Why Some Western Snow Is Turning Pink

Algae bring a rosy hue to some mountain snowpacks, which might accelerate melting

Pink snow in mountains
Watermelon snow near the summit of the Chilkoot Trail in Alaska. Stefan Wackerhagen via Getty Images

High in the mountains of the western United States, patches of gleaming white snow are streaked with bright pink. It looks as though someone squirted the powder with watermelon-flavored syrup. Some say it even has a faintly fruity smell. But the rosy-hued snow—also called watermelon snow or glacier blood—isn’t artificial. It’s a phenomenon caused by blooming green algae called Chlamydomonas nivalis

C. nivalis can be found in mountain ranges across the world, and it has been studied for more than 100 years. But in the drought-stricken American West, which relies heavily on snowmelt for its water supply, scientists say this algal growth could be cause for concern. 

“There’s a lot of evidence now that shows that these algal blooms contribute rather significantly to overall melt of snowpack around the West,” Scott Hotaling, a professor in the Watershed Sciences Department at Utah State University, tells KUER’s Kristine Weller. 

Normally, bright white snow has a very high albedo, meaning much of the sunlight that hits the surface gets reflected away. But when algae bloom and turn red, they absorb more light and heat, which melts the snow around them. As the snow turns to liquid, the algae, which thrive on water, light and nutrients, grow and continue the melting cycle. 

When snow melts gradually, it creates a predictable water supply for reservoirs downstream and allows for colder water to flow into streams during the hot summer months, providing a lifeline for aquatic creatures living in them, writes Kylie Mohr for High Country News (HCN). Faster melting caused by algae could heat up streams and lead to less water in the summer, per HCN.

“It’s a pretty big deal,” Hotaling tells the publication. “We talk about the whole West being in a drought, and if there’s going to be another factor that perpetuates earlier melt, that’s important.”

The western U.S. is facing its worst drought in more 1,200 years, which has been exacerbated by climate change. Some experts say conditions have gotten so dry that “drought” is no longer an accurate term. 

“This isn’t a drought, it’s something else,” Brad Udall, senior water and climate research scientist at Colorado State University’s Colorado Water Institute, told Vail Daily’s Sean Naylor last year. “Myself and other scientists are trying to use a different term: Aridification.”

The aridification of the West has led to unprecedented water cuts and extremely low water levels in Lake Mead and Lake Powell, two of the nation’s largest reservoirs. Scientists say one more dry winter could either lead to draining of Lake Powell or force the government to take emergency action. In such dry conditions, the amount of snowfall can sometimes decrease. But that isn’t the only important factor—how quickly the snow melts also plays a role. Still, scientists debate whether these algal blooms are serious enough to be included in snowmelt models, or whether they’re not any worse than dust or ash on snow. 

“There are so many variables in snowmelt that one really just needs to stick to the basics of climate variabilities,” Scott Pattee, a water supply specialist with the Natural Resources Conservation Service Washington Snow Survey, tells HCN. “It’s really no more concerning than dirty or trashy snow, which can [also] accelerate the melt.”

Researchers still have a lot of questions about why algal blooms are occurring, what causes them to grow, how exactly they’re impacting the snowmelt and how climate change is contributing to the algae’s spread. But they’re working on finding answers through research, including a citizen science initiative called The Living Snow Project. People recreating in the mountains across the West can document algal blooms they come across on the organization’s smartphone app. They can also collect and mail samples to researchers in Washington. 

“When we sequence the DNA, it lets us know what algae species are present, which algae species coexist, and what other organisms are living with the algae,” Robin Kodner, a professor at Western Washington University, tells Claire McArthur of the Tahoe Daily Tribune. “Do we see blooms at the same time each year? How long-lived are these blooms? Do we see them in the same places? A lot of this data that we get from observations from volunteers can help us address some of those questions in addition to the other work that we’re doing in our labs.”