Yellowstone National Park covers nearly 3,500 square miles atop an ancient volcanic hotspot in the western United States. At the heart of the park sits Yellowstone Lake, a large and shallow body of water formed within the Yellowstone volcano caldera some 640,000 years ago. The caldera itself was created during a cataclysmic eruption and was preceded by two more blasts, about 1.3 million years ago and 2.1 million years ago.
And much like the surrounding areas, which see up to 3,000 earthquakes a year, Yellowstone Lake is a dynamic and shifting environment.
More than three years ago, in August 2017, a team of researchers from the University of Minnesota deployed a number of autonomous sensors to the lake’s bottom.
The mission, which lasted until August 2018, saw the sensors survive scorching temperatures, high pressures and acidic waters as well as possible hydrothermal explosions.
The scientists have now presented their findings, describing some of the “surprising discoveries” they have made about the lake.
Their study was published in the Journal of Volcanology and Geothermal Research.
Two of the researchers’ sensors were deployed at the lake’s deepest part, an area known as the “Deep Hole”.
There, the titanium-covered instruments were placed atop of hydrothermal vents where “unusually hot” water temperatures hit up to 150C (302F).
Chunyang Tan, Andrew Fowler, and William Seyfried from the University of Minnesota likened the bottom of Yellowstone Lake to a pressure cooker.
The researchers wrote in the US Geological Survey’s (USGS) Caldera Chronicles column: “The vent fluids formed where hot streams push through clay on the lake floor and then mixes with cold water lake.
“The location is much like the steam-fed fumaroles of the Mud Volcano area of Yellowstone National Park, but higher temperatures are reached at the lake floor because the weight of overlying lake water acts like a pressure cooker that raises the boiling point at the steam vents.”
Surprisingly, at each vent, the remote sensors detected different temperatures when compared to thermal loggers embedded deeper into the vents.
In one vent, temperatures remained steady throughout the study while the other plummetted for months on end before picking up again.
At vent “A”, temperatures recorded by the thermal logger were found to be more than 50C (90F) higher than the sensor positioned higher up.
The researchers said: “More surprising, the PVC-encased battery and electronics placed in cold lake water over a meter (three feet) from the vent and buried only three to five centimetres (about one inch) in sediment was thermally deformed – the PVC was partially melted!
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“This outcome revealed an extreme environment where high temperatures in the lake sediment are more widely distributed than previously thought.
“At location B, the chemical sensor had been dislodged from the vent and submerged in about 20 cm of sediment.
“Despite the carnage, successful chemical measurements were obtained for several months.”
The dislocation of the sensor most likely occurred during a slumping of sediment.
This may have been triggered by small hydrothermal explosions, which are a frequent occurrence in Yellowstone’s geyser basin.
Scientists speculate these same explosions take place on the lake floor.
Alternatively, the slump may have bee caused by seismic activity in the area.
The researchers added: “Whereas the cause of the slumping is speculative, identification of extreme temperatures mere centimetres beneath the lake floor and the tortured journey of the two robust sensor packages are a testament to the dynamic and extreme environment beneath Yellowstone Lake.
“We are excited to continue exploring this dynamic landscape—a setting that is every bit as wondrous as the geyser basins that are enjoyed by millions of visitors every year!”
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