Grand Prismatic Spring is one of the largest and most beautiful examples of a common hydrothermal feature in Yellowstone National Park and one of the largest hot springs in the United States. The prismatic, colorful features come from several sources; the deep blue in the center is the clear super-heated water circulating up from the subterranean heat source and shows a pair of convection currents, like a pair of eyes. As the water cools at the edges of the pool and on the sinter terraces, bacteria and algae produce the rainbow of colors. This hot spring was specifically mentioned in Osborne Russell's Journal of a Trapper, by the name of Boiling Lake, which apparently was a name given to it by Rocky Mountain fur trappers in the 1830s, in Yellowstone National Park; Wyoming, United States of America, Photo by Tom Murphy / Design Pics