Yellowstone

A small mudpot vent in Pocket Basin at the north end of Yellowstone's Lower Geyser Basin produced this intriguing feature that mimics a spatter cone that issued a lava flow. Mudpots form in areas of intense, clay-rich hydrothermal alteration where the thermal system is dominated by the gas phase.

Yellowstone

Riverside Geyser in the Upper Geyser Basin is the most regular of Yellowstone's geysers. Every six hours it erupts a 25-m-high inclined jet from a small vent hole on the east bank of the Firehole River 2 km downstream from Old Faithful.