In two studies appearing in April issue of GSA Today and the May issue of Geology, the scientists present new insights into the potential for volcanoes to produce gigantic eruptions — explosions thousands of times larger than the 1980 eruption of Mount Saint Helens.
“Although evidence for such massive eruptions is found throughout the geologic record, our investigation of magmas frozen below long-extinct volcanoes in California’s Sierra Nevada led us to conclude that the largest eruptions are significantly less likely than many people believed,” Glazner said.
In their investigation, team members studied magma bodies that cooled beneath the land’s surface. Those bodies, called “plutons” after Pluto, the Greek god of the underworld, are the chief building blocks of the Earth’s crust, he said. Vast pieces of formerly molten rock, they contain many known rock and mineral resources.
“Much of Chapel Hill, for example, lies on the Chapel Hill Granite pluton and its associated volcanic rocks,” the geologist said. “Most scientists picture plutons as solidifying from enormous underground blobs of molten rock known as magma that feed overlying volcanoes.”
Typically, plutons are hundreds to thousands of cubic kilometers in volume. For that reason, geologists long assumed that huge stores of magma are commonplace active volcanoes, Glazner said. They also reasoned that the potential for truly catastrophic eruptions exists in many volcanically active areas.
“Our new work casts doubt on the assumption that gigantic eruptions should be relatively common,” he said.
Glazner, Coleman and Bartley combined observations of the deep Earth provided by seismic waves produced during earthquakes with mathematical modeling of magma cooling and precise dating and field mapping Sierra Nevada plutons.
Because small percentages of liquid in a rock slow seismic waves dramatically, the waves are sensitive probes for the tiniest volumes of molten rock, Glazner said.
“However, even under active volcanoes, seismic waves show little evidence for big blobs of magma,” Coleman said. “Our mathematical models indicate that if big magma chambers existed, they should solidify in less than a million years, but new high-precision age determinations completed here at UNC indicate that plutons can take up to 10 million years to form.”
New field mapping demonstrated that plutons once thought to be thousands of cubic kilometers of homogeneous rock that cooled from a single magma reservoir preserve subtle evidence of a much slower, piecemeal assembly, he said.
The results suggest that plutons are likely to be built by a multitude of small molten intrusions over millions of years and that plutons are not like a closed can of food waiting to explode when heated, Coleman said.
“We conclude that volcanoes are more prone to chugging along, producing many small — though still dangerous — eruptions such as the 1980 eruption of Mount Saint Helens, rather than huge civilization-destroying eruptions,” he said.
Former UNC College of Arts and Sciences students Walt Gray and Ryan Z. Taylor, now with the Southwest Research Institute and the U.S. Forest Service, respectively, contributed to the new work. The National Science Foundation supported it.
The good news is that it is not common for large blobs of magma to be near the surface, thus even the active volcanoes are unlikely to be involved in a monstrous explosion.
The bad news is that a tiny tendril of magma is sufficient to produce big eruptions. There is a lot of power in any little pipe that approaches the surface.
Yes, rather than being due to volcanic gases or magma build up, many volcanic explosions involve situations such as suddenly released steam pressure. Since water so widely present, including in very deep rocks, this does not reduce the dangers.
… completely ignore the observations that
those are all completly irrelevent to the likelyhood that Yellowstone will errupt as a supervolcano at any time in the next 200,000 years.
Well, I feel re-assured. (actually I feel if we succeed in surviving till it does go, we will possibly survive even that, though I don’t want to think about the odds of either.)
-Rusty
…is the Roman god of the underworld, not Greek.
I did a little looking for that information which is being ignored.
First, look at the nice picture of the Snake River Valley cutting through Idaho. The river didn’t make that huge slash. The hotspot has been chewing up the terrain for a while as it moves on. Yellowstone is at the northeast end. But the mark is also due to many lava flows, not only explosions.
More details: Yellowstone National Park
Yellowstone Caldera
USGS Yellowstone FAQs
Consider the time between these 3 recent big eruptions when compared to recent ice ages.
Mental picture for the day: Yellowstone erupts under a mile of ice.
The only thing certain is a lot of big numbers.
SE, I’d LOVE to see you post a story a week like this. Excellent job. I’ve learned something.