Unleashing Nature’s Fury: The Captivating Tale of Excelsior Geyser

The Yellowstone Caldera Chronicles is a weekly piece authored by scientists and partners of the Yellowstone Volcano Observatory. This week’s entry comes from Michael Poland, a geophysicist with the U.S. Geological Survey and the Scientist-in-Charge of the Yellowstone Volcano Observatory.

On the morning of July 23, 2024, a hydrothermal blast from Black Diamond Pool in Biscuit Basin caused bystanders to seek shelter. The incident was triggered by liquid water rapidly turning into steam within a blocked hot-water plumbing system just below the surface, propelling steam, water, mud, and rocks several hundred feet upward. Thankfully, there were no reported injuries.

These types of blasts are relatively frequent within Yellowstone National Park, though seldom so thoroughly recorded. Explosions that formed craters approximately 10 feet (3 meters) in diameter occurred in Norris Geyser Basin—in 1989 at Porkchop Geyser and more recently on April 15, 2024, above Porcelain Basin. Hydrothermal explosions of such magnitude likely occur every year or a few years somewhere within the extensive terrain of Yellowstone National Park but often go unnoticed due to their occurrence at night, during winter, or in remote areas. Events comparable in size to the Black Diamond Pool incident of 2024 probably happen every few decades in Yellowstone.

Prior to the 2024 Black Diamond Pool explosion, the most thoroughly documented front-country hydrothermal blasts were those of Excelsior Geyser in the late 1800s.

Excelsior Geyser is situated in Midway Geyser Basin, adjacent to the magnificent Grand Prismatic Spring. The geyser is believed to have formed sometime in the mid-1800s—it was not recorded by a trapper who visited and described Grand Prismatic Spring in 1839 but was noted by 1871, when it was referred to as “The Cauldron.”

Activity at Excelsior Geyser during the late 1800s showcases the range of hydrothermal activity, from geyser eruptions to hydrothermal blasts. Some of the activity could be characterized as muddy geyser eruptions that were forceful enough to eject small rock fragments, while other occurrences involved boulders and substantial material plumes thrown high into the atmosphere. The first of these significant eruptions was seemingly witnessed in 1878, but it was from 1881 to 1882 that well-documented eruptions propelled material 30–110 meters (100–360 feet) into the sky. Intervals between eruptions could be as short as an hour, and eruptions might persist for several minutes. The water discharge during these eruptions was so substantial that the flow of the Firehole River noticeably surged when the geyser was active, and the plume from certain eruptions could be seen 160 kilometers (100 miles) away due to the steam forming clouds. Park Superintendent Philetus W. Norris deemed the eruptions sufficiently remarkable to warrant the name “Excelsior.” Tour guide Nestor Henderson described the activity in the following manner:

“The conclusion of each eruption was accompanied by violent seismic shocks that shattered the geyserite walls and added significantly to both the danger and [to the] grandeur of the spectacle. These masses of fractured wall were propelled into the air several hundred feet above the highest waves during each eruption, colliding with one another in their descent into the gaping chasm, producing a deafening noise that was truly terrifying.”

The geyser fell dormant by late 1882. While it may have erupted once or twice between 1883 and 1887, activity resumed with renewed vigor in 1888. During a series of eruptions, some of which were captured in photographs, rocks 30 centimeters (1 foot) across were ejected up to 150 meters (500 feet) away. Remarkable eruptions and explosions persisted into 1890. The geyser then entered a phase of dormancy that lasted nearly one hundred years (although there may have been some additional activity in 1901).

Once again, the geyser erupted over a 46-hour duration during September 14–16, 1985. These eruptions were significantly smaller than those of the 1800s but still contained mud, lasted for minutes, and were spaced out by several minutes to about an hour. Since that time, no further activity, aside from some intense boiling in 2000, has been documented. This does not imply that Excelsior is “finished,” of course. Like most geysers in Yellowstone, Excelsior’s activity is erratic and unpredictable. And equally magnificent. As Stan Lee would declare, “Excelsior!”