Magma held in ‘cold storage’ before giant volcano eruption


Long Valley, California, has long defined the "super-eruption." About 765 000 years ago, a pool of molten rock exploded into the sky. Within one nightmarish week, 760 km3 (182 mi3) of lava and ash spewed out in the kind of volcanic cataclysm we hope never to witness. The ash likely cooled the planet by shielding the Sun, before settling across the western half of North America.

Here's a rule of geoscience: The past heralds the future. So it's not just morbid curiosity that attracts geoscientists to places like Long Valley. It's an ardent desire to understand why super-eruptions happen, ultimately to understand where and when they are likely to occur again.

A report published this week in the Proceedings of the National Academy of Sciences shows that the giant body of magma – molten rock – at Long Valley was much cooler before the eruption than previously thought.

"The older view is that there's a long period with a big tank of molten rock in the crust," says first author Nathan Andersen, who recently graduated from the University of Wisconsin-Madison with a Ph.D. in geoscience. "But that idea is falling out of favor.


A new study looks at rock from the titanic eruption that formed Long Valley Caldera in California 765 000 years ago. Calderas occur when a volcano collapses after an eruption. Long Valley has been studied by Wes Hildreth (in background ), an author of the new PNAS study, for decades. The study signals that we don't fully understand these giant eruptions. Credit: U.S. Geological Survey

"A new view is that magma is stored for a long period in a state that is locked, cool, crystalline, and unable to produce an eruption. That dormant system would need a huge infusion of heat to erupt."

It's hard to understand how the rock could be heated from an estimated 400 °C (752 °F) to the 700 to 850 °C (1 300 –  1500 °F) needed to erupt, but the main cause must be a quick rise of much hotter rock from deep below.

Instead of a long-lasting pool of molten rock, the crystals from solidified rock were incorporated shortly before the eruption, Andersen says. So the molten conditions likely lasted only a few decades, at most a few centuries. "Basically, the picture has evolved from the 'big tank' view to the 'mush' view, and now we propose that there is an underappreciation of the contribution of the truly cold, solidified rock."

The new results are rooted in a detailed analysis of argon isotopes in crystals from the Bishop Tuff – the high-volume rock released when the Long Valley Caldera formed. Argon, produced by the radioactive decay of potassium, quickly escapes from hot crystals, so if the magma body that contained these crystals was uniformly hot before eruption, argon would not accumulate, and the dates for all 49 crystals should be the same.

And yet, using a new, high-precision mass spectrometer in the Geochronology Lab at UW-Madison, the research group's dates spanned a 16 000-year range, indicating the presence of some argon that formed long before the eruption. That points to unexpectedly cool conditions before the giant eruption.

Better tools make better science, Andersen says. "The new instrument is more sensitive than its predecessors, so it can measure a smaller volume of gas with higher precision. When we looked in greater detail at single crystals, it became clear some must have been derived from magma that had completely solidified — transitioned from a mush to a rock."

"Nathan found that about half of the crystals began to crystallize a few thousand years before the eruption, indicating cooler conditions," says Brad Singer, a professor of geoscience at UW-Madison and director of the Geochronology Lab. "To get the true eruption age, you need to see the dispersion of dates. The youngest crystals show the date of eruption."

The results have meaning beyond volcanology, however, as ash from Long Valley and other giant eruptions is commonly used for dating.

"These huge eruptions deposit ash all over the place, and that lets you make correlations in the rock record to aid geologic, biologic and climatic studies across the continent," says Andersen. "This blanket of ash anchors you in time. The closer we can pin down the eruption age, the better we can study all facets of Earth's history."

"It's controversial, but finding these older crystals means that part of this large magma body was very cool immediately prior to eruption," says Singer, a volcanologist who was Andersen's UW advisor. "This flies in the face of a lot of thermodynamics."

A better understanding of the pre-eruption process could lead to better volcano forecasting – a highly useful but difficult proposition at present.

"This does not point to prediction in any concrete way," says Singer, "but it does point to the fact that we don't understand what is going on in these systems, in the period of 10 to 1 000 years that precedes a large eruption."

Provided by University of Wisconsin-Madison

Featured image: Laguna del Maule, whose geology resembles that of Long Valley, is a restive volcanic region in Chile that was the scene of many explosive eruptions over the last million years. It is undergoing the fastest uplift of any known volcanic region on Earth, possibly heralding a major eruption. Image credit: David Tenenbaum


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  1. Steven wrote: “It’s hard to understand how the rock could be heated from an estimated 400 °C … to the 700 to 850 °C … needed to erupt, but the main cause must be a quick rise of much hotter rock from deep below.”

    It is not hard to understand, Steven – a rapid rise in the temperature resulted in the explosion, that’s true – what would cause a rapid rise in the temperature?

    It’s easy to understand when you know the truth about our Earth but so long as you cling to theories, the chance of you understanding will be next to zero.

    If you want to know the the truth about our Earth, if you want the true timeline for the eruptions of the supervolcanoes, you can find them all in the historic documents – every one of them. None of them happened millions of years ago, none of the supervolcanoes erupted hundreds of thousands of years ago and none of them erupted thousands of years ago – shocking?

    If you cling to unsubstantiated ” millions of years ago ” nonsense, you will never know the truth about our Earth … you will tell yourself and others, ” … it’s hard to understand … ” when it is not hard to understand at all.

    If you want the true history of our Earth, study the old maps from the 1400’s through the 1800’s – which includes the maps of the Chinese, Japanese, Portuguese, French, Italian, Spanish, Greeks, Hebrews, Arabs, Dutch, etc. – study the old maps without assuming the map-makers and cartographers were all incompetent when it came to North America and Terra Australis – the Greeks and Hebrews were sailing since how long?

    As you begin to open your mind to the true history of our Earth, read the captain’s logs going back hundreds of years, study the bathymetric charts going back several decades, study dozens and dozens of topographic maps, study dozens of maps of the tectonic plates, subduction zones and volcanoes, study the history of the cities, study the illustrations of the landscapes all across the world from the 1400’s through the 1800’s, study the old photographs of the landscapes going back nearly 200 years – especially the illustrations and photos from the early Antarctic expeditions – read the descriptions of cataclysms in the old literature, etc. Study chemistry and physics for decades and study geological anomalies and cataclysms for decades – and then, if you have any intelligence, you will realize the geological timeline is a load of garbage and you will realize the fake biblical timeline of 6,000 years is also intentional disinfo.

    If you want to know the truth of our Earth, you can find in the historic documents – the exact date of the Eltanin tsunami, the exact date of the Nuuanu landslide and tsunami, you can discover the catastrophic decimation that resulted from the Nuuanu tsunami, you can find the exact date for the eruption of Long Valley, the exact date of the eruption of Yellowstone, Wah Wah Springs, etc. You can also have the exact date that the Grand Canyon was formed – if you think it wasn’t formed in one day, study the 600 foot high canyons resulting from the eruption of Mount St. Helens which stacked up in under two hours – even though the debris was estimated at only one cubic km while the supervolcanoes are over 1,000 cubic km.

    If you want to know the truth about our Earth, do a thorough study of the evidence recommended above and you will understand the forces that broke and subducted the tectonic plates, you will understand the forces that formed the island archipelago’s and the forces that formed the ocean trenches – all of this is found in the evidence going back 600 years.

    You can have the truth about the history of Antarctica and you will know the timeline from the ice core samples is another pile of lunacy.

    If you want to know when the tectonic plates of India and Tibet were fractured and subducted, you can find that in the historic documents as well.

    As you compile thousands of independent sources, from all across the world, you will realize our mountains are not millions of years old – none of them. You will realize the mountains are not even thousands of years old. You prefer to cling to lies? You are free to do so – but if you study the evidence, rather than believe in unsubstantiated speculation, you will cheat yourself out of knowing the truth. You are free to do this – I’m simply mentioning that thousands of independent sources from all across the world are available which corroborate one another and present a much shorter timeline for our mountains, volcanoes, continents, oceans, etc.

    The historic documents clearly show that the mountains are surprisingly young and the glaciers are also surprisingly young. The continents and oceans are also shockingly young. I don’t expect you to believe this, of course, I’m simply mentioning that if you want to look at the thousands of independent sources of evidence, it’s available for anyone who is unwilling to accept wild speculation from unintelligent science gods that are propped up the system that is controlled and manipulated by a small group.

    Since psychologists have uploaded the IQ’s of geologists – we know they are typically 85 to 115 – which is equivalent to the smart kid in sixth grade. If you want to trust your understanding of the history of our Earth to those with the intellect of an 11-year-old, you are free to do so. Meanwhile, the billionaires get their science reports from the magna cum laude PhD’s who graduated from highly-selective universities like Oxford, Cambridge, MIT, etc. – their IQ’s hover around 200 while the IQ of the geologists that the public gets are the C average graduates from low level institutions with IQ’s that are about 100 points lower. Keep in mind that the developmentally challenged have the mind of a child even though their IQ’s are typically only 15 to 20 points lower than average which is a quick reminder that the general public is five to ten times closer to having the mind of a child than they are to understanding the most brilliant scientists that work for the billionaires.

    If you want to believe the public is told the truth about geology, chemistry, our air and water, minerals, etc., you are free to cling to that fantasy – the truth is that the public is lied to about all that – like a child, most people bow down to their unintelligent fake science gods instead of wondering who owns the publishing houses that print the schoolbooks, college textbooks, the fake science magazines, etc. If you think science is sacred and no one would dare lie about it – not even for money – then consider yourself well programming.

    The truth about our Earth is awesome but you – and the public – are cheated out of knowing the truth because of the unintelligent fake science gods that prefer to be outside gawking at geological anomalies and then conjuring up their wild imaginings – we can’t expect those with the mind of an 11 year old to have the intellectual stamina to do decades of scholarly research.

    I don’t expect you to care about the truth, Steven. You’ve clearly swallowed – and regurgitated – what you were spoon-fed, which is something I refused to do. For me, listening to the professors was like watching children trying to explain the history of our Earth. I didn’t need psychologists to tell me geologists were simple-minded fools – I already knew it – the fact that they’re given job titles and paychecks doesn’t make them experts in the field of geology.

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