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What is Watermelon Snow?

Mary McMahon
Updated May 21, 2024
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Watermelon snow is snow which has become discolored due to the presence of cold-loving algae, specifically Chlamydomonas nivalis, an alga with a distinctive pink to red color. When this organism colonizes a section of snow, the snow appears pinkish to red, depending on how compressed it is, and it even has a faint watermelon scent. Watermelon snow tends to appear at high altitude, and it can be found all over the world, including regions where snow appears seasonally, rather than year-round.

People have been noticing watermelon snow for thousands of years. The Ancient Greeks, for example, puzzled over the phenomenon, as did 19th century explorers in the New World, who concluded that the strange red color was due to the presence of iron. Only with the assistance of microscopes did people realized that watermelon snow was caused by a living microorganism. The existence of cold-loving algae also suggested that other extremophilic organisms might someday be discovered, and this proved to be the case, illustrating that life will thrive just about anywhere, if given a chance to do so.

The red color isn't just for looks. The carotenoid pigment which turns the algae pink helps to insulate it from the cold, and to protect it from harmful UV radiation. The evidence seems to suggest that the algae actually colonizes the ground, and when it becomes covered with snow, it slowly works its way to the surface, creating streaks, pits, and patches of reddish color in the snow. Watermelon snow can sometimes extend across a very large area, creating a very striking sight.

When people walk on watermelon snow, they compress the algae, resulting in a deeper red color. They also pick up the color on their shoes and pantlegs, leaving a trail of pink footprints in the snow until all of the algae has been scuffed off their garments and shoes. Since watermelon snow is so visually distinctive, it often becomes a topic of conversation on hikes, not least because it looks like the ghoulish remains of a climbing accident.

Technically, watermelon snow is edible. However, snow can easily be contaminated with bacteria and algae which are not safe to eat, and eating large quantities of watermelon snow can lead to intestinal distress. Therefore, eating this discolored snow is not recommended, although people interested in the science might want to collect a small sample to examine under a microscope at home. Magnified, the algae which causes the peculiar red color is actually quite pretty.

Frequently Asked Questions

What causes watermelon snow to appear pink or red?

Watermelon snow gets its distinctive pink or red color from a type of cold-loving algae called Chlamydomonas nivalis. These algae contain a red pigment called astaxanthin, which protects them from ultraviolet light and gives the snow its watermelon-like hue. The phenomenon is most common in alpine and coastal polar regions during the warmer months.

Is watermelon snow harmful to humans or animals?

While watermelon snow is a natural occurrence, it can be harmful if ingested in large quantities. The algae can act as a laxative, potentially leading to digestive upset. According to research, it's generally advised to avoid consuming snow with visible algae to prevent any adverse effects on health for both humans and animals.

Can watermelon snow contribute to climate change?

Yes, watermelon snow can accelerate melting and contribute to climate change. The red pigments in the algae reduce the snow's albedo (reflectivity), causing it to absorb more heat and melt faster. This can expose darker underlying surfaces, which absorb even more heat, creating a feedback loop that exacerbates melting, as noted by climate scientists.

Where is watermelon snow commonly found?

Watermelon snow is commonly found in alpine regions and coastal polar areas around the world. It typically occurs during the spring and summer months when the temperatures are warmer, and the snow is melting. Notable locations include the Rocky Mountains, the Alps, and the Arctic and Antarctic regions.

How does watermelon snow affect the ecosystem?

Watermelon snow can have a significant impact on the ecosystem. By accelerating snowmelt, it can alter the availability of freshwater for plants and animals. Additionally, the algae serve as a food source for microorganisms and can influence nutrient cycles within the snowpack ecosystem, as detailed in ecological studies.

Can watermelon snow be used to track climate patterns?

Scientists use the presence of watermelon snow as an indicator of climate patterns and change. By studying the algae's growth and distribution, researchers can gain insights into temperature trends and snowmelt rates. This data is valuable for understanding the impacts of global warming on delicate mountain and polar ecosystems.

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Mary McMahon
By Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a AllThingsNature researcher and writer. Mary has a liberal arts degree from Goddard College and spends her free time reading, cooking, and exploring the great outdoors.

Discussion Comments

By anon1001073 — On Feb 27, 2019

I tasted it when I was in Mount Lasson. It tasted a bit like watermelon.

By peabody — On Jul 24, 2011

@chivebasil - Did your father say what the watermelon snow tasted like? I'm curious to know if the actual taste had any resemblance to watermelon, given the similarity in smell.

By LTimmins — On Jul 24, 2011

@turquoise - In Quebec too there is a tradition of pouring hot maple syrup over snow and then eating it when it has cooled down. As the article mentions however, large amounts of watermelon snow can cause digestive illness, so it's definitely not recommended!

By AnnBoleyn — On Jul 24, 2011

@alisha - You're right; I think the natural reaction for many people is to fear things that are strange or unknown to them. In the case of watermelon snow, it certainly looks alarming to those who don't know the true cause of it. I wonder if people in the old times would have believed it if they were told that the snow was red only because of algae!

By discographer — On Jul 23, 2011

I read that when the British expedition ships came back and mentioned watermelon snow that they had seen in Greenland in the 1800s, everyone thought that the snow fall in Greenland was naturally red. People had lots of different ideas about why it was red but then scientists found out about the algae.

It's so funny how our imagination runs wild when we don't know what we are dealing with. I think I would have thought the same way if I lived in that time period. I would have probably thought that it was blood, or maybe even some sort of divine sign.

Thank goodness we have enough scientific knowledge and tools to find out the real causes of things.

By chivebasil — On Jul 22, 2011

I saw watermelon snow once in Colorado. I was pretty shocked at first. I actually thought we might have come across a crime scene or something. The color is not that deep of a red but I was young and the mind wanders to weird places sometimes.

My dad explained what it was and he actually stooped down to eat some. He seemed to like it but no one else in my family would try it.

By burcidi — On Jul 22, 2011

@turquoise-- No, it's not tempting at all. It doesn't have a uniform red color. I've seen watermelon snow a couple of times in California. It was just in some places (not like hills of red snow) and in small streaks like someone spilled their fruit punch.

I don't know, I sure wasn't tempted to try it. The scent is interesting, maybe reminiscent of watermelon but not exactly. You should look up pictures of watermelon snow, you'll know what I mean better then.

By turquoise — On Jul 21, 2011

I wonder if anyone has actually eaten this snow because it looks like snow cones and smells like watermelon? I think I would be willing to try it.

My family is from Kashmir and my mom told me that they actually sold snow sweets in Kashmir in the summer time. They would bring down clean snow from the mountains and pour sweet fruity syrups on top to basically make a snow cone. The snow was also used to keep foods cool because refrigerators weren't common then.

So I guess if it is clean, snow could be eaten but probably not watermelon snow. I bet the algae would cause a stomach upset.

Mary McMahon

Mary McMahon

Ever since she began contributing to the site several years ago, Mary has embraced the exciting challenge of being a...

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