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  • richardmitnick 7:30 am on May 25, 2017 Permalink | Reply
    Tags: , , Geology, IDEAS.TED.COM, The amazing world that scientists are uncovering beneath the Earth’s crust   

    From IDEAS.TED.COM: “The amazing world that scientists are uncovering beneath the Earth’s crust” 

    1

    IDEAS.TED.COM

    May 24, 2017
    Hailey Reissman

    There are continents to explore right below our feet — including two giant blobs 100 times as tall as Everest. Here’s how seismologist and geophysicist Ed Garnero is studying this unseen and largely uncharted territory.

    For most people, everything they know about the composition of the Earth is what they were taught in elementary school: that our planet is made up of an eggshell-like crust over a thick mantle surrounding a super-hot core. In the last decade, scientists have made some super-interesting — and even strange or profound — discoveries that can add detail to that picture. Among their recent subterranean findings are a river of liquid metal that moves more swiftly than the tectonic plates, “bubbles” at the crust-mantle boundary, a new species of mineral that is somehow capable of holding water hundreds of miles within the mantle, chambers of magma where rocks are heating up like popcorn and expelled.

    3
    A visualization of the seismic waves from six Gulf of California earthquake events, over the years of 2007 to 2013, created by a team led by Manochehr Bahavar of the IRIS Data Management Center.

    Like the deep oceans, our planet’s innards are extremely difficult to study. Since humans can’t travel very far into the Earth (and certainly not the 3,963 miles to its core), investigation has largely depended upon the development of technology that can sense what lies below. The existence of tectonic plates was confirmed only around fifty years ago when sonar was used to map the ocean floor. Why is venturing below so difficult? For starters, the pressure. Just eight miles down, you’d feel the equivalent of 131 elephants of force pressing down on your head. And it’s unbearably hot. The temperature at the bottom of the top layer of the crust is roughly 1,600 degrees Fahrenheit. That’s breezy compared to the Earth’s core, which is thought to be about 10,800 degrees (as hot as the surface of the sun). So far, the farthest down that humans have tunneled is 7.6 miles.

    4
    Scientists have found two enormous, mysterious blobs of super-hot material that lie under the earth’s crust. In this visualization, seismic wave paths are shown passing through the blob. The blue and red features represent, respectively, high- and low-velocity material, discovered from tomography. Visualization by Ed Garnero.

    Geophysicists use seismometers to “see” inside the Earth, similar to how X-rays see inside our bodies. We tend to think of the Earth as fairly solid, except perhaps when hit by an earthquake. In reality, though, we live on chunks of crust that are constantly doing a dance that we can’t feel but scientists are always monitoring. For example, Phoenix, Arizona, rises and falls by about 40 centimeters twice a day, due to the sun’s and moon’s gravitational pulls. And Southern California has about 10,000 earthquakes a year, most a magnitude two or less. Each of these quakes — and every rise and fall — creates seismic waves that are recorded by instruments called seismometers. Like an X-ray machine, a seismometer assesses how energy moves through an object to infer what’s happening inside that object. Right now, the Global Seismographic Network (GSN) has more than 150 seismic stations distributed throughout the world, while the Incorporated Research Institutions for Seismology (IRIS) network includes over 250 stations.

    In 2016, Ed Garnero from Arizona State University’s School of Earth & Space Exploration (TEDxManhattanBeach talk: An amazing look into the center of the earth) and a team used this trove of seismological data to delve into an ongoing mantle mystery. For decades, geophysicists had observed seismic waves slowing down in two areas beneath the crust on roughly opposite sides of the Earth: one below the Pacific Ocean and the other below Africa. They discerned that the masses were huge — each the size of a continent, 100 times the height of Mount Everest, and around 1,800 miles beneath the surface. And they assumed the areas were extra-warm, since unusually hot zones can cause waves to slow down. Garnero and his researchers were determined to find out more. “They are the largest parts of our Earth that we [have identified but] know nothing about,” he says.

    Garnero’s team looked at the data — and made a major discovery. The giant blobs are not just a different temperature from the rest of the mantle; the researchers think they have a distinctly different chemical composition too. “We see from the seismic waves that go near the boundaries of the blobs that they split into a wave that goes into the blob and slows down, while a wave that continues along the blobs’ outside margin goes at normal speed,” Garnero says. “Scientists believe temperature alone cannot do that, so the blobs being compositionally distinct is the easiest explanation.” Researchers don’t know what the blobs are made of — yet — but they can tell the masses are denser and more stable than what’s around them. And they’re most likely feeding volcanoes. “On Earth above the blobs, there are volcanoes past and present, from small to massive,” Garnero says. For example, the hotspots that formed Hawaii, Samoa and Iceland are all fed by extremely deep plumes of magma that appear to be connected to the blobs.

    Which leads to the question: Where did these blobs come from? One intriguing theory is that they’re leftovers from our planet’s formation — remnants of some primordial layer of the Earth that eroded away over billions of years through the power of convection. “Our core ‘cooks’ the mantle rock, which makes up about half of the Earth, from below, causing it to slowly turn and move,” Garnero says. “If you did a timelapse of millions of years of Earth’s rocky mantle, you’d see it swirl around just like smoke moving around a bonfire.” And perhaps some of the material was swirled into forming the continent-sized blobs. Garnero and his team have used the seismic data to construct intriguing images of the Earth that include the mantle blobs, essentially giving us an MRI of our planet.

    5
    Inside the Earth’s mantle, heat from the core (in red) cooks the mantle rock (in blue), causing the rock to move like smoke around a bonfire. The motions visualized here would happen over a few million years. Visualization by Dr. Allen K. McNamara of Arizona State University.

    Garnero wants to share with the public the thrill of searching inside the Earth. Recently, he and a group of artists from Arizona State University, led by Lance Gharavi, created Beneath: a journey within, a film-music-dance performance designed to immerse the public in seismic data. Garnero says the cross-disciplinary collaboration has been exhilarating: “The scientists give the artists a platform to create, and then the artists give the scientists a new way to see their data.” The performance, which featured artists including a bass-playing geophysicist interacting with his data through trip-hop bass-lines and a belly-dancing theoretical astrophysicist embodying seismic waves, is being held inside a 3D theater on campus.

    Next for geophysicists: Combing through data from the world’s seismometers to add to the expanding pool of subterranean knowledge. In 2017, an extremely detailed map of the inner Earth was created by a team from Princeton University with the help of one of the world’s fastest supercomputers, Titan, which can perform over 20 quadrillion calculations per second.

    ORNL Cray XK7 Titan Supercomputer

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    This visualization provides another view of the two continent-sized blobs of unknown material, deep within the Earth. Created by geophysicists Scott W. French and Barbara Romanowicz of the Physique du Globe and the Collège de France and UC Berkeley.

    As for Garnero, his ambitions are galactic. He and his students are now working “to get the most detailed information out of seismic data,” he says, including revisiting an earlier study of the moon that confirmed it has a solid, iron-rich core. His department is also developing a tiny seismometer for NASA to take on a mission to Jupiter’s moon Europa; it would measure tremors on Europa’s crust and possibly locate as-yet-undiscovered bodies of water beneath its icy exterior. Designing such a device is not easy, according to Garnero. Seismometers are ultra-sensitive pieces of equipment, and this machine would need to be sturdy enough to handle a rough spacecraft landing and the other extremes that come with extraterrestrial travel.

    The key to future discoveries, either here on or on other spheres, lies in increasing the variety, amount and sensitivity of seismometers. “The more sensors we have, the more we study things like the blobs, and the more other things we can see,” Garnero says. “That’s good for me because that means there are more things to discover.”

    See the full article here .

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  • richardmitnick 12:23 pm on May 23, 2017 Permalink | Reply
    Tags: , Cosmic Muons Reveal the Land Hidden Under Ice, , Geology,   

    From Eos: “Cosmic Muons Reveal the Land Hidden Under Ice” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    5.23.17
    Jenny Lunn
    jlunn@agu.org

    Scientists accurately map the shape of the bedrock beneath a glacier using a new technique.

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    Aletsch glacier seen from Jungfraujoch. A tunnel runs through the bedrock below this glacier; researchers placed sensors within this tunnel to help map the shape of the bedrock under the ice. Credit: Alessandro Lechmann

    The land surface under a glacier is sculpted and shaped by the ice passing over it. Data about the shape of the bedrock yield information crucial to understanding erosional processes underneath a glacier. However, the inaccessibility of sites where glacial erosion currently occurs presents big challenges for advancing this understanding.

    A range of techniques has been used to map the bedrock beneath glaciers, including drilling, seismic surveys, multibeam bathymetry, gravity measurements, and radio-echo soundings. The accuracy of results has been limited, so Nishiyama et al [Geophysical Research Letters]. tested a different technique: emulsion film muon radiography.

    2
    A muon detector in the Jungfrau railway tunnel awaiting arrival of the cosmic ray muons. Credit: Nishiyama et al.

    Muons are formed when cosmic rays collide with atoms in Earth’s upper atmosphere. They descend toward Earth, with about 10,000 muons reaching each square meter of Earth’s surface every minute. One of their significant properties is that they can pass through matter, even dense and solid objects on Earth.

    Particle detectors can be used to measure the quantity of muons and their trajectories, which can reveal information about the materials that they have passed through.

    Because cosmic muons travel only downward, detectors need to be located below the objects to be surveyed. This technique has been used by geophysicists to scan the interior architecture of volcanoes, seismic faults, and caves and to detect carbon leaks, but it has posed a challenge for surveying the bedrock beneath glaciers.

    The team of researchers found a solution in the central Swiss Alps: the Jungfrau railway tunnel, which runs through the bedrock beneath the Aletsch glacier. They set up three particle detectors in the tunnel that are oriented upward with a view of the bedrock beneath the base of the largest glacier of Europe.

    3
    Three-dimensional reconstructed bedrock shape (blue) under the uppermost part of the Aletsch glacier. The shape of the interface was determined from the cosmic ray muon measurement performed at three muon detectors (D1, D2, and D3) along the railway tunnel (gray line). Bedrock that pokes through ice is in gray tones. Jungfraufirn is a small glacier that feeds the Aletsch glacier. Blue dots on the gray line represent points where scientists sampled rocks within the tunnel. The image is Figure 5b in Nishiyama et al.; dashed lines outline a cross section of this 3-D map that can be found in Figure 5c. Credit: Nishiyama et al.; base map from SWISSIMAGE, reproduced by permission of swisstopo (BA17061)

    Different types of particle detectors are available for muon radiography, but the team selected emulsion films, a special type of photographic film that can be used in remote and harsh environments because it does not require any electric power or computers for operation.

    Because of the density contrast between ice and rock, the patterns of muons captured on the film over a 47-day period could be used to accurately map the shape of the bedrock below the glacier.

    Using this technique, the researchers were able to map the bedrock-ice interface beneath the glacier over a 4000-square-meter area. They were also able to infer the glacier’s response to global warming. In particular, the team predicts a larger frequency of rock avalanches as the ice shrinks, exacerbated by reconstructed bedrock geometry beneath the glacier. This increase is of particular concern because buildings are situated on top of the bedrock. These include tourist facilities, a research station, and communications infrastructure, as well as the railway tunnel itself, which cuts through the bedrock.

    The use of cosmic muon radiography is spreading in various fields, including geophysics and civil engineering. This first application of the technique in glacial geology complements data collected by other methods and has the potential to be applied in other glacial locations underlain by a tunnel. (Geophysical Research Letters, https://doi.org/10.1002/2017GL073599, 2017)

    See the full article here .

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  • richardmitnick 12:05 pm on May 8, 2017 Permalink | Reply
    Tags: , Competing Models of Mountain Formation Reconciled, , , Geology   

    From Eos: “Competing Models of Mountain Formation Reconciled” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    5.8.17
    Andy Parsons

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    View towards Everest Base Camp along the Khumbu Valley, central Nepal, with Pumori (7,161 m) on the left and Nuptse on the right (7,861 m). These rocks have been exhumed from mid-crustal levels where they once formed a weak viscous flow during the early development of the Himalaya. Credit: Andy Parsons

    Andy Parsons was recently awarded the 2017 Ramsay Medal by the Geological Society of London for his research article published in Geochemistry, Geophysics, Geosystems [Parsons et al., 2016]. The Ramsay Medal is an annual international award for the best publication in the field of tectonics and structural geology during the last year from a postgraduate or recent postgraduate. His study tested datasets against different models of mountain formation to explain the evolution of the Himalaya, resolving some long-standing arguments between advocates of competing models. Andy answers some questions about research in this field.

    The Ramsay Medal is an annual international award for the best publication in the field of tectonics and structural geology during the last year from a postgraduate or recent postgraduate. His study tested datasets against different models of mountain formation to explain the evolution of the Himalaya, resolving some long-standing arguments between advocates of competing models. Andy answers some questions about research in this field.

    How did the Himalayan mountain chain form?

    50 million years ago, tectonic plate motion caused India to collide with Asia. This movement has continued ever since, resulting in formation of the world’s largest mountain range; the Himalaya. Understanding the geological processes responsible for the formation of mountain belts is challenging and, for many years, researchers have been debating two seemingly incompatible ideas for the formation of the Himalaya: channel flow and duplex formation.

    The channel flow model proposes that the Himalaya formed by southwards horizontal flow of a weak mid-crustal layer. Flow was driven by the weight of the overlying thickened crust, similar to the squeezing of a tube of toothpaste. On the other hand, duplex formation involves vertical stacking of multiple layers of the crust in a similar fashion to a wedge of snow piling upward as it is pushed by a plow. This model requires strong and rigid crust with deformation occurring along planes of weakness that allow slices of the crust to slide over and on top of each other.

    The mechanical differences between these models led many researchers to believe that they were mutually exclusive, and arguments for and against both models have been equally strong. More recent research in the Himalaya is beginning to show that these models are not mutually exclusive but rather operate at different times and positions during formation of the mountain belt. Key to this reconciliation is the recognition that the mechanical properties of the crust can vary in both space and time during the development of large, long-lived mountain belts.

    What particular aspects of mountain formation are the focus of your research?

    During continental collision, crustal thickening and erosion leads to uplift and exposure of rocks that were once located tens of kilometers below the surface. These rocks preserve a record of deformation that occurred at depth as the mountain belt was forming. My research focuses on unraveling this record of deformation at the macroscale in mountain-sides and cliff exposures and at the microscale in hand samples and crystal lattices. In particular, I look at the temperature and depth at which different rocks and minerals deform in order to determine how spatial and temporal variations in the mechanical properties of the crust control the formation of mountain belts.

    How does your research contribute to a new understanding or synthesis?

    The Himalaya comprises domains of rocks deformed at high temperatures deep within the crust, juxtaposed against domains rocks deformed at lower temperature and shallower depths. In our recent study we investigate rocks of both types, looking particularly at how the preserved record of deformation changed within and between these domains. By understanding how different minerals deform at different depths and temperature we were able to show how different parts of the Himalaya deformed under different conditions at different times. We found that deformation preserved in the high temperature domains matched the predictions of the channel flow model, whilst deformation preserved in the lower temperature domains matched the predictions of duplex formation.

    We also saw evidence of lower temperature deformation overprinting higher temperature deformation. This led us to the understanding that as the mid-crustal rocks cooled, they strengthened and transformed from a weak crustal flow to a strong crustal block. Thus, the channel flow model was applicable to the early high temperature evolution of rocks at mid-crustal levels and duplex formation applied to the lower temperature evolution of rocks at upper-crustal levels. Importantly, the overprinting relationship between different types of deformation corresponds to changes in pressures and temperature felt by rocks from mid-crustal levels as they were uplifted to the surface.

    What are the implications for better understanding mountain forming processes in other regions?

    Despite its complexities, the Himalaya has a relatively simple geological history. As such, it provides a unique opportunity to determine the physical properties that control the formation of mountain belts and how these properties are interrelated. Such studies provide an invaluable modern day analogue for studying ancient, eroded, and now inactive mountain belts of which the geological record presents only a muddled and incomplete snapshot. Our study contributes to a growing understanding that the development of mountain belts is controlled primarily by its mechanical properties and that these properties change over space and time.

    What are the major unsolved or unresolved questions in this field and where are additional data or modeling efforts needed?

    Conceptual and numerical models are always an approximation of reality. Numerical models provide valuable insight into the boundary conditions that control tectonic process. In the broadest sense, such models have demonstrated that deformation of the lithosphere may be defined by a generalized mechanical stratigraphy typically corresponding to the upper and lower crust and lithospheric mantle. The ability of these models to reproduce observations reported from the geological record is testament to their validity and importance. Despite this, we know from geological observations that the mechanical properties of the lithosphere are highly variable and such variabilities have a first order control on the distribution of deformation from scales of microns to kilometers.

    Our study and others also demonstrate how mechanical properties of rocks change drastically over time and space as they are pushed and pulled through different parts of a mountain chain. Bringing the capabilities of numerical simulation of lithospheric deformation closer to reality is one of the key efforts needed in the field of tectonics. At the same time, it is vital that researchers studying the geological record understand the boundary conditions that govern tectonic processes and how changes in these boundary conditions are reflected in the rocks that lie before them.

    See the full article here .

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  • richardmitnick 8:37 pm on May 5, 2017 Permalink | Reply
    Tags: , , Geology, , New theory on how Earth's crust was created   

    From McGill: “New theory on how Earth’s crust was created” 

    McGill University

    McGill University

    May 5, 2017

    1
    A composite image of the Western hemisphere of the Earth. Credit: NASA

    More than 90% of Earth’s continental crust is made up of silica-rich minerals, such as feldspar and quartz. But where did this silica-enriched material come from? And could it provide a clue in the search for life on other planets?

    Conventional theory holds that all of the early Earth’s crustal ingredients were formed by volcanic activity. Now, however, McGill University earth scientists Don Baker and Kassandra Sofonio have published a theory with a novel twist: some of the chemical components of this material settled onto Earth’s early surface from the steamy atmosphere that prevailed at the time.

    First, a bit of ancient geochemical history: Scientists believe that a Mars-sized planetoid plowed into the proto-Earth around 4.5 billion years ago, melting the Earth and turning it into an ocean of magma. In the wake of that impact – which also created enough debris to form the moon — the Earth’s surface gradually cooled until it was more or less solid. Baker’s new theory, like the conventional one, is based on that premise.

    The atmosphere following that collision, however, consisted of high-temperature steam that dissolved rocks on the Earth’s immediate surface — “much like how sugar is dissolved in coffee,” Baker explains. This is where the new wrinkle comes in. “These dissolved minerals rose to the upper atmosphere and cooled off, and then these silicate materials that were dissolved at the surface would start to separate out and fall back to Earth in what we call a silicate rain.”

    To test this theory, Baker and co-author Kassandra Sofonio, a McGill undergraduate research assistant, spent months developing a series of laboratory experiments designed to mimic the steamy conditions on early Earth. A mixture of bulk silicate earth materials and water was melted in air at 1,550 degrees Celsius, then ground to a powder. Small amounts of the powder, along with water, were then enclosed in gold palladium capsules, placed in a pressure vessel and heated to about 727 degrees Celsius and 100 times Earth’s surface pressure to simulate conditions in the Earth’s atmosphere about 1 million years after the moon-forming impact. After each experiment, samples were rapidly quenched and the material that had been dissolved in the high temperature steam analyzed.

    The experiments were guided by other scientists’ previous experiments on rock-water interactions at high pressures, and by the McGill team’s own preliminary calculations, Baker notes. Even so, “we were surprised by the similarity of the dissolved silicate material produced by the experiments” to that found in the Earth’s crust.

    Their resulting paper, published in the journal Earth and Planetary Science Letters, posits a new theory of “aerial metasomatism” -– a term coined by Sofonio to describe the process by which silica minerals condensed and fell back to earth over about a million years, producing some of the earliest rock specimens known today.

    “Our experiment shows the chemistry of this process,” and could provide scientists with important clues as to which exoplanets might have the capacity to harbor life Baker says.

    “This time in early Earth’s history is still really exciting,” he adds. “A lot of people think that life started very soon after these events that we’re talking about. This is setting up the stages for the Earth being ready to support life.”

    See the full article here .

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    All about McGill

    With some 300 buildings, more than 38,500 students and 250,000 living alumni, and a reputation for excellence that reaches around the globe, McGill has carved out a spot among the world’s greatest universities.
    Founded in Montreal, Quebec, in 1821, McGill is a leading Canadian post-secondary institution. It has two campuses, 11 faculties, 11 professional schools, 300 programs of study and some 39,000 students, including more than 9,300 graduate students. McGill attracts students from over 150 countries around the world, its 8,200 international students making up 21 per cent of the student body.

     
  • richardmitnick 12:52 pm on May 4, 2017 Permalink | Reply
    Tags: , Geology, Hawaii volcanoes, Hot spot, Pacific Plate, Tectonic swerve responsible for creation of Hawaiian islands,   

    From COSMOS: “Tectonic swerve responsible for creation of Hawaiian islands” 

    Cosmos Magazine bloc

    COSMOS

    04 May 2017
    Andrew Masterson

    A change in direction of the Pacific Plate 3 million years ago created the conditions for turbulent volcanic eruptions.

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    Pu‘u ‘O‘o, a volcanic cone on Kilauea, Hawaii. G. E. Ulrich

    Hawaii was born in fire and eruption and today boasts the biggest and most active volcanoes in the world – a fact that has long puzzled geologists.

    The islands – which together comprise 20 extinct or active volcanoes – are situated well away from tectonic plate boundaries, the moving stress zones that typically produce volcanism.

    Now, however, questions surrounding the mysteries of Hawaii’s origin have been answered, thanks to research led by Tim Jones from Australian National University.

    The research, published in Nature, found that the volcanoes were catalysed three million years ago by a sudden change of direction by the Pacific Plate, the 103-million-square-kilometre tectonic plate that has Baja California at one end, New Zealand at the other – and Hawaii pretty much in the middle.

    As early as 1849, geologists – notably American explorer James Dwight Dana – suggested that Hawaii arose because the earth beneath the seabed was moving in two directions.

    In 1963, Canadian geophysicist J. Tuzo Wilson developed the theory by posting the existence of a “hot spot” – a section of the mantle through which a thermal plume rises, melting the rock above. Magma from beneath the mantle rises up, and forms a volcano. Gradually, each new volcano moves away from the hotspot, which then repeats the process.

    Indeed, the volcanoes and submerged mountains that extend northwest from Hawaii grow progressively more ancient the further away they are from the islands.

    Using complex computer modeling, Jones and colleague Rhodri Davies have effectively confirmed Dana’s and Wilson’s insights.

    “The analysis we did on past Pacific Plate motions is the first to reveal that there was a substantial change in motion three million years ago,” says Jones.

    “It helps to explain the origin of Hawaii, Earth’s biggest volcanic hotspot.”

    Once the critical section of the Pacific Plate had shifted course, its movement was at odds with the force of the thermal plume, thus creating the conditions for turbulent eruptions.

    The change of direction that caused the volcanic birth of the islands is not unique. Jones said something similar happened to bring Samoa into existence, at roughly the same time.

    Three million years might seem like a very long period, but in geologic terms it is nothing special. At some point in the future, the researchers predict, the misalignment of plate and plume may well fix itself.

    “Our hypothesis predicts that the plate and the plume will realign again at some stage in the future, and the two tracks will merge to form a single track once again,” says Davies.

    See the full article here .

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  • richardmitnick 7:51 am on April 25, 2017 Permalink | Reply
    Tags: , , Geology, Rock Avalanches   

    From Eos: “What Causes Rock Avalanches?” 

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    Eos news bloc

    Eos

    4.24.17
    Terri Cook

    1
    A giant rock avalanche preserved in the Nyainqentanglha Mountains of the Tibetan Plateau, China. Researchers use soil sampled from the avalanche to assess the mechanics behind the frictional weakening of the soil and its implications for the hypermobilty of rock avalanches. Credit: Yufeng Wang.

    Rock avalanches, sudden rock slope failures characterized by very rapid velocities, long runouts, and large volumes, pose some of the most dangerous and expensive geological hazards in mountainous regions. Although numerous mechanisms, including air pockets, fine powder along their base, and elevated pore fluid pressure, have been proposed to explain rock avalanches’ distinctive characteristics, the specific reasons for their “hypermobility” are still vigorously debated by scientists.

    To improve our understanding of what causes these disasters, Wang et al. conducted a series of laboratory tests to examine the weakening mechanisms that contributed to the high-speed motion of the Yigong rock avalanche on the Tibetan Plateau in 2000. This event dislodged 110 million cubic meters of material, which traveled more than 10 kilometers in 10 minutes before reaching and damming the Yigong River. Two months later, when the river finally broke through the avalanche debris, it unleashed a devastating flood that killed 94 people and destroyed the homes of more than 2 million citizens.

    Using a shear rotary apparatus, which rapidly rotates ring-shaped samples to simulate motion along a fault, the team varied the rate at which they applied shear stress to samples of soil obtained from the base of the Yigong rock avalanche and then analyzed each deformed sample’s features. The results indicate that elevated temperatures caused by frictional heating weakened the Yigong basal soil through the combined effects of two mechanisms: moisture fluidization, which both lubricates the sample and reduces the adhesion between its fine particles, and thermal pressurization, which causes friction-heated water to expand, further weakening the fault zone.

    Although the generation of nanoparticles from particle fragmentation may also facilitate soil weakening, this mechanism did not play a key role in generating the Yigong rock avalanche, the team reports. The results have implications for researchers in many geologic disciplines, including landslide dynamics, earthquake mechanics, and risk assessment. (Journal Geophysical Research: Solid Earth, https://doi.org/10.1002/2016JB013624, 2017)

    See the full article here .

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  • richardmitnick 2:39 pm on April 21, 2017 Permalink | Reply
    Tags: Antarctic bedrock, , Geology, The Antarctic Sun, US Antarctic Program   

    From The Antarctic Sun: “Ancient Ice Levels” Very cool. 

    USAP

    The Antarctic Sun

    April 20, 2017
    Michael Lucibella

    Scientists drill into Antarctic bedrock to see if the Icy Continent was once a bit less icy

    1
    The scientists and drillers set up camp at the foot of Mount Tidd in the Pirrit Hills. Photo Credit: John Stone

    Today, a massive sheet of ice covers nearly all of West Antarctica, but it likely hasn’t always been that way.

    2
    After positioning the drill platform, engines and hydraulic controls, IDDO drillers Mike Jayred (right) and Tanner Kuhl (center) look on as Clayton Armstrong raises the drill mast. Photo Credit: John Stone

    Over the past few hundred thousand years, researchers think that the ice sheets have waxed and waned, varying in size as the region’s climate changed. As they fluctuated, the ice sheets would have captured so much frozen water that sea levels around the world would have risen and dropped accordingly.

    The fate of the Antarctic ice sheets affects all parts of the planet. For scientists modelling future climate, the role the ice sheets play is one of the great unknowns, but it would certainly be significant. They estimate that if the entire West Antarctic Ice Sheet were to collapse, for example, it could raise global sea level by up to 15 feet on average.

    Counterintuitively, because of the interactions between the ice sheet and the Earth’s crust, the Northern Hemisphere would experience the biggest sea level rise from melting Antarctic ice.

    To gather hard geologic evidence of how dynamic the ice cover has been in the past, and may be in the future, John Stone of the University of Washington and his team traveled to a remote region of the continent this past season.

    “The aim of this project is to determine whether the ice sheet in West Antarctica has been thinner in the past,” Stone said. “Whether it has collapsed and contracted to a much smaller version of its present self.”

    3
    Once the drill was erected, the team built a tent around it to shelter drilling operations from snow and winds. Photo Credit: John Stone

    They flew deep into the barren landscape to drill down and collect a bedrock sample buried under more than 100 meters of ice. By analyzing its atomic properties, they’re able to test to see whether there was a time when the ice sheets of West Antarctica were once just a shadow of what they are today. The research was supported by the National Science Foundation, which manages the U.S. Antarctic Program.

    “There’s a good deal of evidence from sea level change that ice sheets globally were smaller during the last interglacial 125,000 years ago,” Stone said. “So it’s widely presumed that West Antarctica participated in that deglaciation that led to higher sea levels.”

    The researchers needed to get at the underlying bedrock beneath the ice that covers most of the continent today. They’re looking for evidence that the rocks once laid out on the surface, free of ice and totally exposed to cosmic rays. While it’s common for glacial researchers to analyze rocks on the surface to see how long they’ve been exposed, taking rock cores from beneath the ice is new.

    “The cosmic radiation interacts with… and induces nuclear reactions inside the minerals of rocks, and changes atoms from one chemical isotope to another,” Stone said. “When rocks become exposed to cosmic rays they begin to build up quantities of isotopes like beryllium-10, aluminum-26, chlorine-36, helium-3 and neon-21, which are otherwise very rare isotopes.”

    Many of these atomic variants are radioisotopes that are unstable and break down into other stable isotopes through radioactive decay. These radioisotopes build up as long as the rocks are exposed, but when these rocks are buried underneath multiple feet of cosmic-ray blocking ice, the radioisotopes break down at predictable rates.

    4
    IDDO driller Mike Jayred (left) prepares to add a rod to the drill string while coring the pilot hole at the first site. Photo Credit: John Stone

    Different isotopes have different rates of decay, or “half-lives,” which range from a few microseconds, to billions of years. Stone and his team focused on isotopes that have half-lives in the thousands and millions of years. By looking at the ratios of these different isotopes, the researchers can discern when the last time this rock had been exposed, and from that, the history of the ice sheet over the last few hundred thousand years.

    “We will measure a whole family of isotopes which have different radioactive half-lives,” Stone said. “By comparing the concentrations of those isotopes, we’ll be able to tell whether the exposure was a long time in the past, or whether it happened fairly recently.”

    In order to get to the rock still covered in ice, the team worked with a drill designed by the U.S. Ice Drilling Program for subglacial bedrock drilling known as the Agile Sub-Ice Geologic drill, or the ASIG drill. It’s adapted from a commercially available drill used for mineral exploration, but with a number of modifications to make it better at drilling through ice rather than rock.

    The team originally hoped to take two cores during their field season. Unfortunately, just feet away from finishing their first hole, there was a problem and it had to be abandoned.

    “That was a big disappointment, especially because it was the first of the two holes,” Stone said.

    What exactly happened is still unclear, but after several days of troubleshooting, they made the decision to give up on their first attempt. Despite the setback, they focused on making sure their second attempt was successful.

    5
    Geologists Perry Spector (foreground) and Trevor Hillebrand prepare to collect a rock sample from glacial deposits on Mt Tidd. In addition to the drill cores, scientists collected rock samples to study the history of the ice sheet above the current ice surface. Photo Credit: John Stone

    “We were able to get some auger bits flown out to us which simplified the business of getting a pilot hole drilled quickly, and with that done we were able to get a second hole started very efficiently,” Stone said. “The drill functioned exactly as it was meant to function for the second hole. It was really a very impressive performance actually.”

    Six days later, after cutting through 150 meters of ice, the researchers bored into the bedrock and extracted an eight-meter rock core.

    “These long profiles give you an idea of how far into rock cosmic rays penetrate,” Stone said. “Five or six feet, maybe a little further is the typical length of the profile where you’ll see the abundance of cosmic ray produced isotopes.”

    Picking the right spot was key for recovering the right kind of rock. The Pirrit Hills are an isolated collection of mountain peaks projecting out of the massive ice sheet in the middle of West Antarctica.

    “The Pirrit Hills are a beautiful place,” Stone said. “They’re actually quite substantial mountains, they’re called the Pirrit Hills but the three big peaks are sort of granite towers that are up to 800 or 900 meters above the ice sheet at that point.”

    These mountaintops, known as nunataks when only their peaks protrude out of the ice, are the ideal location in the region in part because they’re made of granite, the best material for isolating these radioisotope ratios.

    “Our knowledge of the subglacial geology and where different rock types are is not excellent over Antarctica,” said Perry Spector, also at the University of Washington. “So the fact that we’re right next to a mountain, a nunatak of granite, means that if we go just a little bit off board of there and drill down, we’re almost guaranteed to hit granite.”

    6
    Clayton Armstrong lowers a core tube into the ASIG drill string prior to drilling the final section of bedrock core as drilling engineer Tanner Kuhl looks on. Photo Credit: John Stone

    The team had visited these peaks before. In 2013 and 2014 they traveled to the Pirrit Hills and two other nunataks in the region, to determine where would be best to drill, and to collect samples up the slopes of the exposed mountaintops.

    “We have samples that currently go from hundreds of meters above the ice, all the way down ridges in the Pirrit Hills, finally at the ice level we have several samples, and our drill core will be the next two samples down the profile,” Stone said.

    Collectively, these samples will give researchers a comprehensive picture of the ice sheet over thousands of years.

    “The ones below the ice sheet can tell us information about if and when the ice has been thinner there, but the ones above the modern ice level can tell you information about if and when the ice was thicker in the past,” Spector said. “You can get information about both times when the West Antarctic ice sheet was thicker and more extensive than it is now, as well as information about if and when it was thinner and less extensive.”

    The Pirrit Hills are also in a key location on the ice sheet itself, a spot that acts like a bellwether, which can reveal much about the West Antarctic Ice Sheet as a whole.

    “Part of the site selection was to find a place where ice thinning would be sensitive to a large scale change in the ice sheet,” Stone said. “Ice sheet model calculations suggest that you’d be looking at substantial deglaciation of West Antarctica in order to uncover that rock.”

    7
    The scientists and drillers recovered 8 meters, or about 26 feet, of bedrock granite. Each section fit perfectly with the sections above and below it, ensuring a complete, uninterrupted record of cosmogonic isotopes. Photo Credit: John Stone

    The researchers are looking to the past to better understand what happens to the massive ice sheets in West Antarctica as climates warm in the modern day.

    “We think of it very much as a test of the sensitivity of ice sheets to climate change,” Stone said. “If we can establish which climates endanger the West Antarctic Ice Sheet then I think we can really make confident statements about future climates and the likely response of the Antarctic ice sheet to that. We sort of see it as looking at the vulnerability of the ice sheet to future climate change.”

    Understanding how the ice sheet behaved in past warm periods takes on extra importance as researchers are now trying to predict what might happen around the world as the current climate warms. As ice sheets melt, that water will flow into oceans and cause sea levels around the world to rise. Understanding how much the West Antarctic Ice Sheet is likely to melt will go a long way towards predicting how much extra water may end up in the oceans.

    Even though the West Antarctic Ice Sheet is on the far side of the planet, it would have a big impact in North America should it collapse. Counterintuitively, the Northern Hemisphere would experience the biggest sea level rise from melting Antarctic ice.

    “[The] deglaciation of Antarctica, rather than Greenland, actually has bigger effects in North America than the same amount of ice being released from Greenland,” Stone said.

    The huge weight of such a massive ice sheet actually deforms the Earth’s crust, flattening it out slightly. Should that ice melt and flow into the oceans, the planet’s surface would rebound and rise up, displacing that water towards the Northern Hemisphere.

    After spending about two months at the site, the team returned with the rock core that they’re now starting to process and analyze.

    “We’ve already started to cut sections from the core,” Stone said.

    They still need to carefully separate the pure mineral samples they want to analyze for the cosmic-ray produced isotopes within.

    “We’ve got measurements planned for four or possibly five cosmic ray produced isotopes in this rock,” Stone said. “They all have different half-lives, so by comparing them we will be able to get information about not only whether the rock was exposed but when.”

    NSF-funded research in this story: John Stone, University of Washington

    See the full articled here .

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  • richardmitnick 8:24 am on April 19, 2017 Permalink | Reply
    Tags: , Climate Change Reroutes a Yukon River in a Geological Instant, , Geology, , Kaskawulsh Glacier, , Slims River Valley   

    From NYT: “Climate Change Reroutes a Yukon River in a Geological Instant” 

    New York Times

    The New York Times

    APRIL 17, 2017
    JOHN SCHWARTZ

    1
    An aerial view of the ice canyon that now carries meltwater from the Kaskawulsh Glacier, on the right, away from the Slims River. “River piracy” refers to one river capturing and diverting the flow of another. Credit Dan Shugar/University of Washington-Tacoma

    In the blink of a geological eye, climate change has helped reverse the flow of water melting from a glacier in Canada’s Yukon, a hijacking that scientists call “river piracy.”

    This engaging term refers to one river capturing and diverting the flow of another. It occurred last spring at the Kaskawulsh Glacier, one of Canada’s largest, with a suddenness that startled scientists.

    A process that would ordinarily take thousands of years — or more — happened in just a few months in 2016.

    Much of the meltwater from the glacier normally flows to the north into the Bering Sea via the Slims and Yukon Rivers. A rapidly retreating and thinning glacier — accelerated by global warming — caused the water to redirect to the south, and into the Pacific Ocean.

    Last year’s unusually warm spring produced melting waters that cut a canyon through the ice, diverting more water into the Alsek River, which flows to the south and on into Pacific, robbing the headwaters to the north.

    2
    Jim Best, a researcher, measuring water levels on the lower-flowing Slims River in early September. Credit Dan Shugar/University of Washington-Tacoma

    The scientists concluded that the river theft “is likely to be permanent.”

    Daniel Shugar, an assistant professor of geoscience at the University of Washington-Tacoma, and colleagues described the phenomenon in a paper published on Monday in the journal Nature Geoscience.

    River piracy has been identified since the 19th century by geologists, and has generally been associated with events such as tectonic shifts and erosion occurring thousands or even millions of years ago. Those earlier episodes of glacial retreat left evidence of numerous abandoned river valleys, identified through the geological record.

    In finding what appears to be the first example of river piracy observed in modern times, Professor Shugar and colleagues used more recent technology, including drones, to survey the landscape and monitor the changes in the water coursing away from the Kaskawulsh Glacier.

    2
    Kaskawulsh glacier junction from air
    29 August 2014
    Author Gstest

    The phenomenon is unlikely to occur so dramatically elsewhere, Professor Shugar said in a telephone interview, because the glacier itself was forming a high point in the landscape and serving as a drainage divide for water to flow one way or another. As climate change causes more glaciers to melt, however, he said “we may see differences in the river networks and where rivers decide to go.”

    Changes in the flow of rivers can have enormous consequences for the landscape and ecosystems of the affected areas, as well as water supplies. When the shift abruptly reduced water levels in Kluane Lake, the Canadian Broadcasting Corporation reported, it left docks for lakeside vacation cabins — which can be reached only by water — high and dry.

    The riverbed of the Slims River basin, now nearly dry, experienced frequent and extensive afternoon dust storms through the spring and summer of last year, the paper stated.

    3
    The ice-walled canyon at the terminus of the Kaskawulsh Glacier, with recently collapsed ice blocks. This canyon now carries almost all meltwater from the toe of the glacier down the Kaskawulsh Valley and toward the Gulf of Alaska. Credit Jim Best/University of Illinois

    The impacts of climate change, like sea level rise or the shrinkage of a major glacier, are generally measured over decades, not months as in this case. “It’s not something you could see if you were just standing on the beach for a couple of months,” Professor Shugar said.

    The researchers concluded that the rerouted flow from the glacier shows that “radical reorganizations of drainage can occur in a geologic instant, although they may also be driven by longer-term climate change.” Or, as a writer for the CBC put it in a story about the phenomenon last year, “It’s a reminder that glacier-caused change is not always glacial-paced.”

    4
    Looking up the Slims River Valley, from the south end of Kluane Lake. The river used to flow down the valley from the Kaskawulsh glacier. (Sue Thomas)

    The underlying message of the new research is clear, said Dr. Shugar in a telephone interview. “We may be surprised by what climate change has in store for us — and some of the effects might be much more rapid than we are expecting.”

    The Nature Geoscience paper is accompanied by an essay from Rachel M. Headley, an assistant professor of geoscience and glacier expert at the University of Wisconsin-Parkside.

    “That the authors were able to capture this type of event almost as it was happening is significant in and of itself,” she said in an interview via email. As for the deeper significance of the incident, she said, “While one remote glacial river changing its course in the Yukon might not seem like a particularly big deal, glacier melt is a source of water for many people, and the sediments and nutrients that glacier rivers carry can influence onshore and offshore ecological environments, as well as agriculture.”

    Her article in Nature Geoscience concludes that this “unique impact of climate change” could have broad consequences. “As the world warms and more glaciers melt, populations dependent upon glacial meltwater should pay special attention to these processes.”

    Another glacier expert not involved in the research, Brian Menounos of the University of Northern British Columbia, said that while glaciers have waxed and waned as a result of natural forces over the eons, the new paper and his own research underscore the fact that the recent large-scale retreat of glaciers shows humans and the greenhouse gases they produce are reshaping the planet. “Clearly, we’re implicated in many of those changes,” he said.

    See the full article here .

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  • richardmitnick 12:44 pm on April 17, 2017 Permalink | Reply
    Tags: , Geology, Mis-Atlantic Ridge, Plate techtonics,   

    From Universe Today: “What is the Mid-Atlantic Ridge?” 

    universe-today

    Universe Today

    17 Apr , 2017
    Matt Williams

    1
    The age of the oceanic crust – red is most recent, and blue is the oldest – which corresponds to the location of mid-ocean ridges. Credit: NCEI/NOAA

    If you took geology in high school, then chances you remember learning something about how the Earth’s crust = the outermost layer of Earth – is arranged into a series of tectonic plates. These plates float on top of the Earth’s mantle, the semi-viscous layer that surrounds the core, and are in constant motion because of convection in the mantle. Where two plates meet, you have what it is known as a boundary.

    These can be “divergent” or “convergent”, depending on whether the plates are moving apart or coming together. Where they diverge, hot magma can rise from below, creating features like long ridges or mountain chains. Interestingly enough, this is how one of the world’s largest geological features was formed. It called the Mid-Atlantic Ridge, which run from north to south along the ocean floor in the Atlantic.

    Description:

    The Mid-Atlantic Ridge (MAR) is known as a mid-ocean ridge, an underwater mountain system formed by plate tectonics. It is the result of a convergent plate boundary that runs from 87° N – about 333 km (207 mi) south of the North Pole – to 54 °S, just north of the coast of Antarctica.

    2
    The different types of Tectonic Plate Boundaries, ranging from convergent and transform to divergent. Credit: USGS/Jose F. Vigil

    3
    Small image showing the location of the Mid-Atlantic ridge. Wikipedia

    Like other ocean ridge systems, the MAR developed as a consequence of the divergent motion between the Eurasian and North American, and African and South American Plates. In the North Atlantic, it separates the Eurasian and North American Plates; whereas in the South Atlantic, it separates the African and South American Plates.

    The MAR is approximately 16,000 km (10,000 mi) long and between 1,000 and is 1,500 km (620 and 932 mi) wide. The peaks of the ridge stand about 3 km (1.86 mi) in height above the ocean floor, and sometimes reach above sea level, forming islands and island groups. The MAR is also part of the longest mountain chain in the world, extending continuously across the oceans floors for a total distance of 40,389 km (25,097 mi).

    The MAR also has a deep rift valley at is crest which marks the location where the two plates are moving apart. This rift valley runs along the axis of the ridge for nearly its entire length, measuring some 80 to 120 km (50 to 75 miles) wide. The rift marks the actual boundary between adjacent tectonic plates, and is where magma from the mantle reaches the seafloor.

    Where this magma is able to reach the surface, the result is basaltic volcanoes and islands. Where it is still submerged, it produces “pillow lava”. As the plates move further apart, new ocean lithosphere is formed at the ridge and the ocean basin gets wider. This process, known as “sea floor spreading”, is happening at an average rate of about 2.5 cm per year (1 inch).

    The tectonic plates of the world were mapped in 1996, USGS.

    In other words, North America and Europe are moving away from each other at a very slow rate. This process also means that the basaltic rock that makes up the ridge is younger than the surrounding crust.
    Notable Features:

    As noted, the ridge (while mainly underwater) does have islands and island groups that were created by volcanic activity. In the Northern Hemisphere, these include Jan Mayen Island and Iceland (Norway), and the Azores (Portugal). In the Southern Hemisphere, MAR features include Ascension Island, St. Helena, Tristan da Cunha, Gough Island (all UK territories) and Bouvet Island (Norway).

    Near the equator, the Romanche Trench divides the North Atlantic Ridge from the South Atlantic Ridge. This narrow submarine trench has a maximum depth of 7,758 m (25,453 ft), one of the deepest locations of the Atlantic Ocean. This trench, however, is not regarded an official boundary between any of the tectonic plates.

    History of Exploration:

    The ridge was initially discovered in 1872 during the expedition of the HMS Challenger. In the course of investigating the Atlantic for the sake of laying the transatlantic telegraph cable, the crew discovered a large rise in the middle of the ocean floor. By 1925, its existence was confirmed thanks to the invention of sonar.

    5
    The super-continent Pangaea during the Permian period (300 – 250 million years ago). Credit: NAU Geology/Ron Blakey

    By the 1960s, scientists were able to map the Earth’s ocean floors, which revealed a seismically-active central valley, as well as a network of valleys and ridges. They also discovered that the ridge was part of a continuous system of mid-ocean ridges that extended across the entire ocean floor, connecting all the divergent boundaries around the planet.

    This discovery also led to new theories in terms of geology and planetary evolution. For instance, the theory of “seafloor spreading” was attributed to the discovery of the MAR, as was the acceptance of continental drift and plate tectonics. In addition, it also led to the theory that all the continents were once part of subcontinent known as “Pangaea”, which broke apart roughly 180 million years ago.

    Much like the “Pacific Ring of Fire“, the discovery of the Mid-Atlantic Ridge has helped inform our modern understanding of the world. Much like convergent boundaries, subduction zones and other geological forces, the process that created it is also responsible for the world as we know it today.

    7
    Pacific Ring of Fire. USGS

    Basically, it is responsible for the fact that the Americas have been drifting away from Africa and Eurasia for millions of years, the formation of Australia, and the collision between the India Subcontinent and Asia. Someday – millions of years from now – the process of seafloor spreading will cause the Americas and Asia to collide, thus forming a new super continent – “Amasia”.

    For more information, check out the Geological Society’s page on the Mid-Atlantic Ridge.

    See the full article here .

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  • richardmitnick 8:46 am on April 14, 2017 Permalink | Reply
    Tags: , Geology, What Led to the Largest Volcanic Eruption in Human History   

    From Eos: “What Led to the Largest Volcanic Eruption in Human History?” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    13 April 2017
    Sarah Witman

    1
    A lake (black) fills Toba’s caldera in Sumatra, Indonesia, as seen in this false-color image from NASA’s Landsat satellite. A supereruption 74,000 years ago is thought to be the largest eruption ever to have been experienced by humans. Credit: NASA

    In the northern part of the Indonesian island of Sumatra lies the Toba caldera, a massive crater formed by what scientists think is the largest volcanic eruption ever experienced by humanity. The eruption, called the Youngest Toba Tuff supereruption, took place about 74,000 years ago.

    By dating zircon, a diamond-like gemstone, and other minerals in the area such as quartz, Reid and Vazquez have pieced together clues about the activity of magma below the surface prior to the supereruption.

    Zircon is the oldest dated mineral on Earth. With a hardness rating of 7.5, it is resistant to chemical and mechanical weathering and can withstand metamorphism (structural changes due to heat, pressure, and other natural processes). All of these factors make it an ideal mineral for geological dating, especially for magma. Because zircon does not gain or lose uranium or lead even at magmatic temperatures, zircon typically contains high uranium and low lead levels, and scientists may use the ratio of these two elements in the zircon to determine the age of the sample.

    The way in which zircon crystals in the Youngest Toba Tuff magma appear to have nucleated and grown over time, the researchers found, provides evidence of intermittent changes in the composition of the underground body of magma that eventually erupted. Certain characteristics of the zircon also indicate repeated episodes of magma recharge—fresh influxes of magma that often trigger eruptions—occurring tens of thousands to hundreds of thousands of years before the supereruption.

    The team’s findings are significant for modern-day humans, given that aerosols and ash that erupted from Youngest Toba Tuff are thought to have entered the atmosphere, causing global cooling and the near extinction of the human race. A supereruption of equal or greater magnitude today could therefore have similarly drastic consequences. By better understanding the conditions that led up to the Youngest Toba Tuff supereruption, scientists can help paint a clearer picture of the future.

    Science paper
    http://onlinelibrary.wiley.com/doi/10.1002/2016GC006641/abstract;jsessionid=C04D6BAFE7F708964146B4B1B210F807.f03t03

    See the full article here .

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    Eos is the leading source for trustworthy news and perspectives about the Earth and space sciences and their impact. Its namesake is Eos, the Greek goddess of the dawn, who represents the light shed on understanding our planet and its environment in space by the Earth and space sciences.

     
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