The Echinus Geyser in Yellowstone’s Norris Basin erupted in February after roughly six years of quiet, briefly reviving interest in one of the park’s most unusual hydrothermal features. Scientists watched a bursty return of activity with multiple eruptions in early to mid February, observers noted vivid mineral colors around the pool, and experts say the chemistry and plumbing of Echinus make its behavior rare and unpredictable. The geyser’s returns tend to be short-lived, and whether this spike will repeat later in the year remains unknown.
Echinus sits in the Back Basin of Norris, a place already famous for rapid change and strange pools. Park visitors and researchers were surprised when the geyser put on shows on Feb. 7, then again on Feb. 9, 12 and 15, marking the first confirmed eruptions since December 2020. That kind of intermittent activity is typical for thermal features that are sensitive to shifting underground plumbing and gas inputs.
By Feb. 16 the U.S. Geological Survey reported that eruptions were occurring every two to five hours, a clear intensification compared with the weeks before. In spasms like that, the geyser cycles between draining and refilling a pool that can take an hour or so to recover after an eruption. Those quick resets are part of what makes Echinus so interesting to researchers tracking fluid and gas movement underground.
Geochemically, Echinus is an oddball because it shows acidic traits without the total breakdown of its rock plumbing. “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. That balance of gas-driven acidity and more neutral waters creates mineral deposits and flow features you rarely see at other thermal sites.
The pool’s rim and nearby slopes glow with minerals: reds from iron and traces of arsenic, pale metal tones where aluminum salts collect, and thorny silica crusts left by silica-saturated waters. Those jagged, white silica formations are part of why the feature earned the name Echinus, which evokes a spiky, sea-urchin look. The visual contrast between the deep pool and its colorful edge makes the geyser an unmistakable landmark in the basin.
When Echinus erupts now, the typical blasts last about two to three minutes and commonly reach twenty to thirty feet in height. During more active decades the geyser produced a wide range of eruptions, from modest bursts to rare columns reported as high as seventy-five feet. Even at lower heights the dramatic drop in pool level during an eruption is a striking sight for anyone watching from the boardwalks.
After an eruption, the pool refills and the system recharges, but the timing isn’t steady; some intervals are hours, others longer, depending on how gas and heat push through the fracture network below. That variability means predicting the next show is tough, and visitors often get surprised by sudden activity. Park scientists monitor these patterns to better understand the connections between steam, gas chemistry and the hot water that drives eruptions.
Historically Echinus has shown short active phases that can last only a month or two, and those episodic runs are followed by years of quiet. This February’s run fits that pattern in both timing and intensity, with most recorded eruptions clustered in the middle to late portion of the month. Since Feb. 24, observers have not reported new eruptions, which leaves the feature back in its uncertain, watchful state.
Whether Echinus will resume activity later in the spring or summer depends on underground conditions that change with time, including gas supply and small shifts in the basin’s plumbing. The Norris Geyser Basin is one of Yellowstone’s most dynamic areas, and its features can change with little warning. That dynamic quality is part of why geologists and park staff keep a close eye on it.
For people planning a visit, the window to see an active Echinus can be narrow, and sightings are never guaranteed even when a run is underway. Park safety rules and viewing distances matter; thermal areas are dangerous and fragile, and boards and barriers exist for good reasons. If you do see Echinus steaming or spouting, you’re witnessing a rare chapter in the life of a geyser that usually prefers to stay quiet.
Scientists will continue to log eruptions, water levels and gas measurements to tease out patterns from each active episode. Each short revival gives researchers new data on how acidic gases mix with neutral waters to produce both geyser behavior and the striking mineral signatures. Until the basin decides to show more, Echinus will remain one of Yellowstone’s more intriguing and temperamental thermal features.
