When I started studying snowmelt in 2009 in Utah and Colorado, I was most interested in quantifying the impact of warming temperatures on melt rates. But when I skied to research sites to collect snow samples, the mountainous landscapes were covered in dust; in Colorado, it was red from desert soils that had blown in. Fourteen years later, it’s clear that 2009 was one of the biggest years for dust deposition onto snow.
Last month, we published research (O. I. Lang et al. Environ. Res. Lett. 18, 064045; 2023) that demonstrated how dust from the exposed Great Salt Lake bed falls in the Wasatch Mountains of Utah. Since 2009, I have spent every March through May skiing to remote sites in Utah and Colorado, where I monitor how dust layers evolve. I usually have to ski several kilometres, carrying a 27-kilogramme pack with a shovel to dig a snow pit, tools to cut snow wedges and measure their density, and containers to collect snow samples for analyses. One year, I hit a dusty patch of snow, broke my ski and sliced my leg open.
In areas with heavy dust deposition, such as the southern Rocky Mountains, dust accelerates melt by one or two months. Warming air temperatures affect snow accumulation, but dust builds up over time and darkens the surface, which then absorbs more sunlight and hastens melt.
We are now exploring different ice and snow landscapes — such as the Himalayas and the Andes — to study, for example, how black-carbon buildup following forest fires affects melting. In this picture from August 2019, I am in Greenland, measuring the ice’s surface reflectivity. Behind me, accumulated dark sediment flows into the stream.
As we move into a future that is likely to be even dustier, I am trying to develop snowmelt models. We need to be able to predict snowmelt for many reasons, including to work out how to use water in the western United States as efficiently as possible.