Ok, so it wasn't enough to get freaked out about the History channel show, oh, no -- I had to do a bit more googling to see what else I could find out. (Me? Obsessive?)
One of the scenarios in the show was the enormous eruption of the Yellowstone caldera, releasing about 1000 cubic km of material into the atmosphere as it did 640,000 years ago. It tends to erupt about every 600K years, according to the layers in the surrounding park, and an eruption of this size would be catastrophic to life in the US. (To compare -- Mt. Saint Helens burped up only 1.2 cubic km of material. A tiny little blip in the company of the "supervolcanos".
So what else do I discover? That the largest supervolcano caldera ever discovered is in Colorado!
La Garita was the site of truly enormous eruptions about 26–28 million years ago, during the Oligocene Epoch. The scale of volcanism was far beyond anything known in human history. The resulting deposit, known as the Fish Canyon Tuff, has a volume of approximately 5,000 cubic kilometers. That is more than enough material to fill Lake Erie. For comparison, the May 18, 1980 eruption of Mt. St. Helens was only 1.2 cubic kilometers in volume. The area devastated by the La Garita eruption must have covered a significant portion of what is now Colorado, and ash could have fallen as far as the east coast of North America and the Caribbean.
It was one of the largest known eruptions, if not the largest, to have occurred in Earth's history.
Well. At least it is considered "extinct" at this point. We hope.
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