–
–
Yellowstone National Park in the United States is famous for its hot springs and geysers. In March 2018, after a long period of dormancy, the largest geyser in the park, the Steamboat, entered an active phase that continues to this day. It is the highest of the currently operating geysers in the world, its emissions reach 115 meters. Scientists are concerned about the activation of the geyser, as a gigantic magmatic system “slumbers” at a depth under the national park. Given that the Yellowstone supervolcano erupts at intervals of about once every half a million years, and more than six hundred thousand years have passed since the last eruption, it is possible to understand the concern of scientists. A volcanic eruption of this magnitude can lead to climate change on the planet and catastrophic consequences for all living things. However, recent research shows that the activation of the Steamer is most likely associated not with large-scale volcanic processes, but with changes in the hydrothermal system of the geyser itself.
Geyser “Steamship” (see. Steamboat Geyser) is located in the northern part Yellowstone National Park within the Norris Geyser Basin (see. Norris Geyser Basin), near the northwestern edge Yellowstone Caldera – a depression formed as a result of the collapse of the crater walls during the last eruption supervolcano 640 thousand years ago. The eruption was so powerful that a layer of ash ejected by the volcano covered two-thirds of the United States.
–
–
The Norris Geyser Basin (Fig. 3) is an extremely dynamic and hot zone formed at the intersection of two deep faults rooted into the magma chamber, with an annular fault that bounds the caldera.
–
–
On March 15, 2018, after three and a half years of complete inactivity and 34 years of relative calm, the Parokhod geyser was actively working again. Since then, it has erupted more than a hundred times – more than in any previous phase of activity in the entire history of observations (Fig. 4). The height of the hot water fountains in the current phase is also greater than ever before. All these facts attract the attention of scientists and the public, they are widely covered in the press, giving rise to rumors and concerns.
–
–
American scientists led by Michael Mang (Michael Manga) and Mary Reed (Mara H. Reed) from University of California at Berkeley decided to find out why the “Steamer” became active again, what tectonic or thermodynamic processes determine the intervals between its eruptions and why the fountains are record high this time. They analyzed data from 109 eruptions of the last phase and compared them with the periods of activity in the 1960s and 1980s, as well as with nine other geysers in Yellowstone.
The authors used seismic, hydrological, geochemical and satellite thermal infrared data as well as soil deformation data. It turned out that just before the beginning of the activation of the geyser in March 2018, geophysical instruments recorded episodes of uplift of the territory, an increase in seismicity and an increase in the background of infrared radiation in the Norris Basin, which may indicate a potential link with deep magmatic activity.
At the same time, after a period of high seismic activity, the temperature of the Norris Basin geothermal reservoir as a whole has not changed. Other dormant geysers (except for the “Steamer”) did not resume their work, although they are all located in a single fault zone of Lake Hebgen (see. Hebgen Lake). Most of the earthquakes in Yellowstone are timed to this zone, including the famous earthquake of 1959 (see. 1959 Hebgen Lake earthquake) with a magnitude of 7.2, the effects of which were felt from Puerto Rico to Hawaii.
Why did the “Steamer” become active? The authors took turns analyzing the main potential causes: changes in precipitation regime, seismicity, processes associated with uplift in the Norris Basin, soil deformation and releases of geothermal energy.
To estimate the total amount of atmospheric precipitation, scientists used observations of the water level in the Yellowstone River from 1960 to 2020. It was not possible to establish any correlation between the number of eruptions of the Parokhod geyser and the annual precipitation rates.
The reactivation of the geyser was preceded by a series of small earthquakes near the northern edge of the Yellowstone Caldera in June-August 2017 and February 2018, but the peak ground wave velocity measured by the YNM seismic station in the Norris Basin never exceeded the critical value of 10−2 m / s, at which the activation of geysers usually begins. So, the assumption about the connection between geyser activity and seismicity was also not confirmed.
With two other factors – vertical tectonic movements and deep heat flow – the relationship turned out to be more definite. Analysis of geophysical data showed that at the end of 2017 there was a sharp jump in geothermal heat and the territory began to rise (Fig. 5). To assess the flow of geothermal heat, the authors used the data of infrared survey of the MODIS spectroradiometer (see. Moderate Resolution Imaging Spectroradiometer) installed on board the research satellite “Terra”, one of the elements of NASA’s Earth Observation Program Earth Observing Systemand for the assessment of ground rise, data from the GPS station of the University of Nevada NRWY, located in the immediate vicinity of the Norris Basin.
–
–
The researchers concluded that the reactivation of the Parokhod geyser, which began in 2018, is associated with the progressive rise of the Norris Basin and the arrival of hot deep fluids (gas-liquid solutions) to the surface, which caused an increase in the geothermal background: from 2013 to 2018 the temperature increased by 0.8 ° C. The growth of seismic activity on the eve of the beginning of mass geyser eruptions, according to the authors, was a consequence of vertical tectonic movements.
At the same time, the connection with magmatic processes remains ambiguous. On the one hand, the rise of volatiles from a deep magma chamber and an increase in the pressure of pore fluids could lead to an increase in enthalpy hydrothermal system that triggered the onset of eruptions. On the other hand, in the Gibbon River, which originates in the Norris Basin, scientists have not recorded an abnormal increase in chlorides or sulfates of hydrothermal origin, usually indicating the input of deep magmatogenic fluids.
Hence, the authors conclude that the activation of the geyser is connected exclusively with the processes taking place in the hydrothermal system of the Steamer itself, which differs from other geysers in greater depth and temperature.
The analysis of data on geysers from different regions of the world showed that the height of the fountain depends on these two parameters, so it is not surprising that the Parokhod geyser has the highest jet in the world (90–120 meters) – the reservoir of its hydrothermal system is located deeper than others and its temperature is higher than that of the others (Fig. 6).
–
–
The intervals between eruptions, according to scientists, are controlled by the seasonal hydrological cycle and the volume of runoff – they are shorter in summer and longer in winter.
A source: Mara H. Reed, Carolina Munoz-Saez, Sahand Hajimirza, Sin-Mei Wu, Anna Barth, Társilo Girona, Majid Rasht-Behesht, Erin B. White, Marianne S. Karplus, Shaul Hurwitz, Michael Manga. The 2018 reawakening and eruption dynamics of Steamboat Geyser, the world’s tallest active geyser // PNAS. 2021. DOI: 10.1073/pnas.2020943118.
Vladislav Strekopytov
–
