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 (61 meters) across. The high temperature of its water 160F (70C) ensures that the spring is often cloaked in steam. Deep beneath Yellowstone, 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 the spring. The yellow, orange, and brown colors encircling the hot spring and lining the runoff channels are caused by thermophiles (heat loving microorganisms). These microbes contain colorful pigments that allow them to make energy from sunlight and thrive in the harsh conditions of hot springs. This is a scene of the runoff from the spring showing the various colors of microorganisms. The temperature of the water determines the colors of the thermophiles. The blue, green and yellow colors are found in the hottest water, while the orange and brown colors are found in the cooler water.