A menace lurks beneath the snow high up in the southern Rocky Mountains.
At first glance it seems innocuous, another piece of a dynamic alpine ecosystem, certainly unable to cause the cascade of problems scientists say it could. How could something so simple undermine our water infrastructure, stress wildlife and lengthen the wildfire season all at once?
For most of the winter it stays hidden, buried under blankets of snow. Then, the days grow longer. The sun’s rays begin to melt the top layers, causing water to percolate through the snow and ice or evaporate, revealing the villain of this story.
Dust.
Luke Runyon visits the dusty mountain peaks of southwestern Colorado.
Snowpack in the Colorado River watershed is already at record lows as we move into the longer and drier days of summer. Water managers and fire forecasters are sounding the alarm about less water flowing in streams and reservoirs. Dust adds one more layer of complexity to an already precarious year.
To see it you need to dig a pit. In the spring, that’s usually where you’ll find Jeff Derry, waist deep in a snow pit somewhere in the southern Rocky Mountains. His job as the director of the Center for Snow and Avalanche Studies in Silverton, Colorado, forces him to pay close attention to the amount of dust that winds up embedded in snow.
Think of it like the rings of a tree. If you dig deep enough, you see the entire winter’s story, made up of layers of snow, reminders of each storm that’s built the snowpack. But when Derry digs pits it’s not just so he can get nostalgic for snow storms of yore. He’s on a fact-finding mission.
“I’ll be curious if you’re going to be able to see the dust event we had February 18 and 19,” Derry says as he shovels snow over the edge of the pit. “Because it is very subtle.”
There are a range of instruments to measure every aspect of snowpack. They’re fine-tuned for temperature, density and reflectivity. Water managers, farmers and cities are always curious about the amount of water held in snow, which gives a glimpse into what the spring runoff will bring. But the best way to gauge the magnitude of a dust layer is with the human eye, Derry says.
“It’s very qualitative in a sense,” he says. “You go out, you look for it, you dig, you see what you see.”
Derry takes his hand, brushes off the cross-sectioned snowpack, and there it is. About seven inches down is a beige-colored band of dust.
This tiny little strip of dust has the potential to upend how we manage water in the West, Derry says. Eventually this snow will melt and empty into the Colorado River, via the Uncompahgre and the Gunnison. The watershed provides water for some 40 million people in the southwest.
The dust, just by showing up, can speed up spring runoff, causing streams to peak weeks earlier and make melting more intense and erratic.
When there’s no dust on the snow, it’s brilliantly white. On a sunny day it’s reflective enough to cause eye damage. Snow has a high albedo, a measurement of reflectivity. Unadulterated snow is the most reflective surface found in nature. Without dirt or dust snow melts off slow and steady like the drumbeat of a drip from a faucet.
This is what water managers love. It’s predictable. But when you add in dust, the snow gets darker, like it’s wearing a black T-shirt, and it absorbs more sunlight.
“It melts the snow faster than it would have otherwise,” Derry says. “And then it melts down to the next dust layer, and so on and so forth until all the dust layers have combined at the surface of the snowpack greatly reducing the albedo.”
When all those dust layers combine, the sun’s radiation quickens the pace of runoff, making it all that more difficult to capture and divvy up the precious resource.
Not only does this make managing water harder, it can also upset mountain ecosystems, causing earlier green up of vegetation. If snow melts earlier that gives wildfires more opportunity to spark and take hold.
Most of the dust that’s settling in places like the San Juan mountains comes from the desert southwest - from land disturbances like farming, oil and gas drilling, cattle grazing, recreation and residential development on the southern end of the Colorado Plateau.
“It’s kind of a slow crisis, a slow disaster,” says Rich Reynolds, an emeritus researcher with the U.S. Geological Survey in Denver. “It’s not like a hurricane. It’s not like an earthquake or a volcano.”
In the last 50 years, as the Sun Belt boomed, scientists have recorded a dramatic rise in the amount of dust being deposited on snow. Reynolds says reversing the trend won’t be an easy task.
“There’s no one size fits all in terms of mitigation for these kinds of source areas. Plus, these are large, large areas,” he says.
By now, the scientific literature confirms dust is forcing fundamental changes in how spring runoff occurs.
In a 2010 study researcher Thomas Painter, now with NASA’s Jet Propulsion Lab in California, and his colleagues found that in heavy dust years the Colorado River’s flow on average peaked three weeks earlier than in years without heavy dust deposition.
The group also found that earlier melt off lessens the amount of water that runs to the Colorado River by about five percent. That’s more water lost than the entire state of Nevada uses from the river in a year.
And then there’s climate change. University of Utah hydrologist McKenzie Skiles recently co-authored a study that looked at which is the greater threat to snowpack: warmer temperatures or dust.
“What we found looking at those two in this region, is that it was actually dust that controlled snowmelt timing and magnitude and sort of how fast snow ran out of the mountains, as opposed to temperature. We didn’t see any relationship to temperature at all,” Skiles says.
Warming temperatures are more likely to affect and diminish total snow accumulation, causing some snow to come down as rain. But when it comes to runoff, dust is the controlling factor. It’s the sun’s rays that force snow to melt, not outside air temperature.
While the science is painting a clearer picture of how this phenomenon plays out, there’s plenty we don’t know about dust on snow, Skiles says.
“We still have some questions on what controls the actual dynamics of the dust events themselves,” she says. “We see dust in every year, but there’s a high variability between the amount of dust that’s deposited each year."
Some years are extreme dust years, like 2009, 2010 and 2013, Skiles says. While others, like 2015, aren’t.
Back in the San Juan mountains, dust detective and snow scientist Jeff Derry says he’s bracing for more dust events this spring. The mountain range has registered five dust events since October. Derry says the San Juans are ground zero for this problem. And because they’re a key part of an already overtaxed Colorado River system, he says everyone in the seven U.S. states and in Mexico that depend on the river should be concerned.
“We’re located at the headwaters of four major watersheds,” Derry says. “And our mountain systems are undergoing change at a fundamental level.”
Change that could make the West an increasingly dry -- and dusty -- place.
This story is part of a project covering the Colorado River, produced by KUNC and supported through a Walton Family Foundation grant. KUNC is solely responsible for its editorial content.
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