Scientists have found the Rosetta Stone of supervolcanoes, those giant pockmarks in the Earth's surface produced by rare and massive explosive eruptions that rank among nature's most violent events.

The eruptions produce devastation on a regional scale - and possibly trigger climatic and environmental effects at a global scale.

A rare uplift of the Earth's crust in the Sesia Valley reveals for the first time the actual "plumbing" of a supervolcano from the surface to the source of the magma deep within the Earth, according to a new research article reporting the discovery. The uplift reveals to an unprecedented depth of 25 kilometers the tracks and trails of the magma as it moved through the Earth's crust.

Supervolcanoes, historically called calderas, are enormous craters tens of kilometers in diameter. Their eruptions are sparked by the explosive release of gas from molten rock or "magma" as it pushes its way to the Earth's surface.

Calderas erupt hundreds to thousands of cubic kilometers of volcanic ash. Explosive events occur every few hundred thousand years. Supervolcanoes have spread lava and ash vast distances and scientists believe they may have set off catastrophic global cooling events at different periods in the Earth's past.

Sesia Valley's caldera erupted during the "Permian" geologic time period, say the discovery scientists. It is more than 13 kilometers in diameter.

"What's new is to see the magmatic plumbing system all the way through the Earth's crust," says Quick, who previously served as program coordinator for the Volcano Hazards Program of the U.S. Geological Survey. "Now we want to start to use this discovery. We want to understand the fundamental processes that influence eruptions: Where are magmas stored prior to these giant eruptions? From what depth do the eruptions emanate?"

Sesia Valley's unprecedented exposure of magmatic plumbing provides a model for interpreting geophysical profiles and magmatic processes beneath active calderas. The exposure also serves as direct confirmation of the cause-and-effect link between molten rock moving through the Earth's crust and explosive volcanism.

"It might lead to a better interpretation of monitoring data and improved prediction of eruptions," says Quick, lead author of the research article reporting the discovery. The article, "Magmatic plumbing of a large Permian caldera exposed to a depth of 25 km.," appears in the July issue of the peer-reviewed journal "Geology."

Calderas, which typically exhibit high levels of seismic and hydrothermal activity, often swell, suggesting movement of fluids beneath the surface.

"Bishop Tuff at Long Valley, from a volcanic event that erupted 140 cubic miles of magma 760,000 years ago."

Source: Southern Methodist University