Super Volcanoes
kaBoom2
The headline of the article in Global Times (8/10/22) sounded ominous: “Earth overdue for volcanic super eruption. Explosive pressure builds up over millions of years, new research finds.”
The article reports that “super eruptions” can be expected to occur once every 20,000 years, and that since “the last massive volcano” erupted about 26,000 years ago, the earth could be overdue for another major event.
“We believe … processes in the Earth … lead to periodic behavior in which large amounts of molten rock accumulate over very long periods of time, and then really quite rapidly in a geological sense, rise to the Earth’s surface and erupt in one go,” According to Professor Stephen Sparks, a volcanologist at the University of Bristol. (BTW: I wonder if Professor Sparks realizes that his work supports and validates the 2nd Law of GeoFantasy.)
There have surely been some large eruptions in the past 20,000 years that apparently weren’t of sufficient magnitude to make the cut. Consider Mt. Mazama in Oregon, which blew its top 7700 years ago, creating Crater Lake. Or the Greek island of Santorini that erupted in the Mediterranean about 3700 years ago, and may be the source of the Atlantis legend.
Or Krakatau in Indonesia that erupted a mere 140 years ago, obliterating the island (see the remains, above), sent a pressure wave that circled the earth seven times at an average rate of 675 miles per hour, and ruptured the eardrums of sailors forty miles away. (It is thought that the vibrant red sunsets that resulted from the pyroclastic debris in the atmosphere for the following decade were the inspiration for “The Scream” by Edvard Munch, who was in Oslo, Norway at the time — nearly 7,000 miles away.
All of these are related to subduction zones, and the article focuses on volcanism in the Andes of South America — also related to subduction of the lithosphere. Oh yeah, there is no doubt that subduction zone volcanism is mighty impressive, and can lead to the extreme events discussed above and by Prof. Sparks.
But there are other “super volcanoes” that — while not associated with subduction zones — may also be worth mentioning.
My personal favorite is the Yellowstone Supervolcano, found in northwestern Wyoming in the United States. Based upon the last three events, this felsic blowtorch seems to reach critical mass every 600,000 to 700,000 years, and leaves behind calderas ranging up to fifty miles in diameter (compare this with Mazama which left behind a crater a measly six miles across). Yellowstone’s periodicity may vary as one goes back in time, but the volume of ejecta seems to be consistent.
I love this Lidar image of the western United States. Some of the things I always enjoy are the lineations: physiological orientations that approach a straight line, and are usually the result of some tectonic process that has helped control the shape of the crust. A few obvious ones (generally going west to east) include: the San Andreas Fault; the Cascades in Oregon and Washington (more subduction zone volcanoes); the eastern face of the Sierra Nevada; the Basin and Range block faulting that runs from the Sierra on the west to Montana, Wyoming, and Colorado; and the Front Range of the Rockies.
You may have been asking yourself “Where is Yellowstone?” in the Lidar image. Well, I have to admit that I Photoshopped the modern-day map (below) to rebuild the block-faulted portions of the Rocky Mountains that have been removed as the North American plate has been moving steadily westward across the Yellowstone Hot Spot.
Oh my!
It is truly sobering to consider that the Snake River Valley in southern Idaho is there because Yellowstone has been blasting a channel through the Rockies for the past twelve million years!
A Supervolcano indeed!
