The Echinus Geyser, recognized as the world’s largest acidic geyser, has captured the attention of geologists and park visitors alike after ending a nearly six-year period of dormancy. Located in the Back Basin of the Norris Geyser Basin within Yellowstone National Park, the geyser began a series of unexpected eruptions in early February 2026, marking its first significant activity since December 2020.
According to the Yellowstone Volcano Observatory (YVO), the renewed activity commenced on 07 February 2026. Between the initial awakening and 24 February 2026, the geyser erupted approximately 40 times. These events were characterized by repeated surges where the pool surface became agitated, sending plumes of water into the air and releasing significant runoff down its drainage channel.
Geological Profile and Acidity
Echinus is a rare geological feature due to its chemical composition. While most geysers in Yellowstone are alkaline, Echinus is highly acidic, with a pH level ranging between 3.3 and 3.6—roughly equivalent to the acidity of vinegar or orange juice. This acidity is caused by the mixing of neutral groundwater with acidic gases rising from the underlying magmatic system.
The geyser’s name is derived from the Greek word for “sea urchin,” a reference to the spiky, iron-rich silica formations (spinose geyserite) that rim its 66-foot-wide pool. These rocks often take on a reddish hue due to iron oxidation, creating a distinct visual contrast against the steaming water.
Historical Context and Future Outlook
The behavior of Echinus has historically been unpredictable:
- 1970s: The geyser was remarkably consistent, erupting every 40 to 80 minutes.
- 1980s–1990s: Eruptions became less frequent but more powerful, sometimes lasting for hours.
- 2000–2025: The geyser entered long periods of dormancy, with only brief periods of activity in 2017 and late 2020.
While the February 2026 activity was vigorous, experts suggest the “comeback” may be short-lived. In a recent update, the U.S. Geological Survey (USGS) noted that it is “not too likely” the eruptions will persist through the summer months. Recent monitoring data from late February suggests the frequency of surges may already be tapering off, following the geyser’s historical pattern of erratic, “stop-and-go” behavior.
For visitors to Yellowstone, the current activity offers a rare window into one of the park’s most unique hydrothermal features. However, scientists emphasize that such fluctuations are a standard part of the Norris Geyser Basin’s dynamic environment, which is the hottest and most changeable thermal area in the park.