The winds kicked up in Utah’s West Desert ahead of a late-season storm blowing out of the south and into the Wasatch Mountains, which were then coated with a heavier-than-usual snowpack. But soon the winds shifted west and scraped up particles from the bed of the Great Salt Lake, left exposed from chronically receding lake levels.
The wind event on April 13, 2017, was just what McKenzie Skiles, a young professor of geography who harbors a deep fascination with snow, was waiting for.
She left her office in Salt Lake City to visit a study plot she and her University of Utah research team set up at the town of Alta high up in the Wasatch’s Little Cottonwood Canyon. Freshly deposited dust was darkening the snow.
From her team’s measurements, Skiles has concluded that these particles, particularly from the Great Salt Lake’s ever-expanding dry bed, are significantly increasing the pace of the Wasatch Mountains’ spring runoff.
“We used the amount of dust in the snowpack to calculate how much additional sunlight the dust would absorb relative to a dust-free snowpack,” Skiles said. “We found that from this one event, dust accelerated snowmelt by five days. And dust from all events [in the spring of 2017] accelerated snowmelt by 25 percent.”
This observation could have serious consequences for the Utah cities that rely on the Central Wasatch for drinking water, according to the team’s paper published Friday in the journal Environmental Research Letters.
Through a property known as albedo, clear snow reflects much of the sun’s radiant energy, but snow covered in dust absorbs that energy and melts faster than it otherwise would, according to Salt Lake City hydrologist Brian McInerney, who was not involved with the study.
“Any time you melt snow earlier than you typically see, it’s much less efficient. You lose much more to evaporation and to the atmosphere,” said McInerney, who works for the National Weather Service.
That leaves less water available for human uses or to eventually return to the Great Salt Lake, further lowering its level and exposing more lakebed that could lead to more dust storms — a troubling feedback loop.
Growing up a skier in Alaska, Skiles picked her college based on its proximity to snow-covered mountains. The logical choice was the University of Utah, where she studied under geographer Tom Painter, who specialized in snow albedo.
“He said, ‘You’re out there skiing a lot; you are obviously interested in snow. If you want to go to graduate school, you could study this further,’” Skiles said. “I was blown away. I didn’t know you could be a snow hydrologist as a career. As soon as I went to the Southern Colorado Rockies to do field work for him, I was hooked.”
She recently landed a tenure-track position at the U. after completing a doctorate at the University of California, Los Angeles, where she studied snow in the Sierra Nevada.
Now she is back in the Wasatch, examining dust on snow in the four major canyons supplying water to Salt Lake City: City Creek, Parleys and Little and Big Cottonwood canyons.
For the new study, her team collected dust samples at the Alta site both in the snow and in the air above and around the site. This was the first time anyone simultaneously gathered dust samples from the air and the snow.
The airborne samples enabled Skiles to identify what days particular dust particles were deposited, which she could then link to specific wind events. There were five major events in the spring of 2017, but the April 13 storm accounted for most of the dust at the Alta site, and most of that dust came from the Great Salt Lake, according to Skiles’ analysis.
The team sampled the size and number of airborne particles, then excavated pits to analyze the snow’s properties and sample dust concentrations. Computer simulations helped them determine where the dust came from.
Dust has specific qualities, depending on where it came from and how far it has traveled. If it has come from a distant source, such as the dry Sevier Playa south of Delta or the Milford Flat burn area, the dust grains are finer, Skiles said, while they are more coarse when they originate from a closer source.
Since the 1980s, the Great Salt Lake has lost more than half of its surface area, exposing 700 square miles of its bed. McInerney attributed the loss to water diversions on the Bear River, the lake’s largest source of in-flows, and rising temperatures, which speed evaporation.
“We keep using more water, pulling it out of the rivers, and it doesn’t make it to the Great Salt Lake and it has all sorts of consequences,” he said. “There is a greater surface area of alkaline dust that comes off there because the lake is getting smaller.”
While researchers are getting a handle on the impact of dust on the Wasatch snowpack, more observations are needed to determine what the main dust sources are. In the meantime, Skiles stressed, Wasatch Front cities have much at stake.
“The Great Salt Lake doesn’t have any protections; there is no minimum lake level,” Skiles said. “It’s important to understand the impact now and see if there is any policy we could put in place that would minimize this impact.”
Skiles’ study was co-authored by U. geographer Steven Clark, and Derek Mallia, A. Gannet Hallar, John Lin, Andrew Lambert and Ross Peterson of the U.’s Department of Atmospheric Sciences.