The World's Largest Acidic Geyser Has Erupted in Yellowstone

"Eruptions of Echinus Geyser varied tremendously when the geyser was vigorously active. They could be vertical or inclined, occasionally soaking onlookers with warm water, and could be regular enough that the park would sometimes post predictions-the duration of an eruption could often be used to forecast the timing of the subsequent eruption."

"In the 1970s, Echinus Geyser erupted every 40 to 80 minutes and the park had viewing platforms so visitors could watch the action. At its peak, Echinus' eruptions would reach 75 feet and last up to 90 minutes, according to the Yellowstone Volcano Observatory and United States Geological Survey."

"Echinus is the largest acidic geyser in the world, meaning it has a mix of acidic gases and neutral water rich in sulfate and chloride. The acid isn't concentrated enough to eat away at the surrounding rock, but the liquid does build up to create the spiny sea urchin-like formations."

Echinus Geyser, located in Yellowstone's Norris Geyser Basin, has returned to activity after nearly a decade of dormancy. Named for the sea urchin-like rocks surrounding its 66-foot-wide opening, this acidic geyser was once a regular performer in the 1970s, erupting every 40 to 80 minutes with heights reaching 75 feet. Activity declined through the early 2000s, becoming increasingly irregular until the geyser was essentially inactive by late 2017. In February 2026, Echinus showed renewed signs of life, with initial eruptions on February 7 followed by regular activity. Current eruptions reach approximately 30 feet and occur every few hours, lasting 3 to 5 minutes. As the world's largest acidic geyser, Echinus contains a mixture of acidic gases and neutral water rich in sulfate and chloride.

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