Like most springs on Geyser Hill, Pump Geyser
is filled by boiling alkaline water, and is one of the most active features in the area; although its eruptions are relatively small they are almost continuous. The water constantly simmers and splashes, rising to heights of a few feet, and sustaining an area of delicate deposited sinter formations. The vent itself is semi-circular and quite colorful, viewable from both sides as the boardwalk trail loops part of the way around the spring. Eruptions are accompanied by a dull thumping noise, on account of which the geyser was named, early in the 20th century.
Back to map of the Upper Geyser Basin