Shaking up geyser theory
New research suggests that carbon dioxide plays a much larger role in eruptions than previously thought.
At Yellowstone National Park, a metric tonne of boiling water shooting out of the ground to the height of a tall building is an everyday occurrence — and in the case of famous geyser Old Faithful, it happens every hour!
Over 1,000 geysers exist in the world, and approximately half of those are located in Yellowstone’s nine geyser basins. Over the past few field seasons, research associate Bethany Ladd, along with her supervisor Cathy Ryan of the Department of Geoscience, spent several weeks monitoring the waters of Yellowstone’s Spouter Geyser, and the results of their study could change what we know about how geysers work.
“Most people typically think of geysers as hot water features where steam builds up in the subsurface and creates a buildup of pressure before some trigger makes the eruption happen,” explains Ladd.
What was that all-important trigger, though? Ladd and Ryan noticed that there were increasing anecdotal accounts, as well as anecdotal mentions in peer-reviewed literature, of episodic gas release — much like geysers. They decided to investigate further and headed out to Yellowstone.
Anecdotes about geyser gas spur research trip
Ladd and Ryan spent a week at Spouter Geyser collecting groundwater samples and various other relevant data, and came up with a simple theory out of some surprising results. Their analyses showed that, just before a geyser erupts, dissolved carbon dioxide (CO2) gas accumulates in the water. Imagine what happens when you open a can of pop that’s been shaken — the effect is similar.
“Our data showed that CO2 levels were highest right before an eruption. When an eruption occurs, we saw decreased CO2 and that pattern was very consistent,” Ladd says. “The theory seems like a simple conclusion, but to reach that, we had to use multiple lines of scientific evidence to understand what the subsurface conditions are.”
Yellowstone’s geysers are fuelled by heat from underground magma. However, measurements first conducted decades ago revealed that many of Yellowstone geysers are not hot enough to boil water not containing any dissolved gases. However, the magma-heated water is extremely hot — about 175 degrees Celsius before it meets Earth’s surface. Using special glass vials, Ladd, Ryan and other members of the Geoscience Department (some as much-appreciated volunteers!) sampled the geyser’s water every 10 to 20 minutes from a side vent in the geyser’s main channel. Over the course of several eruptions, they collected data on numerous factors in the groundwater including temperature, pH, electrical conductivity and oxygen levels.
“The CO2 alone doesn’t reach solubility, nor is the temperature of the water hot enough to reach vapour saturation. The thing is, you need the combination of water and CO2 to reach vapour saturation, and that’s what we call the ‘trigger’,” she explains. “Once that free gas forms, it initiates a series of events that lead to an eruption.”
The experience in Yellowstone created lasting memories for Ladd, as well as enduring contributions to geyser research. Yellowstone prefers that scientists who are doing intrusive work do it during the off-season. Yellowstone closes for a few weeks twice a year between seasons, so Ladd and Ryan were asked to come during that period.
Researcher Bethany Ladd spent a week at Spouter Geyser in Yellowstone National Park collecting groundwater samples and other data. Photo courtesy Bethany Ladd
Seeking a clearer picture of Yellowstone's subsurface
“We got the incredible park all to ourselves, which is an amazing opportunity,” she enthuses. We saw so much wildlife that we would never have seen when the tourists were there — including a pack of wolves!” One of the major takeaways from their findings is the implication that other scientists should do more dissolved gas monitoring to truly understand geysers and hydrothermal systems in general. “Dissolved gases are typically not mentioned in the literature we use,” Ladd says. “But recently, we’ve found out that our group and the USGS are simultaneously reaching similar conclusions — which provides more and more evidence that we need to do dissolved gas monitoring. It’s really important and provides a bunch of extra information. We could be missing a large part of the story if we don’t monitor that.”
Ladd and Ryan will be heading back to Yellowstone to study and test their theory on other geysers. The pair also hope to access bore holes drilled by the United States Geological Survey (USGS) and do a series of measurements to give them a clearer picture of the park’s subsurface.
Ryan’s research is partly funded by a Natural Science and Engineering Research Council of Canada (NSERC) Discovery Grant.