Possible trigger for volcanic 'super-eruptions' found

The eruption of Mount St. Helens in 1980. Credit: Austin Post, USGS

The "super-eruption" of a major volcanic system occurs about every 100,000 years and is considered one of the most catastrophic natural events on Earth, yet scientists have long been unsure about what triggers these violent explosions.

However, a new model presented this week by researchers at Oregon State University points to a combination of temperature influence and the geometrical configuration of the magma chamber as a potential cause for these super-eruptions.

Results of the research, which was funded by the National Science Foundation, were presented at the annual meeting of the in Minneapolis, Minn.

Patricia "Trish" Gregg, a post-doctoral researcher at OSU and lead author on the modeling study, says the creation of a ductile halo of rock around the magma chamber allows the pressure to build over tens of thousands of years, resulting in extensive uplifting in the roof above the magma chamber. Eventually, faults from above trigger a collapse of the caldera and subsequent .

"You can compare it to cracks forming on the top of baking bread as it expands," said Gregg, a researcher in OSU's College of Oceanic and Atmospheric Sciences. "As the magma chamber pressurizes at depth, cracks form at the surface to accommodate the doming and expansion. Eventually, the cracks grow in size and propagate downward toward the magma chamber.

"In the case of very large volcanoes, when the cracks penetrate deep enough, they can rupture the magma chamber wall and trigger roof collapse and eruption," Gregg added.

The eruption of super-volcanoes dwarfs the eruptions of recent volcanoes and can trigger planetary climate change by inducing Ice Ages and other impacts. One such event was the Huckleberry Ridge eruption of present-day Yellowstone Park about two million years ago, which was more than 2,000 times larger than the 1980 eruption of Mount St. Helens in Washington.

"Short of a , these super-eruptions are the worst environmental hazards our planet can face," Gregg said. "Huge amounts of material are expelled, devastating the environment and creating a gas cloud that covers the globe for years."

Previous modeling efforts have focused on an eruption trigger from within the magma chamber, which scientists thought would leave a visible trace in the form of a precursor eruption deposits, according to Shanaka "Shan" de Silva, an OSU geologist and co-author on the study. Yet there has been a distinct lack of physical evidence for a pre-cursor eruption at the site of these super-volcanoes.

The model suggests the reason there may be no precursor eruption is that the trigger comes from above, not from within, de Silva pointed out.

"Instead of taking the evidence in these eruptions at face value, most models have simply taken small historic eruptions and tried to scale the process up to super-volcanic proportions," de Silva said. "Those of us who actually study these phenomena have known for a long time that these eruptions are not simply scaled-up Mt. Mazamas or Krakataus – the scaling is non-linear. The evidence is clear."

It takes a "perfect storm" of conditions to grow an eruptible magma chamber of this size, Gregg says, which is one reason super-volcano eruptions have occurred infrequently throughout history. The magma reservoirs feeding the eruptions could be as large as 10,000- to 15,000- cubic kilometers, and the chamber requires repeated intrusions of magma from below to heat the surrounding rock and make it malleable. It is that increase in ductility that allows the chamber to grow without magma evacuation in a more conventional manner.

When are smaller, they may expel magma before maximum pressure is reached through frequent small eruptions.

The Yellowstone eruption is one of the largest super-volcano events in history and it has happened several times. Other super-volcano sites include Lake Toba in Sumatra, the central Andes Mountains, New Zealand and Japan.

Gregg said that despite its explosive history, it doesn't appear that Yellowstone is primed for another super-eruption anytime soon, though the slow process of volcanic uplift is taking place every day.

"The uplift of the surface at Yellowstone right now is on the order of millimeters," she explained. "When the Huckleberry Ridge eruption took place, the uplift of the whole Yellowstone region would have been hundreds of meters high, and perhaps as much as a kilometer."

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Oct 12, 2011
At Krakatoa, the proximal cause of the explosion was sudden mixing of the gassy rhyolitic magma with an intruding tongue of much hotter basaltic magma, with the heat causeing the explosive pressure increase of the gases:
The size of the chamber was mainly relevant to the *scale* of the explosion, and the presence of fractures in the chamber wall probably controlled the dispersion of the explosion like the convolutions in the casing of a fragmentation grenade.

Oct 12, 2011
Good thing it's not going to to off for awhile. One of these things blowing up would most certainly gum up the works of technocivilization version 1.0 for awhile.

Oct 12, 2011
I still think we should be fracking near Yellow Stone. What could possibly go wrong?

Oct 12, 2011
I still think we should be fracking near Yellow Stone. What could possibly go wrong?

Lol sarcasm, too bad yellowstone caldera has shown recent signs of activity and chances are we will see it erupt sometime within the next 100-1000 years.

Oct 12, 2011
"it has a wonderfull defense mechanism; you don't dare kill it." - Yaphet Kotto as Parker in the movie "Alien."

Oct 12, 2011
'10,000- to 15,000-square cubic kilometers' should be '10,000 to 15,000 cubic kilometers'.

Oct 12, 2011
Some of us will have to relocate to preserve our species.
I don't know if you realize it, but these super-eruptions have occurred numerous times before, and both our species as well as lesser ape species are still here. Would it suck severely? Yes, indeed. Would it be the end of the world? Not even close.

Oct 13, 2011
I think in the Sumatran eruption only 15,000 "people" were left standing. That was 70,000 years ago. I would think total extinction of mankind is entirely likely.
Meh. Consider the geographical spread and technological adaptations of ancient vs. modern humans.

World-wide famines and die-offs could happen (and yeah, it would really suck), but civilization as a whole won't go away. For instance, in comparison to 70,000 years ago, modern humans know how to build nice warm shelters, make nice warm clothes, build nice cost-effective greenhouses and grow nice productive veggies in there. Never mind that even a global volcanic winter -- which might lower temperatures by, say 10 degrees on average -- still won't come close to making the tropics uninhabitable to modern humans, who manage to live and thrive in places like Alaska and Norway (never mind the South Pole).

Oct 13, 2011
A 10 Degree drop in the Global temperature would devestate every living organism on the planet. The average change in Global temperature over the past several million years has been no more than 1 to 2 degrees. This is a good thing because a ten degree drop would freeze the entire planet, probably and most likely to never thaw out again. If a supervolcano did erupt I doubt there would be much more than a 3-5 degree change still this would be a daunting prospect that would severly impact the entire ecological system. Human survival would not be based soleley on our ability to adapt to climate change, but our ability to maintain our grip with the entire ecological system in upheaval, and whether enough resources could be sustained to allow our survival. The biosphere is very fragile and all living organisms are inter-dependent, this is where the greatest challange would occur as we would need to revitalize those organisms on which we depend for survival a 50-50 proposition at best.

Oct 13, 2011
a ten degree drop would freeze the entire planet
It would take more than a few years of lowered temperatures to freeze an entire planet. The aerosols launched into the stratosphere by a mega-eruption won't stay there long enough to cause a snowball effect.
maintain our grip with the entire ecological system in upheaval, and whether enough resources could be sustained to allow our survival
Far from everyone would survive, but small populations indeed can and would survive. The culling process would be rather mega-tragic, needless to say...
The biosphere is very fragile
I'd say after 4 Billion years of surviving all manner of catastrophy, the biosphere can cope with a measly mega-eruption. Sure, it would be an extinction event, and possibly a major one, but hardier organisms like mice and cockroaches have been there, done that, and are still here to pester us in spite of it all.

Oct 13, 2011
We need to hurry up with our global warming efforts so that when it blows we've already offset the cooling effect.


Oct 13, 2011
i smell an excellent speculative fiction based on your collective comments..super interesting

Oct 15, 2011
A cataclysmic event like this -- even if it doesn't kill off humanity -- would cause huge disruptions to our food supply WHICH IN TURN WOULD CAUSE MASS WARFARE between nations for access to food supplies. This ABC (Atomic, Biological, Chemical) World War 3 would probably finish the job, even if Nature couldn't.

Oct 16, 2011
tadchem the first posting mentioned factors in the Krakatoa eruption but neglected to include the inrush of massive amounts of sea water that helped to pulverize the entire island thus providing the entire globe with red sunsets for 5 years. Reports of the time have the explosion as being heard in Japan 5000 kms away and the tidal effects as being felt on the east coast of Africa almost 13000 kms away. Glad I wasn't nearby.

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