Friday, June 12, 2009

Accretionary Wedge: A Time Warp!

For this month's Accretionary WedgeLet’s Do a Time Warp!- I’d like to warp forward an unknown amount of time, with whatever special technology and safety suits are required, to see the next large-scale caldera-forming eruption. Inactive large-scale calderas are found scattered through the Tertiary of Nevada; active examples include Yellowstone caldera in Yellowstone National Park.lake
Yellowstone Lake with Mt. Sheridan in the middle distance on the right and Mt. Moran of the Tetons in the far distant center. NPS Photo by Jim Peaco, 1987.

The calderas formed by these large-scale volcanic eruptions are truly huge, and some people have taken to calling them “supervolcanoes,” although it should be noted that the U.S. Geological Survey says,

“The term supervolcano has no specifically defined scientific meaning. It was used by the producers of a British TV program in 2000 to refer to volcanoes that have generated Earth's largest volcanic eruptions. As such, a supervolcano would be one that has produced an exceedingly large, catastrophic explosive eruption and a giant caldera,”
and the Yellowstone Volcano Observatory says, using the word “supervolcano” in quotes,

“The term "supervolcano" implies a volcanic center that has had an eruption of magnitude 8 on the Volcano Explosivity Index (VEI), meaning the measured deposits for that eruption is greater than 1,000 cubic kilometers (240 cubic miles).”
I don't much like calling these things supervolcanoes myself, although there can be a certain utility in using the word when talking to lay people, and I'm glad to finally see widespread recognition of eruptions that are much, much larger than the 1980 eruption of Mt. St. Helens in Washington - and much larger than the eruption of Mt. Mazama, which formed Crater Lake, in Oregon.

Geology and volcanology have seen some warranted increase in notoriety and recognition since the release of movies like Supervolcano, and since the publication of supervolcano articles in popular scientific magazines like Scientific American and Discover, however overdramatized or inexact the popular renditions might be. The Wikipedia article Supervolcano, for example, says that "Supervolcanoes are relatively new to science; they were previously unknown because they do not fit the stereotypical model of volcanoes." This statement is incorrect: very large-scale explosive caldera-forming eruptions have been known to geologists for quite some time. Hey, I knew about them way back in the dark ages, before I reached the age of thirty!
west thumb
Potts Hot Spring, West Thumb Geyser Basin, Yellowstone National Park. NPS photo by J Schmidt, 1977.

Time warp! Now we jump into the unkown future, and we are able to see the exact unfolding of the next large-caldera-forming eruption at Yellowstone. We are finally able to answer our many questions. When will the next caldera at Yellowstone erupt, how long will the eruption take, where will the ash flows flow, how thick will they be, and how hot? Will we all be on Mars or orbiting in space so we won't be wiped out? Where exactly in the developing Snake River Plain will the caldera form, will the magma come through Yellowstone Lake thus making the normally and hugely explosive eruption even more explosive? These are some of the many questions that occur to me when thinking of the Yellowstone area. I'd prefer to watch this sometime in the distant future, and not too soon on any human scale.
Looking south from Conway Summit; photo from Wikimedia.

Along those same lines, I have long planned to be standing on Conway Summit, looking south across Mono basin, when the next caldera-sized eruption occurs at the Long Valley caldera, whenever it will be erupting the next version of the Bishop Tuff (Bishop Tuff II ?). The wind will not be to the north while I'm there watching; that would make conditions unbearable (read: deadly), and it would destroy the visibility. I'm thinking, however, that Conway Summit - at about 30 miles or 50 kilometers away - might really be too close. The ash-flow tuff, which would probably go mostly south the way the Bishop Tuff did last time (about 760,000 years ago), could conceivably run northward and boil off the water in Mono Lake, instantly covering all existing tufa spires, domes, and other formations, preserving them for the future of our time-warped future time. One might not think favorably of the natural destruction of Mono Lake, but then at least the L.A. basin wouldn't be taking any of it's water anymore.

Accretionary Wedge #17: Let's Do a Time Warp!

1 comment:

Lockwood said...

Logged and queued. Fun one! Actually I was a little nervous you might have arrived at the same idea I'm trying to piece together... you'll see.