Yellowstone’s Largest Acid Geyser Erupts

Clear Facts

• Echinus Geyser, world’s biggest acidic geyser in Yellowstone’s Norris Geyser Basin Back Basin, erupted February 7 after six years dormant.
• First activity since December 2020, with bursts February 9, 12, 15; frequent eruptions every 2-5 hours from February 16.
• Eruptions last 2-3 minutes reaching 20-30 feet; pool refills in one hour after significant drop.
• All activity mid-to-late February, last eruption February 24; no further bursts observed.

Echinus features a rare acidic system sustained by mixing acidic gases and neutral waters.

“At Echinus Geyser, however, the composition is due to mixing between acidic gases and neutral waters, and the acidity is not sufficient to eat away at the rock,” states the USGS.

This unique chemistry forms striking red edges of arsenic, iron, and aluminum around the pool, plus nearby thorny silica rocks.

Historically active phases lasted 1-2 months with taller 75-foot bursts; continuation into summer unlikely amid basin changes.

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Full details on eruption