the altered hydrology caused by the vagrant dust in the Southwest, where about 85 percent of water originates in the higher elevation mountains, mostly as snow.Even if the reservoirs can hold the flood waters of a rapid spring runoff, she says, the rhythm is changed. “It’s all fine during the ‘whoosh,’ but afterward then you will have more problems.”There will be multiple problems with water quality, including increased sediment loading. Already, she notes, water providers are looking at desalinization plants, despite their great expense. But desalinization is no panacea, because it yields large amounts of material that must then be landfilled.Brad Udall, director of the Bolder-based Western Watershed Assessment, believes Painter’s study has not yet caused major eyebrow-lifting among climate scientists. But water managers are paying attention.”It’s certainly a wild card,” he says. “It’s something about which we need to know a lot more.”In California, hydrologist Frank Gehrke says the San Juan study may – or may not – have applications to the Sierra Nevada snowpack. Study there would be necessary, said Gehrke, who works for the state water agency.
Painter believes the timing of the dust storms does matter. Earlier in winter, because the sun’s rays arrive at long angles, there is little effect. But in spring, as days grow longer, the sun arrives more directly, the snow’s reflectivity, or albedo, matters even more.After several years in Boulder, Painter is moving to the Park City area, where he will be affiliated with the University of Utah in nearby Salt Lake CityA skier from his youth, Painter studied mathematics and excelled. But along the way he struggled at times to find his way. He dropped out of college, working at Snowbird. For a time in the early 1990s he lived in the Vail area and aspired to become a bump skier.Finally, studying for his master’s degree in Santa Barbara under the supervision of Dozier, skiing on weekends at Mammoth, he became energized by working with snow in a different way, as a scientist.Now with a major project under him, he sees his life’s work lying in front of him, trying to solve yet more mysteries in the snowpacks that are so important to us.Allen Best writes from the Denver area. He can be reached at firstname.lastname@example.org.
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