Yellowstone volcano: Geologists expose ‘extreme’ explosions hidden under Yellowstone Lake

Yellowstone volcano: 'Super-eruption' predicted by expert

Yellowstone volcano in the western United States is perhaps best known for its supervolcanic activity. In the past 2.1 million years, the supervolcano had at least three major eruptions one of which was about 6,000 more powerful than the eruption of Mt St Helens in Washington State in 1980. But the volcanic caldera, which stretches some 34 by 45 miles across, is also known for another, much more frequent sign of activity – hydrothermal explosions.

Located at the heart of Yellowstone National Park in Wyoming sits Yellowstone Lake, a 136 square-mile body of water that is surrounded by geysers, fumaroles and hot springs.

And although the lake appears fairly serene at first glance, US Geological Survey (USGS) scientists believe these looks are somewhat deceiving.

Lisa Morgan, an emeritus research geologist with the USGS, explained how the bottom of Yellowstone Lake is a pockmarked landscape shaped by ancient explosive events.

She said: “Hydrothermal explosions are considered one of the most serious natural hazards in Yellowstone.

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“On land, hydrothermal explosion craters, especially large ones, hundreds of meters in diameter, are easily identified.

“Within the Yellowstone Caldera, their bowl-shaped depressions are commonly filled with lakes surrounded raised rims composed of explosion breccia ejecta.”

Some of the most well-known explosion craters include Turbid Lake and Mary Bay craters north of Yellowstone Lake, as well as Pocket Basin in Yellowstone’s famous Lower Geyser Basin.

Dr Morgan added: “Their explosions occurred thousands of years ago and were extreme events where boiling water, steam, hot mud, and rock fragments up to several meters in diameter were ejected hundreds of meters above the crater and rained down on the landscape.”

But it is a different story at the bottom of Yellowstone Lake, where the craters are not readily visible to geologists and Yellowstone’s visitors.

One of these craters is Elliott’s Crater, which is only one of many crater features found at the bottom of the lake.

And it was not until concentrated efforts to map these features some 20 years ago that scientists knew exactly what was lurking under Yellowstone Lake’s waters.

Elliott’s Crater, for instance, is a nearly 2,759ft-wide depression in the lake’s northern part that was unknown until the lake’s bottom was mapped between 1999 and 2003.

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The crater is named after environmentalist Henry Elliott who in 1871 carried out some of the first soundings on Yellowstone Lake.

Dr Morgan said: “Despite the crater being less than 2km south of the northern lake shoreline, no deposits from this explosion have been mapped on land, whereas hydrothermal explosion deposits from the 13,000-year-old Mary bay, the 9,400-year-old Turbid Lake, and the 2,900-year-old Indian Pond explosion events are well exposed.”

Scientists originally estimated Elliott’s Crater formed some 8,000 years ago, based on the thickness of deposits in the crater.

The dating was later supported by radiocarbon gas dating.

The crater is still active today and appears to have a number of smaller craters on its western and southern side.

Dr Morgan said: “Recent imaging and sampling of active, hot hydrothermal vents inside and along the edge of Elliot’s Crater indicate this feature has been active for over 8,000 years and will continue into the future.

“Exploration and discovery in Yellowstone Lake opens our eyes to previously unknown hydrothermal activity, and the lake sediments preserve features that cannot be studied by other means, allowing us to understand the processes that create these events.

Earlier this year, Yellowstone scientists revealed how the bottom of Yellowstone Lake is still a very active place, comparing the system to a “pressure cooker”.

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