Scientists find 79-million-gallon reservoir beneath Yellowstone's Old Faithful

Scientists have discovered a 79-million-gallon reservoir of hot water beneath Yellowstone's Old Faithful geyser, according to a landmark 2017 study titled "Anatomy of Old Faithful From Subsurface Seismic Imaging of the Yellowstone Upper Geyser Basin." Researchers from the University of Utah used 133 small, portable seismometers to map the hidden reservoir by analyzing ambient noise from wind, water, tourists, and the geyser's own boiling.

This technique allowed them to create a detailed picture of the near-surface geology and fluid pathways that power Old Faithful's eruptions. The reservoir is estimated to hold around 300,000 cubic meters of water, or about 79 million gallons, making it vastly larger than any single eruption of the geyser.