Last caldera forming eruption was a minor one that formed west thumb caldera in Yellowstone lake “174,000” years before present.
A minor eruption.
Probably one of several that precede a large eruption.
“Modern geological surveys have shown that this supervolcano erupts catastrophically every 600,000 years.”
http://www.dailygalaxy.com/my_weblog/2013/12/the-yellowstone-supervolcano-2-12-times-larger-than-earlier-estimates-potential-to-erupt-2000-times-.html
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