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How does the Old Faithful geyser in Yellowstone National Park work?

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Yellowstone National Park: Old Faithful — Yellowstone National Park Old Faithful geyser erupting, Upper Geyser Basin, Yellowstone National Park, northwestern Wyoming, U.S.

Old Faithful geyser in Yellowstone National Park operates due to the interaction of groundwater with magma or hot igneous rocks beneath the surface. Water deep within the geyser's conduits heats up and approaches its boiling point. As steam bubbles form and rise, they reduce the pressure on the water column below. This causes the superheated water to flash into steam, forcing a column of water and steam to erupt from the vent.1

After an eruption, groundwater refills the conduits, and the heating process begins again. The duration of an eruption influences the interval until the next one; longer eruptions typically lead to longer recharge periods. Old Faithful erupts approximately every 90 minutes, ejecting thousands of gallons of water and steam to heights of about 130-140 feet.12