The "Rosetta Stone" of Volcanoes
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 fossil supervolcano has been discovered in the Italian Alps' Sesia Valley
by a team led by James E. Quick, a geology professor at Southern Methodist
University. The discovery will advance scientific understanding of active
supervolcanoes, like Yellowstone, which is the second-largest supervolcano
in the world and which last erupted 630,000 years ago.
The Deep Plumbing of a Supervolcano
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
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
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.
Understanding Magma and Explosive Volcanism
"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.
"We want to better understand the tell-tale signs that a caldera is
to eruption so that we can improve warnings and avoid false alerts," Quick
A Rare View of Volcanic Anatomy
To date, scientists have been able to study exposed caldera "plumbing"
from the surface of the Earth to a depth of only 5 kilometers. Because of
scientific understanding has been limited to geophysical data and analysis
erupted volcanic rocks. Quick likens the relevance of Sesia Valley to seeing
bones and muscle inside the human body for the first time after previously
envisioning human anatomy on the basis of a sonogram only.
"We think of the Sesia Valley find as the 'Rosetta Stone' for supervolcanoes
because the depth to which rocks are exposed will help us to link the
and geophysical data," Quick says. "This is a very rare spot. The base of
Earth's crust is turned up on edge. It was created when Africa and Europe
began colliding about 30 million years ago and the crust of Italy was turned
Bristish researchers introduced the term "supervolcano" in the last 10
Scientists have documented fewer than two dozen caldera eruptions in the
1 million years.
Besides Yellowstone, other monumental explosions have included Lake Toba
on Indonesia's Sumatra island 74,000 years ago, which is believed to be
the largest volcanic eruption on Earth in the past 25 million years.
Described as a massive climate-changing event, the Lake Toba eruption
is thought to have killed an estimated 60% of humans alive at the time.
Another caldera, and one that remains active, Long Valley in California
erupted about 760,000 years ago and spread volcanic ash for 600 cubic
kilometers. The ash blanketed the southwestern United States, extending
from California to as far east as Nebraska.
"There will be another supervolcano explosion," Quick says. "We don't know
where. Sesia Valley could help us to predict the next event."
Quick is a professor in the SMU Roy M. Huffington Department of Earth
Sciences as well as SMU associate vice president for research and dean
of graduate studies. Co-authors of the report are Silvano Sinigoi,
Gabriella Peressini and Gabriella Demarchi, all of the Universita di
Trieste; John L. Wooden, Stanford University; and Andrea Sbisa, Universita
di Trieste. - Margaret Allen
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|Minerals: Information about ore minerals, gem materials and rock-forming minerals.|
|Sesia Valley is located in the Alps mountain range in northwestern Italy. Map by Geology.com and MapResources.
|Photograph of the "Bishop Tuff" at Long Valley Caldera, from a volcanic event that erupted 140 cubic miles of magma 760,000 years ago.
This exposure is in a rock quarry in Chalfant Valley about 15 miles southwest of Long Valley. The two main units of the Bishop Tuff deposit are visible: (1) the lower 15 feet consists of pumice that fell to the ground downwind from the eruption; and (2) the upper 15 feet consists of the basal part of pyroclastic flows that swept away from the eruption. The thin dark "layers" just below the contact between the units are stains from an ancient groundwater table (manganese oxide stains). Image by USGS. Enlarge Image
|USGS map showing the enormous size of the Yellostone Caldera. Enlarge Image
|Cross-section of the Yellowstone Caldera that formed in a cataclysmic eruption 640,000 years ago. The magma reservoir includes both rhyolitic and basaltic magma. Capping the magma reservoir is a zone of hot, ductile rock that can slowly flow to close any fractures and is therefore relatively impermeable (meaning that fluids cannot easily pass through). The cooler rock above behaves in a more brittle manner and can be readily fractured. Image by USGS. Enlarge Image