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  • richardmitnick 1:45 pm on December 7, 2017 Permalink | Reply
    Tags: , , Each volcano like each individual person has its own unique “personality.”, , Mount Agung in Bali - when will it blow?, Volcanoes,   

    From COSMOS: “Each volcano has unique warning signs that eruption is imminent” 

    Cosmos Magazine bloc

    COSMOS Magazine

    07 December 2017
    Tracy K. P. Gregg

    1
    Mount Agung in Bali. Just a burp, or indication of coming disaster? AP Photo/Firdia Lisnawati..

    Mount Agung in Bali has been thrusting ash thousands of feet into the sky for almost two weeks. Lava is burbling at the volcano’s peak. Indonesian authorities have ordered evacuations around Agung, while tourists are stranded at the closed airport. The volcano’s flanks are bulging from magma trying to push its way out, and earthquake frequency has been increasing. Heat from the magma has melted snow and ice at Agung’s summit, causing volcanic mudflows called lahars. It’s looking like an eruption is imminent… but how do volcanologists know for sure what’s to come?

    Each volcano, like each individual person, has its own unique “personality.” You may know, for example, that you can tease your brother mercilessly – up until the point where his eyebrows crease together because that means he’s going to blow his top. But do you know what it means if my eyebrows crease together? (It’s a surefire sign I’m thinking really hard.)

    Similarly, one volcano might reveal an imminent eruption by a sudden increase in the frequency and strength of earthquakes located directly below it. A different volcano might not show an increase in earthquake strength but instead display an increase in elevation as magma swells beneath its surface – just as air filling a balloon causes it to increase in size.

    2
    This fall showed a spike in number and magnitude of earthquakes around Agung. MAGMA Indonesia.

    The best way scientists can determine whether a volcano is about to erupt is to study its past behavior: How did this volcano act before it erupted last time? Our ability to predict eruptions is directly related to the amount of historic data we have for a given volcano.

    For most of Earth’s active volcanoes, though, we don’t have detailed information. The last time Agung volcano erupted, for example, was in 1963. And that was before it was closely monitored with seismometers. Satellite observations of volcanoes were not commonplace then, as they are now. We therefore don’t know what specific type, frequency or size of volcanic precursors – that is, events that precede an eruption – to look for with Agung volcano.

    Mount Pinatubo, Philippines, for example, erupted catastrophically in 1991; before that, its most recent eruption was around 500 years earlier. Precursors at Mount Pinatubo included ash explosions at the summit, increases in the number of vents spewing hot gas, changes in the volcano’s shape and increases in both the frequency and size of earthquakes. Two months of increasing activity preceded the 1991 paroxysmal eruption.

    In contrast, Mount St. Helens volcano in the U.S. is probably the most closely watched volcano on the planet. Decades of detailed observations allow geologists to make fairly precise predictions about Mount St. Helens: a specific pattern of earthquakes, for example, means that new lava will erupt within two weeks.

    We don’t yet know if Agung volcano is currently giving us two weeks, two months or two years (or more) of warning because we don’t know precisely what it did before its 1963 eruption.

    3
    GPS measurements provide models of the direction and rate (length of arrow) of deformation at the summit of Mauna Loa, a potential eruption precursor. USGS

    As technology advances, volcanologists and experts in collecting and interpreting satellite data (including remote-sensing scientists and geodesists) are improving our ability to predict eruptions. Now we can collect important information about volcano shape, temperature and changes in those parameters using satellites that provide the view from space. Satellites give volcanologists a good overall view of the volcano, but can’t supply human-scale details. Satellite orbits typically allow them to pass over a given volcano only once every week or two. We still require seismometers on the ground to detect and report earthquakes caused by magma moving beneath the volcano, but seismometers are too expensive to deploy and maintain everywhere.

    Accurate predictions of volcanic eruptions – particularly the size of the eruption and whether the volcano will explode or generate lava flows – are essential for local authorities to make life-and-death decisions about people in the vicinity of an active volcano. If an evacuation is ordered and a volcano explodes, lives are saved. This happened in the 1991 Pinatubo eruption. If an evacuation is ordered and the volcano doesn’t explode, economic losses and human suffering can be catastrophic. This scenario played out in Mammoth Mountain, California, in 1984, where the local community lost millions of tourist dollars – and there was no eruption.

    To predict eruptions on the scale of hours, days or weeks, we need detailed information about each potentially threatening volcano. Without that, we are forced to make comparisons: will Agung volcano behave more like Mount St Helens or Mount Pinatubo, for example? In other words, do creased eyebrows on someone you’ve just met (or, for example, increased seismicity at Agung volcano) mean that person is about to blow its top (like Mount Pinatubo did in 1991) or is just thinking really hard? More data, from more volcanoes, make for better comparisons, but nothing beats really getting to know the behavior of an individual volcano.

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  • richardmitnick 1:28 pm on December 6, 2017 Permalink | Reply
    Tags: , , , Huge Bubble of Hot Rock May Be Rising Under New England, , Volcanoes   

    From natgeo.com: “Huge Bubble of Hot Rock May Be Rising Under New England” 

    National Geographic

    National Geographics

    December 5, 2017
    Erin Blakemore

    1
    Colorful forests fill the landscape in the Berkshires of western Massachusetts. Photograph by Berthold Steinhilber, laif, Redux

    At first glance, New England doesn’t seem like a hotbed of geologic activity. The region doesn’t have any rumbling volcanoes. Earthquakes are almost unheard of. And its mountains are mere hills compared to ranges like the Rockies or the Sierra Nevada in the western U.S.

    But don’t underestimate what’s going on beneath the surface: It turns out this idyllic pocket of the northeastern U.S. may sit atop a rising mass of warm rock—a smaller, slower version of the magma pockets under well-known volcanic zones.

    The findings, recently published in the journal Geology, suggest that New England may not be so immune to abrupt geological change.

    A team of researchers at Rutgers University and Yale University made this surprising discovery using an advanced array of seismic sensors, which show what lies in the otherwise hidden rock below our feet.

    “Ten years ago, this would not have been possible,” says study coauthor Vadim Levin, a professor at Rutgers University-New Brunswick’s department of Earth and planetary sciences.

    “Now, all of a sudden, we have a much better eye to see inside the Earth.”

    Rising Rock

    Inside our planet, heat from the volatile core makes its way up through the mantle—the hot, high-pressure zone that lies below the planet’s crust. That heat causes the crust’s tectonic plates to slip and slide around. Where those plates collide or divide is where we most often see mountains, earthquakes, and volcanoes.

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

    Since we can’t see that deep into the planet, geologists use seismic vibrations caused by earthquakes to visualize the features within rock. Sensing how fast seismic ripples move, for instance, provides details about the structure and temperature of Earth’s mantle.

    In this case, Levin’s team studied data from EarthScope, a National Science Foundation program that deploys hundreds of geophysical instruments across the United States. The project’s Transportable Array, a temporary network of seismic sensors, made its way around the country starting in 2007. The array picked up readings from small earthquakes and observed the motions of seismic waves in various regions.

    The team piggybacked off previous research showing a relatively hot spot beneath New England’s upper mantle. Using data from EarthScope, they then observed a localized plume of warm rock beneath central Vermont, western New Hampshire, and western Massachusetts—and found geologic evidence that it’s on the move.

    Less dense areas are where the rock is hotter, and seismic waves move more slowly. That’s what the team saw under New England. They also observed wave patterns that suggest deformations in the rock itself.

    Normal plate motion leaves the geologic equivalent of skid marks in its wake, which seismic sensors can detect. In this region, however, the skid marks were gone—erased by the upward movement of warmer rock.

    Shifting Perspectives

    New England residents don’t need to panic. The upwelling is likely tens of millions of years old, which would make it a relatively recent development in geological terms, and it’s moving very slowly. For now, it certainly hasn’t gotten close enough to the surface to shape New England’s geography or create a volcano.

    “Maybe it didn’t have time yet, or maybe it is too small and will never make it,” says Levin. “Come back in 50 million years, and we’ll see what happens.”

    Instead, the discovery is a sign that it may be time to rethink the region’s geology.

    The big takeaway from this paper is that Earth’s structure is even more intricate and dynamic than anyone realized, says Meghan S. Miller, a structural seismologist and associate professor at the Australian National University’s Research School of Earth Sciences who was not involved in the project.

    “I think that kind of sounds simple and obvious in retrospect, but the Transportable Array data has allowed us to visualize how complex Earth’s structure really is,” she says.

    The find also helps put the planet in perspective, says Levin. New England has traditionally been considered a place of little geologic change, but EarthScope data suggests that the subsurface reality is anything but stagnant.

    “People think of mountains and lakes and geology as forever—there’s a general sense that Earth is a permanent thing,” says Levin. “Well, it’s not.”

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    The National Geographic Society has been inspiring people to care about the planet since 1888. It is one of the largest nonprofit scientific and educational institutions in the world. Its interests include geography, archaeology and natural science, and the promotion of environmental and historical conservation.

     
  • richardmitnick 9:51 am on December 4, 2017 Permalink | Reply
    Tags: An Antarctic eruption could ‘significantly disrupt’ international air traffic, , , , Volcanoes   

    From Science Magazine: “An Antarctic eruption could ‘significantly disrupt’ international air traffic” 

    ScienceMag
    Science Magazine

    1
    A climber stands near Mount Erebus, an active volcano in Antarctica. Galen Rowell/Getty Images

    Dec. 1, 2017
    Katherine Kornei

    Dig into the black sand of Deception Island, off the coast of the Antarctic Peninsula, and hot water percolates up, heated by geothermal activity. The horseshoe-shaped spit of land is itself the flooded caldera of an active volcano and home to more than 50 volcanic craters—markers of past eruptions. Now, scientists have shown that ash lofted by a hypothetical eruption on Deception Island would potentially disrupt air traffic as far away as South America, Australia, and Africa.

    The findings show that Antarctica’s volcanoes can have an effect across the world, says Charles Connor, a geoscientist at the University of South Florida in Tampa not involved in the research. “We have to reassess the potential hazards for global transportation networks posed by even these remote volcanoes.”

    Adelina Geyer, a geologist at the Institute of Earth Sciences Jaume Almera in Barcelona, Spain, and colleagues focused on Deception Island because of its history of eruptions—30 or so in the past 10,000 years, and one as recently as 1970. It is also a popular destination: Both Argentina and Spain manage scientific research bases on the island, and tourists come to admire the world’s largest colony of chinstrap penguins and the rusted boilers and tanks that are relics of the early 20th century whaling industry there.

    Geyer’s team modeled an eruption on Deception Island by simulating different column heights for volcanic ash: 5, 10, and 15 kilometers. (Indonesia’s Mount Agung, when it erupted last month, sent ash billowing up 9 kilometers.) The height of the plume determines which wind patterns it encounters, which, in turn, affects its dispersal. The researchers used an atmospheric transport model to track the way ash would disperse on regional and global scales and assess its possible effect on air travel.

    Airborne ash is a serious problem for aircraft because it melts inside of engines and gums up fuel lines. And it doesn’t show up on radar. There have been hundreds of reported incidents of aircraft encountering volcanic ash, including the 1989 case of KLM flight 867, which lost power in all four engines and fell more than 13,000 feet after flying through an ash cloud from Alaska’s Redoubt Volcano. (The pilots managed to restart the engines, and the plane landed safely in Anchorage.) When Iceland’s Eyjafjallajökull erupted in 2010, its ash clouds prompted officials to close airspace across Europe, resulting in economic losses estimated to be billions of dollars.

    For large eruptions on Deception Island, ash would be prevalent on global scales, the team concludes this week in Scientific Reports. Ash spewed high up into the stratosphere would encounter strong winds whipping around the South Pole. These circular winds—known as the polar vortex—move at speeds up to 60 meters per second and can send ash swirling far from its source. The team found that dangerous levels of airborne ash—exceeding flight safety thresholds of 2 milligrams per cubic meter—persisted thousands of kilometers from Deception Island, rendering routes toward major airports such as Buenos Aires unsafe for flying.

    But even ash that wasn’t lofted as high still tended to disperse widely, the team found. That’s because ash injected into a lower layer of the atmosphere known as a troposphere encountered chaotic, meandering atmospheric waves that carried it as far away as South America, Australia, and Africa.

    The researchers also tested moving the site of the eruption to Mount Erebus, another active Antarctic volcano located at a latitude of –77° near McMurdo Station, the largest research base in Antarctica. They found that higher plumes still resulted in transcontinental ash dispersal, but ash from lower plumes—generally less than 10 kilometers—tended to remain confined near the South Pole because of the less-intense, low-elevation winds at high latitudes.

    In February 2018, part of Geyer’s team will embark on a roughly weeklong journey to Deception Island via air and sea to gather data that could help calibrate their model. She says she and her colleagues will be studying recent eruptions “to determine what kind of eruptions we can expect in the future.”

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  • richardmitnick 6:45 pm on November 27, 2017 Permalink | Reply
    Tags: , Stratovolcano, The Geology of Bali’s Simmering Agung Volcano, Volcanoes   

    From smithsonian.com: “The Geology of Bali’s Simmering Agung Volcano” 

    smithsonian
    smithsonian.com

    11.27.17
    Jason Daley

    The high viscosity magma of stratovolcanoes like Agung makes them extremely explosive—and potentially deadly.

    1
    Mount Agung (MAGMA Indonesia)

    Bali authorities have issued evacuation orders for 100,000 people living within a six-mile radius of volcanic Mount Agung, the highest point on the Indonesian island.

    Trouble has been brewing at the volcano for quite some time. Researchers recorded seismic activity at Agung beginning in August, with the unrest increasing in the following weeks, according to the Earth Observatory of Singapore. On September 22, authorities raised to the volcano’s status to level 4, its highest warning category. Then, last Tuesday the volcano began emitting plumes of smoke and mudflows streamed through local waterways. Over the weekend, the ash cloud reached 30,000 feet and magmatic eruptions began, reports the Associated Press. About 59,000 travelers are currently stuck on the island after the ash caused the international airport to close.

    While authorities tell the AP they don’t expect a major eruption, the activity changed early this morning from emission of steam to magma. So officials are playing it safe. Last time Agung erupted in 1963, an estimated 1,100 people died. And since the 1963 catastrophe, population density has only intensified on Agung’s slopes.

    So what makes Agung so dangerous? Blame its geology.

    Agung is what’s known as a stratovolcano. Also known as composite volcanoes, these formations occur at tectonic subduction zones, areas where two tectonic plates meet and one plate slides underneath another, geophysicist Jacqueline Salzer at the German Research Centre for Geosciences tells Fabian Schmidt at Deutsche Welle.

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

    The lava in those areas is usually thick and sticky, causing pressures to build within the steep cones, which results in highly explosive—and deadly—eruptions.

    As Janine Krippner, a volcanologist at the University of Pittsburgh, writes for the BBC, Agung has gone through the predictable stages of a waking volcano. In August, small earthquakes were measured, but the mountain appeared unchanged. Then, in September, as rising magma heated the interior of the cone, plumes of steam were observed as the water in the mountain heated up.

    Beginning last week, steam-driven or phreatic eruptions began. During this time, steam inside the volcano built up pressure causing small explosions to shoot ash, crystals and rock into the air. Now the magma has reached the surface—the point at which it is called lava—and its glow can be seen at the top of the mountain.

    Authorities are hopeful the eruption won’t continue further but if it does, several types of disasters could unfold. The cloud of gas and steam will blow off larger pieces of the mountain off, shooting rock “bombs” into the air. Actual lava flows could also stream down the mountain for several miles. But the most dangerous element of the eruption is the pyroclastic flow, an explosion of hot gas and debris that follows valleys or low-lying areas. These flows can race down the mountain at 50 miles per hour, destroying everything in its path.

    Another major concern is lahars which occur when volcanic debris and ash mixes with water, creating a slurry the consistency of wet concrete. Lahars can rush down slopes at up to 120 miles per hour and swell in volume, destroying any villages or structures in its path.

    According to John Seach at VolcanoLive, during the 1963 Agung eruption, 820 people were killed by pyroclastic flows, 163 died from falling ash and rock and 165 were killed by lahars.

    The 1963 eruption also had global consequences. Alle McMahon at the Australia Broadcasting Corporation reports that the sulphur dioxide blown into the atmosphere by that event temporarily cooled the Earth by 0.1-0.4 degrees Celsius by reflecting some of the sun’s ultraviolet radiation.

    If Agung does have another major eruption, this miniscule amount of cooling is likely too small to be noticed. But the immediate consequences of such an eruption can be deadly, so authorities are encouraging locals to heed the evacuation notices.

    See the full article here .

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    Smithsonian magazine and Smithsonian.com place a Smithsonian lens on the world, looking at the topics and subject matters researched, studied and exhibited by the Smithsonian Institution — science, history, art, popular culture and innovation — and chronicling them every day for our diverse readership.

     
  • richardmitnick 11:47 am on November 24, 2017 Permalink | Reply
    Tags: , , , , Looking Inside an Active Italian Volcano, Volcanoes   

    From Eos: “Looking Inside an Active Italian Volcano” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    17 November 2017
    Emily Underwood

    1
    Fumarolic emissions at Italy’s Solfatara crater. Credit: Marceau Gresse

    Italy’s Solfatara crater lies in the Phlegraean Fields caldera, near Mount Vesuvius, the volcano that buried the city of Pompeii in 79 CE. The Phlegraean Fields caldera is located inside the metropolitan area of Naples, and it is one of the largest volcanic systems on Earth. This caldera is currently showing significant volcanic unrest, mainly located around the Solfatara volcano. The crater’s boiling, sulfurous mud pools and fumaroles indicate an intense volcanic activity, which many scientists view as a serious potential threat to the roughly 3 million inhabitants of this region.

    Scientists have long struggled to track Solfatara’s activity because the interactions between the gases in magma, water, and steam within volcanoes are still poorly understood. Now, however, a 3-D map of the complex water and gas-bearing tunnels and chambers within the caldera could aid that effort.

    Gresse et al [Journal of Geophysical Research]. used electrical resistivity tomography (ERT), a technique commonly used to study aquifers and other underground structures, to map the structure of Solfatara’s inner cracks and chambers. In ERT, researchers induce an electrical current between multiple electrodes placed on the ground and then collect profiles of the resistance it encounters as it passes through substances such as water, rock, mud, or gas. After doing this repeatedly, they can compile a 3-D picture of what lies below.

    This study reveals, for the first time, the structure of a gas-filled reservoir 50 meters below the surface of the Solfatara caldera. It shows that the reservoir is attached to a 10-meter-thick channel that turns into an opening known as the Bocca Grande fumarole, a vent through which foul-smelling volcanic gases escape to the surface. It also reveals the hidden condensate water channels beneath the surface, as well as the precise dimensions of features such as the cryptodome, a body of magma that can make the surface of a volcano bulge without erupting.

    Solfatara releases thousands of tons of hot carbon dioxide and water through vents such as the Bocca Grande fumarole every day. As pressure within the volcano builds over time, the ground above often rises and can cut off or change the shape of these internal release valves. Although the Phlegraean Fields caldera hasn’t erupted since 1538 CE, three ground uplift events have occurred since the 1950s, suggesting to some that the next eruption could be coming soon.

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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.

     
  • richardmitnick 7:36 am on November 2, 2017 Permalink | Reply
    Tags: , Bárðarbunga is also a subglacial stratovolcano, Bárðarbunga on Iceland, , The pressure of magma in the magma chamber is increasing, Volcanoes   

    From Science Alert: “Iceland’s Biggest Volcano Is Getting Ready to Erupt Again” 

    ScienceAlert

    Science Alert

    1
    (Paddy Scott/Shutterstock)

    2 NOV 2017
    MICHELLE STARR

    At least it’s easier to pronounce than Eyjafjallajökull.

    Earthquake rumbles under the Vatnajökull glacier in Iceland could be signs of an impending eruption by the country’s biggest volcano.

    Bárðarbunga, which stands 2,009 metres (6,591 ft) above sea level, is one of a number of volcanoes that geologists are carefully monitoring after a spate of recent earthquake activity – indicating that the pressure in the volcano is increasing.

    1
    Bárðarbunga. Pictures taken by Peter Hartree between 14.30 and 15.00 on September 4th 2014.

    “The reason for the earthquakes in this place is that the volcano Bárðarbunga is inflating, i.e. the pressure of magma in the magma chamber is increasing,” volcano expert Páll Einarsson at the University of Iceland told the Daily Star.

    “The volcano is clearly preparing for its next eruption, that may happen in the next few years. The earthquakes last week are just the symptoms of this process, they do not cause the volcano to erupt.”

    Bárðarbunga has been rumbling, he said, since February 2015 – when the volcano’s last eruption, beginning August 2014, ended. Prior to that event, the volcano had been causing earthquakes with increasing frequency since 2007 – and the eruption itself was preceded by a swarm of 1,600 eruptions within 48 hours.

    The 2014-2015 eruption of Bárðarbunga was relatively light in consequences compared to the earlier 2010 eruption of the smaller Eyjafjallajökull. A subglacial stratovolcano, Eyjafjallajökull’s modest-sized eruption caused unusual and disproportionate havoc.

    The heat of the volcano melted the ice cap, which caused floods. Then it spewed ash several kilometres into the atmosphere – where it was carried thousands of kilometres over Europe by the jet stream above.

    So thick and far-reaching was the ash that air travel all over Europe was disrupted for weeks after the eruption.

    Bárðarbunga is also a subglacial stratovolcano, and although a repeat of Eyjafjallajökull’s havoc is possible, it’s unlikely – as demonstrated by the volcano’s 2014-15 eruption.

    Disaster expert Simon Day of University College London told the Daily Star that Bárðarbunga “is statistically unlikely to do so.”

    There are other rumblings in Iceland too – earlier this year, Einarsson told the Iceland Monitor that four volcanoes were on the path to eruption sometime in the next few years.

    The other three are Grímsvötn, Hekla, and Katla – the latter of which is considered the most dangerous volcano in Iceland.

    But the world has also been waiting on an eruption from Katla for decades.

    The Iceland Meteorological Office is not concerned yet. All four volcanoes – in fact, most of the country’s volcanoes – are marked green under the aviation colour code map. This denotes that the volcanoes are “in a normal, non-eruptive state.”

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  • richardmitnick 8:27 am on October 30, 2017 Permalink | Reply
    Tags: , , Volcanoes,   

    From Science: “Yellowstone’s massive volcano could erupt more frequently than scientists thought” 

    ScienceMag
    Science Magazine

    Oct. 25, 2017
    Paul Voosen

    1
    iStock.com/kwiktor

    Some 630,000 years ago, the supervolcano beneath Yellowstone National Park in Wyoming recorded its last catastrophic eruption, forming a caldera that nearly spans the park’s width and belching a thick layer of ash, or tephra, across North America. But rather than a single event, Yellowstone may have erupted twice in a span of 270 years, new evidence from mud cores discovered off the coast of Santa Barbara, California, indicates. The cores, presented here today at the annual meeting of the Geological Society of America, were captured at the farthest extent of the ash’s reach, recorded as wisps of tephra in finely sedimented, ancient mud uplifted near the ocean floor. Most evidence of the Yellowstone eruption (the park’s Grand Prismatic geyser is pictured) is found on land in thick layers of compacted, weathered rock, which could have easily hidden the dual eruption, the researchers say. Both tephra layers also coincide with a stark temperature decline of 3°C, according to the core’s records of oxygen isotopes and fossilized plankton, with each episode lasting 100 years or more. If confirmed, the research could indicate that Yellowstone can recharge its eruptions much more quickly than typically thought—and that traditional views of volcanic winter, the period of cooling caused by a volcano’s reflective droplets and ash, fail to explain how a century of cooling could follow the eruptions.

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  • richardmitnick 11:36 am on October 18, 2017 Permalink | Reply
    Tags: , , , Volcanoes,   

    From NYT: “A Surprise From the Supervolcano Under Yellowstone” 

    New York Times

    The New York Times

    OCT. 10, 2017
    SHANNON HALL

    1
    The Grand Prismatic Spring in Yellowstone National Park, a large hot spring known for its vibrant coloration. Beneath the park is a powerful supervolcano which drives the spring and other geological activity. Credit Marie-Louise Mandl/EyeEm, via Getty Images.

    Beneath Yellowstone National Park lies a supervolcano, a behemoth far more powerful than your average volcano. It has the ability to expel more than 1,000 cubic kilometers of rock and ash at once — 2,500 times more material than erupted from Mount St. Helens in 1980, which killed 57 people. That could blanket most of the United States in a thick layer of ash and even plunge the Earth into a volcanic winter.

    Yellowstone’s last supereruption occurred 631,000 years ago. And it’s not the planet’s only buried supervolcano. Scientists suspect that a supereruption scars the planet every 100,000 years, causing many to ask when we can next expect such an explosive planet-changing event.

    To answer that question, scientists are seeking lessons from Yellowstone’s past. And the results have been surprising. They show that the forces that drive these rare and violent events can move much more rapidly than volcanologists previously anticipated.

    The early evidence, presented at a recent volcanology conference, shows that Yellowstone’s most recent supereruption was sparked when new magma moved into the system only decades before the eruption. Previous estimates assumed that the geological process that led to the event took millenniums to occur.

    To reach that conclusion, Hannah Shamloo, a graduate student at Arizona State University, and her colleagues spent weeks at Yellowstone’s Lava Creek Tuff — a fossilized ash deposit from its last supereruption. There, they hauled rocks under the heat of the sun to gather samples, occasionally suspending their work when a bison or a bear roamed nearby.

    Ms. Shamloo later analyzed trace crystals in the volcanic leftovers, allowing her to pin down changes before the supervolcano’s eruption. Each crystal once resided within the vast, seething ocean of magma deep underground. As the crystals grew outward, layer upon layer, they recorded changes in temperature, pressure and water content beneath the volcano, much like a set of tree rings.

    “We expected that there might be processes happening over thousands of years preceding the eruption,” said Christy Till, a geologist at Arizona State, and Ms. Shamloo’s dissertation adviser. Instead, the outer rims of the crystals revealed a clear uptick in temperature and a change in composition that occurred on a rapid time scale. That could mean the supereruption transpired only decades after an injection of fresh magma beneath the volcano.

    The time scale is the blink of an eye, geologically speaking. It’s even shorter than a previous study that found that another ancient supervolcano beneath California’s Long Valley caldera awoke hundreds of years before its eruption. As such, scientists are just now starting to realize that the conditions that lead to supereruptions might emerge within a human lifetime.

    “It’s shocking how little time is required to take a volcanic system from being quiet and sitting there to the edge of an eruption,” said Ms. Shamloo, though she warned that there’s more work to do before scientists can verify a precise time scale.

    Kari Cooper, a geochemist at the University of California, Davis who was not involved in the research, said Ms. Shamloo and Dr. Till’s research offered more insights into the time frames of supereruptions, although she is not yet convinced that scientists can pin down the precise trigger of the last Yellowstone event. Geologists must now figure out what kick-starts the rapid movements leading up to supereruptions.

    “It’s one thing to think about this slow gradual buildup — it’s another thing to think about how you mobilize 1,000 cubic kilometers of magma in a decade,” she said.

    As the research advances, scientists hope they will be able to spot future supereruptions in the making. The odds of Yellowstone, or any other supervolcano, erupting anytime soon are small. But understanding the largest eruptions can only help scientists better understand, and therefore forecast, the entire spectrum of volcanic eruptions — something that Dr. Cooper thinks will be possible in a matter of decades.

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  • richardmitnick 1:06 pm on October 16, 2017 Permalink | Reply
    Tags: , , , , Volcanic Unrest at Mauna Loa Earth’s Largest Active Volcano, Volcanoes   

    From Eos: “Volcanic Unrest at Mauna Loa, Earth’s Largest Active Volcano” 

    AGU bloc

    AGU
    Eos news bloc

    Eos

    Weston Albert Thelen
    Asta Miklius
    Christina Neal

    Mauna Loa is stirring—is a major eruption imminent? Comparisons with previous eruptions paint a complicated picture.

    1
    Oblique aerial view looking north-northeast toward the summit area of Mauna Loa volcano (elevation 4,169 meters) on 15 January 1976. The summit caldera (Moku’āweoweo) is 6 kilometers long and 2.5 kilometers wide. The pit crater in the foreground marks the start of the Southwest Rift Zone. Mauna Kea volcano is on the skyline in the distance. Credit: D. Peterson, USGS

    Mauna Loa is showing persistent signs of volcanic unrest. Since 2014, increased seismicity and deformation indicate that Mauna Loa, the volcano that dominates more than half of the island of Hawaiʻi, may be building toward its first eruption since 1984.

    Thousands of residents and key infrastructure are potentially at risk from lava flows, so a critical question is whether the volcano will follow patterns of previous eruptions or return to its now historically unprecedented 33-year slumber.

    Mauna Loa has erupted 33 times since 1843, an average of one eruption every 5 years [Trusdell, 2012]. Typical of shield-building Hawaiian volcanoes, Mauna Loa hosts a summit caldera and two rift zones, the Northeast Rift Zone (NERZ) and the Southwest Rift Zone (SWRZ; Figure 1, inset).

    Since the two most recent eruptions, in 1975 and 1984, monitoring by the U.S. Geological Survey’s Hawaiian Volcano Observatory has changed dramatically. Ground-based instruments continuously record signals from global navigation satellite systems (GNSS, of which GPS is one example), measuring the changing shape of the ground surface in near-real time, and interferometric synthetic aperture radar (InSAR) provides extensive spatial coverage of deformation. Seismic monitoring has also improved with the addition of more stations, increased data fidelity, and improved data analysis.

    More people live on the slopes of Mauna Loa now than in the 1970s and 1980s, so improvements in monitoring technology are of more than just academic interest.

    How does this recent period of unrest compare with the periods just before previous eruptions? How reliable are these comparisons in predicting the next eruption?

    2
    Fig. 1. The Italian satellite system COSMO-SkyMed acquired radar images of Mauna Loa on 1 January 2013 and 30 April 2017 to produce this ascending mode interferogram. Each fringe represents 1.5 centimeters of motion in the line-of-sight direction to the satellite. The butterfly pattern of fringes suggests an inflating tabular body beneath the caldera and uppermost Southwest Rift Zone (see inset map). The sizes of the white dots represent the magnitudes of earthquakes that occurred during this period. The arrow at the bottom left shows the direction of the satellite’s motion. The satellite’s interferometric synthetic aperture radar (InSAR) antenna looks to the right of the satellite track, and the radar contacts the land surface at about 35° off vertical. The inset is a digital elevation map of Mauna Loa showing lava flows since 1843 in red. The box shows the approximate extent of the interferogram image. COSMO-SkyMed data were provided by the Agenzia Spaziale Italiana via the Hawaiʻi Supersite.

    The Current Unrest

    Several periods of unrest have occurred at Mauna Loa since the 1984 eruption. The shallow magma storage complex started refilling (inflating) immediately following the eruption, but inflation soon slowed, and stopped altogether in the mid-1990s (Figure 2). A short-lived inflation episode began in 2002 [Miklius and Cervelli, 2003], and another began in 2004. By 2009, inflation had largely ceased. Unlike the current unrest, these previous two inflation episodes were not associated with significant numbers of shallow earthquakes; rather, they started with brief periods of deep seismicity approximately 45 kilometers beneath the surface [Okubo and Wolfe, 2008].

    3
    Fig. 2. Changes in distance across Moku’āweoweo, Mauna Loa’s summit caldera, and earthquakes shallower than 15 kilometers from 1973 through April 2017 in the same area as Figure 1. Because today’s sensitive instruments can detect earthquakes that previous instruments would have missed, only earthquakes greater than M1.7 are plotted. Large, abrupt extensions are associated with the formation of volcanic dikes during the 1975 and 1984 eruptions; other extensions are mostly due to accumulation of magma in shallow reservoirs. Note that this distance change is not sensitive to extension across the upper SWRZ, where most of the magma accumulation occurred between October 2015 and mid-2016. (EDM is electronic distance measuring, and MOKP and MLSP are GPS instrument sites.)

    The current unrest started in earnest in 2014 (Figure 2). Seismicity rates began to rise above background levels as early as March 2013, and by summer 2014, both seismicity and deformation rates had increased significantly. The pattern of ground deformation indicated inflation of a magma storage complex beneath the caldera and uppermost SWRZ, areas that were also the most seismically active (Figure 3).

    Beneath the caldera, seismicity consists of mostly small earthquakes (magnitude M of less than 2.5) at depths of 2–3 kilometers. These earthquakes occur in swarms lasting days to weeks, separated by months of minor activity. Event rates have been as high as 15 earthquakes per hour, with most earthquakes too small to be formally located.

    4
    Fig. 3. Blue arrows (with gray 95% confidence error ellipses) show the average horizontal velocities of GNSS stations on Mauna Loa from mid-2014 through 2016. Red arrows represent velocities predicted by a model of a horizontally opening tabular body extending from about 3 to 6 kilometers beneath the summit and upper Southwest Rift Zone and a radially expanding body at about 3 kilometers beneath the southeastern wall of the caldera. The surface projections of these magma reservoirs are indicated by the black line and black circle. The average rate of magma accumulation in these shallow reservoirs is on the order of 13 million cubic meters per year.

    The uppermost SWRZ has been the most seismically active region during the current unrest, in terms of overall energy release and number of earthquakes. These earthquakes are typically 3–4 kilometers below the surface. Another area of seismicity has been high on the west flank of the volcano, where swarms of small earthquakes (mostly less than M2.5) at an average depth of about 7 kilometers typically last days to a week.

    In addition to shallow seismicity, there have been several deep (greater than 20 kilometers), long-period earthquakes loosely scattered beneath the summit area. During previous periods of inflation, earthquakes with similar characteristics have been associated with magma ascent [Okubo and Wolfe, 2008].

    Short-term rates of seismicity and deformation have varied in magnitude, with weeklong to monthlong periods of relative quiescence interspersed within longer-term trends of heightened activity. Although there is general long-term correlation between deformation and seismicity rates, there is no obvious relationship between them in the short term.

    The spatial pattern of deformation and seismicity has also varied. In fall 2015, after several months of decreased inflation at the summit, seismicity beneath the caldera largely ceased, and inflation in the upper SWRZ increased (Figure 4). In May 2016, inflation and seismicity beneath the caldera slowly resumed, but as of mid-2017, rates are low compared with those seen prior to fall 2015.

    5
    Fig. 4. COSMO-SkyMed ascending mode interferograms show the shift in locus of inflation toward the upper Southwest Rift Zone in October 2015. Each image covers about the same length of time: (left) 18 March 2015 to 9 August 2015 and (right) 24 July 2015 to 31 December 2015. Each full-color cycle represents 1.5 centimeters of motion in the line-of-sight direction toward the satellite. Arrow shows direction of motion of the satellite. The SAR antenna looks to the right of the satellite track; the incidence angle is about 35° off vertical. COSMO-SkyMed data were provided by the Agenzia Spaziale Italiana via the Hawaii Supersite.

    Comparison with Past Eruptions

    Deformation monitoring networks in place before the 1975 and 1984 eruptions were sufficient to provide long-term indications of inflation that along with increased seismicity, led to a general forecast for the 1984 eruption [Decker et al., 1983]. However, measurements were not frequent enough to evaluate whether there were precursory changes in extension or uplift in the summit area just prior to eruption.

    Direct comparison of magma storage geometries and volumes derived from deformation patterns is also not possible because of the limited spatial and temporal extent of the early geodetic monitoring networks. Pre-1984 measurements are consistent with, but cannot confirm, the existence of a large-volume tabular storage complex (a vertical, dikelike body) beneath the summit and upper SWRZ, similar to what we currently model from GNSS and InSAR data.

    Similarly, differences in seismic network sensitivity and data processing preclude direct comparison of current seismicity rates with pre-1975 and pre-1984 rates. Patterns in the locations of earthquakes stronger than about M1.7, however, are comparable, and these patterns show a clear coincidence between the locations of seismicity during the current unrest and previous preeruption patterns (Figure 5).

    Another approach to comparing precursory seismicity is to evaluate cumulative seismic energy release, which mainly reflects energy released by larger-magnitude earthquakes (energy release increases logarithmically with respect to earthquake magnitude). Between 1 May 2013 and 30 April 2017, energy release on the west flank was equivalent to an M4.1 earthquake. For the same region, energy releases during the 4 years prior to the 1975 and 1984 eruptions were M4.2 and M4.5, respectively. In the caldera and uppermost SWRZ, the current energy release sums to M4.4, compared with M4.9 and M4.4 for the 1975 and 1984 precursory periods.

    Thus, the energy released during the current 4 or so years of unrest is approaching that released during the 4 years prior to the 1975 and 1984 eruptions. In some volcanic systems, the amount of energy release compared with previous eruptions may be an indicator of whether a period of unrest results in an eruption [Thelen et al., 2010], but this relationship has not been established on shield volcanoes such as Mauna Loa.

    One to 2 years prior to the 1975 and 1984 eruptions, swarms of small earthquakes increased in intensity. The strongest swarms included hundreds of small earthquakes per day for weeks. Bursts, as they were called, were separated by 3–6 months of relative quiet [Koyanagi et al., 1975]. Recently, swarms on the west flank have increased in number and size, but the durations of the swarms are less than pre-1975 and 1984 levels. Similarly, swarms of tiny earthquakes beneath the caldera have not occurred at rates seen in the months prior to the 1975 and 1984 eruptions.

    Interestingly, during the days to weeks prior to the past two eruptions, the number of small earthquakes fluctuated instead of building up steadily, even reaching relatively low rates for short periods prior to eruption [Koyanagi, 1987; Lockwood et al., 1987]. However, both eruptions had distinct short-term seismic precursors. The 1975 eruption was preceded by less than an hour of strong tremor in the summit caldera area [Lockwood et al., 1987]. In 1984, small (less than M0.1) earthquakes increased in frequency, shaking the ground two or three times per minute about 2.5 hours before the eruption [Koyanagi, 1987]. Harmonic tremor began about 2 hours prior to eruption, with a large increase in tremor amplitude and a swarm of earthquakes 30 minutes prior to eruption. Seven earthquakes larger than M3 occurred during a period from 30 minutes before the 1984 eruption until just over 1 hour after the onset of the eruption.

    5
    Fig. 5. Earthquake epicenters for (a) the 4 years prior to the 1975 eruption, (b) the 4 years prior to the 1984 eruption, and (c) the latest 4 years of unrest (1 May 2013 to 30 April 2017). Earthquake symbol size is based on magnitude, and color is based on depth. Only earthquakes above M1.7 are included, in an attempt to compensate for differences in network sensitivity since 1975. All earthquakes are analyst reviewed. Because the analysis of earthquakes above M1.7 is only partially complete for the current episode of unrest, event rates since 2013 may actually be slightly higher than shown here.

    Is an Eruption in Our Near Future?

    Mauna Loa’s long history of observed activity aids in forecasting another eruption, but at present, any forecast still contains a high degree of uncertainty. Some aspects of the current unrest are similar to unrest prior to eruptions in 1975 and 1984. Earthquake locations, temporal behavior, and energy release suggest that the volcano may be following a similar pattern. Other aspects, however, differ from the periods prior to the 1975 and 1984 eruptions.

    During the current unrest period, we have not observed the kind of moderate to large flank earthquakes that preceded many historical eruptions [Walter and Amelung, 2006], including the 1975 and 1984 eruptions. Also, as of fall 2017, we have not seen the high rates of small earthquakes observed about 7–14 months prior to the 1975 and 1984 eruptions, even though our ability to detect them has improved. Thus, if current unrest follows previous patterns of seismicity, we may expect that the volcano is still many months from eruption.

    We must also consider that current unrest might not follow previous patterns, and an eruption could occur without months of elevated microseismicity. It is possible that after years of intermittent inflation, shallow magma storage is exerting pressures already near the breaking point of the overlying rock.

    We can’t say for certain whether there will be a precursory months-long increase in microseismicity before the next Mauna Loa eruption. However, an eruption will likely be immediately preceded by an hours-long, dramatic increase in small earthquakes (at least one earthquake per minute), strong tremor, and the occurrence of several M3 or stronger earthquakes, similar to the lead-up to the 1975 and 1984 eruptions. Real-time deformation data from tiltmeters and GNSS stations will show large anomalies as magma moves from storage reservoirs toward the surface to the eventual eruption site in the summit area and/or along one of the rift zones or (less likely) from radial vents on the west flank.

    It is also possible that current elevated rates of seismicity and deformation may not culminate in eruption anytime soon; rather, this could be yet another episode of unrest that gradually diminishes. During the 25-year repose between the 1950 and 1975 eruptions, seismic unrest in 1962, 1967, and 1970 did not lead to eruption, although in hindsight, each is considered a long-term precursor to the 1975 eruption [Koyanagi et al., 1975].

    The high rate of volcanic activity at neighboring Kīlauea volcano complicates assessing the likelihood of a Mauna Loa eruption in the coming months or years. Klein [1982] noted that longer repose intervals at Mauna Loa were statistically correlated with eruptive activity at Kīlauea. Indeed, the current long repose time at Mauna Loa is occurring at the same time as the long-lived Puʻu ʻŌʻō eruption at Kīlauea, which began in 1983 and continues today. Even so, the most recent eruption of Mauna Loa in 1984 occurred during this eruption at Kīlauea, so the impact of nearby volcanic activity on Mauna Loa’s behavior over short timescales is unknown.

    We can make one forecast with relative certainty: On the basis of nearly 200 years of documented activity, it is highly likely that the next eruption will begin in the summit region and then, within days to years, migrate into one of the two primary rift zones [Lockwood et al., 1987].

    It is important to note that seismicity and inflation beneath the uppermost SWRZ do not imply an increased likelihood of eruption along the SWRZ. Similar patterns of seismicity prior to the 1975 and 1984 eruptions did not result in sustained activity in the SWRZ. In 1984, the eruption began at the summit and migrated to the upper SWRZ before activity focused along the NERZ, suggesting that a magma body extending into the uppermost SWRZ—similar to that inferred from current data—was also active prior to that eruption.

    Communicating the Hazards

    In response to more than a year of persistently elevated rates of seismicity and deformation, the Hawaiian Volcano Observatory (HVO) elevated the Volcano Alert Level and Aviation Color Code for Mauna Loa to advisory/yellow on 17 September 2015, indicating that the volcano was restless and that monitoring parameters were above the long-term background levels.

    Since then, HVO has continued public education efforts and engaged agency partners, including Hawaiʻi County Civil Defense and the National Park Service, to discuss preparedness and response planning. In 2016, HVO installed new web cameras and upgraded real-time gas and temperature sensors in the summit caldera. Alarms have been set to alert scientists to significant changes in several data streams, including real-time seismic amplitude (a measure of seismic energy release), ground tilt, and satellite- and ground-based thermal imagery. Revised maps showing potential inundation zones and likely lava flow paths based on topography derived from digital elevation maps have been prepared.

    As with any precursory volcanic eruption sequence, it will be challenging to choose the correct time to alert authorities and elevate public concern about a possible eruption. Once an eruption has commenced, pinpointing the exact location of the outbreak—especially at night or in cloudy conditions—may not be straightforward and may require the use of new tools such as infrasound. Vent location determines which downslope areas are at greatest risk, so addressing this capability gap is a high priority.

    As of this writing, elevated rates of seismicity and deformation continue. Improvements in monitoring networks and alarming systems since 1984 put HVO in a better position to provide early warning and, once an eruption has commenced, help guide emergency response. Additional efforts to inform and prepare the public for the eventual eruption are an important step in minimizing impacts to life and property.

    References

    Decker, R. W., et al. (1983), Seismicity and surface deformation of Mauna Loa volcano, Hawaii, Eos Trans. AGU, 64(37), 545–547, https://doi.org/10.1029/EO064i037p00545-01.

    Klein, F. W. (1982), Patterns of historical eruptions at Hawaiian volcanoes, J. Volcanol. Geotherm. Res., 12, 1–35, https://doi.org/10.1016/0377-0273(82)90002-6.

    Koyanagi, R. Y. (1987), Seismicity associated with volcanism in Hawaii: Application to the 1984 eruption of Mauna Loa volcano, U.S. Geol. Surv. Open File Rep., 87-277, 76 pp.

    Koyanagi, R. Y., E. T. Endo, and J. S. Ebisu (1975), Reawakening of Mauna Loa volcano, Hawaii: A preliminary evaluation of seismic evidence, Geophys. Res. Lett., 2(9), 405–408, https://doi.org/10.1029/GL002i009p00405.

    Lockwood, J. P., et al. (1987), Mauna Loa 1974–1984: A decade of intrusive and extrusive activity, in Volcanism in Hawaii, chap. 19, U.S. Geol. Surv. Prof. Pap., 1350, 537–570.

    Miklius, A., and P. Cervelli (2003), Interaction between Kīlauea and Mauna Loa, Nature, 421, 229, https://doi.org/10.1038/421229a.

    Okubo, P. G., and C. J. Wolfe (2008), Swarms of similar long-period earthquakes in the mantle beneath Mauna Loa volcano, J. Volcanol. Geotherm. Res., 178, 787–794, https://doi.org/10.1016/j.jvolgeores.2008.09.007.

    Thelen, W. A., S. D. Malone, and M. E. West (2010), Repose time and cumulative moment magnitude: A new tool for forecasting eruptions?, Geophys. Res. Lett., 37, L18301, https://doi.org/10.1029/2010GL044194.

    Trusdell, F. A. (2012), Mauna Loa—History, hazards, and risk of living with the world’s largest volcano, U.S. Geol. Surv. Fact Sheet, 2012-3104, 4 pp., https://pubs.usgs.gov/fs/2012/3104/.

    Walter, T. R., and F. Amelung (2006), Volcano-earthquake interaction at Mauna Loa volcano, Hawaii, J. Geophys. Res., 111, B05204, https://doi.org/10.1029/2005JB003861.

    Author Information

    Weston Albert Thelen (email: wthelen@usgs.gov), Cascade Volcano Observatory, U.S Geological Survey, Vancouver, Wash.; and Asta Miklius and Christina Neal, Hawaiian Volcano Observatory, U.S. Geological Survey, Hawaiʻi National Park, Hawaii

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  • richardmitnick 2:33 pm on October 10, 2017 Permalink | Reply
    Tags: , , , Ritter Island, , Volcanic islands are the source of some of the world’s largest landslides, Volcanoes   

    From Eos: “An 1888 Volcanic Collapse Becomes a Benchmark for Tsunami Models” 

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    Eos

    10.10.17
    Aaron Micallef
    Sebastian F. L. Watt
    Christian Berndt
    Morelia Urlaub
    Sascha Brune
    Ingo Klaucke
    Christoph Böttner
    Jens Karstens
    Judith Elger

    1
    Scientists aboard the R/V Sonne (shown here) profiled the seafloor and subsurface structures near Ritter Island, north of New Guinea, in 2016. A large portion of this volcanic island collapsed and slid into the sea in 1888, making it an ideal case study for modeling volcanic collapse landslides and the tsunamis they generate. Credit: Christian Berndt

    Early one March morning in 1888, a 4-cubic-kilometer chunk of the Ritter Island volcano collapsed into the Bismarck Sea northeast of New Guinea. This volume of land was about twice that of the Mount St. Helens landslide in 1980, and it is the largest historically recorded tsunami-causing volcanic sector collapse.

    The ensuing landslide triggered a tsunami tens of meters high. The waves were still 8 meters high when they reached parts of the island of New Guinea that are several hundreds of kilometers away, according to observers who witnessed the event [Ward and Day, 2003].

    Volcanic islands are the source of some of the world’s largest landslides. These landslides have the potential to generate large tsunamis. Scientists have debated the magnitude of these tsunamis, but much uncertainty remains over landslide dynamics and how far a tsunami can travel across an ocean basin while remaining large enough to cause damage.

    Studies of Ritter Island’s landslide and ensuing tsunami could significantly reduce that uncertainty. During a 6-week-long expedition in November and December 2016 aboard the German R/V Sonne, we mapped the Ritter Island collapse scar and deposit using hull-mounted multibeam sonar systems, which produced high-resolution bathymetry (Figure 1) and acoustic backscatter data.

    We are using data from this expedition, alongside a range of direct observations and samples, to generate a detailed interpretation of the Ritter Island landslide. With these robust field data, we set the stage for testing coupled landslide-tsunami models.

    An Ideal Study Site

    Ritter Island’s historic landslide, along with a heightened awareness of tsunami hazards following several recent devastating events, has caused some to wonder if other volcanic islands could experience flank or total collapse and, if so, how far tsunamis could reach. One hypothetical scenario that captured the attention of the popular media in 2004 involves a potential collapse of the Cumbre Vieja volcano on the southern half of the island of La Palma, one of the Canary Islands off the northwest coast of Africa.

    Such a collapse could trigger a tsunami that races across the Atlantic Ocean. However, recent tsunami models span an order of magnitude in their predictions of far-field wave heights for the La Palma collapse scenario.

    Resolving such discrepancies in our understanding of landslide and tsunami processes requires a field data set in which both phenomena can be observed to test current models. The sector collapse of Ritter Island, Papua New Guinea, in 1888 meets both these criteria.

    The landslide generated a tsunami that devastated shorelines as far as 600 kilometers away [Day et al., 2015]. An important factor is that there are eyewitness observations of the tsunami height, arrival time, and frequency at a range of locations around the Bismarck Sea [Day et al., 2015]. The event can thus be used as a benchmark for testing models of landslide-generated tsunamis if the volume, distribution, and dynamics of the landslide mass can be reconstructed.

    2
    Fig. 1. (a) Three-dimensional view of the Bismarck Sea between Umboi and Sakar islands compiled using data from the SO-252 multibeam echo sounder, bathymetric data from the General Bathymetric Chart of the Oceans (GEBCO), and altimetry from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) satellite. The gray transparent cone represents Ritter Island before the 1888 event. Black lines and the red box indicate 2-D and 3-D seismic reflection data, respectively, acquired during the SO-252 expedition. The white arrows here and below indicate the direction of material mobilization during the 1888 event. (b) Three-dimensional reflection seismic data (from the area in the red box above) showing the Ritter Island deposit, remnant block, and parasitic volcanic cone. No image credit.

    Geological Setting

    Ritter Island is located north of Australia in the Bismarck Sea about 80 kilometers north of New Guinea and some 20 kilometers off the western end of New Britain. Situated between the islands of Umboi and Sakar (Figure 1), it forms part of the Bismarck Volcanic Arc, which results from the northward subduction of the Solomon Plate underneath the Bismarck Plate [Baldwin et al., 2012]. Today, Ritter Island is a narrow, crescent-shaped island, around 1.2 kilometers long and 200 meters wide, reaching an elevation of approximately 140 meters above sea level.

    This island is all that remains of a larger, steep-sided conical island that was around 750 meters high before it collapsed in 1888 [Day et al., 2015]. During the 19th century, Ritter Island was known among navigators in the region as a highly active volcano, characterized by frequent Strombolian activity [Johnson, 2013].

    There is evidence for several submarine eruptions since 1888 that have constructed a cone with a current summit around 200 m beneath sea level. The remnant of the island above the waterline is dominated by interbedded sequences of basaltic scoria and thin lava flows that are consistent with low-level Strombolian activity.

    3
    This arc is all that remains of the Ritter Island volcanic cone. Underwater deposits show clear evidence of the landslide triggered by the collapsing cone, and eyewitness accounts described the resulting tsunami. Credit: Christian Berndt.

    Contemporary observations of the tsunami triggered by the 1888 event suggest a single wave train, which is consistent with one main phase of landslide movement and tsunami generation [Day et al., 2015]. The landslide deposit is young enough to be preserved at the seafloor without significant overlying sedimentary cover, so it can be examined today to understand the emplacement dynamics of a large volcanic island landslide.

    Volcanic island landslides with volumes of 1 to 10 cubic kilometers, such as the Ritter Island landslide, have a global recurrence interval of 100 to 200 years [Day et al., 2015]. Therefore, a similar event is likely to occur in the next 100 years, in contrast to the extremely large ocean island collapses (e.g., Canary Islands and Lesser Antilles) that have recurrence intervals of tens of thousands of years or more.

    Collecting the Field Data Set

    During our 2016 expedition, we used a Parasound subbottom profiler with 10-centimeter resolution, as well as 2-D multichannel seismic data and P-Cable 3-D reflection seismic data acquisition systems to image the collapse deposit with 5-m vertical and horizontal resolution (Figure 1). Additional observations and samples collected across the deposit and island flanks, using towed video cameras and sediment samplers, provide ground truthing of the geophysical data and allow us to construct a detailed interpretation of landslide emplacement processes.

    The acquired data show the three-dimensional structure of the Ritter Island landslide deposit and enabled us to reconstruct the kinematics of the emplacement process. The new data set will be used to do the following:

    quantify the overall volume of the material that has been mobilized
    decipher the nature and extent of landslide disintegration
    determine the location, distribution, and size of transported blocks
    identify the nature and origin of different regions of the landslide deposit
    understand the relationship between landslides and the eruption history of Ritter Island and surrounding volcanoes

    These are key parameters for determining the landslide failure and emplacement process and the dynamics of the 1888 tsunami. An initial assessment of the data indicates that the flanks of Ritter Island below sea level expose clastic sequences similar to those in the scar above the water, with an increase in more massive lava units in the lowermost part of the edifice. The landslide cuts deeply into the island structure, and the scar exposures suggest an edifice that is dominated by loosely compacted layers of volcanic rock fragments.

    The landslide mass split and flowed around a remnant block of the island and dispersed within the channel between Umboi and Sakar (Figure 1), where it formed a deposit that is relatively flat at the margins and has irregular channelization in the central part. Parts of the landslide deposit traveled through a constriction between Umboi and Sakar and incorporated underlying seafloor sediment.

    A Framework for Future Models

    Our observations indicate that minor changes in slope gradient can strongly affect landslide dynamics. The deposition of the Ritter landslide entailed a progressive, multiphase, brittle to plastic failure that mobilized material over a considerable distance. The distal deposit, near the leading edge of the landslide, incorporates a major proportion of underlying seafloor sediment.

    Seismic profiles through the distal deposit indicate that the 1888 landslide was only the latest of a series of large-volume volcanic landslides from the surrounding islands. Some blocks piercing the seafloor are, in fact, rooted within older and much larger landslide deposits.

    How large a tsunami a volcanic collapse landslide of a given size will generate and how far the tsunami will travel before it dissipates remain open questions. The information we gathered on this expedition will provide the framework for coupled landslide-tsunami models, which are required to assess the destructive potential of sector collapse–related tsunamis.
    Acknowledgments

    This work reflects the joint effort of the SO252 expedition’s shipboard scientific party. We thank Simon Day, Eli Silver, and Russell Perembo for sharing data and helping with the survey planning. We thank the master and crew of R/V Sonne and our technicians for support during the cruise. Data collection was funded through the BMBF project Ritter Island 03G0252A. A.M. acknowledges funding from the European Research Council under the European Union’s Horizon 2020 Programme (MARCAN, grant agreement 677898).

    References

    Baldwin, S. L., P. G. Fitzgerald, and L. E. Webb (2012), Tectonics of the New Guinea region, Annu. Rev. Earth Planet. Sci., 40, 495–520, https://doi.org/10.1146/annurev-earth-040809-152540.

    Day, S., et al. (2015), Submarine landslide deposits of the historical lateral collapse of Ritter Island, Papua New Guinea, Mar. Pet. Geol., 67, 419–438, https://doi.org/10.1016/j.marpetgeo.2015.05.017.

    Johnson, R. (2013), Fire Mountains of the Islands: A History of Volcanic Eruptions and Disaster Management in Papua New Guinea and the Solomon Islands, ANU Press, Acton, Australia, https://doi.org/10.26530/OAPEN_462202.

    Ward, S. N., and S. Day (2003), Ritter Island volcano—Lateral collapse and the tsunami of 1888, Geophys. J. Int., 154, 891–902, https://doi.org/10.1046/j.1365-246X.2003.02016.x.

    Author Information

    Aaron Micallef, Marine Geology and Seafloor Surveying group, University of Malta, Msida; Sebastian F. L. Watt, School of Geography, Earth and Environmental Sciences, University of Birmingham, U.K.; Christian Berndt (email: cberndt@geomar.de) and Morelia Urlaub, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany; Sascha Brune, GFZ German Research Centre for Geosciences, Potsdam; and Ingo Klaucke, Christoph Böttner, Jens Karstens, and Judith Elger, GEOMAR Helmholtz Centre for Ocean Research Kiel, Germany
    Citation: Micallef, A., S. F. L. Watt, C. Berndt, M. Urlaub, S.Brune, I. Klaucke, C. Böttner, J. Karstens, and J. Elger (2017), An 1888 volcanic collapse becomes a benchmark for tsunami models, Eos, 98, https://doi.org/10.1029/2017EO083743. Published on 10 October 2017.

    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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