Unlike hot springs, the small bodies of very hot water known as geyser pools are part of a geyser system. They develop on the surface at places where Earth’s underground volcanic pressures have diminished so much that pooling has replaced eruption. Most geyser pools are deep, and beneath some, magically, are ﬂooded caves. Because they’re part of a geyser system, the water level in geyser pools often drops just before an eruption. Many geyser pools support life. Those lower in temperature are sometimes brown with microorganisms. Others support larger life forms, including insects. Many Yellowstone pools contain the bones of buffalo and elk that have stumbled into them. One preserves, in its clear water, the complete skeleton of a coyote.