Yellowstone National Park
(May 2023)

Midway Geyser Basin contains a small collection of mammoth-sized springs. Midway is part of the Lower Geyser Basin, but because of its isolated location between the main features of Lower and Upper geyser basins it became known as Midway. Rudyard Kipling, who visited Yellowstone in 1889, immortalized this basin by referring to it as "Hell's Half Acre." Even today it is still remembered by that name. Despite its small size Midway possesses two of the largest hot springs in the world. Grand Prismatic Spring, nearly 370 feet in diameter, sits upon a large mound surrounded by small step-like terraces. The other feature, Excelsior Geyser, erupted nearly 300 feet high before the 1900s. It is now a dormant geyser and is considered a hot spring, discharging more than 4050 gallons of boiling water per minute. Other colorful springs include Turquoise and Indigo springs, known for their pale and dark blue colors. Across the Firehole River from Excelsior and Grand Prismatic springs are a series of small isolated, pristine springs and mud pots.

Extremely hot water travels 121 feet from a crack in the Earth to reach the surface of the spring.  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.  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.  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. These microbes even led to the development of the PCR test, which has been instrumental in creating COVID-19 rapid test to slow the spread of the virus.