Exploring the history of hydrothermal eruptions in Biscuit Basin

The Yellowstone Caldera Chronicle is a weekly column written by Yellowstone Volcano Observatory scientists and collaborators. This week’s contributors are Yellowstone geology volunteer Tara Cross and UC Berkeley doctoral candidate Mara H. Reed.

Scientists are working hard to study Hydrothermal explosion exist July 23, 2024, Biscuit Basin Black Diamond PoolAn important part of understanding recent activity is investigating similar events in the past. This has happened several times in the Biscuit Basin.

At the beginning of the 20th century, Biscuit Basin looked slightly different than it does today. Sapphire Pool still retains its Biscuit-shaped fountain rock Famous for photography F. Jay Haynesbut Black Diamond Pool apparently does not exist. Early maps of the area, including those produced by the U.S. Geological Survey, do not show any thermal features between Sapphire Pool and Firehole River. Although little is known about the formation of Black Diamond Pool and its neighbors, Wall and Black Opal Pools, there is evidence that they were explosive.

The earliest record is a photograph taken by Haines’ son Jack around 1912 showing what we now call Black Diamond Pool after an apparent hydrothermal explosion blew open its vents and ejected large chunks of rock from the crater. The exact date of the first explosive event is unknown, but dates on the photograph and map suggest it occurred between 1902 and 1912. Preserved at Yellowstone Heritage and Research Center The results suggest that more explosions occurred in 1918 and 1925, expanding the Black Diamond Pool’s crater and forming the Wall Pool. Additional explosions in 1934 and 1953 created the Black Opal Pool’s crater, which then expanded again. Unfortunately, no one witnessed these explosions, and records describe only the aftermath: new pool shapes, heavy washouts, and newly ejected boulders. No eruptive or explosive activity was reported from any of these pools for decades after 1953.

Piecing together a history is often complicated because new attractions are called by many names before one name finally becomes standard. Some early observers used the name “Black Pearl” to refer to both Wall Pool and Black Opal Pool. Further confusing matters, the name actually belonged to a distinct attraction north of Jewel Geyser, also in Biscuit Basin. In 1959, park geologist George Mahler named the easternmost pool “Black Opal Pool” because it was “dark and milky in color,” and he used the name “Wall Pool” to refer to the other two pools collectively because of the pronounced cliffs around their edges. Park Ranger Frank Childs used the name “Black Diamond” in the 1930s, but it was not widely used as the name for the larger of the two Wall Pools until the mid-21st century.

In early 2006, Biscuit Basin showed signs of increased heat flow, with hot areas and new vents appearing between three pools and rivers. This became the prelude to the Black Diamond Geyser eruption in July 2006. Geyser enthusiast Kendall Madsen witnessed the first eruption and took a photo of dark water being ejected to a height of 40-50 feet (12-15 meters). Witnesses near the pools heard explosions and loud roars. Over the next two months, Black Diamond Geyser erupted irregularly every 2-5 days, sometimes as short as 5 hours. After mid-September 2006, the eruptions became sporadic. With the exception of an eruption in late 2011, it was normal for the eruptions to be separated by weeks or months. This phase seemed to have completely ended in late 2012, with only three eruptions reported before 2024, in 2013, 2015, and 2016.

Over the years, tourists, geyser enthusiasts, tour guides, and park rangers have witnessed many of these eruptions. Most eruptions reach 6-20 feet (2-6 meters) in height, last 10-20 seconds, and are accompanied by pops and thumps. Eruptions often eject small rock fragments and lumps of mud. In 2009, a group of geologists Field Trip In 2006, geyser enthusiast Bill Warnock witnessed an eruption comparable in strength to the first eruption in 2006, reaching 50 feet (15 meters) high and sending rocks flying. Geyser enthusiast Bill Warnock saw and photographed an eruption in 2011 that he estimated was 50 feet (15 meters) high, sending a large amount of water into the river. Some unconfirmed reports in 2006 and 2011 suggested eruptions as high as 60-100 feet (18-30 meters). Finally, an eruption in April 2015 sprayed mud onto a boardwalk and killed a flock of cormorants that approached at the wrong time.

Aside from the possible absence of witnessed hydrothermal eruptions, Black Diamond Pool’s most recent activity, on July 23, 2024, is the largest yet. Its history points to scientific questions that will help guide the investigation of the 2024 eruption. For example, why did Black Diamond Pool go dormant for decades before reactivating as a violent geyser, and why do hydrothermal eruptions recur in some locations but not others? Studying such events, past and present, will help provide new insights into Yellowstone’s eruptions. The most common and underestimated hazards.