On Earth Day, let"s journey to one of nature"s most stunning displays of geothermal power—Grand Prismatic Spring in Yellowstone National Park, Wyoming. The largest hot spring in the United States, it spans 113 metres across and reaches temperatures of 71°C. This geothermal marvel is fuelled by the immense heat of the massive Yellowstone volcano beneath the surface. Its vivid rings of blue, green, yellow and orange are created by heat-loving microorganisms—called thermophiles—that thrive in the mineral-rich waters.