Yasur Volcano Research Articles

Volcano Opto‐Acoustics: Mapping the Infrasound Wavefield at Yasur Volcano (Vanuatu)

AbstractWe explore the capabilities of volcano opto‐acoustics, a promising technique for measuring explosion and infrasound resonance phenomena at open‐vent volcanoes. Joint visual and infrasound study at Yasur Volcano (Vanuatu) demonstrate that even consumer‐grade cameras are capable of recording infrasound with high fidelity. Passage of infrasonic waves, ranging from as low as 5 Pa to hundreds of Pa, from both explosions and persistent tremor, pressurizes and depressurizes ambient plumes inducing visible vaporization and condensation respectively. Optical tracking of these pressure wavefields can be used to identify spectral characteristics, which vary within Yasur's two deep craters and are distinct for explosion and tremor sources. Wavefield maps can illuminate the propagation of blasts as well as the dynamics of persistent infrasonic tremor associated with standing waves in the craters. We propose that opto‐acoustic monitoring is useful for extraction of near‐vent infrasound signal and for tracking volcanic unrest from a remote distance.

Long range infrasound monitoring of Yasur volcano

The atmospheric injection of gas and material produced by an explosive volcanic eruption determines a rapid compression of the atmosphere, which subsequently propagates as longitudinal elastic waves (sound). The size of the source, generally greater than tens of meters, and its duration, longer than a few seconds, result into an emitted signal that is particularly rich in low frequencies (f < 20 Hz), thus determining an efficient infrasound radiation. Thanks to the low spectral content and the reduced attenuation in the atmosphere, infrasound is capable of propagating for very large distances.In this study we show how the infrasonic monitoring at regional distances (> 100 km) is efficient in recording and characterizing volcanic events. For the purpose of our study, infrasound signal radiated from Yasur volcano (Tanna Island, Vanuatu) was studied for a period of twelve years (January 2008 – December 2019). Signals from Yasur were registered at a source-to-receiver distance of 400 km by the IS22 infrasound array, located in New Caledonia, part of the Comprehensive Nuclear-Test-Ban Treaty (CTBT) International Monitoring System (IMS). The predominantly explosive Strombolian activity of this volcano makes it a perfect subject to be studied by infrasound technology. Detections of volcanic infrasound are modulated according to the seasonal variation of stratospheric winds and corrected for attenuation accounting for real atmospheric specification between the source and the receiver to retrieve the pressure at the source. Next, they are used to evaluate long-term (yearly) and short term (hourly) variations of activity over the period of analysis. Results are compared with thermal anomalies recorded by the MODerate resolution Imaging Spectroradiometer (MODIS) installed on NASA's Terra and Aqua satellites.We show that even at regional distances (400 km) it is possible to follow the long term (yearly) fluctuations of ordinary explosive activity during periods of optimal propagation of infrasonic waves in the atmosphere. In addition, we show that the time resolution retrieved from the signal analysis allows to follow variations of volcanic activity at hourly time scale, thus representing a valuable source of information, in particular in areas where local geophysical observations are missing.

Waveform Features Strongly Control Subcrater Classification Performance for a Large, Labeled Volcano Infrasound Dataset

Abstract Volcano infrasound data contain a wealth of information about eruptive patterns, for which machine learning (ML) is an emerging analysis tool. Although global catalogs of labeled infrasound events exist, the application of supervised ML to local (&amp;lt;15 km) volcano infrasound signals has been limited by a lack of robust labeled datasets. Here, we automatically generate a labeled dataset of &amp;gt;7500 explosions recorded by a five-station infrasound network at the highly active Yasur Volcano, Vanuatu. Explosions are located via backprojection and associated with one of Yasur’s two summit subcraters. We then apply a supervised ML approach to classify the subcrater of origin. When trained and tested on data from the same station, our chosen algorithm is &amp;gt;95% accurate; when training and testing on different stations, accuracy drops to about 75%. The choice of waveform features provided to the algorithm strongly influences classification performance.

Evidence for near-source nonlinear propagation of volcano infrasound from Strombolian explosions at Yasur Volcano, Vanuatu

Volcanic eruption source parameters may be estimated from acoustic pressure recordings dominant at infrasonic frequencies (< 20 Hz), yet uncertainties may be high due in part to poorly understood propagation dynamics. Linear acoustic propagation of volcano infrasound is commonly assumed, but nonlinear processes such as wave steepening may distort waveforms and obscure the sourcing process in recorded waveforms. Here we use a previously developed frequency-domain nonlinearity indicator to quantify spectral changes due to nonlinear propagation primarily in 80 signals from explosions at Yasur Volcano, Vanuatu. We find evidence for le 10−3 dB/m spectral energy transfer in the band 3–9 Hz for signals with amplitude on the order of several hundred Pa at 200–400 m range. The clarity of the nonlinear spectral signature increases with waveform amplitude, suggesting stronger nonlinear changes for greater source pressures. We observe similar results in application to synthetics generated through finite-difference wavefield simulations of nonlinear propagation, although limitations of the model complicate direct comparison to the observations. Our results provide quantitative evidence for nonlinear propagation that confirms previous interpretations made on the basis of qualitative observations of asymmetric waveforms.

High-rate very-long-period seismicity at Yasur volcano, Vanuatu: source mechanism and decoupling from surficial explosions and infrasound

SUMMARYYasur volcano, Vanuatu is a continuously active open-vent basaltic-andesite stratocone with persistent and long-lived eruptive activity. We present results from a seismo-acoustic field experiment at Yasur, providing locally dense broad-band seismic and infrasonic network coverage from 2016 July 27 to August 3. We corroborate our seismo-acoustic observations with coincident video data from cameras deployed at the crater and on an unoccupied aircraft system (UAS). The waveforms contain a profusion of signals reflecting Yasur’s rapidly occurring and persistent explosive activity. The typical infrasonic signature of Yasur explosions is a classic short-duration and often asymmetric explosion waveform characterized by a sharp compressive onset and wideband frequency content. The dominant seismic signals are numerous repetitive very-long-period (VLP) signals with periods of ∼2–10 s. The VLP seismic events are ‘high-rate’, reoccurring near-continuously throughout the data set with short interevent times (∼20–60 s). We observe variability in the synchronization of seismic VLP and acoustic sources. Explosion events clearly delineated by infrasonic waveforms are underlain by seismic VLPs. However, strong seismic VLPs also occur with only a weak infrasonic expression. Multiplet analysis of the seismic VLPs reveals a systematic progression in the seismo-acoustic source decoupling. The same dominant seismic VLP multiplet occurs with and without surficial explosions and infrasound, and these transitions occur over a timescale of a few days during our field campaign. We subsequently employ template matching, stacking, and full-waveform inversion to image the source mechanism of the dominant VLP multiplet. Inversion of the dominant VLP multiplet stack points to a composite source consisting of either a dual-crack (plus forces) or pipe-crack (plus forces) mechanism. The derived mechanisms correspond to a point-source directly beneath the summit vents with centroid depths in the range ∼900–1000 m below topography. All mechanisms suggest a northeast trending crack dipping relatively shallowly to the northwest and indicate a VLP source centroid and mechanism controlled by a stable structural geologic feature beneath Yasur. We interpret the results in the framework of gas slug ascent through the conduit responsible for Yasur explosions. The VLP mechanism and timing with infrasound (when present) are explained by a shallow-buffered top-down model in which slug ascent is relatively aseismic until reaching the base of a shallow section. Slug disruption in this shallow zone triggers a pressure disturbance that propagates downward and couples at the conduit base (VLP centroid). If the shallow section is open, an explosion propagates to the surface, producing infrasound. In the case of (the same multiplet) VLPs occurring without surficial explosions and weak or no infrasound, the decoupling of the dominant VLPs at ∼900–1000 m depth from surficial explosions and infrasound strongly indicates buffering of the terminal slug ascent. This buffering could be achieved by a variety of conditions at or directly beneath the vents, such as a high-viscosity layer of crystal-rich magma, a debris cap from backfill, a foam layer, or a combination of these. The dominant VLP at Yasur captured by our experiment has a source depth and mechanism separated from surface processes and is stable over time.

Synthetic Evaluation of Infrasonic Multipole Waveform Inversion

AbstractAcoustic source inversions estimate the mass flow rate of volcanic explosions or yield of chemical explosions and provide insight into potential source directionality. However, the limitations of applying these methods to complex sources and their ability to resolve a stable solution have not been investigated in detail. We perform synthetic infrasound waveform inversions that use 3‐D Green’s functions for a variety of idealized and realistic deployment scenarios using both a flat plane and Yasur volcano, Vanuatu as examples. We investigate the ability of various scenarios to retrieve the input source functions and relative amplitudes for monopole and multipole (monopole and dipole) inversions. Infrasound waveform inversions appear to be a robust method to quantify mass flow rates from simple sources (monopole) using deployments of infrasound sensors placed around a source, but care should be taken when analyzing and interpreting results from more complex acoustic sources (multipole) that have significant directional components. In the examples we consider the solution is stable for monopole inversions with a signal‐to‐noise ratio greater than five and the dipole component is small. For most scenarios investigated, the vertical dipole component of the multipole explosion source is poorly constrained and can impact the ability to recover the other source term components. Because multipole inversions are ill‐posed for many deployments, a low residual does not necessarily mean the proper source vector has been recovered. Synthetic studies can help investigate the limitations and place bounds on information that may be missing using monopole and multipole inversions for potentially directional sources.

Variability of naturally occurring fluoride in diverse community drinking-water sources, Tanna Island, Vanuatu

Abstract Large variations in fluoride concentrations exist in natural waters, many of which are the source of community drinking-water supplies. Determining fluoride concentrations in community drinking waters can be challenging in developing Pacific countries such as Vanuatu that have limited laboratory capacity. Knowledge of naturally elevated fluoride concentrations that cause irreversible, adverse health outcomes may allow communities the opportunity to treat and manage their drinking-water supplies. Community drinking-water samples (n = 69), sourced from groundwaters, roof catchment rainwaters, surface waters and springs, were sampled on Tanna Island, Vanuatu between 2017 and 2020. In an 18 km2 area of Western Tanna, a set of 30 groundwater-based drinking-water samples had a median fluoride concentration of 3.3 mg/L, with 20 samples &amp;gt;1.5 mg/L and seven samples &amp;gt;4.0 mg/L. These concentrations increase the risk of dental and skeletal fluorosis, respectively. Repeat resampling at five sites showed little variation over the sampling period. Rainwater-fed drinking-water supplies were lower overall and highly variable in fluoride concentrations (&amp;lt;0.05–4.0 mg/L, median of 0.53 mg/L), with variable inputs from volcanic emissions from Yasur volcano. We recommend a comprehensive oral health and bone health study for the whole island to determine adverse health effects of excess fluoride in this vulnerable population.

Local Explosion Detection and Infrasound Localization by Reverse Time Migration Using 3-D Finite-Difference Wave Propagation

Infrasound data are routinely used to detect and locate volcanic and other explosions, using both arrays and single sensor networks. However, at local distances (&amp;lt;15 km) topography often complicates acoustic propagation, resulting in inaccurate acoustic travel times leading to biased source locations when assuming straight-line propagation. Here we present a new method, termed Reverse Time Migration-Finite-Difference Time Domain (RTM-FDTD), that integrates numerical modeling into the standard RTM back-projection process. Travel time information is computed across the entire potential source grid via FDTD modeling to incorporate the effects of topography. The waveforms are then back-projected and stacked at each grid point, with the stack maximum corresponding to the likely source. We apply our method to three volcanoes with different network configurations, source-receiver distances, and topography. At Yasur Volcano, Vanuatu, RTM-FDTD locates explosions within ∼20 m of the source and differentiates between multiple vents. RTM-FDTD produces a more accurate location for the two Yasur subcraters than standard RTM and doubles the number of detected events. At Sakurajima Volcano, Japan, RTM-FDTD locates the source within 50 m of the active vent despite notable topographic blocking. The RTM-FDTD location is similar to that from the Time Reversal Mirror method, but is more computationally efficient. Lastly, at Shishaldin Volcano, Alaska, RTM and RTM-FDTD both produce realistic source locations (&amp;lt;50 m) for ground-coupled airwaves recorded on a four-station seismic network. We show that RTM is an effective method to detect and locate infrasonic sources across a variety of scenarios, and by integrating numerical modeling, RTM-FDTD produces more accurate source locations and increases the detection capability.

Volcanic ballistic projectile deposition from a continuously erupting volcano: Yasur Volcano, Vanuatu

Volcanic ballistics are the main hazard to life and infrastructure from Strombolian eruptions, which are a tourist drawcard, exposing people to this hazard. Most research to date has been to understand this style of eruption and how ballistics form and travel. However, little focus has been placed on how ballistics are distributed within ballistic fields or the inclusion of this data into hazard and risk assessments. In this study we used a UAV to image the ballistic field, and cameras to record eruptions at Yasur Volcano, Vanuatu from 28 July – 2 August and 17 – 19 October 2016. We present the mapped distributions from the two trips, how the field changes with distance and direction from the vent, and how eruption dynamics influence these changes. Our evidence for directionality results in considerable variation in summit ballistic hazard and is an important consideration for ballistic hazard and risk assessments.

Ultraviolet Camera Measurements of Passive and Explosive (Strombolian) Sulphur Dioxide Emissions at Yasur Volcano, Vanuatu

Here, we present the first ultraviolet (UV) camera measurements of sulphur dioxide (SO2) flux from Yasur volcano, Vanuatu, for the period 6–9 July 2018. These data yield the first direct gas-measurement-derived calculations of explosion gas masses at Yasur. Yasur typically exhibits persistent passive gas release interspersed with frequent Strombolian explosions. We used compact forms of the “PiCam” Raspberry Pi UV camera system powered through solar panels to collect images. Our daily median SO2 fluxes ranged from 4 to 5.1 kg s−1, with a measurement uncertainty of −12.2% to +14.7%, including errors from the gas cell calibration drift, uncertainties in plume direction and distance, and errors from the plume velocity. This work highlights the use of particle image velocimetry (PIV) for plume velocity determination, which was preferred over the typically used cross-correlation and optical flow methods because of the ability to function over a variety of plume conditions. We calculated SO2 masses for Strombolian explosions ranging 8–81 kg (mean of 32 kg), which to our knowledge is the first budget of explosive gas masses from this target. Through the use of a simple statistical measure using the moving minimum, we estimated that passive degassing is the dominant mode of gas emission at Yasur, supplying an average of ~69% of the total gas released. Our work further highlights the utility of UV camera measurements in volcanology, and particularly the benefit of the multiple camera approach in error characterisation. This work also adds to our inventory of gas-based data, which can be used to characterise the spectrum of Strombolian activity across the globe.

Spatiotemporal variations in eruption style, magnitude and vent morphology at Yasur volcano, Vanuatu: insights into the conduit system

Using visual, seismic, SO2-gas and thermal infrared data collected over 3 months, we observed systematic variations in the steady-state Strombolian-style activity of Yasur volcano. Observations reveal insights into the relationship between explosion magnitude and style with shallow conduit and magmatic conditions. Powerful eruptive phases are dominated by lava-rich activity, suggesting a high magma and volatile flux from depth that fills hot conduit pathways with mobile magma. Weak eruptive phases produced low-frequency ash-dominated explosions, indicative of cooling and stagnant magma near the top of the conduit and/or a debris layer covering the vent. Statistical forecast modelling was applied to explore if information on the previous days’ activity could forecast the next day and provide insights into multi-vent eruption patterns. Results suggest that North and South crater conduits are separated at significant depths and changes to either crater represent the variable proportions of magma and volatile flux directed into one pathway or the other. Zones A and B within the South crater have an alternating relationship, swapping between periods of active-inactive, or high-low magnitude. This appears to reflect the shallow diversion of magma and volatile flux between each vent, likely due to temporary conduit blockage and clearance cycles. Multiple timescales of eruptive behaviour change were revealed. Approximately 5-day cycles show changes in explosion parameters at individual vent zones, reflecting magma-level fluctuations and convection within the higher levels of each conduit. Cycles 10 to 20 days long occur in overall eruptive activity, and may reflect magma chamber processes that distribute magma and volatile flux differentially between the North and South conduits.

Strombolian eruptions and dynamics of magma degassing at Yasur Volcano (Vanuatu)

Open vent basaltic volcanoes account for a substantial portion of the global atmospheric outgassing flux, largely through passive degassing and mild explosive activity. We present volcanic gas flux and composition data from Yasur Volcano, Vanuatu collected in July 2018. The average volcanic plume chemistry is characterised by a mean molar CO2/SO2 ratio of 2.14, H2O/SO2 of 148 and SO2/HCl of 1.02. The measured mean SO2 flux in the period of 6th to 9th July is 4.9 kg s−1. Therefore, the mean fluxes of the other species are 7.5 kg∙s−1 CO2, 208 kg∙s−1 H2O and 4.8 kg∙s−1 HCl. The degassing regime at Yasur volcano ranges from ‘passive’ to ‘active’ styles, with the latter including Strombolian activity and spattering. Gases emitted during active degassing are enriched in SO2 over HCl and CO2 over SO2 relative to passive degassing, with CO2/SO2 ratios of 2.85 ± 0.17, SO2/HCl of 1.6 ± 0.22, and H2O/SO2 of 315 ± 78.8. Gases emitted during passive degassing have CO2/SO2 ratios of 1.96 ± 0.12, SO2/HCl of 0.50 ± 0.07 and H2O/SO2 of 174 ± 43.5. We use a model of volatile degassing derived from melt inclusion studies (Metrich et al., 2011), combined with our observations of chemical variations in the outgassing bubbles to propose a mechanism for magma degassing in the conduit at Yasur. We envisage a shallow conduit filled with crystal-rich magma, forming a viscous and mobile plug that develops an effective yield strength from the surface to a depth of at least 2000 m, in which bubbles are trapped, grow, ascend towards the surface and burst in a typical Strombolian eruption. Deeper bubbles released during active degassing are enriched in CO2 and SO2 compared to bubbles released during ‘passive degassing’, which are sourced from close to the surface, and are, consequently, HCl-rich.

Spatiotemporal Relationships between Two Closely‐spaced Strombolian‐style Vents, Yasur, Vanuatu

AbstractThis study details a case of transition of volcanic activity between two closely spaced (20–40 m) vents within the southern crater of Yasur Volcano, Vanuatu, over a period of 12 days. The transition from one vent to another newly emerged one was captured by a multi‐instrument array, with broadband seismic, thermal‐IR camera, and visual recordings presented. The results describe systematic changes in explosive parameters (e.g., style, power, and frequency) at both vents that reflect the transfer of magma and volatile gas flux within a shallow branching conduit system. The decline of activity at the initial vent corresponds with a shift from bomb‐rich to ash‐rich behavior indicating a progressive decrease in magma and volatile gas flux and increasing shallow conduit magma viscosity. The concurrent increase in activity at the emerging vent accompanies more bomb‐rich behavior that indicates increased flux and lower magma viscosity. During the transition period, most explosions were systematically paired between the two vents, occurring within &lt;1 to up to 45 s of each other. Broadband seismic data show that paired explosions produce a common seismic signal that resembles that of a single, nonpaired explosion. The presence of a common low‐frequency (0.06–1 Hz) signal indicates that multiple shallow conduits may transmit the same gas and impulsive energy differently from a single gas rise and burst event. Temporal offsets between paired explosions reflect the different conduit pathways and viscosity states of the magma in each conduit, with the lagging vent always displaying greater ash‐rich activity indicating higher magma viscosity and gas path tortuosity.

Three‐Dimensional Acoustic Multipole Waveform Inversion at Yasur Volcano, Vanuatu

AbstractAcoustic waveform inversions can provide estimates of volume flow rate and erupted mass, enhancing the ability to estimate volcanic emissions. Previous studies have generally assumed a simple acoustic source (monopole); however, more complex and accurate source reconstructions are possible with a combination of equivalent sources (multipole). We deployed a high‐density acoustic network around Yasur volcano, Vanuatu, including acoustic sensors on a tethered aerostat that was moved every ∼15–60 min. Using this unique data set we invert for the acoustic multipole source mechanism using a grid search approach for 80 events to examine volume flow rates and dipole strengths. Our method utilizes finite‐difference time‐domain modeling to obtain the full 3‐D Green's functions that account for topography. Inversion results are compared using a monopole‐only, multipole (monopole and dipole), simulations that do not include topography, and those that use a subset of sensors. We find that the monopole source is a good approximation when topography is considered. However, initial compression amplitude is not fully captured by a monopole source so source directionality cannot be ruled out. The monopole solution is stable regardless of whether a monopole‐only or multipole inversion is performed. Inversions for the dipole components produce estimates consistent with observed source directionality, though these inversions are somewhat unstable given station configurations of typical deployments. Our results suggest that infrasound waveform inversion shows promise for realistic quantitative source estimates, but additional work is necessary to fully explore inversion stability, uncertainty, and robustness.

Metal transport in volcanic plumes: A case study at White Island and Yasur volcanoes

We report new data on trace metal emissions at White Island volcano (2015–2016), the first estimates from Yasur volcano (2016), and a brief review of global volcanic metal fluxes. Bi, Cd, Tl, Se, Sb, Te and Au are the most enriched metals and metalloids in the particulate phase of volcanic plumes. Observations of the particulate phase from the volcanic plumes of White Island, Yasur and Etna reveal abundant silicates and sulfates, sulfuric acid and more interestingly Zn oxide containing variable amounts of Cu. Thermodynamic speciation calculations show chloride species to be very important in terms of gaseous metal transport. Complexation with sulfur, in contrast, appears significant only in S-rich and Cl-poor gases, at high (>700 °C) temperature. Bromine, despite being a minor component of volcanic gases, is very efficient at complexing with metals, and especially with Cu, Pb, Bi, Zn and Cr. Metal emission rates in the study period at White Island are one to two orders of magnitude lower than reported previously, with ~6–10 kg/d of Cu, As, Se and Zn, and <2 kg/d of Pb, Bi, Tl, Sb, Te and Cd. Higher values were measured at Yasur volcano, ranging from ~175 kg/d of Cu, ~30 kg/d of As, Zn and Pb, and ~3 kg/d of Tl and Cd. Such fluxes of toxic metals are significant, representing a potential threat for local populations. We compare our new data to previously reported metal emissions from volcanoes worldwide, and show that high halogen emissions appear as the critical parameter controlling metal emissions, explaining the high metal fluxes measured at some intraplate volcanoes.

Capturing volcanic plumes in 3D with UAV-based photogrammetry at Yasur Volcano – Vanuatu

As a precise volume of volcanic ash-plume is essential to understand the dynamic of gas emission, exchanges and the eruptive dynamics, we have measured in 3D using photogrammetry a small-size volcanic plume at the summit of Yasur Volcano, Vanuatu. The objective was to collect the altitude and planform shape of the plume as well as the vertical variations of the shape and size. To reach this objective, the authors have used the Structure from Motion photogrammetric method applied to a series of photographs captured in a very short period of time around and above the plume. A total of 146 photographs at 3000×4000 pixel were collected as well as the geolocation, the pitch, tilt and orientation of the cameras. The results revealed a "mushroom"-like shape of the plume with a narrow ascending column topped by a turbulent mixing zone. The volume of the plume was calculated to be ~13,430m3±512m3 (with the error being the cube of the linear error from the Ground Control Points) for a maximum height above the terrain of 63m. The included error was also kept high because of the irregular distribution of the Ground Control Points that could not be collected in dangerous areas due to the ongoing eruption. Based on this research, it is therefore worth investigating the usage of multiple cameras to capture plumes in 3D over time and the method is also a good complement to the recent development of photogrammetry from space, which can tackle larger-scale eruption plumes.

Capturing the Acoustic Radiation Pattern of Strombolian Eruptions using Infrasound Sensors Aboard a Tethered Aerostat, Yasur Volcano, Vanuatu

AbstractWe obtained an unprecedented view of the acoustic radiation from persistent strombolian volcanic explosions at Yasur volcano, Vanuatu, from the deployment of infrasound sensors attached to a tethered aerostat. While traditional ground‐based infrasound arrays may sample only a small portion of the eruption pressure wavefield, we were able to densely sample angular ranges of ~200° in azimuth and ~50° in takeoff angle by placing the aerostat at 38 tethered loiter positions around the active vent. The airborne data joined contemporaneously collected ground‐based infrasound and video recordings over the period 29 July to 1 August 2016. We observe a persistent variation in the acoustic radiation pattern with average eastward directed root‐mean‐square pressures more than 2 times larger than in other directions. The observed radiation pattern may be related to both path effects from the crater walls, and source directionality.

Spaceborne detection of localized carbon dioxide sources.

Spaceborne measurements by NASA's Orbiting Carbon Observatory-2 (OCO-2) at the kilometer scale reveal distinct structures of atmospheric carbon dioxide (CO2) caused by known anthropogenic and natural point sources. OCO-2 transects across the Los Angeles megacity (USA) show that anthropogenic CO2 enhancements peak over the urban core and decrease through suburban areas to rural background values more than ~100 kilometers away, varying seasonally from ~4.4 to 6.1 parts per million. A transect passing directly downwind of the persistent isolated natural CO2 plume from Yasur volcano (Vanuatu) shows a narrow filament of enhanced CO2 values (~3.4 parts per million), consistent with a CO2 point source emitting 41.6 kilotons per day. These examples highlight the potential of the OCO-2 sensor, with its unprecedented resolution and sensitivity, to detect localized natural and anthropogenic CO2 sources.

Seismo-acoustic wavefield of strombolian explosions at Yasur volcano, Vanuatu, using a broadband seismo-acoustic network, infrasound arrays, and infrasonic sensors on tethered balloons

Seismo-acoustic wavefields at volcanoes contain rich information on shallow magma transport and subaerial eruption processes and inform our understanding of how volcanoes work. Acoustic wavefields from eruptions are predicted to be directional, but sampling this wavefield directivity is challenging because infrasound sensors are usually deployed on the ground surface. We attempt to overcome this observational limitation using a novel deployment of infrasound sensors on tethered balloons in tandem with a suite of dense ground-based seismo-acoustic, geochemical, and eruption imaging instrumentation. We conducted a collaborative multiparametric field experiment at the active Yasur volcano, Tanna Island, Vanuatu, from 26 July to 2 August 2016. Our observations include data from a temporary network of 11 broadband seismometers, 6 single infrasonic microphones, 7 small-aperture 3-element infrasound arrays, 2 infrasound sensor packages on tethered balloons, an FTIR, a FLIR, 2 scanning Flyspecs, and various visual imaging data; scoria and ash samples were collected for petrological analyses. This unprecedented dataset should provide a unique window into processes operating in the shallow magma plumbing system and their relation to subaerial eruption dynamics.

Short term precursors of Strombolian explosions at Yasur volcano (Vanuatu)

AbstractThe seismic wavefield associated with Strombolian activity is usually dominated by explosion quakes (EQs), tremor, and various signals generated by surface phenomena. Looking at the seismicity recorded at Yasur volcano in 2008, we found that beside the transient events which occur simultaneously with surface explosions, the seismicity includes events related to a deeper process. These long period (LP) events form a family of similar events located below the southeastern part of the crater rim at a depth of about 700–1200 m below the summit. They are commonly followed by EQs with a variable delay. The examination of about 20,000 LP‐EQ sequences at several stations near the summit shows that interevent delays follow distributions peaked around 11–12 s. This short delay compared to the relatively great source depth of the LPs favors a causal relationship linked to pressure transfer rather than gas slug propagation after nucleation at the LP source.