While much of the public’s attention on Yellowstone focuses on its potential to produce large super eruptions, the risks are much more likely to occur with smaller, violent hydrothermal explosions. Hydrothermal explosions occur when almost boiling water suddenly flashes to steam and releases large amounts of energy. The energy release breaks the stone down and often leaves a crater. The same sources that can cause these explosions are what give Yellowstone its well-known hot springs, geysers and fumaroles.
The Yellowstone Lake area of Yellowstone National Park hosts at least eight large craters produced by hydrothermal explosions, including three of the largest hydrothermal explosion craters known on Earth. Compared to other areas of interest within Yellowstone, hydrothermal explosion craters have not been studied as carefully. In a new study published on Tuesday in GSA BulletinResearchers evaluated the history of hydrothermal vents at Yellowstone Lake over the past 14,000.
“The Yellowstone hydrothermal system is the largest in the world and is driven by high heat flow over a large area, by high precipitation rates and by active seismicity and deformation. Over 10,000 hydrothermal properties are found in Yellowstone,” said Lisa Morgan, lead author of the study. “For this study, we wanted to know more about the recent geological history of the Yellowstone Lakes and the role of hydrothermal activity in the lake, especially the role of hydrothermal explosions and their triggering mechanisms.”
The research team collected sediment cores from the entire northern part of Yellowstone Lake and correlated them with cores previously collected in the vicinity, with the aim of characterizing their chemical and physical properties and identifying hydrothermal explosion deposits in the cores.
“Hydrothermal explosion sediments deposited underwater had never been described in published literature. When we analyzed the cores, we made many discoveries and received several surprises. Number one was how different the explosion deposits found in the cores looked from explosion deposits on land. It was to be expected because a was deposited through a water column and one was deposited on land, says Morgan.
The researchers found evidence of at least 16 deposits in the cores produced by hydrothermal vents. While 14 of the deposits represented more localized explosive events, two of the deposits were associated with two of Yellowstone’s largest hydrothermal explosion craters: Mary Bay and Elliott’s craters.
The hydrothermal explosion in Mary Bay occurred 13,000 years ago and resulted in a 2.5 km (1.5 ml) wide crater, which is partially submerged under the lake. While deposits from the Mary Bay explosion on land had previously been studied, the sediment cores from the lake showed that the extent of its deposits was greater than previously thought and that the lake level must have been lower at the time of the explosion.
The researchers concluded that the Mary Bay explosion was triggered by a sudden 14-m (46-ft) drop in sea level caused by a seismic event and a tsunami that eroded the Yellowstone Lakes outlet.
The Elliott’s Crater explosion occurred 8,000 years ago and produced a 700 m wide crater. The crater is completely submerged under water and no deposits from the explosion are exposed on land. Based on registrations in the cores, the deposits from Elliott’s crater were also more widely distributed than previously thought.
Unlike how the Mary Bay crater was probably formed, the researchers determined that Elliott’s crater was formed when a seismic event cracked the dome lid on the hydrothermal system. In Yellowstone Lake, hydrothermal vents form when underlying pockets of gas or gas-laden liquids cause the overlying sediments to bend upward. Bursting this dome would result in a sudden loss of pressure, triggering a hydrothermal explosion.
Many of the smaller deposits in the sediment cores came from previously unknown younger hydrothermal explosions. Consistent with previous studies of the explosion craters, there appears to be no link between them and volcanic eruptions at Yellowstone.
“Given what we see from Yellowstone Lake and elsewhere in Yellowstone, hydrothermal explosions of various scales will continue to occur,” Morgan said.
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