During the recent "Sniper" scare I was chatting with a tourist on the street in Cody. He was a retired gentleman from Michigan, and while we talked his wife seemed blissfully lost in a paperback in the cab of an RV parked nearby. The man told me that I was lucky to live in Wyoming, not only due its natural beauty, but because it looked to be a safe place to be in our difficult times. I told him that I thought that to be true as long as the Caldera didn't blow up again.
Visitors to Yellowstone National Park quickly notice the Park's famed "geothermal features," and through interpretive signs and didactic rangers, soon learn all about geysers, hot springs, steam vents, fissures, fumaroles, mudpots and travertine terraces. Some 10,000 of these steamy attractions are scattered across the Park, and along with those seen in Iceland, are the majority found in the world. Tourists also learn that these are the result of a semi-dormant, collapsed volcano called "magma," a forty miles wide pool of hot lava stewing forty miles underground.
The first tourist to see these other-worldly sights was the mountain man John Colter. He traveled through the present Park in 1807, while exploring the region and seeking the scattered bands of friendly Crow Indians that his boss Manuel Lisa had instructed him to find to establish trading contacts. Since geology in the early nineteenth century was an arcane science studied in European universities, it is certain that Colter was wholly ignorant of geothermal features as natural and explainable phenomena. One wonders what his state of mind was as he wandered among them. I think of him as a half curious-half scared buckskin-clad Dantesque traveler through a perceived Hell, and he was probably privy to dark Indian superstitions about the place. But a later generation of mountain men (Jim Bridger, Thomas Fitzpatrick, Joe Meek, et al.) lost their trepidations concerning "Colter's Hell," and occasionally interrupted their own journeys for a long soak in a hot spring. Bridger -- in his homespun colloquial way -- called them "the bilings."
A look at the detailed map of Yellowstone handed to every visitor upon entrance to the Park is to see a slightly left-of-center oblong circle that covers roughly a quarter of it (about 50 x 40 miles, and covering the underground magma "hotspot"). Contained within this border is the Yellowstone "Caldera" (a fancy word for ancient volcanic-born craters), that collapsed volcano responsible for all of Yellowstone's steaminess over many millennia. About 650,000 years ago there was a massive explosion of the Caldera with the force of 2,500 Mount St. Helens, and Wyoming's Big Horn Basin (and other points downwind) piled up with many feet of ash and debris. Heart Mountain, a Cody landmark, was literally of a piece blown free from the Beartooth Mountains forty miles to the northwest. It landed upside down, becoming a geologic anomaly because its most ancient features are found at the summit.
I recently read an article in the paper about all this, and was surprised to learn that this cataclysm occurs approximately every 650,000 years, and that it hasn't happened in, well, 650,000 years, give or take ten or twenty thousand.
This wouldn't be so alarming except that -- according to seismologists -- since 1959 (the year of the massive 7.5 Hebgen Lake earthquake that created Quake Lake by damming the Madison River west of the Park with a massive rockslide) there has been a marked increase in mostly minor earthquakes in the Caldera area. These are the kind of quakes that are so small as to register only on seismographs, but can be counted on to reactivate previously dormant geysers. In May 2000, Steamboat Geyser in the Norris Geyser Basin came out of a nine-year retirement with a spectacular daybreak 300-foot steam blast that awakened and alarmed some tourists in a nearby campground. Like geyser cops, Park Service geologists soon showed up to look around, and take photos and eyewitness statements.
Will the Yellowstone Caldera blow sky high soon? Hopefully not in our lifetimes. But as John McPhee said in one of his popular geology books: "It's only a matter of Time".
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