This colorful hot spring in Yellowstone National Park, located in Midway Geyser Basin, is the largest hot spring in the United States and the third largest in the world. It's approximately 370 feet (112.8 m) in diameter and 121 feet (37 m) deep. It's rich color is the result of thermophilic (“heat loving”) organisms living along the edges of the hot spring, whose​ ​colors change throughout the seasons.​ ​Hot springs, like Grand Prismatic, are fueled by heat from a large reservoir of partially molten rock (magma), just a few miles beneath Yellowstone, that drives one of the world’s largest volcanic systems. ​ Photo Credit: Thanks to Ann-Marie Mair (@ringlitephotography on Flickr) for sharing this with us!​