Old Faithful may be more famous, but the Grand Prismatic Hot Spring is the most photographed thermal feature in Yellowstone. That's because of its crazy-bright colors and enormous size.
What Makes the Grand Prismatic so Grand?
Deeper than a 10-Story Building
Extremely hot water travels 121 feet from a crack in the Earth to reach the surface of the spring.
Football Field on Steroids
The third largest spring in the world, the Grand Prismatic is bigger than a football field at 370 feet in diameter. A gridiron is 360 feet long and 160 feet wide.
Rainbow of Colors
The hot spring has bright bands of orange, yellow, and green ring the deep blue waters in the spring. The multicolored layers get their hues from different species of thermophile (heat-loving) bacteria living in the progressively cooler water around the spring. And the deep blue center? That’s because water scatters the blue wavelengths of light more than others, reflecting blues back to our eyes.
A Living Thermometer
What living thing in Yellowstone has helped investigators solve crimes and NASA search for extraterrestrial life on seemingly inhospitable planets? Heat-loving microbes living in the Yellowstone's thermal pools. In 1968, researcher Thomas Brock discovered a microbe living in one of Yellowstone’s extremely hot springs. In the years since, research on Yellowstone’s microbes has led to major medical and scientific advances, including the sequencing of the entire human genome.
A Foreign Object in Grand Prismatic
When a tourist from the Netherlands accidentally—and illegally—flew a drone into the ecologically fragile Grand Prismatic in 2014, the drone disappeared and has never been recovered. Read more about things stuffed down geysers and hot springs.
More Pools and Geysers at Midway Geyser Basin
Yellowstone's Midway Geyser Basin may be small, but it packs a big punch: In addition to Grand Prismatic Spring, see Excelsior Geyser, an enormous geyser crater, Turquoise Pool, and Opal Pool. You can get up close by strolling across the Firehole River and along the short boardwalk that snakes through the thermal area. Be sure to stay on the boardwalk. It is illegal and very dangerous to walk in the geyser basin.
Excelsior Geyser Crater
Today, this steaming, bright blue pool is essentially a hot spring. But in its heyday in the late 1800s, Excelsior erupted to heights of about 300 feet. It went dormant for much of the 20th century, only to suddenly erupt for two days in 1985—some of its blasts reached 80 feet in height. Though it’s a quiet pool now, Yellowstone’s constantly changing thermal landscape could revive Excelsior Geyser to its former glory once again.
Getting to the Midway Geyser Basin
The Midway Geyser Basin is a short distance north from the Old Faithful area and the west side of the Grand Loop Road. Or, from the West Entrance, drive about 25 miles on the West Entrance Road and Grand Loop Road to the Midway Geyser Basin parking area. Tip: Get there early or late in the day to avoid the tour bus crowds at this justifiably popular spot.