Clepsydra Geyser, Hydrothermal geyser in Lower Geyser Basin, Yellowstone National Park, United States.

Clepsydra Geyser is a hydrothermal hot spring in the Lower Geyser Basin of Yellowstone National Park. Water shoots up from the ground in nearly constant bursts, creating a display of steaming spray and heat that visitors can watch from a safe boardwalk path.

The geyser was named during an expedition in 1878 and was once famous for erupting at regular three-minute intervals. A powerful earthquake in 1959 shifted its behavior, transforming it into the nearly continuous erupting feature that exists today.

T. B. Comstock named the geyser during the 1878 Captain Jones expedition, taking the term from the Greek word for water clock, klepsydra. The name records how it behaved then: before the 1959 Hebgen Lake earthquake it erupted about every three minutes.

The best viewing spot is the Fountain Paint Pot Nature Trail boardwalk, where visitors can safely keep their distance from the hot water. Wear sturdy shoes and watch for sudden bursts of steam that can appear without warning.

Clepsydra Geyser was named by T. B. Comstock during the 1878 Captain Jones expedition, taking its name from the Greek word for water clock. Before the 1959 Hebgen Lake earthquake it erupted on a regular three-minute cycle; since then it has played almost without pause, reaching about 45 feet (14 m).