The amount of heat flowing out of hydrothermal vents in the floor of Yellowstone Lake appears to be much higher than previously thought.
“We often measured 100 watts per meter squared, which is ginormous,” said Rob Sohn, a geophysicist at Woods Hole Oceanographic Institution who is leading the three-year, $5 million Hydrothermal Dynamics of Yellowstone Lake study. “The highest before was 16 watts, which was considered ginormous at the time.”
Sohn said that if he calculated the heat from the vents near Stevenson Island it would be somewhat equal to a "typical" geothermal power plant, which produces about 4 megawatts.
The measurements gathered were so high compared to the past that the crew wondered if they were faulty, he said. But it’s more likely that the technology deployed by the HD-YLAKE researchers is better and so well positioned that the values are just more accurate, Sohn said.
“We hope to understand the plumbing of this vent field, by the flow paths of water, how fast the water is moving and how much heat the water is carrying,” said Rob Harris, a geophysicist at Oregon State University involved in the study.
The last time measurements were taken in Yellowstone Lake was about 40 years ago. At that time, scientists didn’t have the detailed mapping of the lake floor like this year’s researchers could access. By precisely knowing where hot vents were located on the lake bottom, the HD-YLAKE crew could guide a remote vehicle into position to insert a temperature probe to measure heat flow.
The highest temperature recorded was around 340 to 350 degrees.
“This is advective heat flow, but we don't know how large those values are because we don't know the discharge rate — just the temperature,” Sohn explained.
The crew also took measurements of the lake floor’s conductive heat flow by inserting a meter-long probe into the lake bed, away from hot vents
“In a matter of 10 to 20 minutes we could get a new value,” by quickly moving to the next area, Sohn said. That’s why the crew collected 62 measurements, instead of eight as originally planned.
Hot water bubbles to the surface all over Yellowstone National Park, that’s one of its main attractions — everything from hot pools and mudpots to geysers and fumaroles. By the time the hot water reaches the surface, though, it has cooled considerably.
The hottest pools in the park are no more than 200 degrees, with most ranging between 140 and 170 degrees. In comparison, the recommended temperature for a home hot water heater is no more than 120 degrees.
By measuring the hot water flows under the heavy pressure of the lake water — each 10 meters of water is equal to the weight of the earth’s atmosphere — the fluid samples are closer to their original temperature, Sohn said. Measuring at the bottom of the lake adds about 13 more atmospheres of pressure.
“I think those fluid samples will be as close as we can get for original hydrothermal fluids in the park,” Sohn said. “This speaks to one of the real motivations for the project in the first place.”
Harris compared the collection of the information to trying to understand a house’s plumbing system by turning on a faucet.
“We’re using temperature as a tracer of the fluids,” he said.
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Another crew involved in the HD-YLAKE project was tasked with taking core samples from the lake bottom to collect sediment. The coring took place at six locations around the margins of old hydrothermal explosion craters.
The scientists cooperating on the project have different aims. Cathy Whitlock, a professor of earth sciences at Montana State University, is hoping to find evidence of what happened before and after the explosions.
“This project is so cool because we’re focusing in on these explosions, how often have we had these catastrophic events, and what were their impacts,” she said.
“Maybe we can find evidence of what happened before and after lake explosions to see how they affect the ecosystem.”
The deepest of the eight cores measured more than 37 feet, much deeper than any previous cores taken from the lake, which topped out at about 24 feet.
“That means we have the last 15,000 years” of sediments, Whitlock said, back to the end of the last ice age.
In January the cores, which are being stored in a University of Minnesota lab, will be opened for sampling. Whitlock will be looking for charcoal from forest fires, pollen that could explain what plants were around before and after an eruption, as well as the remains of any animal and plant life that may have been killed. The cores will also be photographed, analyzed for chemical composition and samples of gases within the cores will be taken.
“With these cores … the HD-YLAKE team can get a better understanding of how the lake’s hydrothermal system has responded to geological events, including earthquakes, volcanic activity, and changing climate…” Chris Linder wrote on the team’s blog.
According to previous research by U.S. Geological Survey scientists, the last big hydrothermal explosions occurred 3,000 to 14,000 years ago. Yellowstone Lake contains the largest known hydrothermal explosion crater in the world, located in Mary’s Bay. The crater from that eruption, which occurred about 13,800 years ago, measures a mile and a half across.
Whitlock said the core samples may help explain what drives explosions like the one in Mary’s Bay. One theory scientists have posed is that dry periods, which would reduce the volume of water in Yellowstone Lake, may lessen the pressure on hydrothermal vents making explosions more likely. Landslides and earthquakes could also trigger the eruptions.
Planning has already started for next year’s research, which will include the placement of 10 seismometers around the lake to measure earthquake activity. That information will be compared with samples of vent water to see if there’s a change during seismic events.
This year, about 30 researchers took part in the research that ran from July through October. Next year’s season will be shorter.
Looking back, Sohn said he was pleased with the first season of work despite the long hours.
“I’d say we did more than we dared hope for,” he said.
“Who knows when that chance will come around again? Given that it’s a unique opportunity, we have to do everything we can.”
And it’s hard to beat the office — the largest freshwater lake in North America above 7,000 feet.
“Once we get on the boat and are tooling out of the marina, watching the sunrise, it’s the most incredible area in terms of scenery and setting,” Sohn said. “That made it pretty easy.”