Inflating Shallow Plumbing System of Bezymianny Volcano, Kamchatka, Studied by InSAR and Seismicity Data Prior to the 20 December 2017 Eruption

Explosive eruptions at steep-sided volcanoes may develop with complex precursor activity occurring in a poorly-understood magma plumbing system so that timelines and possible interactions with the geologic surrounding are often unresolved. Here we investigate the episode prior to the energetic December 20, 2017 eruption at Bezymianny volcano, Kamchatka. We compare degassing activity inferred from time-lapse camera images, seismicity and real-time seismic amplitude (RSAM) data derived from a temporary station network, as well as high-resolution InSAR displacement maps. Results show that the first changes can be identified in low-frequency seismicity and degassing at least 90 days before the eruption, while the first volcano-tectonic (VT) seismicity occurred 50 days before the eruption. Coinciding with significant changes of the RSAM, surface displacements affect the volcanic flanks at least 9 days prior to the eruption. Inversion modeling of the pre-eruptive surface deformation as well as deflation-type, co-eruptive surface changes indicate the presence of a shallow and transient reservoir. We develop a conceptual model for Bezymianny volcano initiating with deep seismicity, followed by shallow events, rockfalls, steaming and an inflating reservoir. The eruption is then associated with subsidence, caused by deflation of the same reservoir. This sequence and conceivable causality of these observations are providing a valuable contribution to our understanding of the shallow magma plumbing system beneath Bezymianny and may have relevance for volcano monitoring and early warning strategies at similar volcanoes elsewhere.

A machine learning based approach to clinopyroxene thermobarometry: model optimisation and distribution for use in Earth Sciences

Thermobarometry is a fundamental tool to quantitatively interrogate magma plumbing systems and broaden our appreciation of volcanic processes. Developments in random forest-based machine learning lend themselves to a more data-driven approach to clinopyroxene thermobarometry. This can include allowing users to access and filter large experimental datasets that can be tailored to individual applications in Earth Sciences. Here we present a methodological assessment of random forest thermobarometry, using the R freeware package “extraTrees”, by investigating the model performance, tuning hyperparameters, and evaluating different methods for calculating uncertainties. We determine that deviating from the default hyperparameters used in the “extraTrees” package results in little difference in overall model performance (<0.2 kbar and <3 ⁰C difference in mean SEE). However, accuracy is greatly affected by how the final pressure or temperature (PT) value from the voting distribution of trees in the random forest is selected (mean, median or mode). This thus far has been unapproached in machine learning thermobarometry. Using the mean value leads to a higher residual between experimental and predicted PT, whereas using median values produces smaller residuals. Additionally, this work provides two comprehensive R scripts for users to apply the random forest methodology to natural datasets. The first script permits modification and filtering of the model calibration dataset. The second script contains pre-made models in which users can rapidly input their data to recover pressure and temperature estimates. These scripts are open source and can be accessed at https://github.com/corinjorgenson/RandomForest-cpx-thermobarometer.

Translithospheric magma plumbing system of intraplate volcanoes as revealed by electrical resistivity imaging

The magma plumbing systems of volcanoes in subduction and divergent tectonic settings are relatively well known, whereas those of intraplate volcanoes remain elusive; robust geophysical information on the magma pathways and storage zones is lacking. We inverted magnetotelluric data to image the magma plumbing system of an intraplate monogenetic volcanic field located above the stagnant Pacific slab in northeast China. We identified a complex, vertically aligned, low-resistivity anomaly system extending from the asthenosphere to the surface consisting of reservoirs with finger- to lens-like geometries. We show that magma forms as CO2-rich melts in a 150-km-deep asthenospheric plume crossing the whole lithosphere as hydrated melt, inducing underplating at 50 km depth, evolving in crustal reservoirs, and erupting along dikes. Intraplate volcanoes are characterized by low degrees of melting and low magma supply rates. Their plumbing systems have a geometry not so different from that of volcanoes in subduction settings.

Machine learning thermobarometry and chemometry using amphibole and clinopyroxene: a window into the volcanic roots of an arc volcano (Mount Liamuiga, Saint Kitts)

The physical and chemical properties of magma govern the eruptive style and behaviour of volcanoes. Many of these parameters are linked to the storage pressure and temperature of the erupted magma, and melt chemistry. However, reliable single-phase thermobarometers and chemometers which can recover this information, particularly using amphibole chemistry, remain elusive. We present a suite of single-phase amphibole and clinopyroxene thermobarometers and chemometers, calibrated using machine learning. This approach allows us to intimately track the range of pre-eruptive conditions over the course of a millennial eruptive cycle on an island arc volcano (Saint Kitts, Eastern Caribbean). We unpick the story of Mount Liamuiga, a stratovolcano that pops its upper-crustal (2 kbar), dacitic cork at the beginning of the Lower Mansion Series eruptive sequence. This permits a progressive increase in the thermal maturity of the magma arriving at the surface from the middle to upper crust (2 – 5.5 kbar) through time. The temperature increase correlates well with matrix plagioclase chemistry, which itself displays a remarkable progression to less evolved (more anorthitic) composition in time. We find that amphibole is a reliable themobarometer (SEE = 1.4 kbar; 40 ˚C), at odds with previous studies. We suggest it is the regression strategy, as opposed to the abject insensitivity to pressure, that has hindered previous calibrations of amphibole only thermobarometers. By recognising this, we have constructed a high-resolution, quantitative picture of the magma plumbing system beneath an arc volcano.

Supplemental Material: Translithospheric magma plumbing system of intraplate volcanoes as revealed by electrical resistivity imaging

Details on the 3-D magnetotelluric inversion, sensitivity test of resistivity anomalies and melt fraction estimation, and Figures S1–S11. <br>

Supplemental Material: Translithospheric magma plumbing system of intraplate volcanoes as revealed by electrical resistivity imaging

Details on the 3-D magnetotelluric inversion, sensitivity test of resistivity anomalies and melt fraction estimation, and Figures S1–S11. <br>