Pump Geyser, Cone geyser in Upper Geyser Basin, Yellowstone National Park, USA

Pump Geyser is a cone geyser in the Geyser Hill Complex of the Upper Geyser Basin, Yellowstone National Park. It splashes 2 to 3 feet high almost constantly and thumps without apparent interval, though less productive periods occur. Since 1990 it has had true eruptions: a small boil domes the water, which bursts up to 15 feet high for a few seconds, then simmers before the cycle restarts after a pause.

Frank Jay Haynes, Yellowstone's park photographer from 1883 to 1916, most likely named Pump Geyser. The name comes from the sound of its constant eruptions, which resembles an old-style mechanical pump. The name may also reflect confusion with another geyser called the Pump, which went extinct. In 1990 Pump began erupting as a true geyser, with intervals and durations of a few seconds.

The natural phenomenon represents the geological power of Yellowstone, drawing visitors who witness frequent water bursts throughout the day.

Visitors can watch eruptions from designated wooden boardwalks in the Geyser Hill Complex, where several thermal features are located close together. The site is easily accessible on foot, and frequent daytime activity provides multiple opportunities to observe the geyser's behavior.

Pump Geyser may share a connection with nearby Sponge Geyser: while Sponge fills, Pump stays quiet, and a few seconds after Sponge drains, Pump resumes spurting. The link is considered likely but has not been studied further.