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  • richardmitnick 6:45 am on July 20, 2016 Permalink | Reply
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    From COSMOS: “Why supervolcanoes erupt with cataclysmic explosions” 

    Cosmos Magazine bloc


    20 July 2016
    Belinda Smith

    Russian geophysicist and artist Ivan Koulakov and colleagues have modelled magma reservoirs beneath supervolcanoes. Here is Koulakov’s impression of the Earth’s magmatic plumbing. Ivan Koulakov

    Lake Toba in North Sumatra today is a calm 100-kilometre stretch of water, flanked by green hills and rocky outcrops.

    But a mere 74,000 years ago, the region couldn’t have been more different: the supervolcano that forms the lake’s bowl blasted up to 5,300 square kilometres of hot rock and dust into the atmosphere and surface, leading to a volcanic winter which dropped global temperatures by 3 to 5 ºC for the best part of a decade.

    There’s no doubt these supereruptions are capable of widespread destruction.

    Some scientists believe the “Toba catastrophe” killed off most humans. And Toba today is one of many supervolcanoes scattered across the globe.

    To better understand why supervolcanoes erupt majestically then sit quiet for hundreds of thousands of years, rather than burble along at a moderate rate, a team from Egypt, France, Russia and Saudi Arabia delved into Toba’s plumbing and found it’s fed by a massive magma reservoir that gradually builds up over millennia before exploding.

    Russian Academy of Sciences Ivan Koulakov and colleagues examined how waves from earthquakes shook the region in 1995 and 2008.

    In particular, they looked at P-waves – which can course through liquid as well as rock and are the first waves of an earthquake to show up on a seismograph – and S-waves, which can only move through solids.

    From these they determined the complex, multi-level structure of the Earth 150 kilometres beneath the Toba caldera and movements of rock and volatiles such as water.

    The “magma factory” starts with the Indo-Australian plate, which is sliding underneath Indonesia at around 56 millimetres each year. It’s torn, too – one end is denser, and sinking faster, than the other end. The tear is known as the Investigator Fracture Zone and runs underneath the Toba caldera.

    At around 150 kilometres below the surface on the frature zone, the plate melts. Volatiles escape the rock to burble up through the mantle and fill a magma reservoir of around 50,000 square kilometres, which sits 30 to 50 kilometres below Lake Toba.

    The magma in the chamber is too dense to make its way any further and the overlying crust hems it in. But as more volatiles rise and join the reservoir, bringing heat with them, they cause more rocks to melt.

    When the molten upper crust is saturated with these volatiles, they cause what the researchers call an “avalanche-style process”. Overheated fluids turn to gases, increasing pressure in the reservoir and bam! The contents empty in a massive eruption.

    The process, then, begins again. It will repeat until the fracture zone is completely subducted.

    So is there going to be another Toba super-explosion soon? Koulakov thinks not – the next will happen in the next tens or hundreds of thousands of years. They found S-waves managed to move through the magma reservoir, signifying a large chunk of solid rock. If it was liquid, though, the next explosion would happen much sooner.

    The work was published in Nature Communications.

    See the full article here .

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  • richardmitnick 8:39 pm on May 15, 2016 Permalink | Reply
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    From livescience: “What Would Happen If Yellowstone’s Supervolcano Erupted?” 


    May 2, 2016
    Becky Oskin

    Hot springs in Yellowstone National Park are just one of the types of thermal features that result from volcanic activity. Credit: Dolce Vita / Shutterstock.com

    Although fears of a Yellowstone volcanic blast go viral every few years, there are better things to worry about than a catastrophic supereruption exploding from the bowels of Yellowstone National Park.

    Caldera at Yellowstone  Image not credited
    Caldera at Yellowstone Image not credited

    Scientists at the U.S. Geological Survey’s (USGS) Yellowstone Volcano Observatory always pooh-pooh these worrisome memes, but that doesn’t mean researchers are ignoring the possible consequences of a supereruption. Along with forecasting the damage, scientists constantly monitor the region for signs of molten rock tunneling underground. Scientists scrutinize past supereruptions, as well as smaller volcanic blasts, to predict what would happen if the Yellowstone Volcano did blow. Here’s a deeper look at whether Yellowstone’s volcano would fire up a global catastrophe.

    Probing Yellowstone’s past Most of Yellowstone National Park sits inside three overlapping calderas. The shallow, bowl-shaped depressions formed when an underground magma chamber erupted at Yellowstone. Each time, so much material spewed out that the ground collapsed downward, creating a caldera. The massive blasts struck 2.1 million, 1.3 million and 640,000 years ago. These past eruptions serve as clues to understanding what would happen if there was another Yellowstone megaexplosion.

    An example of the possible ashfall from a month-long Yellowstone supereruption. Credit: USGS –

    If a future supereruption resembles its predecessors, then flowing lava won’t be much of a threat. The older Yellowstone lava flows never traveled much farther than the park boundaries, according to the USGS. For volcanologists, the biggest worry is wind-flung ash. Imagine a circle about 500 miles (800 kilometers) across surrounding Yellowstone; studies suggest the region inside this circle might see more than 4 inches (10 centimeters) of ash on the ground, scientists reported* Aug. 27, 2014, in the journal Geochemistry, Geophysics, Geosystems.

    The ash would be pretty devastating for the United States, scientists predict. The fallout would include short-term destruction of Midwest agriculture, and rivers and streams would be clogged by gray muck. People living in the Pacific Northwest might also be choking on Yellowstone’s fallout. “People who live upwind from eruptions need to be concerned about the big ones,” said Larry Mastin, a USGS volcanologist and lead author of the 2014 ash study. Big eruptions often spawn giant umbrella clouds that push ash upwind across half the continent, Mastin said. These clouds get their name because the broad, flat cloud hovering over the volcano resembles an umbrella. “An umbrella cloud fundamentally changes how ash is distributed,” Mastin said. But California and Florida, which grow most of the country’s fruits and vegetables, would see only a dusting of ash. A smelly climate shift.

    Yellowstone Volcano’s next supereruption is likely to spew vast quantities of gases such as sulfur dioxide, which forms a sulfur aerosol that absorbs sunlight and reflects some of it back to space. The resulting climate cooling could last up to a decade. The temporary climate shift could alter rainfall patterns, and, along with severe frosts, cause widespread crop losses and famine.

    The walls of the Grand Canyon of Yellowstone are made up predominantly of lava and rocks from a supereruption some 500,000 years ago. Credit: USGS

    But a Yellowstone megablast would not wipe out life on Earth. There were no extinctions after its last three enormous eruptions, nor have other supereruptions triggered extinctions in the last few million years.

    “Are we all going to die if Yellowstone erupts? Almost certainly the answer is no,” said Jamie Farrell, a Yellowstone expert and assistant research professor at the University of Utah. “There have been quite a few supereruptions in the past couple million years, and we’re still around.” However, scientists agree there is still much to learn about the global effects of supereruptions. The problem is that these massive outbursts are rare, striking somewhere on Earth only once or twice every million years, one study found. “We know from the geologic evidence that these were huge eruptions, but most of them occurred long enough in the past that we don’t have much detail on what their consequences were,” Mastin said. “These events have been so infrequent that our advice has been not to worry about it.” A far more likely damage scenario comes from the less predictable hazards — large earthquakes and hydrothermal blasts in the areas where tourists roam. “These pose a huge hazard and could have a huge impact on people,” Farrell said.

    Supereruption reports are exaggerated

    Human civilization will surely survive a supereruption, so let’s bust another myth. There is no pool of molten rock churning beneath Yellowstone’s iconic geysers and mud pots. The Earth’s crust and mantle beneath Yellowstone are indeed hot, but they are mostly solid, with small pockets of molten rock scattered throughout, like water inside a sponge. About 9 percent of the hot blob is molten, and the rest is solid, scientists reported on May 15, 2015, in the journal Science. This magma chamber rests between 3 to 6 miles (5 to 10 km) beneath the park. Estimates vary, but a magma chamber may need to reach about 50 percent melt before molten rock collects and forces its way out. “It doesn’t look like at this point that the [Yellowstone] magma reservoir is ready for an eruption,” said Farrell, co-author of the 2015 study in the journal Science.

    How do researchers measure the magma? Seismic waves travel more slowly through hot or partially molten rock than they do through normal rock, so scientists can see where the magma is stored, and how much is there, by mapping out where seismic waves travel more slowly, Farrell said.

    The magma storage region is not growing in size, either, at least for as long as scientists have monitored the park’s underground. “It’s always been this size, it’s just we’re getting better at seeing it,” Farrell said.

    Watch out for little eruptions

    As with magma mapping, the science of forecasting volcanic eruptions is always improving. Most scientists think that magma buildup would be detectable for weeks, maybe years, preceding a major Yellowstone eruption. Warning signs would include distinctive earthquake swarms, gas emissions and rapid ground deformation.

    Someone who knows about these warning signals might look at the park today and think, “Whoa, something weird is going on!” Yellowstone is a living volcano, and there are always small earthquakes causing tremors, and gas seeping from the ground. The volcano even breathes — the ground surface swells and sinks as gases and fluids move around the volcanic “plumbing” system beneath the park.

    But the day-to-day shaking in the park does not portend doom. The Yellowstone Volcano Observatory has never seen warning signs of an impending eruption at the park, according to the USGS.

    What are scientists looking for? For one, the distinctive earthquakes triggered by moving molten rock. Magma tunneling underground sets off seismic signals that are different from those generated by slipping fault lines. “We would see earthquakes moving in a pattern and getting shallower and shallower,” Farrell said. To learn about the earthquake patterns to look for, revisit the 2014 eruption of Bardarbunga Volcano in Iceland. Both amateurs and experts “watched” Bardarbunga’s magma rise underground by tracking earthquakes. The eventual surface breakthrough was almost immediately announced on Twitter and other social media. As with Iceland, all of Yellowstone’s seismic data is publicly available through the U.S. Geological Survey’s Yellowstone Volcano Observatory and the University of Utah.

    “We would have a good idea that magma is moving up into the shallow depths,” Farrell said.

    “The bottom line is, we don’t know when or if it will erupt again, but we would have adequate warning.”

    *Science paper:
    Modeling ash fall distribution from a Yellowstone supereruption

    See the full article here .

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  • richardmitnick 9:19 pm on April 15, 2016 Permalink | Reply
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    From New Scientist: “Waking supervolcano makes North Korea and West join forces” 


    New Scientist

    15 April 2016
    Andy Coghlan

    The crater atop Mount Paektu. Raymond Cunningham/Getty

    If it blows again, it could make Vesuvius look like a tea party.

    Now, in a ground-breaking collaboration between the West and North Korea, vulcanologists are gaining new insights into Mount Paektu, on North Korea’s border with China, and whether it might blow its top any time soon.

    If it does, the outcome could be catastrophic. Paektu’s last eruption, a thousand years ago, is the second largest ever recorded, topped only by the eruption of Mount Tambora in Indonesia in 1815.

    “If it erupted, it would have impacts way beyond Korea and China,” says James Hammond of Birkbeck, University of London, one of the scientists involved.

    In 946 AD, the eruption of Mount Paektu, Korea’s highest mountain, blasted 96 cubic kilometres of debris into the sky, 30 times more than the relatively puny 3.3 cubic kilometres that Vesuvius spewed over Pompeii in AD 79.

    Yet despite is size and the potential impact of an eruption, little is known about this enigmatic volcano.

    Growing fears

    Western researchers got involved because the team investigating the volcano in North Korea, led by Ri Kyong-Song of the government’s Earthquake Administration in Pyongyang, needed access to extra scientific equipment and know-how.

    Chinese vulcanologists, who have been monitoring the volcano they call Changbaishan from their side of the border, also wanted more information from the Korean side.

    They and the Koreans have been monitoring the volcano closely ever since suspicious bulges were seen in and around the volcano between 2002 and 2005. These involved ground deformations measured by GPS, increased gas emissions and seismic rumbles.

    “It’s a priority for both countries, and both have monitoring networks on the volcano, keeping an eye on it,” says Hammond.

    Hammond and others from the West were invited to Korea in 2011 to install six seismometers at distances up to 60 kilometres from the volcano. These were sited to detect seismic waves from earthquakes elsewhere in the world passing through the ground beneath Paektu.

    Seismic waves travel at different speeds through solid and molten rock, giving the researchers crucial information about what lies beneath.

    The results reveal that there is indeed extensive magma beneath the volcano. “It’s a mushy mixture of molten rock and crystals that goes down right through the crust around 35 kilometres deep,” says Hammond.

    It’s rare to see a partially melted type of magma with such a large fluid component throughout the whole crust, he says.

    These are the first known estimates of the crustal structure of the volcano’s North Korea side and for anywhere beneath North Korea.

    The partially melted crust is a potential source for magma in past eruptions and it may be associated with the recent volcanic unrest there.

    At the moment, though, there’s no pool of liquid magma gathering near the surface – often a prelude to an eruption.

    “One of the challenges now is to go beyond simply saying there’s magma in the crust, discovering instead how it’s sitting, how much there is and what are the implications,” says Hammond. “It’s only when it gets to a certain amount and a certain overpressure that it will erupt.”

    At present, the researchers are not sure how much has to accumulate before the volcano erupts, he says.

    That’s why the collaboration is set to continue for some time, with Hammond due back in Pyongyang next week. “We’ll be discussing what we’ll do over the next 12 months, and longer term over the next five to 10 years,” says Hammond.

    After years working together, the two teams have got to know each other well, talking geology through an interpreter during the day, and in the evening heading for a restaurant or karaoke bar.
    No politics, just science

    “With what we’re doing, there’s no political element – we’re involved to understand a huge volcano, and the fact we’re having this dialogue is a great example of science transcending political differences,” says Hammond.

    Ri also spent a month in the UK finalising the results and the draft for publication*. “Our project is an example that it’s possible to build these collaborations and establish mutual trust,” says Hammond. “It’s been an advantage that our science doesn’t come with much political baggage.”

    North Korea is keen to open doors for more scientists through an institution called Piintec, Hammond says. “The Koreans are very open to science engagement in most areas.”

    “This is a bit of a first, in terms of a collaboration resulting in publication in a high-profile Western journal,” says Hammond.

    So next week, when he reaches Pyongyang, he and his Korean colleagues will be celebrating, probably in a karaoke bar in Pyongyang, drinking soju, the rice liquor popular in the country.

    “We get on very well,” says Hammond. “That’s why it works, through relationships and trust, and for that to work you need to understand each other.”

    Journal reference: Science Advances, DOI: 10.1126/sciadv.1501513

    *Science paper:
    Evidence for partial melt in the crust beneath Mt. Paektu (Changbaishan), Democratic People’s Republic of Korea and China

    Science team:
    Ri Kyong-Song1, James O. S. Hammond2,*, Ko Chol-Nam1, Kim Hyok1, Yun Yong-Gun1, Pak Gil-Jong1, Ri Chong-Song1, Clive Oppenheimer3, Kosima W. Liu4, Kayla Iacovino5 and Ryu Kum-Ran6

    1Earthquake Administration, Pyongyang, Democratic People’s Republic of Korea.
    2Department of Earth and Planetary Sciences, Birkbeck College, University of London, London WC1E 7HX, UK.
    3Department of Geography, University of Cambridge, Cambridge CB2 3EN, UK.
    4Environmental Education Media Project, Beijing 100025, China.
    5U.S. Geological Survey, Menlo Park, CA 94025, USA.
    6Pyongyang International Information Centre of New Technology and Economy, Pyongyang, Democratic People’s Republic of Korea.

    ↵*Corresponding author. E-mail: j.hammond@ucl.ac.uk

    See the full article here .

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  • richardmitnick 12:44 pm on April 14, 2016 Permalink | Reply
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    From SA: “Yellowstone’s Supervolcano Gets a Lid” 

    Scientific American

    Scientific American

    March 7, 2016 [Just appeared in social media.]
    Shannon Hall

    Steamboat geyser is just one of the 10,000 hot spots in Yellowstone National Park. Credit: Shannon Hall

    [Editor’s note: This story was corrected to say that a mantle plume emerges from the mantle and not the core on March 10, 2016]

    Simmering deep below the geysers and hot springs of the Yellowstone caldera is a dormant supervolcano—a powerful behemoth with the ability to blanket the western U.S. with many centimeters of ash in a matter of hours. What could spark such a powerful eruption? Scientists have long debated over the origins of Yellowstone’s supervolcano, with the most widely accepted idea suggesting that it was formed by a mantle plume—a column of hot rocks emerging from deep within our planet, in the mantle layer. But a new simulation shows that the conventional wisdom was wrong. The plume could not have reached the surface because it was blocked by a slab from an ancient tectonic plate.

    The simulation results of the model, which is the first to replicate the complex interaction between a mantle plume and a sinking slab, was detailed* last month in Geophysical Research Letters. Lijun Liu, a geologist at the University of Illinois at Urbana–Champaign, and his graduate student Tiffany Leonard built the model to replicate both the plate tectonic history of the surface and the geophysical image of Earth’s interior. “No one had modeled it this vigorously,” says Brandon Schmandt, a geologist at the University of New Mexico who was not involved in the study. Not only did Liu and Leonard create a three-dimensional view of Yellowstone’s underbelly, they did so over the past 40 million years in an attempt to re-create the eruptions that have dotted the U.S. from Oregon to Wyoming.

    No matter how they tweaked the parameters, Liu and Leonard could not re-create most of the recent eruptions. The reason is simple: “Slabs are the bully,” says Eugene Humphreys, a geophysicist at the University of Oregon who was also not involved in the study. “Plumes are just pretty wimpy in comparison.”

    The slab in question was driven deep into Earth’s mantle about 100 million years ago when the Pacific and North American plates began converging. Like a canoe paddle pushing through water, the mantle flows around the sinking slab causing pressure to build toward the front. But 15 million years ago the model shows that the pressure difference became too much to bear and the slab began to tear. The plume below pulsed through the slab, leading to massive outpourings of magma, the pattern and timing of which appear consistent with the Steens–Columbia River flood basalts, which spewed out one million times more molten rock than the 1980 Mount Saint Helens eruption.

    But that’s where the similarities between the model and geologic surface features end. Despite the gaping hole in the center of the sunken slab, the plume did not continue to rise through it. That is because the mantle is more like honey than water—it’s highly viscous. So as the slab continued to sink, it pulled the surrounding mantle down with it, ultimately sealing the hole and blocking the plume from reaching the surface for the next 15 million years. The favored hypothesis cannot explain the string of volcanic eruptions since those first flood basalts, including the formation of Yellowstone’s caldera, which happened only 2.1 million years ago. “Ultimately, we need a new explanation for Yellowstone’s formation,” Liu says.

    In other words, the team needs to find an additional heat source. Leonard thinks this could come from the Juan de Fuca Ridge—a jagged volcanic seam where magma oozes up between spreading plates to create a new seafloor—in the Pacific Ocean. Although that’s almost 1,600 kilometers away from Yellowstone’s hotspot today, the ridge can easily affect the middle of the North American Plate. Because it lies just slightly west of the Cascadia subduction zone, the young seafloor is easily shoveled east beneath the North American Plate. So it is likely that some event, millions of years ago, spurred a lot of heat within the Juan de Fuca Plate, which was then shoveled underneath the North American Plate and swept along with that string of volcanic eruptions until it eventually helped form Yellowstone’s gaping caldera in the Rocky Mountains.

    Although scientists will continue to argue over Yellowstone’s murky origin, the model makes it clear that slabs are much more important than previously thought. “It’s like smoke from a chimney that’s getting swept up in some sort of windstorm,” Humphreys says. “But it’s not this vigorous plume that just blasts through everything.”

    *Science paper:
    The role of a mantle plume in the formation of Yellowstone volcanism
    Science team:
    Lijun Liu, Tiffany Leonard

    University of Illinois at Urbana–Champaign

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  • richardmitnick 3:50 pm on February 17, 2016 Permalink | Reply
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    From Science Node: “Blue Waters solves Yellowstone mystery” 

    Science Node bloc
    Science Node

    17 Feb, 2016
    Lance Farrell

    Once Lijun Liu saw the proximity of subduction zones to supervolcanoes, the game was afoot. His NSF-funded research project is a harbinger of the age of numerical exploration.

    The Old Faithful geyser at Yellowstone National Park has thrilled park visitors for over a century, but it wasn’t until this year that scientists figured out the geophysical factors powering it.

    With over 2 million visitors annually, Yellowstone remains one of the most popular nature destinations in the US. Spanning an area of almost 3,500 square miles, the park sits atop the Yellowstone Caldera. This caldera is the largest supervolcano in North America, and is responsible for the park’s geothermal activity.

    Caldera at Yellowstone.
    Caldera at Yellowstone

    Until last week, most geologists had explained this activity with the so-called mantle plume hypothesis. This elegant theory proposed an idealized situation where hot columns of mantle rock rose from the core-mantle boundary all the way to the surface, fueling the supervolcano and the geothermal geysers.

    Supervolcanoes worldwide
    Neighborhood watch. A map of the worldwide distribution of supervolcanoes. The light reddish lines are subduction zones, the thick blue lines are mid-ocean ridges, and the size of the circles scales with the magnitude of supervolcanoes. Courtesy Lijun Liu.

    This theory didn’t sit well with Lijun Liu, assistant professor in the department of Geology at the University of Illinois, however. “If you look at the distribution of supervolcanoes globally, you’ll find something very interesting. You will see that most if not all of them are sitting close to a subduction zone,” Liu observes. “This close vicinity made me wonder if there were any internal relations between them, and I thought it was necessary and intriguing to further investigate this.”

    Solving the mystery

    To investigate the formation of Yellowstone volcanism, Liu and co-author Tiffany Leonard turned to the supercomputers at the Texas Advanced Computing Center (TACC) and the National Center for Supercomputing Applications (NCSA). Using Stampede for benchmarking work in 2014, and Blue Waters for modeling in 2015, Liu and Leonard ran 100 models, each requiring a few hundred core hours. The models weren’t too computationally intensive, using only 256 cores and generating only about 10 terabytes of data. In subsequent research, Blue Waters, more attuned to extreme scale calculations, has allowed Liu to scale up experiments up to 10,000 cores.

    Texas Stampede Supercomputer
    TACC Stampede

    Blue Waters supercomputer
    NCSA Blue Waters

    To make the Yellowstone discovery, Liu received valuable technical assistance from the Extreme Science and Engineering Discovery Environment (XSEDE). “We have been using XSEDE machines from very early on, Lonestar, Ranger, and, more lately, Stampede. We got a lot of assistance from XSEDE on installing the code, so by the time we got to this particular project we were pretty fluent using the code.”

    Liu and Leonard’s models, recently published in American Geophysical Union, simulated 40 million years of North American geological activity. By using the most well accepted history of surface plate motion and matching the complex mantle structure seen today with geophysical imaging techniques, Liu’s team imposed two powerful constraints to make sure their models didn’t deviate from reality. The models left little doubt that the flows of mantle beneath Yellowstone are actually modulated by moving plates rather than a single mantle plume.

    Analytical evolution

    According to Liu, prior to high-performance computing (HPC), debates about Yellowstone volcanic activity were like the proverbial blind men touching and describing the elephant. Without HPC, scientists lacked the geophysical data or imaging techniques to see under the surface. Most of the models of that time relied heavily on surface records only.

    “Numerical simulations are so important, especially now we are moving away from simple explanations and analytical solutions,” Liu admits. “We are definitely in the numerical era now. Most of these problems we couldn’t have solved a few years ago.”

    But with the advent of HPC and seismic tomography about 10 years ago, geologists were finally able to peer into the subsurface. By 2010, the scientific landscape had shifted dramatically when the US National Science Foundation (NSF) -funded nationwide seismic experiment called Earthscope unearthed an unprecedented amount of data and corresponding good imagery of the underlying mantle.

    From these images, geologists could see not only localized slow seismic structures called putative plumes, but also widespread fast anomalies often called slabs, or subducting oceanic plates. This breakthrough has created the opportunity for more questions, spawning even more models and hypotheses. Because of the complexity of the system, this is a situation ripe for HPC, Liu reasons.

    Understanding the volcanism powering Yellowstone is important because if this supervolcano erupts, it will affect a large area of the US. “That’s a real threat and a real natural hazard,” Liu quips. “But more seriously, if a mantle plume is powering the Yellowstone flows, then in theory its distribution could be more random — it can form almost anywhere. So it is possible that people in the Midwest who never worry about volcanoes are sitting right above a mantle plume.”

    But if the subduction process is more responsible for Yellowstone, and most of us sit further away from the subduction zone, we can rest a little bit easier.

    Liu’s research was made possible by funding from the NSF, support that procured not only supercomputing time but also student assistance. Providing an educational advantage is the more important benefit of NSF support, Liu says.

    In sum, Liu is convinced of the importance of HPC to the future of geological analysis. “HPC and models with a multidisciplinary theme should be the trend and should be encouraged for future research because this is really the way to solve complex natural systems like Yellowstone.”

    See the full article here .

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  • richardmitnick 11:08 am on November 16, 2015 Permalink | Reply
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    From livescience: “Earthquakes Could Trigger Massive Supervolcano Eruptions, Study Suggests” 


    November 13, 2015
    Charles Q. Choi

    In Yellowstone National Park, the rim of a supervolcano caldera is visible in the distance.Credit: National Park Service

    Supervolcanoes, such as the one dormant under Yellowstone National Park, may erupt when cracks form in the roofs of the chambers holding their molten rock, according to a new study.

    If scientists want to monitor supervolcanoes to see which ones are likely to erupt, this finding suggests they should look for telltale signs, such as earthquakes and other factors that might crack the magma chambers of these giant volcanoes.

    Supervolcanoes are capable of eruptions overshadowing anything in recorded human history — ones in the past could spew more than 500 times more magma and ash than Mount St. Helens did in 1980, the researchers said. These massive eruptions would also leave behind giant craters known as calderas that measure up to 60 miles (100 kilometers) wide. Twenty or so supervolcanoes exist today, including one beneath Yellowstone in the United States.

    Much remains unknown about what triggers supervolcano eruptions because no supervolcano has been active since the earliest human records began. Conventional volcanoes are known to erupt as molten rock flows into and pressurizes their magma chambers. However, previous research suggested this kind of trigger does not work for supervolcanoes, whose magma chambers can be dozens of miles wide and several miles thick — magma cannot fill these chambers fast enough to generate enough pressure for an eruption.

    “Supereruptions are very rare because they are very difficult to trigger,” study lead author Patricia Gregg, a volcanologist at the University of Illinois at Urbana-Champaign, told Live Science. “Part of what makes supereruptions so intriguing is that they are so infrequent. This indicates that there must be something different about supervolcano evolution and eruption versus smaller volcanoes that erupt more frequently.”

    Scientists recently suggested that supervolcanic eruptions occur because magma might be less dense than the rock surrounding it. This could force magma to buoy up through the ground, the way a balloon floats upward in water, potentially pressurizing magma chambers enough for eruptions.

    However, at supervolcano sites, “we don’t see a lot of evidence for pressurization,” Gregg said in a statement. When she and her colleagues incorporated magma buoyancy into their numerical models of supervolcanoes, they found it could not trigger eruptions.

    “We have ruled out a potential triggering mechanism for supereruptions,” Gregg said. “This is particularly important when investigating unrest at a supervolcano. If all it takes is buoyancy to trigger a catastrophic caldera-forming eruption, we should be very concerned when we see images of the large magmatic systems at Yellowstone and Toba, Indonesia, for example. However, through rigorous testing, we have found no link between buoyancy and the potential to erupt one of these systems. Buoyancy just does not produce a force strong enough to do it.”

    Yellowstone sits on top of four overlapping calderas. (US NPS)

    Instead, Gregg and her colleagues found the size of a supervolcano’s magma chamber is a much greater factor than magma buoyancy when it comes to eruptions.

    “As a magma chamber expands, it pushes the roof up and forms faults,” Gregg said in a statement. “As these very large magma chambers grow, the roof above may become unstable, and it becomes easier to trigger an eruption through faulting or failure within the rock.”

    The research team’s model suggests that, if a crack in the roof penetrates the magma chamber, the magma within uses the fault or crack as a vent to shoot to the surface. This could trigger a chain reaction that “unzips” the whole supervolcano, the researchers said.

    These findings suggest that if supervolcano eruptions are triggered by external factors, such as faults in the roofs of their magma chambers, “then we should look at seismicity, what types of faults are being developed, what is the stability of the roof and what kinds of activities are happening on the surface that could cause faulting,” Gregg said in a statement.

    In the future, Gregg and her colleagues want to use supercomputers to track the evolution of supervolcano magma chambers over time in greater detail. “I am very excited to see how the research develops over the next five to 10 years,” Gregg said.

    The scientists detailed their findings Nov. 2 at the annual meeting of the Geological Society of America in Baltimore

    See the full article here .

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