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YELLOWSTONE NATIONAL PARK — In the latest edition of Caldera Chronicles, geologists in Yellowstone National Park (YNP) break down the science behind sulfur dioxide and discuss why the park’s geysers and fumaroles hardly emit any of the volcanic haze.
This week’s column, published by the Yellowstone Volcano Observatory (YVO), was written by Jennifer Lewicki, a research geologist with the U.S. Geological Survey California Volcano Observatory.
According to Lewicki, YNP is one of the volcanic systems that emits the highest amount of carbon dioxide on earth. The hydrothermal areas are constantly letting off steam plumes and rotten-egg smells from hydrogen sulfide. However, there is hardly any detectable sulfur dioxide transmitted.
This is partially due to the depth of the magma chambers below YNP’s surface. The upper rhyolitic magma chamber sits between 2.5 and 10 miles deep, while a larger basaltic reservoir lies from 12 to 30 miles deep. Lewicki explains that this is considerably deeper than where magma resides under an active volcano.
“When magma ascends toward the surface, decreasing pressure allows dissolved gases to escape, much like bubbles forming when you open a soda bottle,” writes Lewicki. “Different gases exsolve at different depths based on their solubility in magma.”
Compared to other gases like carbon dioxide, sulfur dioxide is released from magma at shallow depths, typically within two miles of the surface. The small amount of sulfur dioxide that does exsolve in Yellowstone has a long journey through the earth’s crust, and the network of hot water and steam can alter the chemical on its way through.
During a process called disproportionation, the sulfur dioxide rapidly dissolves when it encounters liquid water in the hydrothermal system. It is then converted into dissolved sulfate ions and elemental sulfur, which causes the yellow deposits that can be seen around many thermal features.
A multi-GAS station at Mud Volcano continuously measures gas concentrations in the park, which helps scientists detect changes in the system’s behavior. Yellowstone’s absence of sulfur dioxide is actually good news for monitoring purposes. An increase in emissions would signal that something major had changed.
“Such an emergence would suggest that magma had risen to much shallower depths and established dry gas pathways through the hydrothermal system — basically that the water had disappeared due to the heat of the magma — which are both indicators of increased volcanic unrest,” Lewicki wrote.
