The nemesis of spring; how this phenomena impacts the environment and outdoor enthusiasts alike
Many of us have heard how important it is to avoid disturbing crusty or cryptobiotic soil surfaces in the Desert Southwest. We may have a visceral understanding of impacts on local ecosystems and erosion. But there is a much bigger picture afoot that ties the ecosystems of the entire Southwest together, from the mountains to the desert, and from the fragile crusts of the desert to the fragile tundra of the high alpine.
WHAT IS DUST ON SNOW?
Movement of dust around the Southwest is a natural phenomenon that has occurred for millions of years, since the Colorado Plateau started weathering. Prominent southwest winds carry dust particles from the Colorado Plateau and deposit them on the mountains in Southwest Colorado. During the winter, layers of dust deposited on the mountain snowpack affect the snow in interesting, and sometimes devastating ways.
The Center for Snow and Avalanche Studies monitors the presence of dust layers in the snow at 11 mountain pass locations throughout Colorado via its Dust-on-Snow (DoS) program, with the Senator Beck Basin study area at Red Mountain Pass being the DoS “sentry” site. Jeff Derry heads up the DoS monitoring effort from Silverton, Colorado.
The effects of DoS are also visceral. A snowstorm typically deposits a new layer of snow whose surface is clean and bright, making us reach for our sunglasses to protect our eyes from the bright sun rays, or solar radiation, reflecting off the surface. A few days later, we notice that the snow surface is not as white and reflective. We are witnessing the change from a high albedo, or high reflective, to a low albedo, or low reflective, snow surface.
The snow grains naturally degrade, and impurities blow onto the snow surface, or become exposed from underneath the surface. A high albedo snow surface reflects upwards to 90 percent of solar radiation back into space. A low albedo snow surface reflects around 30-70 percent solar radiation back into space. The rest is absorbed into the snow and goes towards warming and melting the snowpack.
The Colorado mountains belong to a “continental-radiative-snow-climate.” That means that absorption of solar radiation is significant here. A common misconception is that the snow melts in response to the air temperature. However, solar radiation accounts for nearly all the energy that goes towards melting the snow (>90 percent).
AN HISTORIC PERSPECTIVE
The Southwest region has had relatively stable dustiness levels over the past 11,000 years. In the last 150 years, dust increased beyond the natural range coincident with disturbance by human activities. Sediment cores from high alpine lakes in Colorado reveal that dust loading increased 500 percent with the arrival of large livestock herds and intensive agriculture at lower elevations of the Western U.S. in the mid- to late-1800s.
The migration of European settlers into the Western U.S. led to widespread expansion of grazing, mining and agricultural activities in the 19th and 20th centuries. In the period following the development of railroad lines (and heavy transport capabilities for livestock) in the late 1860s, cattle and sheep grazing greatly intensified across the Western U.S. In the Navajo Nation tribal lands to the south and southwest of the San Juan Mountains, high animal densities and impacts of overgrazing became a major issue by the early 1890s. By the early 1930s, heavy livestock use significantly disturbed two-thirds of the land area in northeast Arizona. Overall, livestock grazing affected nearly 70 percent of the natural ecosystems of the Western U.S., resulting in the loss of soil stability and an increase in wind erosion of soil.
The extensive degradation of Western U.S. rangelands led to the Taylor Grazing Act of 1934 that imposed regulations and restrictions on grazing activities in those rangelands. Dust production fell roughly a quarter from pre-disturbance accumulation amounts as seen in the lake core samples, coincident with a reduction in numbers of grazing animals.
WHY CARE ABOUT DUST ON SNOW?
The DoS phenomenon affects anyone who uses water. High levels of dust on the melting snowpack can drastically shorten the snowpack melt cycle (the snow melts earlier and faster), reduce water supply (early snow melt means soils and plants are active earlier in season) and affect alpine plant life cycles. Outdoor adventurers feel the effects too, from the mountains to the desert.
Ski seasons may be shortened, especially the coveted “Spring Corn,” snowpack. Backcountry travelers experience increased danger from avalanches triggered at prominent layers of dust in the snowpack and decreased ride quality. Summer trail users experience longer durations of increased erosion and shortened wildflower seasons due to the melt cycle abbreviated by rapidly melting dust-covered snowpack. River rafters, fishing enthusiasts and other river recreationalists experience higher intensity, shorter duration runoff in the rivers more heavily laden with sediments and debris. Trail users along the Colorado Plateau experience increased periods of dry and dusty conditions, and decreased access to public lands where sensitive soils exist. Moreover, decreased water supply and water quality affect every facet of life throughout the Southwest from where the dust originates to where it lands in the mountains.
WHAT CAN WE DO?
Understanding the DoS phenomenon and its impact on the Southwest is key to comprehending how humans and their activities fit into the bigger picture — a necessary step toward understanding how we can affect the process in positive ways. Supporting research efforts like the Dust-on-Snow Program makes this understanding possible through science, monitoring and education. Studying the DoS phenomenon is an adventure, whose destination only becomes clear with further understanding of the process from each microclimate to a regional scale.
Outdoor adventurers can be conscious of the phenomenon and our current understanding of its impacts on the Southwest. Simple things, like being cognizant of where and how we travel in the sensitive soils of the Southwest, can go a long way toward reducing the effects of DoS.
Adventurers can step it up even further by helping coordinate with land managers for management and design of public trail systems that reduce the effects while keeping our public lands accessible for the many adventure opportunities that exist. They can support water managers in their attempts to adapt to a changing climate, a changing water supply and evolving water needs. If none of that is of interest, adventurers can simply donate to the science programs, to their respective trail user groups and to recreation advocates seeking to balance recreation opportunities with the myriad of other challenges and needs.
ABOUT THE AUTHORS
ROBERT STUMP is a project manager with a civil and geotechnical engineering background, working closely with water and land managers throughout the Southwest. He spends most of his free time skiing or mountain biking in the backcountry, and loves to photograph and write about the outdoors.
JEFF DERRY is from Colorado Springs and earned a B.S. in Geography from the University of Colorado Colorado Springs. His passion for polar regions led him to work seasonally in Antarctica and Greenland for over 10 years. Jeff then earned a M.S. in Watershed Science from Colorado State University with an emphasis in snow hydrology. The arc of Jeff’s life brought him to the Center for Snow and Avalanche Studies in September 2015, where he now draws upon his range of skills and experience to contribute to the future development of CSAS.