Great Fountain Geyser

Great Fountain Geyser is a large geyser in Lower Geyser Basin, near Fountain Paint Pot. Its eruptions average about 100 feet (31 m); rare superbursts reach 200 feet (61 m) or more. The display comes in successive bursts over roughly 45–60 minutes. This is a stop for a flexible schedule, since geyser activity can be irregular.

The pool slowly refills over a cycle that usually takes 10–14 hours. Water commonly starts to spill over 70–100 minutes before an eruption, a useful sign to watch alongside the park's current eruption estimate. Neither gives a guaranteed start time. During the wait, keep an eye on nearby White Dome Geyser too.

The broad, scalloped mineral apron and shallow pools make a useful foreground for the tall burst. A view that holds both the terraces and plume shows the scale; low sun can backlight spray and steam and catch their reflections in the water.

Underground constrictions trap hot water and let steam pressure build. When pressure forces water past those narrow points, the geyser erupts in a succession of bursts. Great Fountain's long display is a good place to watch that force work through a large pool rather than a single brief jet.

Lower Geyser Basin contains about 14 square kilometres (5.5 square miles) of actively hot ground. Rhyolite lava flows, glaciers, hydrothermal activity and climate have all shaped its broad, grassy landscape. In some hot areas, lodgepole pine cannot grow, leaving the thermal ground open across the meadow.

Sediment from nearby Goose Lake preserves clues from pollen, charcoal and diatoms. A core collected there in 2018 helped researchers reconstruct vegetation, fire and lake changes. Around 3,800 years ago, hydrothermal activity stopped in some parts of the basin and became widespread in others; an earthquake or severe drought may have contributed, but the cause is uncertain.

Remain on boardwalks and designated trails around the thermal features. The hot water can cause severe burns, and children need close supervision. The site also has interpretive information about its history and geology.