Grand Prismatic Spring is the largest and one of the most brilliant of Yellowstone’s many colorful hot springs. Its massive expanse stretches approximately 200 feet across, and the high temperature of its water—160 degrees—ensures that the spring is often cloaked in steam. Deep beneath, magma from an active volcano heats water that rises to the surface through fissures in the rocks. The result is a hot spring that pours almost 500 gallons of hot water each minute into the Firehole River. Minerals dissolved in the hot water are deposited and gradually build the gracefully terraced shoulders of this feature. The intense blue color in the center is due to sunlight being scattered by fine particles suspended in the water, while the yellow, orange, and brown colors around the spring and along the runoff channels are caused by thermophiles, heat-loving microorganisms whose colorful pigments allow them to make energy from sunlight and thrive in the harsh conditions of hot springs.

Photo: Dan Fisher

Photo: Bernard Fisher

Photo: Bernard Fisher

Mammoth, Wyoming · USA