Abstract: Large volcanic eruptions are an important driving factor of natural climate variability. A sound assessment of the role of volcanoes in the climate system in comparison to other forcing factors is therefore a prerequisite for understanding future and past climate variability. New advances in understanding volcanic climate effects have been achieved by using comprehensive climate and Earth system models. New insights have been gained over the last decade about volcanic impacts on atmospheric composition and dynamics, but most notably also about their impact on ocean dynamics, the hydrological and the carbon cycle and on marine and terrestrial biogeochemistry. An important achievement is the improved understanding of the volcanic imprint on decadal to multidecadal time scales. Climate model simulations of past eruptions are highly dependent not only on the quality of the model and of the volcanologcial input data but also on the treatment of the aerosol size distribution in chemistry and radiation calculations. Further knowledge has to be achieved about the relation between the initial climate state at the time of the eruption and the volcanic climatic impact. A challenging task for climate models is also the simulation of the Northern Hemisphere winter climate response after a large tropical eruption. Model intercomparison studies and cross validations of model simulations with observations are essential to better constrain the radiative forcing of large volcanic eruptions and their climate impact. WIREs Clim Change 2012, 3:545–564. doi: 10.1002/wcc.192 This article is categorized under: Climate Models and Modeling > Earth System Models

Abstract: Most volcanic ash particles with diameters <63 lm settle from eruption clouds as particle aggregates that cumulatively have larger sizes, lower densities, and higher terminal fall velocities than individual constituent particles. Particle aggregation reduces the atmospheric residence time of fine ash, which results in a proportional increase in fine ash fallout within 10–100 s km from the volcano and a reduction in airborne fine ash mass concentrations 1000 s km from the volcano. Aggregate characteristics vary with distance from the volcano: proximal aggregates are typically larger (up to cm size) with concentric structures, while distal aggregates are typically smaller (sub-millimetre size). Particles comprising ash aggregates are bound through hydro-bonds (liquid and ice water) and electrostatic forces, and the rate of particle aggregation correlates with cloud liquid water availability. Eruption source parameters (including initial particle size distribution, erupted mass, eruption column height, cloud water content and temperature) and the eruption plume temperature lapse rate, coupled with the environmental parameters, determines the type and spatiotemporal distribution of aggregates. Field studies, lab experiments and modelling investigations have already provided important insights on the process of particle aggregation. However, new integrated observations that combine remote sensing studies of ash clouds with field measurement and sampling, and lab experiments are required to fill current gaps in knowledge surrounding the theory of ash aggregate formation.

Abstract: To facilitate the assessment of hazards and risk from volcanoes, we have created a comprehensive global database of Quaternary Large Magnitude Explosive Volcanic Eruptions (LaMEVE). This forms part of the larger Volcanic Global Risk Identification and Analysis Project (VOGRIPA), and also forms part of the Global Volcano Model (GVM) initiative (http://www.globalvolcanomodel.org). A flexible search tool allows users to select data on a global, regional or local scale; the selected data can be downloaded into a spreadsheet. The database is publically available online at http://www.bgs.ac.uk/vogripa and currently contains information on nearly 3,000 volcanoes and over 1,800 Quaternary eruption records. Not all volcanoes currently have eruptions associated with them but have been included to allow for easy expansion of the database as more data are found. Data fields include: magnitude, Volcanic Explosivity Index (VEI), deposit volumes, eruption dates, and rock type. The scientific community is invited to contribute new data and also alert the database manager to potentially incorrect data. Whilst the database currently focuses only on large magnitude eruptions, it will be expanded to include data specifically relating to the principal volcanic hazards (e.g. pyroclastic flows, tephra fall, lahars, debris avalanches, ballistics), as well as vulnerability (e.g. population figures, building type) to facilitate risk assessments of future eruptions.

Abstract: Geologic controls on development of high-flux hydrothermal conduits that promote epithermal ore formation are evaluated at large and small scales for geothermal systems of the Taupo Volcanic Zone, New Zealand. Most geothermal systems occur within a rifted volcanic arc (~150 km long) dominated by silicic volcanism, and they occur in association with major faults near caldera structures or within accommodation zones that transfer ex tension between rift segments . The geothermal systems are hosted in a thick sequence (1:>3 km) of young vol canic deposits that rest unconformably on weakly metamorphosed Mesozoic argillite and graywacke. Flow regimes and permeability controls in one extinct (Ohakuri) and six active (Broadlands-Ohaaki, Waiotapu, Roto kawa, Waimangu, Te Kopia, and Orakeikorako) geothermal systems show that in general, hydrothermal fluid flow is controlled by (1) heat from magmatic intrusions which drives convective circulation; (2) intergranular host-rock porosity and permeability; (3) fault-fracture network permeability produced by tectonism, volcanism, and/or diking; (4) pipelike vertical conduits produced by volcanic and hydrothermal eruptions; and (5) hydro thermal alteration and mineral deposition that may cause heterogeneity in the porosity and permeability of a fluid reservoir. Such controls influence fluid flow within three distinctive depth zones: (1) a feed zone (>2,000 m depth), (2) an epithermal mineralization zone ( 100 km 3 that encloses geothermal reservoirs and high-flux fluid conduits. Fracture-dominated flow becomes important with decreasing porosity induced by hydrothermal alteration. In the discharge zone, the re duction in confining pressure, combined with mineral deposition and alteration, hydrothermal eruptions, and interplay of hot and cold waters create complex, but strongly localized flow paths that feed hot springs. The permeability structure conducive to epithermal vein formation is analogous to a geothermal well: short in horizontal dimension (10s:100s m) but long in vertical dimension (>1,500 m) and possibly pipelike in shape. Episodic high-flux occurs over time scales of tens to thousands of years to accumulate sufficient amounts of gold and silver to form orebodies. During these episodes when faults and fractures are dilated, development of an upward-expanding column of boiling fluid promotes rapid ascent and high mass flow but also promotes silica and calcite precipitation, which can quickly reduce hydrothermal flow. Seismic activity and/or dike intru sion create and reactivate these high-flux pathways through extension and extensional shearing, caused by low differential stresses. The Taupo Volcanic Zone is highly prospective for epithermal-style mineralization, but the predominance of weak porous host rocks at shallow depths is prone to disseminated-style mineralization (e.g., Ohakuri). Structurally controlled mineralization forms in volcanic rocks where they have been embrittled by silicification through seismicity and fault displacement, caldera-forming eruptions, and dike intrusion.

Abstract: [1] We present the analysis of 205 spatially resolved measurements of the surface composition of Mercury from MESSENGER’s X-Ray Spectrometer. The surface footprints of these measurements are categorized according to geological terrain. Northern smooth plains deposits and the plains interior to the Caloris basin differ compositionally from older terrain on Mercury. The older terrain generally has higher Mg/Si, S/Si, and Ca/Si ratios, and a lower Al/Si ratio than the smooth plains. Mercury’s surface mineralogy is likely dominated by high-Mg mafic minerals (e.g., enstatite), plagioclase feldspar, and lesser amounts of Ca, Mg, and/or Fe sulfides (e.g., oldhamite). The compositional difference between the volcanic smooth plains and the older terrain reflects different abundances of these minerals and points to the crystallization of the smooth plains from a more chemically evolved magma source. High-degree partial melts of enstatite chondrite material provide a generally good compositional and mineralogical match for much of the surface of Mercury. An exception is Fe, for which the low surface abundance on Mercury is still higher than that of melts from enstatite chondrites and may indicate an exogenous contribution from meteoroid impacts.

Abstract: [1] We introduce a novel analytical expression that allows for fast assessment of mass flow rate of both vertically-rising and bent-over volcanic plumes as a function of their height, while first order physical insight is maintained. This relationship is compared with a one-dimensional plume model to demonstrate its flexibility and then validated with observations of the 1980 Mount St. Helens and of the 2010 Eyjafjallajokull eruptions. The influence of wind on the dynamics of volcanic plumes is quantified by a new dimensionless parameter (Π) and it is shown how even vertically-rising plumes, such as the one associated with the Mount St. Helens 1980 eruption, can be significantly affected by strong wind. Comparison between a one-dimensional model and the analytical equation gives anR2-value of 0.88, while existing expressions give negativeR2-values due to their inability to adapt to different source and atmospheric conditions. Therefore, this new expression has important implications both for current strategies of real-time forecasting of ash transport in the atmosphere and for the characterization of explosive eruptions based on the study of tephra deposits. In addition, this work provides a framework for the application of more complete three-dimensional numerical models as it greatly reduces the parameter space that needs to be explored.

Abstract: Volcanic eruptions are an important cause of nat- ural climate variability. In order to improve the accuracy of climate models, precise dating and magnitude of the climatic effects of past volcanism are necessary. Here we present a 2000-yr record of Southern Hemisphere volcanism recorded in ice cores from the high accumulation Law Dome site, East Antarctica. The ice cores were analysed for a suite of chemistry signals and are independently dated via annual layer counting, with 11 ambiguous years at 23 BCE, which has presently the lowest error of all published long Antarc- tic ice cores. Independently dated records are important to avoid circular dating where volcanic signatures are assigned a date from some external information rather than using the date it is found in the ice core. Forty-five volcanic events have been identified using the sulphate chemistry of the Law Dome record. The low dating error and comparison with the NGRIP (North Greenland Ice Core Project) volcanic records (on the GICC05 timescale) suggest Law Dome is the most accurately dated Antarctic volcanic dataset, which will im- prove the dating of individual volcanic events and potentially allow better correlation between ice core records, leading to improvements in global volcanic forcing datasets. One of the most important volcanic events of the last two millennia is the large 1450s CE event, usually assigned to the eruption of Kuwae, Vanuatu. In this study, we review the evidence sur- rounding the presently accepted date for this event, and make the case that two separate eruptions have caused confusion in the assignment of this event. Volcanic sulphate deposition es- timates are important for modelling the climatic response to eruptions. The largest volcanic sulphate events in our record are dated at 1458 CE (Kuwae?, Vanuatu), 1257 and 422 CE (unidentified).

Abstract: . The polarization lidar photometer networking (POLIPHON) method introduced to separate coarse-mode and fine-mode particle properties of Eyjafjallajokull volcanic aerosols in 2010 is extended to cover Saharan dust events as well. Furthermore, new volcanic dust observations performed after the Grimsvotn volcanic eruptions in 2011 are presented. The retrieval of particle mass concentrations requires mass-specific extinction coefficients. Therefore, a review of recently published mass-specific extinction coefficients for Saharan dust and volcanic dust is given. Case studies of four different scenarios corroborate the applicability of the profiling technique: (a) Saharan dust outbreak to central Europe, (b) Saharan dust plume mixed with biomass-burning smoke over Cape Verde, and volcanic aerosol layers originating from (c) the Eyjafjallajokull eruptions in 2010 and (d) the Grimsvotn eruptions in 2011. Strong differences in the vertical aerosol layering, aerosol mixing, and optical properties are observed for the different volcanic events.

Abstract: Density muon radiography is a new method to determine the average density of geological bodies by measuring the attenuation produced by rocks on the flux of cosmic muons. We present such density radiographies obtained for the Soufri'ere of Guadeloupe lava dome, both in the north-south and east-west planes. These radiographies reveal the highly heterogeneous density structure of the volcano, with low-density regions corresponding to recognized hydrothermally altered areas. The main structures observed in the density radiographies correlate with anomalies in electrical resistivity cross-sections and a density model obtained from gravity data.

Abstract: A model of subduction that reveals a long tear under Oregon and Nevada provides a new mechanism for the origin of Columbia River flood basalt, resolving previous hypotheses. A flood basalt is the product of a volcanic eruption that covers large areas with basalt lava. The origin of the Steens–Columbia River flood basalts, thought to be associated with the onset of volcanism within the Yellowstone hotspot, has remained controversial. Using geodynamic modelling, Lijun Liu and Dave Stegman show that an episode of slab tearing about 17 million years ago under eastern Oregon quickly ruptured north and south, covering a distance of about 900 kilometres along eastern Oregon and northern Nevada. This is consistent both in space and time with the Steens–Columbia River–Northern Nevada Rift flood basalt event. The model also predicts the sequence of flood basalt composition, which should help to reconcile controversies regarding the origin of these flood basalts and involvement of the putative Yellowstone plume. The origin of the Steens–Columbia River (SCR) flood basalts, which is presumed to be the onset of Yellowstone volcanism, has remained controversial, with the proposed conceptual models involving either a mantle plume1,2,3,4,5 or back-arc processes6,7,8. Recent tomographic inversions based on the USArray data reveal unprecedented detail of upper-mantle structures of the western USA9 and tightly constrain geodynamic models simulating Farallon subduction, which has been proposed to influence the Yellowstone volcanism5,6. Here we show that the best-fitting geodynamic model10 depicts an episode of slab tearing about 17 million years ago under eastern Oregon, where an associated sub-slab asthenospheric upwelling thermally erodes the Farallon slab, leading to formation of a slab gap at shallow depth. Driven by a gradient of dynamic pressure, the tear ruptured quickly north and south and within about two million years covering a distance of around 900 kilometres along all of eastern Oregon and northern Nevada. This tear would be consistent with the occurrence of major volcanic dikes during the SCR–Northern Nevada Rift flood basalt event both in space and time. The model predicts a petrogenetic sequence for the flood basalt with sources of melt starting from the base of the slab, at first remelting oceanic lithosphere and then evolving upwards, ending with remelting of oceanic crust. Such a progression helps to reconcile the existing controversies on the interpretation of SCR geochemistry and the involvement of the putative Yellowstone plume. Our study suggests a new mechanism for the formation of large igneous provinces.

Abstract: [1] Over 12 years of continuous monitoring of Changbaishan volcano in the border region of China and North Korea by means of volcanic seismicity, ground deformation, and volcanic gas geochemistry yields new evidence for magmatic unrest of the volcano between 2002 and 2006. In this so-called “active period,” the frequency of volcanic earthquakes increased by about 2 orders of magnitude compared to that of the background “inactive periods.” The active period was also accompanied by ground inflation, high values of CO2, He, H2, and high ratios of N2/O2 and 3He/4He in volcanic gases released from three hot springs near the caldera rim. The monitoring evidence implies pressurization of the magma chamber, possibly caused by incremental magma recharge. The ground deformation data from both GPS and precise leveling are modeled to suggest the corresponding deformation source is at 2–60 km depth beneath the volcano's summit, where earthquake swarms were detected in 2002 and 2003. Our findings suggest that the magma chamber beneath Changbaishan volcano has awakened and resumed activity after remaining dormant since AD 1903. There is an urgent need to keep close watch on this active and very hazardous volcano in northeast China.

Abstract: High-temperature volcanic gas is widely considered to originate from ascending, mantle-derived magma. In volcanic arc systems, crustal inputs to magmatic gases mainly occur via subducted sediments ...

Abstract: The violent August 16–17, 2006 Tungurahua eruption in Ecuador witnessed the emplacement of numerous scoria flows and the deposition of a widespread tephra layer west of the volcano. We assess the size of the eruption by determining a bulk tephra volume in the range 42–57 × 106 m3, which supports a Volcanic Explosivity Index 3 event, consistent with calculated column height of 16–18 km above the vent and making it the strongest eruptive phase since the volcano’s magmatic reactivation in 1999. Isopachs west of the volcano are sub-bilobate in shape, while sieve and laser diffraction grain-size analyses of tephra samples reveal strongly bimodal distributions. Based on a new grain-size deconvolution algorithm and extended sampling area, we propose here a mechanism to account for the bimodal grain-size distribution. The deconvolution procedure allows us to identify two particle subpopulations in the deposit with distinct characteristics that indicate dissimilar transport-depositional processes. The log-normal coarse-grained subpopulation is typical of particles transported downwind by the main volcanic plume. The positively skewed, fine-grained subpopulation in the tephra fall layer shares close similarities with the elutriated co-pyroclastic flow ash cloud layers preserved on top of the scoria flow deposits. The area with the higher fine particle content in the tephra layer coincides with the downwind prolongation of the pyroclastic flow deposits. These results indicate that the bimodal distribution of grain size in the Tungurahua fall deposit results from synchronous deposition of lapilli from the main plume and fine ash elutriated from scoria flows emplaced on the western flank of the volcano. Our study also reveals that inappropriate grain-size data processing may produce misleading determination of eruptive type.

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Abstract: This is the publisher’s final pdf. The published article is copyrighted by The Oceanography Society and can be found at: http://www.tos.org/.

Abstract: [1] Broadband MT (magnetotelluric) data were recorded that form an array of measurements at the south-eastern margin of the TVZ (Taupo Volcanic Zone), in the central North Island of New Zealand. These array data are used to investigate mechanisms by which the TVZ's extraordinarily high heat flux is transported to the surface. Taken together with seismological data, these MT data show compelling evidence that support a model of hydrothermal convection within the brittle (upper ∼6–7 km) part of the crust. Both 2-D and 3-D inversion models of these MT data show vertical low-resistivity zones that connect surface geothermal fields to an inferred magmatic heat source that lies below the brittle-ductile transition.

Abstract: [1] We develop a transient, 3-D Eulerian model (Ash3d) to predict airborne volcanic ash concentration and tephra deposition during volcanic eruptions. This model simulates downwind advection, turbulent diffusion, and settling of ash injected into the atmosphere by a volcanic eruption column. Ash advection is calculated using time-varying pre-existing wind data and a robust, high-order, finite-volume method. Our routine is mass-conservative and uses the coordinate system of the wind data, either a Cartesian system local to the volcano or a global spherical system for the Earth. Volcanic ash is specified with an arbitrary number of grain sizes, which affects the fall velocity, distribution and duration of transport. Above the source volcano, the vertical mass distribution with elevation is calculated using a Suzuki distribution for a given plume height, eruptive volume, and eruption duration. Multiple eruptions separated in time may be included in a single simulation. We test the model using analytical solutions for transport. Comparisons of the predicted and observed ash distributions for the 18 August 1992 eruption of Mt. Spurr in Alaska demonstrate to the efficacy and efficiency of the routine.

Abstract: A new volcano-tectonic map of Etna volcano has been compiled through a morphotectonic analysis performed with detailed field mapping, high-resolution DEM and orthoimages, constrained by seismotectonic data In this study, we present a homogeneous mapping of the volcano-tectonic and tectonic elements on the whole volcano, consistent with the updated knowledge on the geology and active tectonics observed in historical times Details of the tectonic features occurring in the lower-middle part of the volcanic edifice, namely the more densely urbanized areas, are described; volcanic elements such as eruptive fissures, caldera and flank collapse rims affecting the upper sectors, are also reported All the volcanic landforms of Etna edifice have been generated by constructive and destructive volcanic processes largely during the last 15 ka activity of Mongibello volcano DEM-derived images (eg slope and aspect maps) were produced and interpreted in order to identify faultrelated surface features based on an explicit list of well-known elements of tectonic geomorphology Subsequently, the morphotectonic mapping has been compared with field data on geologic marker offsets, as well as evidence of surface faulting, including coseismic displacements and creeping of historical and recent events This combined approach has enabled classifying each element reported in the map as (i) exposed faults, (ii) buried faults and (iii) hidden faults The analysis of slip-rates confirms the exceptional dynamics of the Pernicana fault, which is characterised by an almost constant slip-rate of 20-36 mm/a over the last 1000 years, while the Timpe fault zone and the structural system in the southern flank accommodate a relevant amount of deformation with slip-rates reported to range of ca 2-4 mm/a Finally, a seismotectonic model summarisesthe information regarding seismic hazard, with reference to the additional, potentially severe effects induced by surface faulting

Abstract: We produce a spatial probability map of vent opening (susceptibility map) at Etna, using a statistical analysis of structural features of flank eruptions of the last 2 ky. We exploit a detailed knowledge of the volcano structures, including the modalities of shallow magma transfer deriving from dike and dike-fed fissure eruptions analysis on historical eruptions. Assuming the location of future vents will have the same causal factors as the past eruptions, we converted the geological and structural data in distinct and weighted probability density functions, which were included in a non-homogeneous Poisson process to obtain the susceptibility map. The highest probability of new eruptive vents opening falls within a N-S aligned area passing through the Summit Craters down to about 2,000 m a.s.l. on the southern flank. Other zones of high probability follow the North-East, East-North-East, West, and South Rifts, the latter reaching low altitudes (∼400 m). Less susceptible areas are found around the faults cutting the upper portions of Etna, including the western portion of the Pernicana fault and the northern extent of the Ragalna fault. This structural-based susceptibility map is a crucial step in forecasting lava flow hazards at Etna, providing a support tool for decision makers.

Abstract: Timescales of magma chamber assembly and recharge are investigated here by applying 1D and 2D diffusion modeling techniques to high-resolution maps of titanium in quartz from a large-volume ignimbrite eruption in the Taupo Volcanic Zone, New Zealand. We compare quartz zonation patterns and associated diffusion timescales from the 340 kaWhakamaru super-eruption (magma volume 1000 km) with the Younger Toba Tuff super-eruption, 74 ka (2000 km), Sumatra, and the smaller volume 50 ka Earthquake Flat eruption (10 km), Okataina Caldera Complex, New Zealand. Two principal timescales are presented: that of chamber recharge and eruption triggering events, and that of magma generation (involving long-term assembly, stirring and reactivation). Synchrotron micro-X-ray fluorescence maps of core^rim quartz transects provide a high-resolution record of magma chamber conditions throughout quartz crystallization. Quartz crystals from the Whakamaru magma display complex zonation patterns indicating fluctuating pressure^temperature conditions throughout the crystallization history. Toba and Earthquake Flat, in contrast, display simple quartz-zoning patterns and record slightly longer periods of crystal residence in the chamber that fed the eruption. We apply Lattice Boltzmann 2D diffusion modeling to reconstruct the timescales of quartz crystal zonation, accounting for crystal boundary complexities. Quartz crystal orientation is also accounted for by using geometry constraints from the synchrotron data. Our calculations suggest that crystal-mush reactivation for the main Whakamaru magma reservoir occured over a period of the order of 10^10 years. Both the Earthquake Flat and Toba eruptions experienced a significant recharge event (causing a temperature and pressure change), which occurred within 100 years of eruption. In comparison, the complex Whakamaru quartz zoning patterns suggest that the magma body experienced numerous thermal and compositional fluctuations in the lead-up to eruption. The final magma recharge event, which most probably triggered the eruption, occurred within 10^60 years of the eruption. Even though the volume of these systems spans two orders of magnitude, there does not appear to be a relationship between magma volume and diffusion timescale, suggesting similar histories before eruption.

Abstract: [1] We use interferometric synthetic aperture radar (InSAR) to study deformation of the summit caldera at Kīlauea Volcano during 2000–2008, which spanned both an east rift zone eruptive event in 2007 and the start of the ongoing summit eruption in 2008. The data set consists of small baseline subset (SBAS) time series generated from 270 acquisitions on three separate beam modes from the Radarsat-1 satellite. We identify 12 time periods with distinct patterns of displacement that we attribute until late 2003 to secular tectonic-driven deformation and from 2004 to 2008 to four different sources in the summit area. We model the shallow magmatic system as a spherical reservoir at 1.9 ± 0.1 km depth below the surface to the northeast of Halemaumau (source 1) and three vertically stacked sills at greater depths in the southern caldera area (source 2 at the southern edge of the caldera at 2.9 ± 0.2 km depth, source 3 to the south-southeast of the caldera at 3.4 ± 0.5 km depth, and source 4 south of the caldera at 3.6 ± 0.4 km depth). The sequence for filling of and withdrawal from these reservoirs reveals a top-down process, with sequences of both inflation and deflation initiating in the shallowest source. Inflation of source 3 is coincident with elevated seismic activity in the upper east rift zone in February 2006 and May 2007. Source 4 is elongated toward the southwest rift zone and also shows elevated seismicity that extends toward the southwest rift zone.