for National Geographic News
Long before Vesuvius blew its top and smothered Pompeii, Italy was rocked by a "supervolcano" eruption so powerful it possibly blocked out the sun and triggered prolonged global cooling, scientists say.
The now fossilized supervolcano last erupted about 280 million years ago, leaving behind an 8-mile-wide (13-kilometer-wide) caldera, which was recently discovered in the Italian Alps' Sesia Valley.
What's more, seismic forces have twisted the volcano's interior, giving scientists an unprecedented glimpse deep into the feature's explosive plumbing—and a better shot at deciphering when the next one might blow.
(Explore the inner workings of a supervolcano in Yellowstone National Park.)
"There will be another supervolcano explosion," team member James Quick, a geologist at Southern Methodist University in Texas, said in a statement.
"We don't know where, [but] Sesia Valley could help us to predict the next event."
The Italian eruption likely lasted for weeks, Quick told National Geographic News.
During that time the supervolcano hefted an estimated 239 cubic miles (1,000 cubic kilometers) of material into the atmosphere—about a thousand times more material than Mount St. Helens spewed during its infamous 1980 eruption.
The ancient eruption would have been accompanied by a steady rain of volcanic ash and superheated rocks, along with earthquakes and fast-flowing rivers of lava and hot mud, or ignimbrite.
"It would have been quite dramatic," Quick said.
What's more, ash and sulfur dioxide ejected into the atmosphere would have blocked sunlight from reaching Earth's surface. That may have led to a global cold snap that lasted decades or even centuries, Quick said.
Plumbing on Edge
Although the Sesia Valley caldera is now extinct, scientists think a similar scene of devastation could be repeated. At least seven other supervolcanoes are known around the world, including one in Yellowstone National Park.
But with these previously known calderas, scientists could see only about 3 miles (5 kilometers) of the massive volcanoes' interior structures.
A collision between Africa and Europe that started 30 million years ago caused Earth's crust to twist, turning the Sesia Valley supervolcano's once vertical plumbing nearly on its edge.
This allows scientists to see 15 miles (25 kilometers) of the supervolcano's inner workings.
By studying the Sesia Valley caldera, Quick said, scientists might better understand the events leading up to an eruption and perhaps create eruption warning systems.
The research is detailed in the July issue of the journal Geology.
SOURCES AND RELATED WEB SITES