The USGS released this video of an eruption at Black Diamond Pool in Yellowstone National Park that happened May 31, 2025.
YELLOWSTONE NATIONAL PARK, Wyo. — Yellowstone’s Echinus Geyser—the largest acidic geyser on Earth—is putting on a show with a rare and spectacular reawakening.
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Located in the Back Basin of the Norris Geyser Basin, the geyser unexpectedly erupted on Feb. 7 after nearly six years of dormancy, marking its first eruption since December 2020, with subsequent bursts on Feb. 9, 12 and 15.
Yellowstone’s Echinus Geyser erupts for the first time since 2020
(USGS)
The activity shifted into high gear on Feb. 16, with eruptions occurring every two to five hours, according to the U.S. Geological Survey (USGS).
The agency noted the rarity of acid geysers, as the acidic water can break down the rock that makes up a geyser’s plumbing system.
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“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,” the USGS said.
Echinus Geyser, located in Yellowstone’s Norris Geyser Basin, is the largest acid-water geyser in the world, with a pH of 3.3–3.6 and water temperatures reaching 176.5°F (80.3°C). Named in the late 1800s for its spiny, sea-urchin-like cone, Echinus once erupted regularly but is now unpredictable, with eruptions reaching 40–60 feet (12–18 m) and lasting about 4 minutes. Once powered by a secondary water source, its activity declined after 1998, though brief active phases were recorded in 2017–2019.
(Getty Images)
The geyser’s unique water composition results in distinct mineral formations.
A vivid red border of iron, aluminum and arsenic surrounds the pool, while the spiny, silica-coated rocks scattered nearby provide the inspiration for the geyser’s name.
Lasting only two to three minutes, the eruptions reach about 20 to 30 feet in height.
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Once the eruption ends, the pool’s water level drops sharply and requires about an hour to refill.
In its heyday when it was more active decades ago, eruptions varied, with some small and others reaching 75 feet.
Echinus Geyser is in the Norris Geyser Basin of Yellowstone National Park. It was named because the cone resembles a sea urchin.
(Getty Images / Getty Images)
The USGS notes that all the eruptions happened in mid to late February, and there hasn’t been another eruption since Feb. 24.
Whether this activity will persist through the summer months, allowing tourists to observe, remains uncertain.
But given Echinus’s history of brief, one-to-two-month active phases, a long-term comeback seems unlikely.
However, because the Norris Geyser Basin is constantly shifting, there is always a chance the display could resume, according to the USGS.
