World Safe From MegaVolcanos – For Now

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.

From a University of North Carolina press release.

6 thoughts on “World Safe From MegaVolcanos – For Now”

  1. 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.

  2. … completely ignore the observations that

    • Yellowstone has a history of making “super volcano erruptions” every 600,000 years or so, the latest one of which was some 600,000 years ago
    • sismic sampling of yellowstone, similar to what the article above shows for the Tetons, suggests a massive liquid magma chamber under Yellowstone
    • the center of same which held elevation from the 20’s to the 60’s rose some six feet from the 70’s to 2000
    • “small” movements in the surface are likely to be significant precursors to significant events in the near future, as has been demonstrated at Mt. St. Hellens, and Pintubo

    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

  3. 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.

    • Yellowstone has a history of making “super volcano erruptions” every 600,000 years or so, the latest one of which was some 600,000 years ago
      • Yellowstone’s Eruptive History – “Three times in the past 2 million years, large reservoirs of rhyolite magma have accumulated in the upper crust at Yellowstone, triggering cataclysmic eruptions and caldera collapses 2.0, 1.3, and 0.6 million years ago.”
      • This “history” is three events. Not much of a pattern.
      • And that looks like two 700,000 year intervals, not 600,000. Another eruption is considered likely…sometime.
      • This story mentions at the end that there have been 30 eruptions since the last big one. Such an eruption is the most likely kind, but an eruption of that type would mostly affect the Park area. (I observe that is also true of Mt. St. Helen’s – a mess nearby but not much effect on neighboring states and cities.)
    • sismic sampling of yellowstone, similar to what the article above shows for the Tetons, suggests a massive liquid magma chamber under Yellowstone
      • The study under discussion implies that small chambers are more likely than previously thought. But however “massive” the hot spot is, there’s a lot of power there. After all, it has melted hundreds of kilometers of rock.
      • Indeed, the hot spot is moving. Canada will get to deal with it eventually. So the Yellowstone area is changing, although on geologic time scales.
      • The velocity and direction of several locations in the area show most movement to the west or southwest (the continent is moving WSW over the hot spot). The movement at right angles in Yellowstone is expected, as the area is expected to drop and separate before filling with lava.
    • the center of same which held elevation from the 20’s to the 60’s rose some six feet from the 70’s to 2000
      • Hmm. The area may have moved up and down 80 meters over recent geologic history.
      • Your information is different from “Precise surveys have detected an area in the center of the caldera that rose by as much as 86 centimeters between 1923 and 1984 and then subsided slightly between 1985 and 1989.”
      • Here’s a summary graph from the Park.
    • “small” movements in the surface are likely to be significant precursors to significant events in the near future, as has been demonstrated at Mt. St. Hellens, and Pintubo
      • Your logic is reversed. Significant events have been likely to have had earlier small movements. Not all small events are precursors of huge eruptions. Fortunately for Japan, California, the Rocky Mountains, and the Andes.
      • 2,000 earthquakes a year in Yellowstone. Year after year. Which ones are the significant precursors?

    More details: Yellowstone National Park
    Yellowstone Caldera
    USGS Yellowstone FAQs

  4. 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.

  5. SE, I’d LOVE to see you post a story a week like this.  Excellent job.  I’ve learned something.

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