Let's Talk About This Giant Steaming Rainbow Hole In The Ground

Find out why this is one of America's coolest, deadliest sights.

Grand Prismatic Spring
The place where hell bubbled up. | Ignacio Palacios/Stone/Getty
The place where hell bubbled up. | Ignacio Palacios/Stone/Getty

In 1869, Yellowstone was nothing but a rumor to European Americans, thought to be a myth propagated by hallucinating mountain men. When Charles Cook -- of the Folsom–Cook–Petersen Expedition -- wrote a seven-page article for Lippincott’s Magazine on the “place where Hell bubbled up,” his editors responded: “Thank you, but we do not print fiction.”

In the intervening years, Yellowstone shed its mythical hell status and became the world’s first national park. But the park is still bubbling, flowing, steaming, and boiling like nowhere else on Earth. And there's no place more otherworldly than the rainbow-colored void known as the Grand Prismatic Spring.

This 160-foot-deep hot spring is in either “the valley of death” or “Wonderland,” depending on how close you are to the steam. But how the heck did this place once thought to be an entrance to Hades actually get to be this way? This rainbow death trap’s got very little to do with hell -- but you still best mind the boardwalks. 

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The Grand Prismatic is the largest hot spring in the US | pabst_ell/E+/Getty

Why the hell is the Grand Prismatic Spring so colorful?

Sitting in Yellowstone’s Midway Geyser Basin -- just north of Old Faithful -- Grand Prismatic is the largest, most colorful spring in the park. “With a circumference of 300 yards,” naturalist John Muir wrote, “it is more like a lake than a spring. This one of the multitude of Yellowstone fountains is of itself object enough for a trip across the continent.”

This not-a-lake hot spring -- the third-largest in the world -- runs at an average of 160ºF. But why is it so colorful? Microbial mats of heat-loving archaea (single-celled, bacteria-like organisms) cling to the edges, with different species congregating at different temperatures and forming the spring’s outer rainbow hues. It’s too hot for these tiny guys toward the center, leading to the rich, sterile blue tones found there. In warmer seasons, the water is fringed with bright oranges and greens; come winter, its hues dull a bit, taking on browner tones.

And while Grand Prismatic’s colors seem entirely one-of-a-kind, “Many other hot springs and pools have, or had, the same beautiful colors,” explains Shaul Hurwitz, Research Hydrologist with the U.S. Geological Survey. “A good example is Morning Glory Pool in Yellowstone’s Upper Geyser Basin, previously known as one of the most spectacular. But because humans continuously threw coins and other trash into the pool, water temperature changed, which resulted in different microbial communities and different colors.” 

The lay of the land affects the colors, too. 

“Grand Prismatic is unique because of the way light is being scattered,” notes Hurwitz. “Many other springs have, for example, trees or cliffs surrounding them, so the sun rays are scattered differently.” As long as humans don’t mess with it, Grand Prismatic’s colors should be here to stay.

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Grand Prismatic
Grand Prismatic Spring is over 300 feet long. | Chase Dekker Wild-Life Images/Moment Open/Getty

It's the result of a super volcano's eating frenzy

The ground the Grand Prismatic Spring sits on is fairly level — that’s how the spring has formed its orange octopus-like tendrils, with silica-rich water flowing away in all directions. But look at a map, and you’ll see mountain ranges on nearly all sides of the park. Yellowstone sits in a convenient, lower-lying gap.

Why? The Yellowstone supervolcano “ate” the mountains around 640,000 years ago. The Lava Creek eruption sent ash as far as Des Moines and New Orleans, forming the current bison-roaming Yellowstone Caldera we know today. And then, of course, the glaciers charged through and left “till” everywhere in their flattening wake -- including under Grand Prismatic.

Through all this, Yellowstone is still an active supervolcano, capable of another such explosion. A giant magma plume -- sort of like an oblong lava balloon -- currently rests under the park, doming the land as it breathes in, falling as it breathes out. Prior explosions were 1.3 and 2.1 million years ago, meaning eruptions are due roughly every 650,000 years. Do the math on that one.

Note: While the magma plume stays stagnant, North America is heading southwest. About 16.1 million years ago, “Yellowstone” used to be in Nevada. (Maybe don’t buy real estate in Billings, Montana in a few million years.) 

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Yellowstone's Midway Geyser Basin
Do NOT wander off the boardwalk. | Cherrys Picks/Moment/Getty

No, it's not a big natural hot tub

A busy boardwalk runs along the spring’s northern edge, on the Excelsior Geyser side, in Yellowstone’s Midway Basin. But for the greatest vantage point, climb the ridge south of the spring, up the trail to the Grand Prismatic Spring Overlook. It’s the closest thing you’ll get to a drone shot, and it’s a quick .6 miles up 105 feet in elevation.

But Hurwitz notes that while the colors are 100% real, you may need to be patient. “Most people that stand near the spring expect to see what they’ve seen in photos. These were taken with favorable light conditions; in addition, depending on wind direction, the steam above the pool can mask the beautiful colors.”

How not to explore it? By jumping in -- or even getting off the boardwalk. This is not some big, natural hot tub.

“I tell everyone that will be coming into the field with me,” explains Dr. Jeff Havig, researcher in the Department of Earth and Environmental Sciences at the University of Minnesota, “that what might seem like a perfectly safe place to step may, in fact, hide a large body of boiling water underneath and could give way the moment you put weight on it.”

Oh,and if you’re able to get out, it’s not infection that would be your demise. “You’d die from dehydration 2-3 days later, skin cooked and no longer able to regulate water retention.” In other words: NPS guidelines are there for a reason. Obey them.

Luckily, there’s a surefire way to see the colors, avoid misstepping, and avoid the crowds. Check out Google Earth’s virtual tour of Yellowstone. 150 years later, the once-mythical “Wonderland” -- and its steaming Grand Prismatic Spring -- can be admired at the click of a button.

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Jacqueline Kehoe is a writer, photographer, and geology geek. See her work on Instagram at @j.kehoe.