Editor's note:Yellowstone Caldera Chronicles is a weekly column written by scientists and collaborators of the Yellowstone Volcano Observatory. This week's contribution is from Shaul Hurwitz, research hydrologist with the U.S. Geological Survey.

Ranger naturalist George D. Marler meticulously documented changes in hydrothermal activity in the geyser basins of Yellowstone National Park for more than three decades in the mid-20th century. His work was especially useful in understanding the significant changes in hydrothermal activity following the August 1959 M7.3 Hebgen Lake, Montana, earthquake.

Marler (1898–1978) was a ranger naturalist for more than four decades starting in 1931. He made long-lasting contributions to the understanding of hydrothermal activity in Yellowstone and published many of his detailed observations and interpretations in a series of seminal peer-reviewed journal papers. His publications mainly described and explained how hot springs in the geyser basins respond to earthquakes and climate. 

George Marler taking the temperature of a pool at the base of Giant Geyser in the 1950s. Photo from the Yellowstone Research Library.

In a 1951 paper titled "Exchange of function as a cause of geyser irregularity [Wyoming]" Marler documented geyser eruptions over more than 50 months of observations, including during Yellowstone's very cold winter months. He demonstrated that many geysers have irregular eruption patterns, which are reflected by changes in the time between successive eruptions. Based on these observations, he inferred that some geysers are connected in the subsurface with other nearby springs and geysers. For example, Marler suggested that in the Upper Geyser Basin, Beauty,m and Chromatic pools, which are located about 150 feet apart, and geysers and pools of the Daisy Group—Comet, Daisy and Splendid Geysers, and Bonita and Brilliant Pools, all within 150 feet of each other—are connected in the subsurface. He termed the shifting flow of groundwater between hot springs that causes the irregular patterns as "exchange of function."

In a 1954 paper titled "Does the cold of winter affect the thermal intensity of the hot springs in Yellowstone Park [Wyoming]?" he examined the effects of extreme seasonal changes on geyser activity in the Upper Geyser Basin and concluded that there are insignificant differences in the eruption patterns of geysers between winter and summer (a more recent study that relied on more frequent measurements of geyser eruptions than were available to Marler found small seasonal variations in eruption patterns of some geysers). In a 1964 paper titled "Seasonal changes in ground water in relation to hot spring activity," Marler suggested that small temperature variation in groundwater flowing towards geysers could have a significant effect on the eruption patterns—for example, at Great Fountain Geyser in Lower Geyser Basin.

Kaleidoscope Geyser in the Lower Geyser Basin. George D. Marler and Donald E. White wrote in their 1975 journal paper that “In 1963, about 18 m northwest of Kaleidoscope Geyser, a violent eruption that may have been a single event scattered scores of blocks of sinter about a newly created crater about 3 m in diameter” but suggested that the event was either directly or indirectly related to the Hebgen Lake earthquake. Photo by George Marler, Yellowstone National Park, in 1965.

A 1956 paper titled "How old is Old Faithful Geyser [Wyoming]?" reported on a silicified wood sample from a tree that grew on the Old Faithful Geyser mound. The wood sample was dated in one of the earliest applications of the radiocarbon method (carbon 14 or 14C) to 730 ± 200 years, which, after calibration, corresponds to 703 ± 200 years before the year 1950, or a date of 1247 ± 200 CE. Marler wrote that, "The data presented in this paper make it reasonably certain that the origin of the intermediate spring goes back to the period dated by carbon 14. The origin of this spring and the age of the wood are essentially the same." Radiocarbon dates of the same silicified wood made more than 65 years after those presented by Marler and with modern techniques turned out to be consistent with the earlier dates. The more recent study, however, suggested that Old Faithful Geyser was erupting long before the tree grew on the geyser’s mound, and that trees grew on and around the mound between approximately 1233 and 1362 CE. This time period is coincident with a series of severe regional droughts in the western United States toward the end of a period called the Medieval Climate Anomaly.

Perhaps George Marler’s most notable work was with USGS scientist Donald E. White describing changes in hot spring discharge and geyser eruption patterns to the August 17, 1959, M7.3 Hebgen Lake, Montana, earthquake, which had an epicenter about 48 km (30 mi) northwest of Upper Geyser Basin. In a 1975 paper, Marler and White documented at least 289 springs in the geyser basins along the Firehole River that erupted as geysers the day after the earthquake, of which 160 were springs with no previous record of eruption. They also reported new hot ground that developed in some places or became apparent by the following spring as new fractures in hot spring sinter deposits or as linear zones of dead or dying trees. Some fumaroles formed in new fractures, and a few of these evolved into hot springs.

Seismic geyser in Yellowstone’s Upper Geyser Basin during an eruption. Based on the study of George Marler and USGS scientist Donald E. White on the effects of the August 1959 Hebgen Lake, Montana, earthquake on hot springs in Yellowstone’s Upper Geyser Basin, fumaroles in what was eventually called “Seismic Geyser” (not listed in the U.S. Board on Geographic Names) were active until late 1962 or early 1963. During the 1962–1963 winter, one or more explosive events enlarged the eastern fracture into a crater. The crater acted as a geyser since 1963, and the western fracture gradually ceased fumarolic activity. Photo by George Marler, Yellowstone National Park, in 1969.

George Marler’s meticulous observations and documentation of hydrothermal activity in Yellowstone National Park have provided future generations of researchers and geyser enthusiasts with invaluable information that has significantly improved the understanding of hydrothermal activity, and particularly the dynamics of geyser eruptions. As a ranger naturalist he wrote many reports on the hydrothermal features in the park, as well as illustrated issues of the employee newsletter Nature Notes. Some of Marler’s other publications, including "The story of Old Faithful," "Studies of geysers and hot springs along the Firehole River, Yellowstone National Park, Wyoming," and "Story of Great Fountain Geyser to 1965" can be found at the Yellowstone Research Library. Marler’s significant contributions were acknowledged in 1962 by Brigham Young University, where he was awarded an Honorary Doctorate in science, and in 1967 by the US Department of Interior distinguished service award for contributions in the field of hydrothermal geology at Yellowstone National Park.