Wed, 29 Mar 2006 12:00 UTC
The explosive formation of Argentina's Vilama Calera volcano seemed to have matched Yellowstone's historic continent-blanketing blast millions of years ago.
Vilama Calera may be another unappreciated 'supervolcano' (like Yellowstone) hidden in a mega-volcano nursery, dubbed the Eduardo Avaroa Caldera Complex in the tri-section of Argentine, Bolivia and Chile.
Geologist Miguel M. Soler of the National University of Jujuy in San Salvador de Jujuy, Argentina, said: "Vilama Caldera formed during a single event that emitted approximately 2000 cubic kilometres (almost 500 cubic miles) of pyroclastic material."
Ash volume and pyroclastic material, called ignimbrites, produced by the 8.4 million-year-old eruption, and the size of the associated caldera, put it among the world's largest known eruptions.
"In contrast, for example, Yellowstone produced its important volumes of ignimbrites and lavas in three cataclysmic events." Soler says. "Eruptions at 2.0, 1.3, and 0.6 million years ago ejected huge volumes of rhyolite magma, and each formed a caldera and extensive layers of thick pyroclastic flow deposits," he adds.
Scientists believe that the Vilama Caldera could have been created when a ten by 24 mile layer collapsed on a chamber of molten rock or magma with explosive results, causing vast amounts of ignimbrites out in many directions. The huge layer, or roof, collapse is what all large calderas have in common and what separates them from smaller 'single vent' volcanic eruptions like Mount St. Helens or Mount Pinatubo.
"But that's where the similarities with Yellowstone end," says Soler. Magma under Yellowstone is thought to be created by the melting of ancient crust under North America where Vilama's magma could have been created by a more complex melting of the crust caused by the South American Plate colliding and overriding the Nazca Plate to the west.
"Much remains unknown about Vilama Caldera," says Soler, "Largely because it is a terribly difficult caldera to study."
"Among the other calderas in the region that need to be studied in detail and which in all cases are also certainly 'supervolcanoes' are Cerro Guacha, Coruto, Pastos Grandes, and Capina," Soler adds. Soler will present his work on Vilama supervolcano on Monday, 3 April at the Backbone of Americas Patagonia to Alaska meeting co-convened by the Geological Society of America and the Asociacion Geologica Argentina, with collaboration of the Sociedad Geologica de Chile.