The curious case of glacier blood

Ever taken a summer hike through the mountains in an alpine environment above tree level? If you have, you’re probably familiar with how the snow and glaciers look during the summer. The pristine white expanses that cap the peaks in the winter turn into small, gritty patches with visible little streams of freshly-melted water running off of them. 

But some glaciers and snowfields have taken on a new, quite concerning look in recent seasons. Blazed with deep crimson streaks, the melting snow and ice look like a too-real victim of climate change’s warming temperatures and depleted snowpacks. It’s only natural at that moment to question: Is that blood?  

The science behind the stranger-than-fiction visuals provides an explanation, though. These red and orange patches are actually comprised of algae, which can be found around the world. There’s a lot we don’t know about the algae, which has been given the macabre nickname of “glacier blood,” due to its color.

Snow algae are a group of green algae (Chlorophyta) that turn red when they create brightly-colored pigments. According to Robin Kodner, the director of the Living Snow Project—an organization that allows scientists and alpine recreationists alike to tag snow algae locations they encounter on an app and collect samples for research—not all pink snow is caused by the same species of alga. Many sources contribute red snow to a specific species called Chlamydomonas nivalis, but there are many different snow algae species that can cause this same effect. 

Currently, there’s much to learn about snow algae and its effects. Where it’s most likely to occur, and what conditions are better and worse for its growth are questions currently being studied. Scientists are studying it to try to understand the role it plays in alpine snow and glacier melt, as well as downstream water supplies.

How this particular snow alga might change the forecasts for future snowpack in a warming climate is still unclear. The red or green algae is darker and less reflective than white snow, so it absorbs and retains more of the sun’s heat—thus creating faster melting—than unblemished snow. Since the algae need liquid water to reproduce, there’s reason to think that it could cause a positive feedback loop of patches melting more snow, then growing larger, on repeat. 

But there are a lot of other factors that could play into the algae’s long-term impact. “Changes in the amount of snow annually, the seasonal rates of snow melt and other environmental factors can also impact snow algae growth in ways we don’t yet understand,” says Kodner, who is also a professor of environmental science at Western Washington University.

In many ecosystems, including much of the Western US, alpine snowpack plays an important role in the water system. In dry regions, snowmelt is a consistent source of water through the summer and fall. If there was less snowmelt or it stopped coming altogether—so-called “snow droughts,” which are already occurring more frequently—the entire region becomes more arid. Large snowpacks melting out too quickly, on the other hand, pose the risk of creating floods and landslides.

At this point, scientists aren’t sure exactly how much Chlamydomonas nivalis changes the rate of glaciers and snowpack melting on an ecosystem-level scale, particularly in alpine areas, but one study measured the overall rate of melting increasing by about 21 percent.

Kodner says that despite the apparent risk they pose to already-threatened alpine snowpack, there’s still no consensus on how to manage the blooms, or even if they should be managed at all. “Snow algae blooms are natural occurrences, and we need to collect large-scale data to know if they are, in fact, increasing over time before we even ask questions about preventing them,” says Kodner.

So, if you see what looks like a giant patch of bleeding snow and ice on any hikes or ski tours in the near future, now you know what it is. Whether it’s harmless or not in the era of human-caused climate change is another question altogether.