The Grand Prismatic Spring at Yellowstone National Park is so colorful that it’s hard to believe there aren't dyes or Photoshop involved. But the formation is totally natural. The hot spring is one of many geysers and hot springs that vent the earth’s heat to the surface at Yellowstone. This one is full of water, and also full of different kinds of bacteria that give it those rainbow colors.
Water at the center of the spring, which bubbles up 121 feet from underground chambers, can reach temperatures around 189 degrees Fahrenheit, which makes it too hot to sustain most life (some life does manage to exist, but its limited to organisms that feed off of inorganic chemicals like hyrdogen gas). Because there's very little living in the center of the pool, the water looks extremely clear, and has a beautiful, deep-blue color (thanks to the scattering of blue wavelengths—the same reason oceans and lakes appear blue to the naked eye). But as the water spreads out and cools, it creates concentric circles of varying temperatures—like a stacking matryoshka doll, if each doll signified a different temperature. And these distinct temperature rings are key, because each ring creates a very different environment inhabited by different types of bacteria. And it's the different types of bacteria that give the spring its prismatic colors.
Smithsonian introduces us to the various types of bacteria that live in the different temperature zones, and tells us how each produces its distinctive color.
(Image credit: Clément Bardot)