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  • richardmitnick 12:40 pm on September 24, 2021 Permalink | Reply
    Tags: "Processes in Earth’s Mantle and Surface Connections", A better understanding of these deep-mantle material cycles and their impact on the long-term evolution of our planet requires integrated approaches that involve all disciplines in the Earth sciences., A book recently published by AGU: "Mantle Convection and Surface Expressions", Despite the common call for transdisciplinary research only little work has been done that truly and quantitatively integrates different approaches., Eos, Our book aimed to unify researchers with expertise in different Earth science disciplines., The connection between chemical variations and physical property changes needs to be quantified by experimental and theoretical mineral physics., The motion of material in Earth’s mantle powered by heat from the deep interior moves tectonic plates on our planet’s surface.   

    From Eos: “Processes in Earth’s Mantle and Surface Connections” 

    From AGU
    Eos news bloc

    From Eos

    9.24.21

    Hauke Marquardt
    hauke.marquardt@earth.ox.ac.uk
    Maxim Ballmer
    Sanne Cottaar
    Jasper Konter

    A new AGU book presents a multidisciplinary perspective on the dynamic processes occurring in Earth’s mantle.

    1
    A synchrotron X-ray diffraction image collected in a high-pressure/-temperature diamond-anvil cell experiment to determine the deformation behavior of ferropericlase. Credit: © Hauke Marquardt.

    The motion of material in Earth’s mantle powered by heat from the deep interior moves tectonic plates on our planet’s surface. This motion generates earthquakes, fuels volcanic activity, and shapes surface landscapes. Furthermore, chemical exchanges between the surface and Earth’s mantle possibly stabilize the oceans and atmosphere on geologic timescales. A book recently published by AGU, Mantle Convection and Surface Expressions, gathers perspectives from observational geophysics, numerical modelling, geochemistry, and mineral physics to construct a holistic picture of the deep Earth. We asked the book’s editors some questions about what readers can expect from this monograph.

    In simple terms for a non-expert, can you start by explaining what the mantle is, how material moves around the mantle, and the effects of this on Earth’s surface?

    The mantle is the largest region in our planet, connecting the hot liquid outer core to Earth’s surface. Convection in the Earth’s mantle is linked to plate tectonic processes and controls the fluxes of heat and material between deep mantle reservoirs and the atmosphere over time. A better understanding of these deep-mantle material cycles and their impact on the long-term evolution of our planet requires integrated approaches that involve all disciplines in the Earth sciences.

    For example, geochemical observations on the surface suggest different chemical reservoirs within the lower mantle. This would imply potentially widespread variations in physical properties driven by the chemical differences between materials.

    The connection between chemical variations and physical property changes needs to be quantified by experimental and theoretical mineral physics. In turn, the constrained variations in physical properties provide the basis for self-consistent state-of-the-art geodynamic models of mantle convection.

    Finally, the predictions of geodynamic models can be quantitatively tested by geophysical observations, which constrain the geometry of sinking slabs and rising plumes, as well as geochemical data.

    Any such models rooted by observational and theoretical constraints can be applied to study the evolution of the mantle over billions of years, thereby linking the accretion of our planet to the present-day. Indeed, such an interdisciplinary effort can even provide insight into the conditions for planetary habitability and sustainability of higher life.

    What motivated you to write a book on mantle processes and surface expressions?

    Our book aimed to unify researchers with expertise in different Earth science disciplines, including observational geophysics, numerical modelling, geochemistry, and mineral physics, to outline current concepts on dynamic processes occurring in the mantle and associated material cycles. We believe that real progress is increasingly made at the intersection between different sub-disciplines and, ultimately, only the synergy between disciplines can truly overcome the limitations of each individual approach. Our book is motivated by the vision of a new holistic picture of deep Earth sciences.

    How is your book structured?

    The overarching idea of the book is to bridge between disciplines. The sub-sections of the book are not sorted by discipline, but rather by research topic. The first part describes key mantle domains and basic properties of the Earth’s mantle. The second part presents reviews and new research related to the dynamic aspects of deep Earth material cycles, integrating all relevant geoscientific disciplines. The third part aims to place the preceding chapters in a broader context, trying to summarize ideas and stimulate new concepts on how the Earth’s deep mantle is connected to our planet’s surface and atmosphere, and how processes might work on other planets.

    What value did you find in bringing together perspectives from different scientific disciplines in your book?

    Several high-profile papers have been published relating to mantle convection and surface connections during the past decade, including materials cycles through the deep Earth interior and its impact on the evolution of the atmosphere.

    Progress has been significant, but often work still falls mostly within one discipline. Some initial progress in multidisciplinary work has been made, but is still often complicated by gaps in knowledge, jargon, and networks.

    The value that our book adds is to summarize existing multidisciplinary work and foster future research across the boundaries.

    How do you hope that your book will inspire further transdisciplinary research?

    Despite the common call for transdisciplinary research only little work has been done that truly and quantitatively integrates different approaches. Sometimes, just the lack of a common language, with different jargon across discipline boundaries, prevents any directed and sustainable progress.

    We are convinced that our book can help to bridge the gaps between different Earth Science communities, resolve some semantic issues, and foster promising future collaborations. In order to achieve this, we took particular care that chapters are written in a style that makes them accessible for researchers from all sub-disciplines (i.e., jargon and pre-conceptions are explained).

    The topic Mantle Convection and Surface Expressions covers an area of central importance for all target research disciplines and is central to our understanding of the evolution of our planet. Thus, we feel that the topic is not only a ‘hot-topic’ of cross-disciplinary importance but is also ideally suited to unify researchers and trigger fruitful future work.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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 1:49 pm on September 21, 2021 Permalink | Reply
    Tags: "Small Climate Changes Could Be Magnified by Natural Processes", An imbalance between global warming and global cooling with a strong bias toward extreme warming events., , , Eos, , The Paleocene-Eocene Thermal Maximum in which global temperatures jumped by more than 5°C and remained elevated for tens of thousands of years.   

    From Eos: “Small Climate Changes Could Be Magnified by Natural Processes” 

    From AGU
    Eos news bloc

    From Eos

    16 September 2021
    Damond Benningfield

    1
    The Sun blazes above Earth in this 2020 image taken from the International Space Station. The changing shape of Earth’s orbit could play a role in climate change, amplified by multiplicative factors in Earth’s biological and chemical processes. Credit: National Aeronautics Space Agency (US).

    A little bit of global warming may go a long way. A recent mathematical analysis of the climate of the Cenozoic­—our current geologic era, starting at the demise of the dinosaurs 66 million years ago—says that natural processes may amplify small amounts of warming, turning them into “hyperthermal” events that can last for thousands of years or longer. This finding suggests that human-induced climate change could make our planet susceptible to more extreme warming events in the future.

    Scientists have studied several major Cenozoic warming events in detail, including the Paleocene-Eocene Thermal Maximum in which global temperatures jumped by more than 5°C and remained elevated for tens of thousands of years. Such events can help scientists understand how the planet responds to climate changes and predict how it might react to current human-caused changes.

    Constantin Arnscheidt and Daniel Rothman of the Lorenz Center at The Massachusetts Institute of Technology (US), however, decided to examine the climate–carbon cycle history of the entire period. Their study was published in Science Advances.

    “We wanted to understand the more general behavior of sub-million-year climate–carbon cycle fluctuations throughout the Cenozoic,” said Arnscheidt, a graduate student and the study’s lead author. “And so, for the first time, we considered all of the fluctuations involved rather than picking out the big ones.”

    Warming Bias

    The researchers used a database of benthic foraminifera found in deep-ocean sediments. The single-celled organisms are protected by shells of calcium carbonate. Changes in surface temperature, surface inorganic carbon, ocean chemistry, and other climate factors alter the carbon and oxygen isotope ratios in the shells, making it possible for scientists to use them as climate proxies.

    Arnscheidt and Rothman used statistical methods to analyze the database. “Climate fluctuations on a wide range of timescales are the result of many complex processes that are impossible to model exactly,” said Arnscheidt. “Stochastic models, which have long been employed to understand shorter-term climate variability, capture essential aspects of this behavior by including random-noise terms.”

    Their results showed an imbalance between global warming and global cooling with a strong bias toward extreme warming events. There were more warming than cooling events, they produced a greater swing in temperatures, and they lasted longer. This trend continued until the start of the Pliocene, about 5.3 million years ago, when the global climate cooled considerably and ice sheets began covering North America.

    The bias in the statistics was consistent with the principle of “multiplicative noise,” in which the extent of changes in a system depends on its state. In this case, if temperature variations over periods of thousands or tens of thousands of years increase as the climate gets warmer, “this would result in a warming bias precisely like the one observed,” Arnscheidt said.

    A warming bias would suggest that a little bit of global warming may trigger natural biological or geochemical processes (which the researchers say still need to be identified) that operate more efficiently under warmer conditions. These processes pump additional carbon and other warming compounds into the atmosphere and increase the temperature even more, leading to extreme and long-lasting warming events.

    The initial impulse for warming events could come from changes in the eccentricity of Earth’s orbit, which varies over a period of about 100,000 years. Scientists have observed that some warming events appear to align with this cycle but haven’t been able to explain how the changing eccentricity could cause large climate swings. The new model suggests that although the initial change in climate caused by the cycle might be small, the multiplier effects could turn it into a major event.

    Exploring Climate’s Operational Boundaries

    “The paper does push us to explore much more Earth’s response to orbital forcing in the different climate states,” said Thomas Westerhold, director of the Center for Marine Environmental Sciences at The University of Bremen [Universität Bremen](DE), who led the development of the foraminifera database but was not involved in this project. “The climate system seems to have operational boundaries that once they are passed, the system moves into a different state….We need to know where those boundaries are that once crossed, we cannot simply make undone.”

    The study doesn’t say that multiplicative effects will boost the effects of anthropogenic climate change anytime soon, Arnscheidt noted. It does, however, suggest that if current warming continues, the climate could become more susceptible to extreme warming events like those seen in the geologic record.

    “Fundamentally, this study highlights that there is much yet to be learned about the mechanisms governing Earth’s long-term climate evolution and that human climate forcing today may have far-reaching effects on the long-term future,” Arnscheidt said.

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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 10:55 am on September 20, 2021 Permalink | Reply
    Tags: "Climate Change Will Alter Cooling Effects of Volcanic Eruptions", , , Eos,   

    From Eos: “Climate Change Will Alter Cooling Effects of Volcanic Eruptions” 

    From AGU
    Eos news bloc

    From Eos

    9.20.21
    Michael Allen

    1
    The eruption of Mount Pinatubo, Philippines, in June 1991 was one of the most powerful of the 20th century. Credit: Dave Harlow, USGS.

    Volcanic eruptions can have a massive effect on Earth’s climate. Volcanic ash and gases from the 1815 eruption of Mount Tambora, Indonesia, for example, contributed to 1816 being the “year without a summer,” with crop failures and famines across the Northern Hemisphere. In 1991, the eruption of Mount Pinatubo in the Philippines cooled the climate for around 3 years.

    Large volcanic eruptions like Tambora and Pinatubo send plumes of ash and gas high into the atmosphere. Sulfate aerosols from these plumes scatter sunlight, reflecting some of it back into space. This scattering warms the stratosphere but cools the troposphere (the lowest layer of Earth’s atmosphere) and Earth’s surface.

    Now new research published in Nature Communications has found that climate change could increase the cooling effect of large eruptions like these, which typically occur a couple of times every century. The study also found, however, that the cooling effects of smaller, more frequent eruptions could be reduced dramatically.

    “What really matters is whether these [volcanic aerosols] are injected into the stratosphere—that is, above 16 kilometers in the tropics under current climate conditions and closer to 10 kilometers at high latitudes,” explained Thomas Aubry, a geophysicist at The University of Cambridge (UK) and lead author of the new study. “If [aerosols] are injected at these altitudes, they can stay in the atmosphere for a couple of years. If they are injected at lower altitudes, they are essentially going to be washed out by precipitation in the troposphere. The climatic effect will only last for a few weeks.”

    The power of a volcanic eruption influences the elevation at which gases enter the atmosphere, with stronger eruptions injecting more aerosols into the stratosphere. The buoyancy of the gases also contributes to the elevation at which they settle in the atmosphere. Climate change could affect this buoyancy: As the atmosphere warms, it becomes less dense, increasing the elevation at which aerosols reach neutral buoyancy.

    Modeling Mount Pinatubo

    Aubry and his colleagues used models of both climate and volcanic plumes to simulate what happens to aerosols emitted by a volcanic eruption in the present climate and how that could change by the end of the century with continued global warming. In their models, all the eruptions occurred at Mount Pinatubo.

    They found that for moderate-magnitude eruptions, the height at which sulfate aerosols settle in the atmosphere remained the same in a warmer climate. But the cooling effect of such eruptions was reduced by around 75%. This discrepancy has less to do with volcanic emissions and more to do with the atmosphere: The height of the stratosphere is predicted to increase with climate change. Aerosols from moderate volcanic eruptions will therefore be more likely to remain in the troposphere and be removed by rain, reducing their potency.

    For large eruptions, models indicated that volcanic plumes will rise around 1.5 kilometers higher in the stratosphere in a warmer climate. This change in elevation will result in the aerosols spreading faster around the world. This increase in aerosol spread is mainly due to a predicted acceleration of the Brewer-Dobson circulation, which moves air in the troposphere upward into the stratosphere and then toward the poles. The change in Brewer-Dobson circulation is associated with climate change.

    In addition to enhancing the global cooling effect of the aerosols, the increase in aerosol spread reduces the rate at which the sulfate particles bump into each other and grow. This further increases their cooling effect by allowing them to better reflect sunlight.

    “There is a sweet spot in terms of the size of these tiny and shiny particles where they are very efficient at scattering back the sunlight,” explained Anja Schmidt, an atmospheric scientist at the University of Cambridge and coauthor of the paper. “It happens to be that in this global warming scenario that [we] simulated, these particles grow close to the size where they are very efficient in terms of scattering.”

    “We find that the radiative forcing (the amount of energy removed from the planet system by the volcanic aerosol) would be 30% larger in the warm climate, compared to the present-day climate,” Aubry said. “Then we suggest that would amplify the surface cooling by 15%.”

    Stefan Brönnimann, a climate scientist at the The University of Bern [Universität Bern](CH) who was not involved in the new research, said that the study is interesting because “it makes us think about the processes involved [between volcanic emissions and climate] in a new way.”

    Brönnimann noted, however, that the simulations limited their models to eruptions of Mount Pinatubo in the summer. It would be interesting to see whether the conclusions still hold for eruptions at different latitudes and in different seasons, he said.

    A Changing Stratosphere

    It is difficult to say whether the amplified cooling from large volcanic eruptions or the decrease in cooling from smaller eruptions will have a net effect on climate, Aubry said.

    Schmidt said that current increases in the frequency and intensity of forest fires could also alter the climatic effects of volcanic eruptions because they are affecting the composition of the stratosphere. “There is really a lot of aerosol pollution in the stratosphere, probably on a scale that we’ve never seen before.”

    See the full article here .

    five-ways-keep-your-child-safe-school-shootings

    Please help promote STEM in your local schools.

    Stem Education Coalition

    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 10:02 am on September 10, 2021 Permalink | Reply
    Tags: "Anticipating Climate Impacts of Major Volcanic Eruptions", , , , Eos, , In the event of future eruptions on par with or larger than those at El Chichón and Pinatubo, Major volcanic eruptions inject large amounts of gases; aerosols; and particulates into the atmosphere., Meanwhile NASA’s Aerosol Robotic Network (AERONET); Micro-Pulse Lidar Network (MPLNET); and Southern Hemisphere Additional Ozonesondes (SHADOZ) would provide real-time observations from the ground., NASA recently developed a volcanic eruption response plan to maximize the quantity and quality of observations it makes following eruptions., National Aeronautics Space Agency (US)’s rapid response plan for gathering atmospheric data amid major volcanic eruptions paired with efforts to improve eruption simulations will offer better views , Rapid mobilization of NASA’s observational and research assets will permit scientists to make early initial estimates of potential impacts., Rapid responses to major volcanic eruptions enable scientists to make timely initial estimates of potential climate impacts to assist responders in implementing mitigation efforts., The threshold amount of volcanic SO2 emissions required to produce measurable climate impacts is not known exactly.,   

    From Eos: “Anticipating Climate Impacts of Major Volcanic Eruptions” 

    From AGU
    Eos news bloc

    From Eos

    31 August 2021

    Simon A. Carn
    scarn@mtu.edu
    Paul A. Newman
    Valentina Aquila
    Helge Gonnermann
    Josef Dufek

    National Aeronautics Space Agency (US)’s rapid response plan for gathering atmospheric data amid major volcanic eruptions, paired with efforts to improve eruption simulations, will offer better views of these events’ global effects.

    1
    A thick cloud of volcanic ash and aerosols rises into the atmosphere above the north Pacific Ocean on 22 June 2019. An astronaut aboard the International Space Station captured this image of the plume during an eruption of Raikoke Volcano in the Kuril Islands. Credit: ISS Crew Earth Observations Facility and the Earth Science and Remote Sensing Unit, Johnson Space Center.

    This year marks the 30th anniversary of the most recent volcanic eruption that had a measurable effect on global climate. In addition to devastating much of the surrounding landscape and driving thousands of people to flee the area, the June 1991 eruption at Mount Pinatubo in the Philippines sent towering plumes of gas, ash, and particulates high into the atmosphere—materials that ultimately reduced average global surface temperatures by up to about 0.5°C in 1991–1993. It has also been more than 40 years since the last major explosive eruption in the conterminous United States, at Mount St. Helens in Washington in May 1980. As the institutional memory of these infrequent, but high-impact, events fades in this country and new generations of scientists assume responsibility for volcanic eruption responses, the geophysical community must remain prepared for coming eruptions, regardless of these events’ locations.

    Rapid responses to major volcanic eruptions enable scientists to make timely initial estimates of potential climate impacts (i.e., long-term effects) to assist responders in implementing mitigation efforts, including preparing for weather and climate effects in the few years following an eruption. These events also present critical opportunities to advance volcano science [National Academies of Sciences, Engineering, and Medicine (NASEM), 2017], and observations of large events with the potential to affect climate and life globally are particularly valuable.

    Recognizing this value, NASA recently developed a volcanic eruption response plan to maximize the quantity and quality of observations it makes following eruptions [NASA, 2018*], and it is facilitating continuing research into the drivers and behaviors of volcanic eruptions to further improve scientific eruption response efforts.

    *See References below

    How Volcanic Eruptions Affect Climate

    Major volcanic eruptions inject large amounts of gases; aerosols; and particulates into the atmosphere. Timely quantification of these emissions shortly after they erupt and as they disperse is needed to assess their potential climate effects. Scientists have a reasonable understanding of the fundamentals of how explosive volcanic eruptions influence climate and stratospheric ozone. This understanding is based on a few well-studied events in the satellite remote sensing era (e.g., Pinatubo) and on proxy records of older eruptions such as the 1815 eruption of Tambora in Indonesia [Robock, 2000]. However, the specific effects of eruptions depend on their magnitude, location, and the particular mix of materials ejected.

    To affect global climate, an eruption must inject large quantities of sulfur dioxide (SO2) or other sulfur species (e.g., hydrogen sulfide, H2S) into the stratosphere, where they are converted to sulfuric acid (or sulfate) aerosols over weeks to months (Figure 1). The sulfate aerosols linger in the stratosphere for a few years, reflecting some incoming solar radiation and thus reducing global average surface temperatures by as much as about 0.5°C for 1–3 years, after which temperatures recover to preeruption levels.

    2
    Fig. 1. In the top plot, the black curve represents monthly global mean stratospheric aerosol optical depth (AOD; background is 0.004 or below) for green light (525 nanometers) from 1979 to 2018 from the Global Space-based Stratospheric Aerosol Climatology (GloSSAC) [Kovilakam et al., 2020; Thomason et al., 2018]. AOD is a measure of aerosol abundance in the atmosphere. Red dots represent annual sulfur dioxide (SO2) emissions in teragrams (Tg) from explosive volcanic eruptions as determined from satellite measurements [Carn, 2021]. The dashed horizontal line indicates the 5-Tg SO2 emission threshold for a NASA eruption response. Vertical gray bars indicate notable volcanic eruptions and their SO2 emissions. From left to right, He = 1980 Mount St. Helens (United States), Ul = 1980 Ulawun (Papua New Guinea (PNG)), Pa = 1981 Pagan (Commonwealth of the Northern Mariana Islands), El = 1982 El Chichón (Mexico), Co = 1983 Colo (Indonesia), Ne = 1985 Nevado del Ruiz (Colombia), Ba = 1988 Banda Api (Indonesia), Ke = 1990 Kelut (Indonesia), Pi = 1991 Mount Pinatubo (Philippines), Ce = 1991 Cerro Hudson (Chile), Ra = 1994 Rabaul (PNG), Ru = 2001 Ulawun, 2002 Ruang (Indonesia), Re = 2002 Reventador (Ecuador), Ma = 2005 Manam (PNG), So = 2006 Soufriere Hills (Montserrat), Ra = 2006 Rabaul (PNG), Ka = 2008 Kasatochi (USA), Sa = 2009 Sarychev Peak (Russia), Me = 2010 Merapi (Indonesia), Na = 2011 Nabro (Eritrea), Ke = 2014 Kelut (Indonesia), Ca = 2015 Calbuco (Chile), Am = 2018 Ambae (Vanuatu). In the bottom plot, circles indicate satellite-measured SO2 emissions (symbol size denotes SO2 mass) and estimated plume altitudes (symbol color denotes altitude) for volcanic eruptions since October 1978 [Carn, 2021].

    Although this direct radiative effect cools the surface, the aerosol particles also promote warming in the stratosphere by absorbing outgoing longwave radiation emitted from Earth’s surface as well as some solar radiation, which affects atmospheric temperature gradients and thus circulation (an indirect advective effect). This absorption of longwave radiation also promotes chemical reactions on the aerosol particles that drive stratospheric ozone depletion [Kremser et al., 2016], which reduces absorption of ultraviolet (UV) radiation and further influences atmospheric circulation. The interplay of aerosol radiative and advective effects, which both influence surface temperatures, leads to regional and seasonal variations in surface cooling and warming. For example, because advective effects tend to dominate in winter in the northern midlatitudes, winter warming of Northern Hemisphere continents—lasting about 2 years—is expected after major tropical eruptions [Shindell et al., 2004].

    Eruptions from tropical volcanoes like Pinatubo typically generate more extensive stratospheric aerosol veils because material injected into the tropical stratosphere can spread into both hemispheres. However, major high-latitude eruptions can also have significant climate impacts depending on their season and the altitude that their eruption plumes reach [Toohey et al., 2019].

    The effects of volcanic ash particles are usually neglected in climate models because the particles have shorter atmospheric lifetimes than sulfate aerosols, although recent work has suggested that persistent fine ash may influence stratospheric sulfur chemistry [Zhu et al., 2020]. This finding provides further motivation for timely sampling of volcanic eruption clouds.

    The threshold amount of volcanic SO2 emissions required to produce measurable climate impacts is not known exactly. On the basis of prior eruptions, NASA considers that an injection of roughly 5 teragrams (5 million metric tons) of SO2 or more into the stratosphere has sufficient potential for climate forcing of –1 Watt per square meter (that is, 1 Watt per square meter less energy is put into Earth’s climate system as a result of the stratospheric aerosols produced from the SO2) and warrants application of substantial observational assets.

    Since the dawn of the satellite era for eruption observations in 1978, this threshold has been surpassed by only two eruptions: at El Chichón (Mexico) in 1982 and Pinatubo in 1991 (Figure 1), which reached 5 and 6, respectively, on the volcanic explosivity index (VEI; a logarithmic scale of eruption size from 0 to 8). Since Pinatubo, the observational tools that NASA employs have greatly improved.

    In the event of future eruptions on par with or larger than those at El Chichón and Pinatubo, rapid mobilization of NASA’s observational and research assets, including satellites, balloons, ground-based instruments, aircraft, and modeling capabilities, will permit scientists to make early initial estimates of potential impacts. Capturing the transient effects of volcanic aerosols on climate would also provide critical data to inform proposed solar geoengineering strategies that involve introducing aerosols into the atmosphere to mitigate global warming [NASEM, 2021].

    NASA’s Eruption Response Plan

    In the United States, NASA has traditionally led investigations of eruptions involving stratospheric injection because of the agency’s global satellite-based observation capabilities for measuring atmospheric composition and chemistry and its unique suborbital assets for measuring the evolution of volcanic clouds in the stratosphere.

    Under its current plan, NASA’s eruption response procedures will be triggered in the event an eruption emits at least 5 teragrams of SO2 into the stratosphere, as estimated using NASA’s or other satellite assets [e.g., Carn et al., 2016]. The first phase of the response plan involves a review of near-real-time satellite data by a combined panel of NASA Headquarters (HQ) science program managers and NASA research scientists in parallel with initial modeling of the eruption plume’s potential atmospheric evolution and impacts.

    The HQ review identifies relevant measurement and modeling capabilities at the various NASA centers and among existing NASA-funded activities. HQ personnel would establish and task science leads and teams comprising relevant experts from inside and outside NASA to take responsibility for observations from the ground, from balloons, and from aircraft. The efforts of these three groups would be supplemented by satellite observations and modeling to develop key questions, priority observations, and sampling and deployment plans.

    Implementing the plan developed in this phase would likely result in major diversions and re-tasking of assets, such as NASA aircraft involved in meteorological monitoring, from ongoing NASA research activities and field deployments. Ensuring that these diversions are warranted necessitates that this review process is thorough and tasking assignments are carefully considered.

    The second phase of NASA’s volcanic response plan—starting between 1 week and 1 month after the eruption—involves the application of its satellite platforms, ground observations from operational networks, and eruption cloud modeling. Satellites would track volcanic clouds to observe levels of SO2 and other aerosols and materials. Gathering early information on volcanic aerosol properties like density, particle composition, and particle size distribution would provide key information for assessing in greater detail the potential evolution and effects of the volcanic aerosols. Such assessments could provide valuable information on the amount of expected surface cooling attributable to these aerosols, as well as the lifetime of stratospheric aerosol particles—two factors that depend strongly on the aerosols’ size distribution and temporal evolution.

    Meanwhile NASA’s Aerosol Robotic Network (AERONET); Micro-Pulse Lidar Network (MPLNET); and Southern Hemisphere Additional Ozonesondes (SHADOZ) would provide real-time observations from the ground. Eruption cloud modeling would be used to calculate cloud trajectories and dispersion to optimize selection of ground stations for balloon launches and re-tasking of airborne assets.

    The third phase of the response plan—starting 1–3 months after an eruption—would see the deployment of rapid response balloons and aircraft (e.g., from NASA’s Airborne Science Program). The NASA P-3 Orion, Gulfstream V, and DC-8 aircraft have ranges of more than 7,000 kilometers and can carry heavy instrumentation payloads of more than 2,500 kilograms to sample the middle to upper troposphere. A mix of in situ and remote sensing instruments would be employed to collect detailed observations of eruption plume structure, evolution, and optical properties.

    NASA’s high-altitude aircraft (ER-2 and WB-57f) provide coverage into the stratosphere (above about 18 kilometers) with payloads of more than 2,200 kilograms. These high-altitude planes would carry payloads for measuring the evolving aerosol distributions along with trace gas measurements in situ to further understand the response of stratospheric ozone and climate forcing to the eruption. In particular, the high-altitude observations would include data on the particle composition and size distribution of aerosols, as well as on ozone, SO2, nitrous oxide and other stratospheric tracers, water vapor, and free radical species. Instrumented balloons capable of reaching the stratosphere could also be rapidly deployed to remote locations to supplement these data in areas not reached by the aircraft.

    The third phase would be staged as several 2- to 6-week deployments over a 1- to 2-year period that would document the seasonal evolution, latitudinal dispersion, and multiyear dissipation of the plume from the stratosphere. These longer-term observations would help to constrain model simulations of the eruption’s impacts on the global atmosphere and climate.

    Enhancing Eruption Response

    An effective eruption response is contingent on timely recognition of the hallmarks of a major volcanic eruption, namely, stratospheric injection and substantial emissions of SO2 (and H2S) amounting to more than 5 teragrams, using satellite data. However, it may take several hours to a day after an event for satellites to confirm that emissions have reached this level. By then, time has been lost to position instruments and personnel to effectively sample the earliest stages of an eruption, and it is already too late to observe the onset of the eruption.

    Hence, a key element in efforts to strengthen eruption responses is improving our recognition of distinctive geophysical or geochemical eruption precursors that may herald a high-magnitude event. Observations of large, sulfur-rich eruptions such as Pinatubo have led to scientific consensus that such eruptions emit “excess” volatiles—gas emissions (especially sulfur species, but also other gases such as water vapor and carbon dioxide) exceeding those that could be derived from the erupted magma alone. Excess volatiles, in the form of gas bubbles derived from within or below a magma reservoir that then accumulate near the top of the reservoir, may exacerbate climate impacts of eruptions and influence magmatic processes like magma differentiation, eruption triggering and magnitude, and hydrothermal ore deposition [e.g., Edmonds and Woods, 2018]. They may also produce detectable eruption precursors and influence eruption and plume dynamics, although how remains largely unknown.

    With support from NASA’s Interdisciplinary Research in Earth Science program, we (the authors) have begun an integrated investigation of eruption dynamics focused on understanding the fate of excess volatiles from their origins in a magma reservoir, through underground conduits and into a volcanic plume, and, subsequently, as they are dispersed in the atmosphere. The satellite observations we use are the same or similar to those required for rapid assessment and response to future high-magnitude events (with a VEI of 6 or greater).

    Our investigation is using data from previous moderate-scale eruptions (VEI of 3–5) with excellent satellite observational records that captured instances in which gases and aerosols displayed disparate atmospheric dispersion patterns. Among the main questions we are examining is whether excess volatile accumulation in magma reservoirs can drive large eruptions and produce enhanced aerosol-related climate impacts resulting from these eruptions. Using numerical model simulations of eruptions involving variable quantities of excess volatiles, we will endeavor to reproduce the specific atmospheric distributions of gases and aerosols observed by satellites after these events and thus elucidate how volatile accumulation might influence plume dispersion and climate impacts.

    We are currently developing a framework to simulate a future eruption with a VEI of 6+. Over the coming year, we hope to produce benchmark simulations that track the fate of volcanic gases as they travel from a subsurface magmatic system into the atmosphere to be distributed globally. This simulation framework will comprise a coupled suite of subsystem-scale numerical models, including models of magma withdrawal from the magma reservoir, magma ascent within the volcanic conduit, stratospheric injection within the volcanic plume, and atmospheric dispersion and effects on climate.

    With these tools, NASA will have gained important capabilities in simulating volcanic eruptions and understanding their potential precursors. These capabilities will complement NASA’s satellite and suborbital observations of volcanic eruptions as they unfold—an important advance for volcano science and a powerful means to assess the climate impacts of future large explosive eruptions.

    References:

    Carn, S. A. (2021), Multi-Satellite Volcanic Sulfur Dioxide L4 Long-Term Global Database V4, USA, Goddard Earth Sci. Data and Inf. Serv. Cent., Greenbelt, Md., https://doi.org/10.5067/MEASURES/SO2/DATA405.

    Carn, S. A., L. Clarisse, and A. J. Prata (2016), Multi-decadal satellite measurements of global volcanic degassing, J. Volcanol. Geotherm. Res., 311, 99–134, https://doi.org/10.1016/j.jvolgeores.2016.01.002.

    Edmonds, M., and A. W. Woods (2018), Exsolved volatiles in magma reservoirs, J. Volcanol. Geotherm. Res., 368, 13–30, https://doi.org/10.1016/j.jvolgeores.2018.10.018.

    Kovilakam, M., et al. (2020), The Global Space-based Stratospheric Aerosol Climatology (version 2.0): 1979–2018, Earth Syst. Sci. Data, 12(4), 2,607–2,634, https://doi.org/10.5194/essd-12-2607-2020.

    Kremser, S., et al. (2016), Stratospheric aerosol—Observations, processes, and impact on climate, Rev. Geophys., 54(2), 278–335, https://doi.org/10.1002/2015RG000511.

    NASA (2018), NASA Major Volcanic Eruption Response Plan, version 11, Greenbelt, Md., acd-ext.gsfc.nasa.gov/Documents/NASA_reports/Docs/VolcanoWorkshopReport_v12.pdf.

    National Academies of Sciences, Engineering, and Medicine (NASEM) (2017), Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing, Natl. Acad. Press, Washington, D.C., https://doi.org/10.17226/24650.

    National Academies of Sciences, Engineering, and Medicine (NASEM) (2021), Reflecting Sunlight: Recommendations for Solar Geoengineering Research and Research Governance, Natl. Acad. Press, Washington, D.C., https://doi.org/10.17226/25762.

    Robock, A. (2000), Volcanic eruptions and climate, Rev. Geophys., 38(2), 191–219, https://doi.org/10.1029/1998RG000054.

    Shindell, D. T., et al. (2004), Dynamic winter climate response to large tropical volcanic eruptions since 1600, J. Geophys Res., 109, D05104, https://doi.org/10.1029/2003JD004151.

    Thomason, L. W., et al. (2018), A global space-based stratospheric aerosol climatology: 1979–2016, Earth Syst. Sci. Data, 10(1), 469–492, https://doi.org/10.5194/essd-10-469-2018.

    Toohey, M., et al. (2019), Disproportionately strong climate forcing from extratropical explosive volcanic eruptions, Nat. Geosci., 12(2), 100–107, https://doi.org/10.1038/s41561-018-0286-2.

    Zhu, Y., et al. (2020), Persisting volcanic ash particles impact stratospheric SO2 lifetime and aerosol optical properties, Nat. Commun., 11, 4526, https://doi.org/10.1038/s41467-020-18352-5.

    See the full article here .

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  • richardmitnick 3:32 pm on September 3, 2021 Permalink | Reply
    Tags: "Making the Most of Volcanic Eruption Responses", , , Eos, ,   

    From Eos: “Making the Most of Volcanic Eruption Responses” 

    From AGU
    Eos news bloc

    From Eos

    31 August 2021

    Tobias P. Fischer
    Seth C. Moran
    Kari M. Cooper
    kmcooper@ucdavis.edu
    Diana C. Roman
    Peter C. LaFemina

    1
    A simulated eruption at Mount Hood, part of the Cascade Volcanic Arc, in Oregon, seen here, was the subject of a November 2020 virtual eruption response exercise intended to optimize scientific data collection. The exercise proved to be a valuable practice run for an actual eruption of Hawaii’s Kīlauea volcano the following month. Credit: Robert DuVernet, CC BY-SA 3.0

    Mount St. Helens, hidden away in a remote forest midway between Seattle, Wash., and Portland, Ore., had been putting out warning signals for 2 months. Still, the size and destruction of the 18 May 1980 eruption took the United States by surprise. The blast spewed ash into the air for more than 9 hours, and pyroclastic density currents and mudflows wiped out surrounding forests and downstream bridges and buildings. Fifty-seven people died as a result of the volcanic disaster, the worst known in the continental United States.

    In addition to its immediate and devastating effects, the 1980 eruption spurred efforts to study volcanic processes and their impacts on surrounding landscapes more thoroughly and to advance monitoring and forecasting capabilities. It also prompted further cooperation among agencies and communities to better prepare for and respond to future volcanic eruptions.

    2
    Mount St. Helens erupts in 1980. Credit: Geological Survey (US).

    According to a 2018 U.S. Geological Survey (USGS) report, there are 161 potentially active volcanoes in the United States and its territories, including 55 classified as high or very high threat [Ewert et al., 2018*].

    *All cited papers in References below.

    Over the past century, especially since 1980, integrated studies of active volcanic systems have shed light on magmatic and volcanic processes that control the initiation, duration, magnitude, and style of volcanic eruptions. However, because there have been few continuously monitored volcanic eruptions with observations that span the entire sequence before, during, and after eruption, our understanding of these processes and the hazards they pose is still limited.

    This limited understanding, in turn, hampers efforts to forecast future eruptions and to help nearby communities prepare evacuation plans and to marshal and allocate resources during and after an event. Thus, a recent consensus study about volcanic eruptions by the National Academies of Sciences, Engineering, and Medicine [2017] highlighted the need to coordinate eruption responses among the broad volcanological and natural hazard scientific community as one of three grand challenges.

    The Community Network for Volcanic Eruption Response (CONVERSE) initiative, which began in 2018 as a 3-year Research Coordination Network supported by the National Science Foundation (US), is attempting to meet this challenge. The charge of CONVERSE is to maximize the scientific return from eruption responses at U.S. volcanoes by making the most efficient use possible of the relatively limited access and time to collect the most beneficial data and samples. This goal requires looking for ways to better organize the national volcano science community.

    A critical component of this organization is to facilitate cooperation between scientists at academic institutions and the U.S. Geological Survey, which is responsible for volcano monitoring and hazard assessment at domestic volcanoes. Since 2019, CONVERSE has conducted several workshops to allow groups representing the various disciplines in volcanology to formulate specific science questions that can be addressed with data collected during an eruption response and assess their capacities for such a response. Most recently, in November 2020, we conducted a virtual response scenario exercise based on a hypothetical eruption of Mount Hood in the Oregon Cascades. A month later, Hawaii’s Kīlauea volcano erupted, allowing us to put what we learned from the simulation to use in a coordinated response.

    A Virtual Eruption at Mount Hood

    To work through a simulated response to an eruption scenario at Mount Hood, our CONVERSE team had planned an in-person meeting for March 2020 involving a 2-day tabletop exercise. Travel and meeting restrictions enacted in response to the COVID-19 pandemic required us to postpone the exercise until 16–17 November, when we conducted it virtually, with 80 scientists participating for one or more days. The goal of the exercise was to test the effectiveness of forming a science advisory committee (SAC) as a model for facilitating communications between responding USGS volcano observatories and the U.S. academic community.

    Mount Hood, located near Portland, Ore., is relatively accessible through a network of roads and would attract a lot of scientific interest during an eruption. Thus, we based our eruption scenario loosely on a scenario developed in 2010 for Mount Hood for a Volcanic Crisis Awareness training course.

    Because a real-life eruption can happen at any time at any active volcano, participants in the November 2020 workshop were not informed of the selected volcano until 1 week prior to the workshop. Then we sent a simulated “exercise-only” USGS information statement to all registrants noting that an earthquake swarm had started several kilometers south of Mount Hood’s summit. In the days leading up to the workshop, we sent several additional information statements containing status updates and observations of the volcano’s behavior like those that might precede an actual eruption.

    During the workshop, participants communicated via videoconference for large group discussions and smaller breakout meetings. We used a business communications platform to share graphics and information resources and for rapid-fire chat-based discussions.

    The workshop started with an overview of Mount Hood’s eruptive history and monitoring status, after which the scenario continued with the volcano exhibiting escalating unrest and with concomitant changes in USGS alert level. Participants were asked to meet in groups representing different disciplines, including deformation, seismicity, gas, eruption dynamics, and geochemistry, to discuss science response priorities, particularly those that required access to the volcano.

    As the simulated crisis escalated at the end of the first day of the workshop, non-USGS attendees were told they could no longer communicate with USGS participants (and vice versa). This break in communication was done to mimic the difficulty that external scientists often encounter communicating with observatory staff during full-blown eruption responses, when observatory staff are fully consumed by various aspects of responding to the eruption. Instead, scientific proposals had to be submitted to a rapidly formed Hood SAC (H-SAC) consisting of a USGS liaison and several non-USGS scientists with expertise on Mount Hood.

    The H-SAC’s role was to quickly evaluate proposals submitted by discipline-specific groups on the basis of scientific merit or their benefit for hazard mitigation. For example, the geodesy group was approved to install five instruments at sites outside the near-field volcanic hazard zone to capture a deep deflation signal more clearly, an activity that did not require special access to restricted areas. On the other hand, a proposal by the gas group to climb up to the summit for direct gas sampling was declined because it was deemed too hazardous. Proposals by the tephra sampling group to collect ash at specific locations were also approved, but only if the group coordinated with a petrology group that had also submitted a proposal to collect samples for characterizing the pressure-temperature and storage conditions of the magma.

    The H-SAC then provided recommendations to the Cascade Volcano Observatory (CVO) scientist-in-charge, with that discussion happening in front of all participants so they could understand the considerations that went into the decisionmaking. After the meeting, participants provided feedback that the SAC concept seemed to work well. The proposal evaluation process that included scientific merit, benefit for hazard mitigation, and feasibility was seen as a positive outcome of the exercise that would translate well into a real-world scenario. Participants emphasized, however, that it was critical that SAC members be perceived as neutral with respect to any disciplinary or institutional preferences and that the SAC have broad scientific representation.

    Responding to Kīlauea’s Real Eruption

    Just 1 month after the workshop, on 20 December 2020, Kīlauea volcano began erupting in real life, providing an immediate opportunity for CONVERSE to test the SAC model. The goals of CONVERSE with respect to the Kīlauea eruption were to facilitate communication and coordination of planned and ongoing scientific efforts by USGS scientists at the Hawaiian Volcano Observatory (HVO) and external scientists and to broaden participation by the academic community in the response.

    3
    Kīlauea’s volcanic lava lake is seen here at the start of the December 2020 eruption. Credit: Matthew Patrick, USGS.

    These goals were addressed through two types of activities. First, a Kīlauea Scientific Advisory Committee (K-SAC), consisting of four academic and three USGS scientists, was convened within a week of the start of the eruption. This committee acted as the formal point of contact between HVO and the external scientific community for the Kīlauea eruption, and it solicited and managed proposals for work requiring coordination between these groups.

    The K-SAC evaluated proposals on the basis of the potential for scientific gain and contributions to mitigating hazards. For example, one proposal dealt with assessing whether new magma had entered the chamber or whether the eruption released primarily older magma already under the volcano. The K-SAC also identified likely benefits and areas of collaboration between proposing groups, and it flagged potential safety and logistical (including permitting from the National Park Service) concerns in proposals as well as resources required from HVO.

    Proposals recommended by the K-SAC were then passed to HVO staff, who consulted with USGS experts about feasibility, potential collaborations, and HVO resources required before making decisions on whether to move forward with them. One proposal supported by the K-SAC involved the use of hyperspectral imaging to quantify in real time the proportion of crystalline material and melt in the active lava lake to help determine the lava’s viscosity, a critical parameter for hazard assessment.

    The second major activity of CONVERSE as the Kīlauea eruption progressed was to provide a forum for communication of science information via a business communications platform open to all volcano scientists. In addition, we posted information about planned and current activities by HVO and external scientists online and updated it using “living documents” as well as through virtual information sessions. As part of this effort, the K-SAC developed a simple spreadsheet that listed the types of measurements that were being made, the groups making these measurements, and where the obtained data could be accessed. For example, rock samples collected from the eruption were documented, and a corresponding protocol on how to request such samples for analytical work was developed. We held virtual town hall meetings, open to all, to discuss these topics, as well as updates from HVO K-SAC members on the status of the eruption and HVO efforts.

    The Future of CONVERSE

    The recent virtual exercise and the experience with the Kīlauea eruption provided valuable knowledge in support of CONVERSE’s mandate to develop protocols for coordinating scientific responses to volcanic eruptions. These two events brought home to us the importance of conducting regular, perhaps yearly or even more frequent, tabletop exercises. Such exercises could be held in person or virtually to further calibrate expectations and develop protocols for scientific coordination during real eruptions and to create community among scientists from different institutions and fields. Currently, workshops to conduct two scenario exercises are being planned for late this year and early next year. One will focus on testing deformation models with a virtual magma injection event; the other will focus on a response to an eruption occurring in a distributed volcanic field in the southwestern United States.

    Future exercises should build on lessons learned from the Hood scenario workshop and the Kīlauea eruption response. For example, although the SAC concept worked well in principle, the process required significant investments of time that delayed some decisions, possibly limiting windows of opportunity for critical data collection at the onset of the eruption. Although CONVERSE is focused on coordination for U.S. eruptions, its best practices and protocols could guide future international eruption responses coordinated among volcano monitoring agencies of multiple countries.

    A critical next step will be the development of a permanent organizational framework and infrastructure for CONVERSE, which at a minimum should include the following:

    A mechanism for interested scientists to self-identify and join CONVERSE so they can participate in eruption response planning and activities, including media and communications training.

    A national-level advisory committee with accessibility to equitable decisionmaking representation across scientific disciplines and career stages. The committee would be responsible for coordinating regular meetings, planning and conducting activities, liaising with efforts like the SZ4D and Modeling Collaboratory for Subduction initiatives, and convening eruption-specific SACs.

    Dedicated eruption SACs that facilitate open application processes for fieldwork efforts, including sample collection, distribution, and archiving. The SACs would establish and provide clear and consistent protocols for handling data and samples and would act as two-way liaisons between the USGS observatories and external scientists.

    A dedicated pool of rapid response instruments, including, for example, multispectral cameras, infrasound sensors, Global Navigation Satellite System receivers, uncrewed aerial vehicles, and gas measuring equipment. This pool could consist of permanent instruments belonging to CONVERSE and housed at an existing facility as well as scientist-owned distributed instruments available on demand as needed.

    The SAC structure holds great promise for facilitating collaboration between U.S. observatories and external science communities during eruptions and for managing the many requests for information from scientists interested in working on an eruption. It also broadens participation in eruption responses beyond those who have preexisting points of contact with USGS observatory scientists by providing a point of contact and process to become engaged.

    We are confident that when the next eruption occurs in the United States—whether it resembles the 1980 Mount St. Helens blast, the recent effusive lava flows from Kīlauea, or some other style—this structure will maximize the science that can be done during the unrest. Such efforts will ultimately help us to better understand what is happening at the volcano and to better assist communities to prepare for and respond to eruptions.

    References:

    Ewert, J. W., A. K. Diefenbach, and D. W. Ramsey (2018), 2018 update to the U.S. Geological Survey national volcanic threat assessment, U.S. Geol. Surv. Sci. Invest. Rep., 2018-5140, 40 pp., https://doi.org/10.3133/sir20185140.

    National Academies of Sciences, Engineering, and Medicine (2017), Volcanic Eruptions and Their Repose, Unrest, Precursors, and Timing, Natl. Acad. Press, Washington, D.C., https://doi.org/10.17226/24650.

    See the full article here .

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  • richardmitnick 8:59 am on September 2, 2021 Permalink | Reply
    Tags: "When Deep Learning Meets Geophysics", , , Eos   

    From Eos: “When Deep Learning Meets Geophysics” 

    From AGU
    Eos news bloc

    From Eos

    9.1.21
    Jianwei Ma
    jwm@pku.edu.cn
    Siwei Yu

    Traditional physical models are no longer the only foundational tools for processing geophysical data; “big data” help to reveal the laws of geophysics from new angles with exciting results so far.

    1
    Understanding deep learning (DL) from different perspectives. Credit: Yu and Ma [2021].

    As artificial intelligence (AI) continues to develop, geoscientists are interested in how new AI developments could contribute to geophysical discoveries. A new article in Reviews of Geophysics examines one popular AI technique, deep learning (DL). We asked the authors some questions about the connection between deep learning and the geosciences.

    How would you describe “deep learning” in simple terms to a non-expert?

    Deep learning (DL) optimizes the parameters in a system, a so-called “neural network,” by feeding it a large amount of training data. “Deep” means the system consists of a structure with multiple layers.

    DL can be understood from different angles. In terms of biology, DL is a bionic approach imitating the neurons in the human brain; a computer can learn knowledge as well as draw inferences like a human. In terms of mathematics, DL is a high-dimensional nonlinear optimization problem; DL constructs a mapping from the input samples to the output labels. In terms of information science, DL extracts useful information from a large set of redundant data.

    How can deep learning be used by the geophysical community?

    2
    Deep learning-based geophysical applications. Credit: Yu and Ma [2021].

    DL has the potential to be applied to most areas of geophysics. By providing a large database, you can train a DL architecture to perform geophysical inferring. Take earthquake science as an example. The historical records of seismic stations contain useful information such as the waveforms of an earthquake and corresponding locations. Therefore, the waveforms and locations serve as the input and output of a neural network. The parameters in the neural network are optimized to minimize the mismatch between the output of the neural network and the true locations. Then the trained neural network can predict locations of new coming seismic events. DL can be used in other fields in a similar manner.

    What advantages does deep learning have over traditional methods in geophysical data processing and analysis?

    Traditional methods suffer from inaccurate modeling and computational bottlenecks with large-scale and complex geophysical systems; DL could be helpful to solve this. First, DL can handle big data naturally where it causes a computational burden in traditional methods. Second, DL can utilize historical data and experience which are usually not considered in traditional methods. Third, an accurate description of the physical model is not required, which is useful when the physical model is not known partially. Fourth, DL can provide a high computational efficiency after the training is complete thus enabling the characterization of Earth with a high resolution. Fifth, DL can be used for discovering physical concepts, such as the solar system is heliocentric, and may even provide discoveries that are not yet known.

    In your opinion, what are some of the most exciting opportunities for deep learning applications in geophysics?

    DL has already provided some surprising results in geophysics. For instance, on the Stanford earthquake data set, the earthquake detection accuracy improved to 100 percent compared to 91 percent accuracy with the traditional method.

    In our review article, we suggest a roadmap for applying DL to different geophysical tasks, divided into three levels:

    Traditional methods are time-consuming and require intensive human labor and expert knowledge, such as in the first-arrival selection and velocity selection in exploration geophysics.
    Traditional methods have difficulties and bottlenecks. For example, geophysical inversion requires good initial values and high accuracy modeling and suffers from local minimization.
    Traditional methods cannot handle some cases, such as multimodal data fusion and inversion.

    What are some difficulties in applying deep learning in the geophysical community?

    Despite the success of DL in some geophysical applications, such as earthquake detectors or pickers, its use as a tool for most practical geophysics is still in its infancy.

    The main difficulties include a shortage of training samples, low signal-to-noise ratios, and strong nonlinearity. The lack of training samples in geophysical applications compared to those in other industries is the most critical of these challenges. Though the volume of geophysical data is large, available labels are scarce. Also, in certain geophysical fields, such as exploration geophysics, the data are not shared among companies. Further, geophysical tasks are usually much more difficult than those in computer vision.

    What are potential future directions for research involving deep learning in geophysics?

    3
    Future trends for applying deep learning in geophysics. Credit: Yu and Ma [2021].

    In terms of DL approaches, several advanced DL methods may overcome the difficulties of applying DL in geophysics, such as semi-supervised and unsupervised learning, transfer learning, multimodal DL, federated learning, and active learning. For example, in practical geophysical applications, obtaining labels for a large data set is time-consuming and can even be infeasible. Therefore, semi-supervised or unsupervised learning is required to relieve the dependence on labels.

    We would like to see research of DL in geophysics focus on the cases that traditional methods cannot handle, such as simulating the atmosphere or imaging the Earth’s interior on a large spatial and temporal scale with high resolution.

    Jianwei Ma (jwm@pku.edu.cn), Peking University [北京大学](CN)
    Siwei Yu, Harbin Institute of Technology [哈尔滨工业大学] (CN)

    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.

     
  • richardmitnick 2:43 pm on August 23, 2021 Permalink | Reply
    Tags: "Earth’s Continents Share an Ancient Crustal Ancestor", , , Eos, ,   

    From Eos: “Earth’s Continents Share an Ancient Crustal Ancestor” 

    From AGU
    Eos news bloc

    From Eos

    8.23.21
    Julie Hollis
    juho@nanoq.gl
    Chris Kirkland
    Michael Hartnady
    Milo Barham
    Agnete Steenfelt

    1
    Researchers collect stream sediments in Greenland. Zircons from these sediments have provided tantalizing clues to how today’s continents came to be. Credit: Agnete Steenfelt.

    The jigsaw fit of Earth’s continents, which long intrigued map readers and inspired many theories, was explained about 60 years ago when the foundational processes of plate tectonics came to light. Topographic and magnetic maps of the ocean floor revealed that the crust—the thin, rigid top layer of the solid Earth—is split into plates. These plates were found to shift gradually around the surface atop a ductile upper mantle layer called the asthenosphere. Where dense oceanic crust abuts thicker, buoyant continents, the denser crust plunges back into the mantle beneath. Above these subduction zones, upwelling mantle melt generates volcanoes, spewing lava and creating new continental crust.

    From these revelations, geologists had a plausible theory for how the continents formed and perhaps how Earth’s earliest continents grew—above subduction zones. Unfortunately, the process is not that simple, and plate tectonics have not always functioned this way [Tectonophysics]. Subsequent research since the advent of plate tectonic theory has shown that subduction and associated mantle melting provide only a partial explanation for the formation and growth of today’s continents. To better understand the production and recycling of crust, some scientists, including our team, have shifted from studying the massive moving plates to detailing the makeup of tiny mineral crystals that have stood the test of time.

    Starting in the 1970s, geologists from the Greenland Geological Survey collected stream sediments from all over Greenland, sieving them to sand size and chemically analyzing them to map the continent-scale geochemistry and contribute to finding mineral occurrences. Unbeknownst to them at the time, tiny grains of the mineral zircon contained in the samples held clues about the evolution of Earth’s early crust. After decades in storage in a warehouse in Denmark, the zircon grains in those carefully archived bottles of sand—and the technology to analyze them—were ready to reveal their secrets.

    3
    This cathodoluminescence image shows the internal structure of magnified zircons analyzed by laser ablation. Credit: Chris Kirkland.

    Zircon occurs in many rock types in continental crust, and importantly, it is geologically durable. These tiny mineral time capsules preserve records of the distant past—as far back as 4.4 billion years—which are otherwise almost entirely erased. More than just recording the time at which a crystal grew, zircon chemistry records information about the magma from which it grew, including whether the magma originated from a melted piece of older crust, from the mantle, or from some combination of these sources. Through the isotopic signatures in a zircon grain, we can track its progression, from the movement of the magma up from the mantle, to its crystallization, to the grain’s uplift to the surface and its later erosion and redeposition.

    The Past Is Not Always Prologue

    New continental crust is formed above subduction zones, but it is also destroyed at subduction zones [e.g., Scholl and von Heune, 2007*]. Formation and destruction occur at approximately equal rates in a planetary-scale yin and yang [Stern and Scholl, 2010; Hawkesworth et al., 2019]. So crust formation above subduction zones cannot satisfactorily account for growth of the continents.

    *See References

    What’s more, plate tectonic movements like we see on Earth today did not operate the same way during Earth’s early history. Although there are indications that subduction may have occurred in Earth’s early history [Nature] (at least locally), many geochemical, isotopic, petrological, and thermal modeling studies of crust formation processes suggest that plate tectonics started gradually and didn’t begin operating as it does today until about 3 billion years ago, after more than a quarter of Earth’s history had already passed [e.g., McClennan and Taylor, 1983; Dhuime et al., 2015; Hartnady and Kirkland, 2019]. Because the mantle was much hotter at that time, more of it melted than it does now, producing large amounts of oceanic crust that was both too thick and too viscous to subduct.

    Nonetheless, although subduction was apparently not possible on a global scale before about 3 billion years ago, geochemical and isotopic evidence shows that a large volume of continental crust had already formed by that time [e.g., Hawkesworth et al., 2019; Condie, 2014; Taylor and McClennan 1995].

    If subduction didn’t generate the volume of continental crust we see today, what did?

    How Did Earth’s Early Crust Form?

    The nature of early Earth dynamics and how and when the earliest continental crust formed have remained topics of intense debate, largely because so little remains of Earth’s ancient crust for direct study. Various mechanisms have been proposed.

    Perhaps plumes of hot material rising from the mantle melted the oceanic crustal rock above [Smithies et al., 2005]. If dense portions of this melted rock “dripped” back into the mantle, they could have stirred convection cells in the upper mantle. These drips might have also added water to the mantle, lowering its melting point and producing new melts that ascended into the crust [Johnson et al., 2014].

    Or maybe meteorite impacts punched through the existing crust into the mantle, generating new melts that, again, ascended toward the surface and added new crust [Hansen, 2015]. Another possibility is that enough heat built up at the base of the thick oceanic crust on early Earth that parts of the crust remelted, with the less dense, buoyant melt portions then rising and forming pockets of continental crust [Smithies et al., 2003].

    By whichever processes Earth’s first continental crust formed, how did the large volume of continental crust we have now build up? Our research helps resolve this question [Kirkland et al., 2021].

    Answers Hidden in Greenland Zircons

    We followed the histories of zircon crystals through the eons by probing the isotopes preserved in grains from the archived stream sediment samples from an area of west Greenland. These isotopes were once dissolved within molten mantle before being injected into the crust by rising magmas that crystallized zircons and lifted them up to the surface. Eventually, wind and rain erosion released the tiny crystals from their rock hosts, and rivulets of water tumbled them down to quiet corners in sandy stream bends. There they rested until geologists gathered the sand, billions of years after the zircons formed inside Earth.

    In the laboratory, we extracted thousands of zircon grains from the sand samples. These grains—mounted inside epoxy resin and polished—were then imaged with a scanning electron microscope, revealing pictures of how each zircon grew, layer upon layer, so long ago.

    3
    Researchers used the laser ablation mass spectrometer at Curtin University (AU) to study isotopic ratios in zircon crystals. Credit: Chris Kirkland.

    In a mass spectrometer, the zircons were blasted with a laser beam, and a powerful magnetic field separated the resulting vapor into isotopes of different masses. We determined when each crystal formed using the measured amounts of radioactive parent uranium and daughter lead isotopes. We also compared the hafnium isotopic signature in each zircon with the signatures we would expect in the crust and in the mantle on the basis of the geochemical and isotopic fractionation of Earth through time. Using these methods, we determined the origins of the magma from which the crystals grew and thus built a history of the planet from grains of sand.

    Our analysis revealed that the zircon crystals varied widely in age, from 1.8 billion to 3.9 billion years old—a much broader range than what’s typically observed in Earth’s ancient crust. Because of both this broad age range and the high geographic density of the samples in our data set, patterns emerged in the data.

    In particular, some zircons of all ages had hafnium isotope signatures that showed that these grains originated from rocks that formed as a result of the melting of a common 4-billion-year-old parent continental crust. This common source implied that early continental crust did not form anew and discretely on repeated occasions. Instead, the oldest continental crust might have survived to serve as scaffolding for successive additions of younger continental crust.

    In addition to revealing this subtle, but ubiquitous, signature of Earth’s ancient crust in the Greenland samples, our data also showed something very significant about the evolution of Earth’s continental crust around 3 billion years ago. The hafnium signature of most of the zircons from that time that we analyzed showed a distinct isotopic signal linked to the input of mantle material into the magma from which these crystals grew. This strong mantle signal in the hafnium signature showed us that massive amounts of new continental crust formed in multiple episodes around this time by a process in which mantle magmas were injected into and melted older continental crust.

    4
    Geologists work atop a rock outcrop in the Maniitsoq region of western Greenland. Credit: Julie Hollis.

    The idea that ancient crust formed the scaffolding for later growth of continents was intriguing, but was it true? And was this massive crust-forming event related to some geological process restricted to what is now Greenland, or did this event have wider significance in Earth’s evolution?

    A Global Crust Formation Event

    To test our hypotheses, we looked at data sets of isotopes in zircons from other parts of the world where ancient continental crust is preserved. As with our Greenland data, these large data sets all showed evidence of repeated injection of mantle melts into much more ancient crust. Ancient crust seemed to be a prerequisite for growing new crust.

    Moreover, the data again showed that these large volumes of mantle melts were injected into older crust everywhere at about the same time, between 3.2 billion and 3.0 billion years ago, timing that coincides with the estimated peak in Earth’s mantle temperatures [Earth and Planetary Science Letters]. This “hot flash” in the deep Earth may have enabled huge volumes of melt to rise from the mantle and be injected into existing older crust, driving a planetary continent growth spurt.

    The picture that emerges from our work is one in which buoyant pieces of the oldest continental crust melted during the accrual and trapping of new mantle melts in a massive crust-forming event about 3 billion years ago. This global event effectively, and rapidly, built the continents. With the onset of the widespread subduction that we see today, these continents have since been destroyed, remade, and shifted around the surface like so many jigsaw pieces in perpetuity through the eons.

    References

    Condie, K. (2014), Growth of continental crust: A balance between preservation and recycling, Mineral. Mag., 78(3), 623–637, https://doi.org/10.1180/minmag.2014.078.3.11.

    Dhuime, B., A. Wuestefeld, and C. J. Hawkesworth (2015), Emergence of modern continental crust about 3 billion years ago, Nat. Geo­sci., 8, 552–555, https://doi.org/10.1038/ngeo2466.

    Hansen, V. L. (2015), Impact origin of Archean cratons, Lithosphere, 7, 563–578, https://doi.org/10.1130/L371.1.

    Hartnady, M. I. H., and C. L. Kirkland (2019), A gradual transition to plate tectonics on Earth between 3.2 and 2.7 billion years ago, Terra Nova, 31, 129–134, https://doi.org/10.1111/ter.12378.

    Hawkesworth, C. J., B. Dhuime, and P. A. Cawood (2019), Rates of generation and growth of the continental crust, Geosci. Front., 10(1), 165–173, https://doi.org/10.1016/j.gsf.2018.02.004.

    Johnson, T. E., et al. (2014), Delamination and recycling of Archaean crust caused by gravitational instabilities, Nat. Geosci., 7, 47–52, https://doi.org/10.1038/ngeo2019.

    Kirkland, C. L., et al. (2021), Widespread reworking of Hadean-to-Eoarchean continents during Earth’s thermal peak, Nat. Commun., 12, 331, https://doi.org/10.1038/s41467-020-20514-4.

    McLennan, S. M., and S. R. Taylor (1983), Continental freeboard, sedimentation rates and growth of continental crust, Nature, 306, 169–172, https://doi.org/10.1038/306169a0.

    Scholl, D. W., and R. von Huene (2007), Crustal recycling at modern subduction zones applied to the past—Issues of growth and preservation of continental basement crust, mantle geochemistry, and supercontinent reconstruction, in 4-D Framework of Continental Crust, edited by R. D. Hatcher et al., Mem. Geol. Soc. Am., 200, 9–32, https://doi.org/10.1130/2007.1200(02).

    Smithies, R. H., D. C. Champion, and K. F. Cassidy (2003), Formation of Earth’s early Archaean continental crust, Precambrian Res., 127(1–3), 89–101, https://doi.org/10.1016/S0301-9268(03)00182-7.

    Smithies, R. H., M. J. Van Kranendonk, and D. C. Champion (2005), It started with a plume — Early Archaean basaltic proto-continental crust, Earth Planet. Sci. Lett., 238, 284–297, https://doi.org/10.1016/j.epsl.2005.07.023.

    Stern, R. J., and D. W. Scholl (2010), Yin and yang of continental crust creation and destruction by plate tectonic processes, Int. Geol. Rev., 52(1), 1–31, https://doi.org/10.1080/00206810903332322.

    Taylor, S. R., and S. M. McLennan (1995), The geochemical evolution of the continental crust, Rev. Geophys., 33(2), 241–265, https://doi.org/10.1029/95RG00262.

    See the full article here .

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  • richardmitnick 2:41 pm on August 20, 2021 Permalink | Reply
    Tags: "Swipe Left on the 'Big One' Better Dates for Cascadia Quakes", , , Coseismic coastal deformation, , , Eos, Geochronometers, Geologic proxies of megathrust earthquakes are generated by different aspects of the rupture process and can therefore inform us about specific rupture characteristics and hazards., , Ghost forests, New data collections from coastal forests that perished in or survived through CSZ earthquakes can now give near-annual dates for both inundations and ecosystem transitions., , , The last behemoth earthquake on the CSZ estimated at magnitude 9 struck on 26 January 1700.   

    From Eos: “Swipe Left on the ‘Big One’- Better Dates for Cascadia Quakes” 

    From AGU
    Eos news bloc

    From Eos

    8.20.21
    Jessie K. Pearl
    Lydia Staisch
    lstaisch@usgs.gov

    1
    The dead trees in this ghost forest in Copalis, Wash., were killed during the last major Cascadia earthquake in January 1700. Credit: Jessie K. Pearl. [Ed.: If it was 1700 C.E., how are they still standing?]

    The CSZ is a tectonic boundary off the coast that has unleashed massive earthquakes and tsunamis as the Juan de Fuca Plate is thrust beneath the North American Plate. And it will do so again. But when? And how big will the earthquake—or earthquakes—be?

    The last behemoth earthquake on the CSZ estimated at magnitude 9 struck on 26 January 1700. We know this age with such precision—unique in paleoseismology—because of several lines of geologic proxy evidence that coalesce around that date, in addition to Japanese historical records describing an “orphan tsunami” (a tsunami with no corresponding local earthquake) on that particular date [Atwater et al., 2015*]. Indigenous North American oral histories also describe the event. Geoscientists have robust evidence for other large earthquakes in Cascadia’s past; however, deciphering and precisely dating the geologic record become more difficult the farther back in time you go.

    *All cited works in References below.

    Precision dating of and magnitude constraints on past earthquakes are critically important for assessing modern CSZ earthquake hazards. Such estimates require knowledge of the area over which the fault has broken in the past; the amount of displacement, or slip, on the fault; the speed at which slip occurred; and the timing of events and their potential to occur in rapid succession (called clustering). The paucity of recent seismicity on the CSZ means our understanding of earthquake recurrence there primarily comes from geologic earthquake proxies, including evidence of coseismic land level changes, tsunami inundations, and strong shaking found in onshore and marine environments (Figure 1). Barring modern earthquakes, increasing the accuracy and precision of paleoseismological records is the only way to better constrain the size and frequency of megathrust ruptures and to improve our understanding of natural variability in CSZ earthquake hazards.

    1
    Fig. 1. Age ranges obtained from different geochronologic methods used for estimating Cascadia Subduction Zone megathrust events are shown in this diagram of preservation environments. At top is a dendrochronological analysis comparing a tree killed from a megathrust event with a living specimen. Here ^14C refers to radiocarbon (or carbon-14), and “wiggle-match ^14C” refers to an age model based on multiple, relatively dated (exact number of years known between samples) annual tree ring samples. Schematic sedimentary core observations and sample locations are shown for marsh and deep-sea marine environments. Gray probability distributions for examples of each 14C method are shown to the right of the schematic cores, with 95% confidence ranges in brackets. Optically stimulated luminescence (OSL)-based estimates are shown as a gray dot with error bars.

    To discuss ideas, frontiers, and the latest research at the intersection of subduction zone science and geochronology, a variety of specialists attended a virtual workshop about earthquake recurrence on the CSZ hosted by the Geological Survey (US) in February 2021. The workshop, which we discuss below, was part of a series that USGS is holding as the agency works on the next update of the National Seismic Hazard Model, due out in 2023.

    Paleoseismology Proxies

    Cascadia has one of the longest and most spatially complete geologic records of subduction zone earthquakes, stretching back more than 10,000 years along much of the 1,300-kilometer-long margin, yet debate persists over the size and recurrence of great earthquakes [Goldfinger et al., 2012; Atwater et al., 2014]. The uncertainty arises in part because we lack firsthand observations of Cascadia earthquakes. Thus, integrating onshore and offshore proxy records and understanding how different geologic environments record past megathrust ruptures remain important lines of inquiry, as well as major hurdles, in CSZ science. These hurdles are exacerbated by geochronologic data sets that differ in their precision and usefulness in revealing past rupture patches.

    One of the most important things to determine is whether proxy evidence records the CSZ rupturing in individual great events (approximately magnitude 9) or in several smaller, clustered earthquakes (approximately magnitude 8) that occur in succession. A magnitude 9 earthquake releases 30 times the energy of a magnitude 8 event, so the consequences of misinterpreting the available data can result in substantial misunderstanding of the seismic hazard.

    Geologic proxies of megathrust earthquakes are generated by different aspects of the rupture process and can therefore inform us about specific rupture characteristics and hazards. Some of the best proxy records for CSZ earthquakes lie onshore in coastal environments. Coastal wetlands, for example, record sudden and lasting land-level changes in their stratigraphy and paleoecology when earthquakes cause the wetlands’ surfaces to drop into the tidal range (Figure 1) [Atwater et al., 2015]. The amount of elevation change that occurs during a quake, called “coseismic deformation,” can vary along the coast during a single event because of changes in the magnitude, extent, and style of slip along the fault [e.g., Wirth and Frankel, 2019]. Thus, such records can reveal consistency or heterogeneity in slip during past earthquakes.

    Tsunami deposits onshore are also important proxies for understanding coseismic slip distribution. Tsunamis are generated by sudden seafloor deformation and are typically indicative of shallow slip, near the subduction zone trench (Figure 1) [Melgar et al., 2016]. The inland extent of tsunami deposits, and their distribution north and south along the subduction zone, can be used to identify places where an earthquake caused a lot of seafloor deformation and can tell generally how much displacement was required to create the tsunami wave.

    Offshore, seafloor sediment cores show coarse layers of debris flows called turbidites that can also serve as great proxies for earthquake timing and ground motion characteristics. Coseismic turbidites result when earthquake shaking causes unstable, steep, submarine canyon walls to fail, creating coarse, turbulent sediment flows. These flows eventually settle on the ocean floor and are dated using radiocarbon measurements of detrital organic-rich material.

    Geochronologic Investigations

    3
    Fig. 2. These graphs show the age range over which different geochronometers are useful (top), the average record length in Cascadia for different environments (middle), and the average uncertainty for different methods (bottom). Marine sediment cores have the capacity for the longest records, but age controls from detrital material in turbidites have the largest age uncertainties. Radiocarbon (^14C) ages from bracketing in-growth position plants and trees (wiggle matching) have much smaller uncertainties (tens of years) but are not preserved in coastal environments for as long. To optimize the potential range of dendrochronological geochronometers, the reference chronology of coastal tree species must be extended further back in time. The range limit (black arrow) of these geochronometers could thus be extended with improved reference chronologies.

    To be useful, proxies must be datable. Scientists primarily use radiocarbon dating to put past earthquakes into temporal context. Correlations in onshore and offshore data sets have been used to infer the occurrence of up to 20 approximately magnitude 9 earthquakes on the CSZ over the past 11,000 years [Goldfinger et al., 2012], although uncertainty in the ages of these events ranges from tens to hundreds of years (Figure 2). These large age uncertainties allow for varying interpretations of the geologic record: Multiple magnitude 8 or magnitude 7 earthquakes that occur over a short period of time (years to decades) could be misidentified as a single huge earthquake. It’s even possible that the most thoroughly examined CSZ earthquake, in 1700, might have comprised a series of smaller earthquakes, not one magnitude 9 event, because the geologic evidence providing precise ages of this event comes from a relatively short stretch of the Cascadia margin [Melgar, 2021].

    By far, the best geochronologic age constraints for CSZ earthquakes come from tree ring, or dendrochronological, analyses of well-preserved wood samples [e.g., Yamaguchi et al., 1997], which can provide annual and even seasonal precision (Figure 2). Part of how scientists arrived at the 26 January date for the 1700 quake was by using dendrochronological dating of coastal forests in southwestern Washington that were killed rapidly by coseismic saltwater submergence. Some of the dead western red cedar trees in these “ghost forests” are preserved with their bark intact; thus, they record the last year of their growth. By cross dating the dead trees’ annual growth rings with those in a multicentennial reference chronology derived from nearby living trees, it is evident that the trees died after the 1699 growing season.

    The ghost forest, however, confirms only that coseismic submergence in 1700 occurred along the 90 kilometers of the roughly 1,300-kilometer-long Cascadia margin where these western red cedars are found. The trees alone do not confirm that the entire CSZ fault ruptured in a single big one.

    Meanwhile, older CSZ events have not been dated with such high accuracy, in part because coseismically killed trees are not ubiquitously distributed and well preserved along the coastline and because there are no millennial-length, species-specific reference chronologies with which to cross date older preserved trees (Figure 2).

    Advances in Dating

    At the Cascadia Recurrence Workshop earlier this year, researchers presented recent advances and discussed future directions in paleoseismic dating methods. For example, by taking annual radiocarbon measurements from trees killed during coseismic coastal deformation, we can detect dated global atmospheric radiocarbon excursions in these trees, such as the substantial jump in atmospheric radiocarbon between the years 774 and 775 [Miyake et al., 2012]. This method allows us to correlate precise dates from other ghost forests along the Cascadian coast from the time of the 1700 event and to date past megathrust earthquakes older than the 1700 quake without needing millennial-scale reference chronologies [e.g., Pearl et al., 2020]. Such reference chronologies, which were previously required for annual age precision, are time- and labor-intensive to develop. With this method, new data collections from coastal forests that perished in or survived through CSZ earthquakes can now give near-annual dates for both inundations and ecosystem transitions.

    4
    Numerous tree rings are evident in this cross section from a subfossil western red cedar from coastal Washington. Patterns in ring widths give clues about when the tree died. Credit: Jessie K. Pearl.

    Although there are many opportunities to pursue with dendrochronology, such as dating trees at previously unstudied sites and trees killed by older events, we must supplement this approach with other novel geochronological methods to fill critical data gaps where trees are not preserved. Careful sampling and interpretation of age results from radiocarbon-dated material other than trees can also provide tight age constraints for tsunami and coastal submergence events.

    For example, researchers collected soil horizons below (predating) and overlying (postdating) a tsunami deposit in Discovery Bay, Wash., and then radiocarbon dated leaf bases of Triglochin maritima, a type of arrowgrass that grows in brackish and freshwater marsh environments. The tsunami deposits, bracketed by well-dated pretsunami and posttsunami soil horizons, revealed a tsunamigenic CSZ rupture that occurred about 600 years ago on the northern CSZ, perhaps offshore Washington State and Vancouver Island [Garrison-Laney and Miller, 2017].

    Multiple bracketing ages can dramatically reduce uncertainty that plagues most other dated horizons, especially those whose ages are based on single dates from detrital organic material (Figure 2). Although the age uncertainty of the 600-year-old earthquake from horizons at Discovery Bay is still on the order of several decades, the improved precision is enough to conclusively distinguish the event from other earthquakes dated along the margin.

    Further advancements in radiocarbon dating continue to provide important updates for dating coseismic evidence from offshore records. Marine turbidites do not often contain materials that provide accurate age estimates, but they are a critically important paleoseismic proxy [Howarth et al., 2021]. Turbidite radiocarbon ages rely on correcting for both global and local marine reservoir ages, which are caused by the radiocarbon “memory” of seawater. Global marine reservoir age corrections are systematically updated by experts as we learn more about past climates and their influences on the global marine radiocarbon reservoir [Heaton et al., 2020]. However, samples used to calibrate the local marine reservoir corrections in the Pacific Northwest, which apply only to nearby sites, are unfortunately not well distributed along the CSZ coastline, and little is known about temporal variations in the local correction, leading to larger uncertainty in event ages.

    These local corrections could be improved by collecting more sampled material that fills spatial gaps and goes back further in time. At the workshop, researchers presented the exciting development that they were in the process of collecting annual radiocarbon measurements from Pacific geoduck clam shells off the Cascadian coastline to improve local marine reservoir knowledge. Geoducks can live more than 100 years and have annual growth rings that are sensitive to local climate and can therefore be cross dated to the exact year. Thus, a chronology of local climatic variation and marine radiocarbon abundance can be constructed using living and deceased specimens. Annual measurements of radiocarbon derived from marine bivalves, like the geoduck, offer new avenues to generate local marine reservoir corrections and improve age estimates for coseismic turbidity flows.

    Putting It All Together

    An imminent magnitude 9 megathrust earthquake on the CSZ poses one of the greatest natural hazards in North America and motivates diverse research across the Earth sciences. Continued development of multiple geochronologic approaches will help us to better constrain the timing of past CSZ earthquakes. And integrating earthquake age estimates with the understanding of rupture characteristics inferred from geologic evidence will help us to identify natural variability in past earthquakes and a range of possible future earthquake hazard scenarios.

    Useful geochronologic approaches include using optically stimulated luminescence to date tsunami sand deposits (Figure 1) and determining landslide age estimates on the basis of remotely sensed land roughness [e.g., LaHusen et al., 2020]. Of particular value will be focuses on improving high-precision radiocarbon and dendrochronological dating of CSZ earthquakes, paired with precise estimates of subsidence magnitude, tsunami inundation from hydrologic modeling, inferred ground motion characteristics from sedimentological variations in turbidity deposits, and evidence of ground failure in subaerial, lake, and marine settings. Together, such lines of evidence will lead to better correlation of geologic records with specific earthquake rupture characteristics.

    Ultimately, characterizing the recurrence of major earthquakes on the CSZ megathrust—which have the potential to drastically affect millions of lives across the region—hinges on the advancement and the integration of diverse geochronologic and geologic records.

    References:

    Atwater, B. F., et al. (2014), Rethinking turbidite paleoseismology along the Cascadia subduction zone, Geology, 42(9), 827–830, https://doi.org/10.1130/G35902.1.

    Atwater, B. F., et al. (2015), The Orphan Tsunami, 2nd ed., U.S. Geol. Surv., Reston, Va.

    Garrison-Laney, C., and I. Miller (2017), Tsunamis in the Salish Sea: Recurrence, sources, hazards, in From the Puget Lowland to East of the Cascade Range: Geologic Excursions in the Pacific Northwest, GSA Field Guide, vol. 49, pp. 67–78, Geol. Soc. of Am., Boulder, Colo. https://doi.org/10.1130/2017.0049(04).

    Goldfinger, C., et al. (2012), Turbidite event history — Methods and implications for Holocene paleoseismicity of the Cascadia Subduction Zone, U.S. Geol. Surv. Prof. Pap., 1661-F, https://doi.org/10.3133/pp1661F.

    Heaton, T. J., et al. (2020), Marine20—The marine radiocarbon age calibration curve (0–55,000 cal BP), Radiocarbon, 62(4), 779–820, https://doi.org/10.1017/RDC.2020.68.

    Howarth, J. D., et al. (2021), Calibrating the marine turbidite palaeoseismometer using the 2016 Kaikōura earthquake, Nat. Geosci., 14(3), 161–167, https://doi.org/10.1038/s41561-021-00692-6.

    LaHusen, S. R., et al. (2020), Rainfall triggers more deep-seated landslides than Cascadia earthquakes in the Oregon Coast Range, USA, Sci. Adv., 6(38), eaba6790, https://doi.org/10.1126/sciadv.aba6790.

    Melgar, D. (2021), Was the January 26th, 1700 Cascadia earthquake part of an event sequence?, EarthArXiv, https://doi.org/10.31223/X5XG78.

    Melgar, D., et al. (2016), Kinematic rupture scenarios and synthetic displacement data: An example application to the Cascadia subduction zone, J. Geophys. Res. Solid Earth, 121, 6,658–6,674, https://doi.org/10.1002/2016JB013314.

    Miyake, F., et al. (2012), A signature of cosmic-ray increase in AD 774–775 from tree rings in Japan, Nature, 486(7402), 240–242, https://doi.org/10.1038/nature11123.

    Pearl, J. K., et al. (2020), A late Holocene subfossil Atlantic white cedar tree-ring chronology from the northeastern United States, Quat. Sci. Rev., 228, 106104, https://doi.org/10.1016/j.quascirev.2019.106104.

    Wirth, E. A., and A. D. Frankel (2019), Impact of down-dip rupture limit and high-stress drop subevents on coseismic land-level change during Cascadia Megathrust earthquakes, Bull. Seismol. Soc. Am., 109(6), 2,187–2,197, https://doi.org/10.1785/0120190043.

    Yamaguchi, D. K., et al. (1997), Tree-ring dating the 1700 Cascadia earthquake, Nature, 389(6654), 922–923, https://doi.org/10.1038/40048.

    See the full article here .

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  • richardmitnick 11:24 am on August 20, 2021 Permalink | Reply
    Tags: "Ice Lenses May Cause Many Arctic Landslides", , , , Eos, ,   

    From Eos: “Ice Lenses May Cause Many Arctic Landslides” 

    From AGU
    Eos news bloc

    From Eos

    13 August 2021
    Morgan Rehnberg

    When permafrost thaw reaches concentrations of ice underneath the surface, it may trigger local soil instability.

    1
    Active layer detachments in the Brooks Range in Alaska. A scar is visible on the hillslope with detached material resting on the valley floor. Credit: H. T. Mithan; satellite images by Maxar Technologies.

    Climate change is driving periods of unusually high temperature across large swaths of the planet. These heat waves are especially detrimental in the Arctic, where they can push surface temperatures in regions of significant permafrost past the melting point of ice lenses. Melting ice injects liquid water into the soil, reducing its strength and increasing the likelihood of landslides. In populated areas, these events can cause economic damage and loss of life.

    Mithan et al. [below] investigate a shallow-landslide formation mechanism called active layer detachment (ALD), in which the upper, unfrozen—or active—layer of soil separates from the underlying solid permafrost base. They analyze the topography in the vicinity of ALD landslides spread over a 100-square-kilometer region of Alaska to characterize the factors that govern such events. This region experienced many ALD landsides after a period of unusually high temperature in 2004.

    The authors identified 188 events in the study area using satellite imagery and established the local topography using a U.S. Geological Survey digital elevation model. To analyze the relationship between ALD landslides and topography, they simulated such events using a set of common software tools.

    Because many Arctic regions have relatively shallow slopes, their modeling finds that the simple flow of water is generally unable to generate sufficient water pressure between soil grains to kick-start a landslide. Rather, a major factor in ALD events appears to be the presence of ice lenses, concentrated bodies of ice that grow underground. When a heat wave pushes the thawing point of the permafrost to the depth of these ice accumulations, their melting strongly raises the local water pressure, creating the conditions for a landslide.

    As ice lens formation is governed by local topography, the authors propose that it may be possible to construct a mechanism for predicting locations likely to be susceptible to ALD landslides using only simple surface observations. As permafrost increasingly thaws in the face of a warming planet, such predictions are likely to take on greater importance in the coming decades.

    Geophysical Research Letters

    See the full article here .

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  • richardmitnick 11:10 am on August 20, 2021 Permalink | Reply
    Tags: "Lava from Bali Volcanoes Offers Window into Earth’s Mantle", , , Eos, ,   

    From Eos: “Lava from Bali Volcanoes Offers Window into Earth’s Mantle” 

    From AGU
    Eos news bloc

    From Eos

    13 August 2021
    Jon Kelvey

    Lava from the Agung and Batur volcanoes provides a near-pristine picture of Earth’s mantle and raises questions about all volcanoes along the Indonesian Sunda Arc and beyond.

    1
    Researchers examined the magma systems of volcanoes in the Sunda Arc, including Agung, in Bali, Indonesia. Credit: O. L. Andersen.

    Volcanoes along the 5,600-kilometer-long Sunda Arc subduction zone in Indonesia are among the most active and explosive in the world—and given the population density on the islands of the archipelago, some of the most hazardous.

    “The most dangerous volcanoes are in subduction zones,” said Frances Deegan, a researcher in the Department of Earth Sciences at Uppsala University [ Uppsala universitet] (SE).

    In a new study published in Nature Communications, Deegan and her colleagues shed more light on the magma systems beneath four volcanoes in the Sunda Arc: Merapi in Central Java, Kelut in East Java, and Batur and Agung on Bali. Using relatively new technology to measure oxygen isotopes in crystals in lava samples from the four volcanoes, the researchers established a baseline measurement of the oxygen isotopic signal of the mantle beneath Bali and Java. That baseline can be used to measure how much the overlying crust, or subjected sediments, influences magmas as they rise toward the surface.

    Volcano Forensics

    2
    Researchers used the Secondary Ion Mass Spectrometer (SIMS) at the Swedish Museum of Natural History in Stockholm. Credit: Frances Deegan.

    In the past, volcano forensic studies have relied on such technologies as conventional fluorination or laser fluorination to measure isotopes and minerals in samples, which are used to analyze pulverized lava samples but also often capture unwanted contaminates. In the new study, the research made use of the Secondary Ion Mass Spectrometer (SIMS) at the Swedish Museum of Natural History. “It allows you to do in situ isotope analysis of really small things like meteorites,” Deegan said, “things that are really precious where you can’t really mash them up and dissolve them.”

    SIMS also allows for targeting of portions of individual crystals as small as 10 microns, which allowed the researchers to avoid the unwanted contamination sometimes found within an individual crystal, according to Terry Plank, a volcanologist at Columbia University (US) who was not involved in the study. “The ion probe lets you avoid that and really analyze the pristine part of the crystal,” she said, “so we can see, in this case, its original oxygen isotope composition.”

    New Measurements

    Researchers can use SIMS to measure oxygen isotope ratios (18O to 16O)—expressed as a δ18O value, which normalizes the ratios to a standard—in various samples. On the basis of previous measurements [Geochemistry Geophysics Geosystems] for mid-ocean ridge basalts, Earth’s mantle is believed to have a δ18O value of around 5.5%, according to Deegan. “The crust is very variable and very heavy, so it can be maybe 15% to 20% to 25%,” she said. “If you mix in even just a little bit of crust with this very heavy oxygen isotope signal, it’s going to change the 5.5%—it’s going to go up.”

    Deegan and colleagues used SIMS to determine δ18O values from the mineral clinopyroxene in samples from the four volcanoes. In lavas from the Sunda Arc, clinopyroxene is a common mineral phase and can potentially shed light on source compositions and magmatic evolution. The results showed that the average δ18O values for each volcano decreased as the researchers moved east, with Merapi in Central Java measuring 5.8%, Kelut in East Java measuring 5.6%, and the Bali volcanoes Batur and Agung measuring 5.3% and 5.2%, respectively.

    “What really surprised me the most was finding this really pristine mantle signature under Bali,” Deegan said. Researchers already knew that the crust grows thinner as you move east from Java to Bali, but Deegan expected to find more evidence of ocean sediment in the measurements under Bali—seafloor material that melts along with the Indo-Australian plate as it slides beneath the Eurasian plate at the Sunda Arc. “We didn’t see that. We actually have a really clean mantle signature, which is unusual to find in a subduction zone,” she said.

    The researchers also measured magma crystallization depths of each of the four volcanoes and found that most of the sampled clinopyroxene from the two Java volcanoes formed in the middle to upper crust, while the crystallization occurred closer to the crust–mantle boundary beneath the Bali volcanoes. “I think that we have found a special view on the Indonesian mantle at Bali,” Deegan said. “Agung volcano on Bali seems to be the best mirror of mantle compositions in the whole region.”

    These findings could help scientists better understand what happens when magma leaves its sources and moves toward the surface. It’s theorized that magma interaction with volatile components in the crust could be a driver of more explosive eruptions, Deegan said, and so having a clean, contained mantle baseline for the Sunda Arc region could aid future research.

    Crust or Sediment?

    Although Plank was excited by the measurements of uncontaminated, unaltered oxygen isotope baselines in the paper, she wondered whether the differences in δ18O values are really explained by thicker crust under Java. “The averages for each volcano almost overlap within 1 standard deviation, so there are more high ones at Merapi than at Agung, but they all have the same baseline,” she said. “[The authors] argue that’s crustal contamination, but I wonder if there are other processes that can cause that.” It’s not always so easy, geochemically speaking, to distinguish between crustal contamination and material from subducted seafloor, Plank added. “The crust erodes and goes into the ocean, and then that material on the seafloor gets subducted and comes back up again,” she said. “It’s the same stuff.”

    As more research is conducted with SIMS, Plank would like to see work similar to Deegan’s done on samples from Alaskan volcanoes, which exhibit low δ18O values—like the Bali volcanoes—as well as on more shallow magma systems, like the Java volcanoes.

    “Any improvement in our knowledge of these volcanoes [in subduction zones] will help us be better prepared when they erupt,” Deegan said.

    See the full article here .

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