Exploring The Mystery Of Watermelon Snow

Exploring The Mystery Of Watermelon Snow

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Activities Activities: Mountaineering, Skiing

Is It Snow, Blood, Or Something Else?

Have you ever been in the backcountry and noticed streams or pockets of reddish-pink snow? Have you ever wondered what causes the phenomenon? Have you ever noticed that walking through the red snow can stain your boots and pants? Have you ever wondered if the red snow is edible? If you answered "yes" to any of those questions, then this article might be suited for you.

For thousands of years, reddish-colored snow has fascinated many people. Although the phenomenon has been referenced many times through the years, its reddish-pink coloration and occasional watermelon-like scent has led to the widely recognized nickname of watermelon snow. Explorers, mountaineers, and skiers have identified watermelon snow for many years, yet until the late 19th Century the cause of the phenomenon remained a mystery.
Watermelon SnowWatermelon Snow

Ancient Greek philosopher Aristotle provided the first-known written accounts of watermelon snow, although no explanation of the phenomenon was given. Centuries later, many Europeans speculated that the reddish color was geological in nature, either being caused by mineral deposits on the snow or chemicals leaching from rocks. However, it would not be until 1818 before the most breakthrough accounts of watermelon snow would finally occur.

During May of that year, four English ships, led by Captain John Ross, were sent to the Arctic Circle on a quest to find a "Northwest Passage" to the Pacific Ocean as well as chart the northern coast of North America. While traveling through the Arctic Circlt, severe weather conditions forced the expedition to end prematurely and the vessels returned back towards England. While passing back by the northwest coast of Greenland, Captain Ross noted many blood-like red streams coming down snowy slopes. He had several crewmembers bring back samples of the red snow with them to England. Of course, by the time the samples reached England, the snow had long-since melted. Fortunately, the leftover colored liquid was still usable to scientists.

Upon arriving back in England, the liquified watermelon snow samples were immediately studied by scientists. The liquid had such a dark red color that it resembled a red wine. The strange coloration of the liquid coupled with Captain Ross' accounts of the red snow streams caused much confusion and speculation. Some scientists even asked Captain Ross if he had seen red snow falling from the sky, which he had not. The British newspaper The Times published an article about the discovery on December 4, 1818. The article did not provide any immediate explanation for the cause of the phenomenon. However, a follow-up article was written three days later that erroneously speculated the reddish color on the snow was caused by meteor deposits, and that the samples retrieved by Captain Ross and his crew were actually iron specimens mixed with snow.

Captain Ross published a full account of his expedition by the end of 1818, and within the documentation he included a botanical appendix written by famed Scottish botanist Robert Brown. In that appendix, Brown speculated the reddish-colored snow was caused by a type of algae. It would not be until the late 1800s before scientists would correctly determine that watermelon snow was actually caused by high concentrations of microscopic algae, known as snow algae, but it was Brown's assessment that provided the foundation for the scientific discovery.

What Is Snow Algae?

Snow algae is also known by the scientific name Chlamydomonas nivalis. Contrary to its appearance, snow algae is actually a type of freshwater green algae. In scientific terms, the genus name Chlamydomonas refers to green algae, and the species name nivalis is a Latin word that refers to snow.

As is true with all species of green algae, the primary pigment of snow algae is green (chlorophyll). However, snow algae also has a secondary pigment that is red. This red carotenoid pigment protects the algae from intense radiation, both visible and ultraviolet. The red pigment also absorbs heat for the algae.

Unlike most freshwater green algae, snow algae thrives in a cold environment. During Winter months, the algae becomes dormant as snowpack covers over them. Then, during Spring and Summer months, increasing amounts of light, snowmelt, and nutrients triggers the germination process of the snow algae to begin. In addition, the red carotenoid pigment of snow algae, by virtue of absorbing heat, causes snow to melt faster than normal around the algae. The algal germination process can then occur rapidly, causing a sudden high concentration, or bloom, of snow algae.
Sperry GlacierBlooms Of Snow Algae On Gunsight Mountain, Montana (Photo by SummitPost member "saintgrizzly")

This algal bloom is then represented by streams, patches, or small pocket-holes (known as sun-cups) of reddish-pink coloration as the algae rises to the surface of the snow. Then, as the nutrients of the immediate area are depleted, the snow algae create thick-walled cells that will remain dormant until the following Spring and Summer months when the cycle will begin again.
Streams Of Watermelon SnowStreams Of Watermelon Snow In North Cascades

Snow algae is commonly found worldwide in alpine and coastal polar areas. In western North America alone, there are over 60 sub-species of Chlamydomonas nivalis. In some locations, such as over 10,000' elevation in the Sierra Nevada range of California, blooms of snow algae have even been known to be so vast that they can be 10" deep in snow. One teaspoon from an algal bloom might contain as much as one million cells of snow algae, with each cell being 25-30 micrometers in diameter.
Looking down at the top of...Snow Algae On Mount Timpanogos, Utah (Photo by SummitPost member "EJBean")

Is Watermelon Snow As Edible As An Actual Watermelon?

Although watermelon snow is a nickname of snow algae, it begs the question: Is watermelon snow actually edible?

In general, most algae is considered edible. Even the faint watermelon-like scent of snow algae might give that impression. The author of this SummitPost article has even tasted very small doses of snow algae, for testing purposes, without feeling sick. However, it is possible that snow algae might be contaminated by bacteria and toxic algae that are harmful to humans. Eating large quantities of watermelon snow has been known to cause digestive ailments, although the tolerance level of each person's digestive system might be different.

Although human consumption of watermelon snow is not wholely recommended, many organisms consider the algae as a delicacy and, for some, an essential food source. Most notably, ice worms, roundworms, snow fleas, and protozoans regularly consume snow algae. At high elevations, it is common to see millions of ice worms atop snowfields during early morning and late evening hours, especially near snow algae blooms.
Pink Snow where Ice Worms growWatermelon Snow In Alaska (Photo by SummitPost member "jmc")

External Links

For more information and accounts about watermelon snow, please feel free to visit the following links:

National Geographic's Article Examining Snow Algae

Australian Anarctic Division's Article Examining Snow Algae

Watermelon Snow: A Strange Phenomenon Caused by Algal Cells Of The Chlorophyta

Are There Other "Exploring The Mystery Of" Articles?

If you enjoyed reading this article, and/or found it interesting, perhaps you might also like to read the other articles in my "Exploring The Mystery Of" series:

Exploring The Mystery Of Summit Ladybugs

Exploring the Mystery Of Glacier Ice Worms


Post a Comment
Viewing: 1-20 of 27

gimpilator - Jul 22, 2010 4:40 pm - Voted 10/10

Watermelon Snow

Thank you for writing this informative article. I see this phenomenon every year in the Cascades and always find it intriguing. A ranger once told me that 50 percent of people can eat this snow with no ill-affects but that half of people get sick from it. I once saw someone get violently ill several hours after eating it. Thankfully he felt fine after vomiting. Another time, we took a sample of pink snow in a jar to be analyzed much as Captain John Ross did in your article. The water in the jar turned very dark after it had all melted. Now I have only one question for you... When will you write an article for snow worms?


Redwic - Jul 22, 2010 4:43 pm - Hasn't voted

Re: Watermelon Snow

Perhaps that will be a future supplemental article to this one.


rasgoat - Jul 25, 2010 6:22 am - Voted 10/10

Red snow

I too have wondered about this! Thanks! and yes, what abbout the snow worms!


EastKing - Jul 25, 2010 9:52 am - Voted 10/10

Great article!

The mystery has been solved! Algae is the cause and I will not be eating much of it.

vancouver islander

vancouver islander - Jul 25, 2010 11:04 am - Voted 10/10

Nice summary

Good idea to put together such a fine summary of the origins of a phenomenon that many have seen and most have only wondered about.

It's very common on the Island and I already knew about its origins. Nevertheless, you provided some great historical and biological detail that I enjoyed very much.

In legend red snow on Forbidden Plateau here on the Island was thought to be all that remained of wives and children left up there for safety by warriors of the Comox First Nations as they fought raiders from the mainland. Hence the name of the place. And preferable, perhaps, to the real reason: an intriguing advertising catch-phrase to lure visitors to the commercial operations up there in the days before it became a park.

Of course there's yellow snow too. Its origins are much more banal but it's also not to be eaten :-)

Cheers, Martin


liferequiresair - Jul 25, 2010 2:33 pm - Hasn't voted


Thanks for the great info. I've wondered about this stuff for a while now and always have people ask me about it. I've always told them not to eat it though because I've heard of those who partake experiencing giardia-like symptoms.


lcarreau - Jul 25, 2010 9:18 pm - Voted 10/10

You just burst my bubble !

I always thought it had something to do with Sasquatch.

Here in Arizona, we don't have a problem with red or yellow snow.

In fact, we don't have any snow, and that's the problem !!!

erny - Jul 26, 2010 1:00 pm - Hasn't voted


we actually knew this about 30+ years ago. Research at CU Boulder and on the snowfields of the Indian Peaks range above Nederland was the research area investigated by John Clark when he worked for NOAA, etc.


Jakester - Jul 28, 2010 11:45 am - Voted 10/10

Re: oldnews

Older News. According to this very article, we've known exactly what watermelon snow is since the late 1800's.


hgrapid - Jul 28, 2010 10:52 pm - Hasn't voted

I always figured...

I always figured it was blood. I figured a large animal ate a smaller one, and left blood on the snow.


GroundControl - Jul 29, 2010 5:39 pm - Voted 10/10


Facinating article...will keep my eye out for this!


Redwic - Aug 1, 2010 2:42 am - Hasn't voted

Re: Thanks!

This article must have really caught the attention of some people, either by those unfamiliar with the phenomenon or by those who have seen it and did not know the cause. I found two people talking about this article this weekend while climbing.

Mike Lewis

Mike Lewis - Aug 1, 2010 12:30 pm - Voted 10/10


I had read about this phenomenon before and long since forgotten (explaination was too brief.) I think your article was very well written and thorough. I love it when SP features interesting and useful information like this. I also agree with Gimpilator: write one about Snow Worms!


mtybumpo - Aug 2, 2010 12:30 pm - Voted 10/10

Great Article!

I've seen a lot of Watermelon Snow but I never knew what it was called or why it was red. Now I know! Very interesting and informative article. Thank you!


Tangeman - Aug 2, 2010 1:51 pm - Voted 10/10


I was just up in the Cascades, and saw it and just thought it was minerals, but this is cool. Thanks for the article!


D-bo - Aug 3, 2010 3:06 pm - Voted 10/10

Now I know...

...And knowing is half the battle.


Redwic - Aug 5, 2010 12:34 am - Hasn't voted

Re: On a Related note:

Very interesting. I love finding out the obscurities and oddities of our world!


gliderman - Aug 5, 2010 7:54 pm - Hasn't voted

Re: On a Related note:

Me, too. I love stumbling onto information about things I am aware of, but explain what is going on. And, new things, too. I may be retired from teaching, but still love learning new things.


JKipple - Aug 6, 2010 2:37 pm - Voted 10/10


I always wondered about that, thanks for the article


EricChu - Aug 12, 2010 6:22 pm - Voted 10/10

A highly interesting article!

Thanks for the work you did and for posting this - I found it all very interesting, for one thing because I have also seen reddish-colored snow many times in the Alps as well. Sometimes it was believed that the coloring of the snow in the Alps was caused by desert sand from the Sahara, which is often blown over to Europe when there are the strong southern winds that create the alpine Foehn, which causes almost "unnaturally" clear light (I've seen some pictures posted of the American mountains here on SP, by the way, which reminded me very strongly of this!). Yet it has been clearly proven that the desert sand has nothing to do with this in the Alps either - it is the algae!

Viewing: 1-20 of 27