In the past week, there have been changes afoot to the thermal features on Geyser Hill in Yellowstone's Upper Geyser Basin. Ear Spring, a normally docile hot pool, had a water eruption that reached 20 to 30 feet high on Saturday, September 15, 2018. The eruption ejected not only rocks, but also material that had fallen or been thrown into the geyser in years past, like coins, old cans, and other human debris. The last known similar-sized eruption of the spring was in 1957, although smaller eruptions occurred as recently as 2004. As a result of these changes, Yellowstone National Park has closed portions of the boardwalk.
Undoubtedly, the most famous thermal feature of Yellowstone National Park's Upper Geyser Basin is Old Faithful. Geyser Hill is located just across the Firehole River from Old Faithful and hosts dozens of other hot springs, geysers, and fumaroles. Hydrothermal activity at several features on Geyser Hill has changed since the eruption of Ear Spring. Most notably, a new feature has formed west of Pump Geyser and north of Sponge Geyser directly under the boardwalk. The feature erupted overnight between September 18th and 19th and continues to pulse water as a small spouter. An approximately 8-foot diameter area of surrounding ground is "breathing" - rising and falling by about 6 inches every 10 minutes. Several other thermal features are more active than usual, including geysering and boiling of Doublet Pool and North Goggles Geyser.
Changes in Yellowstone's hydrothermal features are common occurrences and do not reflect changes in activity of the Yellowstone volcano. Shifts in hydrothermal systems occur only the upper few hundred feet of the Earth's crust and are not directly related to movement of magma several kilometers deep. There are no signs of impending volcanic activity. There has been no significant increase in seismicity nor broad-scale variations in ground movement.
The outcome of the current changes on Geyser Hill in the Upper Geyser Basin is uncertain. The two most likely possibilities are: