Feb. 7, 2008 -- The fault-riddled landscape of northern Nevada has sliced and diced the remains of one of the world's largest volcanoes, providing a rare chance to inspect the innards of the so-called "supervolcano."
The Caetano caldera was a 12-mile-wide crater after it erupted 33.8 million years ago and sent a catastrophic ejection of more than 270 cubic miles of molten, lathered rock into the air.
"This is an eruption very much on the scale as the Yellowstone eruption," said caldera volcano expert Peter Lipman of the U.S. Geological Survey (USGS). The hot springs and geysers at Yellowstone National Park are remnants of the last catastrophic eruption there about 600,000 years ago.
The Caetano caldera is not related to the Yellowstone eruption, but both were caused by a gigantic plume of hot rock moving up through the crust. Calderas like these are so large that they can't erupt through a single opening, like most volcanoes. Instead, a caldera ejects molten material and gas in a ringed fracture zone.
The land in the center of the ring, which acts like a lid on the huge pool of magma, collapses. The collapsing lid provides even more oomph to the explosion of hot, foaming magma out of the ring of fractures.
Caldera eruptions, the most powerful volcanic eruptions on Earth, have never occurred during recorded history, Lipman told Discovery News. That makes them all the more difficult to study.
That's one reason the Caetano caldera is so special -- Nevada's faulted, blocky crust there has slid and tilted so the insides are visible on the surface, like books on a shelf without a bookend.
"You can actually put your hands on the rocks," said geologist David John, also of the USGS. John is also the author of a paper about the Caetano caldera in the February edition of the journal Geosphere.
This close encounter with the long-dead supervolcano's guts is a good way to learn what makes active places like Yellowstone tick.
Among the surprises John and his colleagues discovered, for instance, is that the collapse of Caetano caldera was a whopping three miles deep -- far deeper than expected in such an eruption.
When the Caetano caldera formed, much of Nevada and Utah was a high continental divide -- perhaps 13,000 feet above sea level, according to some estimates. The region was riddled with supervolcanoes, said Lipman, of which Caetano was just one. An analogous region today would be the Altiplano of South America -- the widest part of the Andes -- which contains many intact calderas.
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