Minerva Terrace, Mammoth Hot Springs.
A hot spring, also known as a thermal spring, is a spring supplied by underground water heated usually by vapor from magma, and most common in recently active volcanic regions. The temperature and rate of discharge of hot springs depend on factors such as the rate at which water circulates through the system of underground channelways, the amount of heat supplied at depth, and the extent of dilution of the heated water by cool ground water near the surface. The water contains dissolved minerals that may form terraces around the the outlet. See also geyser.