Young Hopeful and Grey Bulger are separate geysers that share a single J-shaped pool in Yellowstone National Park’s Lower Geyser Basin as part of the Black Warrior Group. Grey Bulger, the more active geyser, has multiple vents around the top of the pool, and its eruptions vary with the seasonal water table, with some vents flowing continuously and others pulsing intermittently. Its largest vents usually rise about 2 feet but can reach around 6 feet, and numerous vents are active or potentially active at once. Young Hopeful, also multi-vented, lies at the lower end of the pool but is currently dormant. Together they show how shared hydrothermal plumbing can produce very different surface behavior.

Mammoth, Wyoming · USA