Grand Prismatic Spring at Yellowstone’s Midway Geyser Basin

Grand Prismatic Spring, Yellowstone’s largest hot spring, is 200-330 feet in diameter and more than 121 feet deep.
Hot Springs
Hot springs are the most common hydrothermal features in Yellowstone. Superheated water cools as it reaches the surface, sinks, and is replaced by hotter water from below. This circulation prevents water from reaching the temperature needed to set off an eruption.
Hydrothermal features are also habitats in which microscopic organisms survive and thrive. They are called thermophiles: "thermo" for heat and "phile" for lover.
Although they are too small to be seen with the naked eye, trillions are grouped together and appear as masses of color. They are nourished by energy and chemical building blocks. Colorless and yellow thermophiles grow in the hottest water. Orange, brown, and green thermophiles grow in cooler waters.