Unfolding the Fiery Secrets of Excelsior Geyser: A Yellowstone Marvel

On the morning of July 23, 2024, a hydrothermal explosion from Black Diamond Pool in Biscuit Basin prompted individuals to flee for safety. The incident resulted from liquid water converting to steam in the blocked hot-water plumbing system just below the surface, propelling steam, water, mud, and rocks several hundred feet into the atmosphere. Thankfully, there were no injuries reported.

These types of explosions are rather typical in Yellowstone National Park, though rarely so thoroughly documented. Explosions that produced craters roughly 10 feet in diameter took place in Norris Geyser Basin — occurring in 1989 at Porkchop Geyser and more recently on April 15, 2024, above Porcelain Basin. Hydrothermal explosions of that magnitude likely take place every year or every few years somewhere within the extensive terrains of Yellowstone National Park, yet they often remain unnoticed due to occurrences during nighttime, winter, or in secluded areas. An event similar in scale to the Black Diamond Pool incident of 2024 likely occurs every few decades in Yellowstone.

Prior to the 2024 Black Diamond Pool explosion, the most extensively observed front-country hydrothermal explosions were those of Excelsior Geyser during the late 1800s.

Excelsior Geyser is situated in Midway Geyser Basin, next to the magnificent Grand Prismatic Spring. The geyser may have emerged at some point in the mid-1800s — it was not documented by a trapper who visited and described Grand Prismatic Spring in 1839, yet it was recorded by 1871 when it had been named “The Cauldron.”

The activity observed at Excelsior Geyser during the late 1800s underscores the variety of hydrothermal phenomena, ranging from geyser eruptions to hydrothermal explosions. Some occurrences could be labeled as turbulent geyser eruptions vigorous enough to expel small rock fragments, while others showcased boulders and significant clouds of material flung high into the atmosphere.

The initial of these substantial eruptions was reportedly witnessed in 1878, but between 1881 and 1882, well-documented eruptions propelled material 100-360 feet into the atmosphere. The intervals separating eruptions could be as short as an hour, with some eruptions enduring for several minutes. The water discharge from these eruptions was so substantial that the flow of the Firehole River noticeably surged during the geyser’s active phases, and the plumes from certain eruptions were visible from 100 miles away as the steam formed clouds. Park Superintendent Philetus W. Norris deemed the eruptions significant enough for the feature to earn the name “Excelsior.”

Tour guide Nestor Henderson characterized the activity in this manner:

“The conclusion of each eruption was accompanied by violent seismic shocks that demolished the geyserite walls, contributing significantly to both the peril and the magnificence of the display. These fragments of collapsed walls were ejected into the air several hundred feet above the highest waves, crashing together on their descent into the gaping chasm with a thunderous roar that was most fearsome.”

The geyser became inactive by the end of 1882. While it may have erupted once or twice between 1883 and 1887, activity resumed energetically in 1888. A series of eruptions, some photographed, sent rocks measuring 1 foot across a distance of 500 feet. Striking eruptions and explosions persisted until 1890. The geyser then entered a dormancy period lasting nearly a century (though there might have been some additional activity in 1901).

Excelsior came back to life over a 46-hour span from September 14-16, 1985. Eruptions during this period were significantly smaller than those of the 1800s, but still involved mud, lasted several minutes, and were spaced several minutes to about an hour apart. Since then, no further activity has been reported, apart from some vigorous boiling in 2000.

This does not imply that Excelsior is “finished,” of course. Like most geysers in Yellowstone, Excelsior’s activity is irregular and unpredictable. And equally spectacular. As Stan Lee might say, “Excelsior!”

The Yellowstone Caldera Chronicles is a weekly column authored by scientists and partners of the Yellowstone Volcano Observatory.