A pool of cinder. Pool of Elk. Springs of Hydrophane. The reservoir. The backcountry of the dynamic and constantly shifting Norris Geyser Basin is home to all of these thermal wonders.
About 800 acres make up the Norris Geyser Basin, one of the few significant thermal basins outside of Yellowstone Caldera. It is situated roughly 2.5 miles north of the caldera lip. It is situated in a structural basin formed by the meeting of the northeast-trending Hebgen Lake Fault System with the north-south running Norris-Mammoth Corridor.
Welded Lava Creek Tuff from the eruption that created Yellowstone Caldera around 631,000 years ago is beneath Norris. Glacial sediments, sinter, and hydrothermal explosion breccias are found on top of the tuff. Tantalus Creek, a Gibbon River tributary that is nearly entirely made up of geothermal water, drains all thermal features from the Norris Geyser Basin, which is essentially a closed thermal basin system with an average flow of 150–250 liters of water per second.
With trails and boardwalks winding through famous features like the world’s tallest active geyser, Steamboat Geyser, two of Norris Geyser Basin’s subbasins, Porcelain and Back Basins, are accessible to the general public. The Gap and 100 Spring Plain, two further subbasins, are inaccessible to the general public.
Time for a virtual tour!
Some of Yellowstone National Park’s most distinctive features, such as acidic mud pots, neutral-chloride inter-deposition features, sulfate-dominated waters with spherules, and sulfur-precipitating springs, can be found on the flat, sandy 100 Spring Plain.
The peculiar, dark-colored, foamy cinders that float on the pool’s surface make Cinder Pool one of its most peculiar features. For more than a century, experts have been captivated by this peculiarity. Research has shown that the cinders are made of sulfur, which appears black because of microscopic pyrite grains. In the acid pool’s plumbing system, a deposit of molten sulfur at least 66 feet deep gave rise to the cinders.
Some of the sulfur is carried toward the surface by gas bubbling through the molten sulfur, where it is quenched by lower temperatures to create the pumice-textured cinders at the pool’s surface. However, the cinders that defined the pool vanished in 2019, possibly as a result of the sulfur deposit in the subsoil being consumed.
The Reservoir, a sizable, steady hot spring that was once utilized as a pool by park staff decades ago when the old road system made it easier to reach, is also located in 100 Spring Plain. It had a diving board, too! Although it is now illegal to swim in hydrothermal features because to the high amounts of dissolved heavy metals (including arsenic) and boiling temperatures, The Reservoir remains one of the largest hot springs in the Norris Geyser Basin.
Traveling over the 100 Spring Plain is risky for a large portion of the year because to the frequent flooding, which makes it difficult to distinguish between a shallow puddle and a deep, boiling thermal feature (the name is not for nothing, as there are numerous thermal features distributed throughout the 100 Spring Plain). Realgar Spring, which Arnold Hague called in 1889 and 1891 for the arsenic sulfides (i.e., the mineral realgar) that precipitated out of the pool, is one of the other prominent chemical features in 100 Spring Plain.
The Gap is a low-lying stretch of thermal features on the west side of the Rough Hills, a little further southwest of 100 Spring Plain. The Ragged Hills and this subbasin were extremely active between 1995 and 2000, and their temperature and thermal activity have fluctuated greatly over time.
On the southwest side of The Gap is one of the biggest hydrothermal explosion craters in the Norris Geyser Basin.The abrupt flashing of liquid water to steam causes hydrothermal explosions by brecciating the rock and launching water, steam, rock, and muck into the air.
Recent examples of hydrothermal explosions include the 1989 explosion of Porkchop Geyser in the Back subbasin of Norris, the recent explosion of Black Diamond Pool in Biscuit Basin, and a minor explosion in the Porcelain subbasin in April 2024. A breccia of drastically changed debris encircles the explosion crater in The Gap, which has been there since at least 1954 (as shown in aerial photographs).
With the world’s tallest geyser erupting, hot springs changing in temperature and appearance, or hydrothermal explosions drastically changing the landscape, the dynamic Norris Geyser Basin never has a boring moment.
However, keep in mind that you should only enjoy these features from well-established pathways and boardwalks. In order to record and investigate these exceptional features, all recent work on the features in 100 Spring Plain and The Gap has been completed by qualified staff using the appropriate safety gear under authorized research permissions.
Future Caldera Chronicles issues will have more information about these incredible locations!
White et al. (1988) The geology and exceptional thermal activity of Norris Geyser Basin, Yellowstone National Park, Wyoming, is a good source of knowledge. Prof. Pap. USGS, 1456, 84 p.
The Yellowstone Volcano Observatory’s scientists and partners write a weekly column called Yellowstone Caldera Chronicles.
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