River Styx, Mammoth Hot Springs, Yellowstone National Park

River Styx, Mammoth Hot Springs, Yellowstone National Park. This thermal feature is actually a subterranean hot water creek that likely collects water discharged from Mammoth Hot Spring pools that, after cooling and outflowing from vents, tends to disappear back underground through the porous travertine. River Styx is a Greek mythology reference to the river that surrounds the underworld and keeps with the tradition of using mythology for names of Mammoth Hot Spring thermal features (other examples include Aphrodite Terrace and Minerva Terrace). It was named in 1885 by G.L. Henderson, a park tour operator. USGS photo by Lauren Harrison, 2018.