Insights into Magma Storage Beneath a Frequently Erupting Arc Volcano (Villarrica, Chile) from Unsupervised Machine Learning Analysis of Mineral Compositions

A key method to investigate magma dynamics is the analysis of the crystal cargoes carried by erupted magmas. These cargoes may comprise crystals that crystallize in different parts of the magmatic system (throughout the crust) and/or different times. While an individual eruption likely provides a partial view of the sub-volcanic plumbing system, compiling data from multiple eruptions builds a picture of the whole magmatic system. In this study we use machine learning techniques to analyze a large (>2000) compilation of mineral compositions from a highly active arc volcano: Villarrica, Chile. Villarrica's post-glacial eruptive activity (14 ka–present) displays large variation in eruptive style (mafic ignimbrites to Hawaiian effusive eruptions) yet its eruptive products have a near constant basalt-basaltic andesite bulk-rock composition. What, therefore, is driving explosive eruptions at Villarrica and can differences in storage dynamics be related to eruptive style? We used hierarchical cluster analysis to detect previously undetected structure in olivine, plagioclase and clinopyroxene compositions, revealing the presence of compositionally distinct clusters. Using rhyolite-MELTS thermodynamic modeling we related these clusters to intensive magmatic variables: temperature, pressure, water content and oxygen fugacity. Our results provide evidence for the existence of multiple discrete (spatial and temporal) magma reservoirs beneath Villarrica where melts differentiate and mix with incoming more primitive magma. The compositional diversity of an erupted crystal cargo strongly correlates with eruptive intensity, and we postulate that mixing between primitive and differentiated magma drives explosive activity at Villarrica.

Flow regimes during fluid-filled crack propagation in elastic media: Applications to volcanology and magma flow within dykes

Scaled analogue experiments were conducted to explore the effect of magma flow regimes, characterised by the Reynolds number (Re), on the transit of magma through the lithosphere via fractures. An elastic, transparent gelatine solid (the crust analogue) was injected by a fluid (magma analogue) to create a thin, vertical, and penny-shaped crack that is analogous to a magma-filled crack (dyke). A vertical laser sheet fluoresced passive-tracer particles suspended in the injected fluid, and particle image velocity (PIV) was used to map the location, magnitude, and direction of flow within the growing dyke from its inception to its surface rupture. Experiments were conducted using water, hydroxyethyl cellulose (HEC) or xanthan gum (XG) as the magma analogue. The results suggest that Re has significant impact on the direction of fluid flow within propagating dykes: Re > 0.1 (jet-flow) is characterised by a rapid central rising fluid jet and downflow at the dyke margin, whereas Re < 0.1 (creeping flow) is characterised by broadly uniform velocities across the dyke plane. Re may be underestimated by up to two orders of magnitude if tip velocity rather than internal fluid velocity is used. In nature, these different flow regimes would affect the petrological, geochemical, geophysical, and geodetic measurements of magma movement, key information upon which reconstructions of volcanic plumbing system architectures and their growth are based.

Crystal rotations and alignment in spatially varying magma flows: Two-dimensional examples of common subvolcanic flow geometries

Summary Elongate inclusions immersed in a viscous fluid generally rotate at a rate that is different from the local angular velocity of the flow. Often, a net alignment of the inclusions develops, and the resulting shape preferred orientation (SPO) of the particle ensemble can then be used as a strain marker that allows reconstruction of the fluid’s velocity field. Much of the previous work on the dynamics of flow-induced particle rotations has focused on spatially homogeneous flows with large-scale tectonic deformations as the main application. Recently, the theory has been extended to spatially varying flows, such as magma with embedded crystals moving through a volcanic plumbing system. Additionally, an evolution equation has been introduced for the probability density function (PDF) of crystal orientations. Here, we apply this new theory to a number of simple, two-dimensional flow geometries commonly encountered in magmatic intrusions, such as flow from a dyke into a reservoir or from a reservoir into a dyke, flow inside an inflating or deflating reservoir, flow in a dyke with a sharp bend, and thermal convection in a magma chamber. The main purpose is to provide a guide for interpreting field observations and for setting up more complex flow models with embedded crystals. As a general rule, we find that a larger aspect ratio of the embedded crystals causes a more coherent alignment of the crystals, while it has only a minor effect on the geometry of the alignment pattern. Due to various perturbations in the crystal rotation equations that are expected in natural systems, we show that the time-periodic behavior found in idealized systems is probably short-lived in nature, and the crystal alignment is well described by the time-averaged solution. We also confirm some earlier findings. For example, near channel walls, fluid flow often follows the bounding surface and the resulting simple shear flow causes preferred crystal orientations that are approximately parallel to the boundary. Where pure shear deformation dominates, there is a tendency for crystals to orient themselves in the direction of the greatest tensile strain rate. Where flow impinges on a boundary, for example in an inflating magma chamber or as part of a thermal convection pattern, the stretching component of pure shear aligns with the boundary, and the crystals orient themselves in that direction. In the field, this local pattern may be difficult to distinguish from a boundary-parallel simple shear flow. Pure shear also dominates along the walls of a deflating magma chamber and in places where the flow turns away from the reservoir walls, but in these locations, the preferred crystal orientation is perpendicular to the wall. Overall, we find that our calculated patterns of crystal orientations agree well with results from analogue experiments where similar geometries are available.

Unveiling Tatun volcanic plumbing structure induced by post-collisional extension of Taiwan mountain belt

The Tatun Volcanic Group (TVG) is proximal to the metropolis of Taipei City (population of ca. 7 million) and has long been a major concern due to the potential risks from volcanic activity to the population and critical infrastructure. While the TVG has been previously considered a dormant or extinct volcano, recent evidence suggests a much younger age of the last eruption event (~ 6000 years) and possible existence of a magma reservoir beneath the TVG. However, the location, dimension, and detailed geometry of the magma reservoir and plumbing system remains largely unknown. To examine the TVG volcanic plumbing structure in detail, the local P-wave travel time data and the teleseismic waveform data from a new island-wide Formosa Array Project are combined for a 3D tomographic joint inversion. The new model reveals a magma reservoir with a notable P-wave velocity reduction of 19% (ca. ~ 19% melt fraction) at 8–20 km beneath eastern TVG and with possible northward extension to a shallower depth near where active submarine volcanoes that have been detected. Enhanced tomographic images also reveal sporadic magmatic intrusion/underplating in the lower crust of Husehshan Range and northern Taiwan. These findings suggest an active volcanic plumbing system induced by post-collisional extension associated with the collapse of the orogen.

Geochemical evidence of volcanic plumbing system processes from fumarolic gases and diffuse CO2 degassing of Taal volcano, Philippines, prior to the January 2020 eruption

&lt;p&gt;Significant temporal variations in the chemical and isotopic composition of Taal fumarolic gas as well as in diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission from Taal Main Crater Lake (TMLC) have been observed across the ~12 years of geochemical monitoring (Arpa et al., 2013; Hern&amp;#225;ndez et a., 2017), with significant high CO&lt;sub&gt;2 &lt;/sub&gt;degassing rates, typical of plume degassing volcanoes, measured in 2011 and 2017. In addition to these CO&lt;sub&gt;2&lt;/sub&gt; surveys at the TCML, soil CO&lt;sub&gt;2&lt;/sub&gt; efflux continuous monitoring was implemented at Taal volcano since 2016 and a clear increasing trend of the soil CO&lt;sub&gt;2&lt;/sub&gt; efflux in 2017 was also observed. Increasing trends on the fumarolic CO&lt;sub&gt;2&lt;/sub&gt;/St, He/CO&lt;sub&gt;2&lt;/sub&gt;, CO/CO&lt;sub&gt;2&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt;/CH&lt;sub&gt;4&lt;/sub&gt; ratios were recorded during the period 2010-2011 whereas increasing SO&lt;sub&gt;2&lt;/sub&gt;/H&lt;sub&gt;2&lt;/sub&gt;S, H&lt;sub&gt;2&lt;/sub&gt;/CO&lt;sub&gt;2&lt;/sub&gt; ratios were recorded during the period 2017-2018. A decreasing on the CO&lt;sub&gt;2&lt;/sub&gt;/CH&lt;sub&gt;4&lt;/sub&gt; and CO&lt;sub&gt;2&lt;/sub&gt;/St ratios was observed for 2017-2018. These changes are attributed to an increased contribution of magmatic fluids to the hydrothermal system in both periods. Observed changes in H&lt;sub&gt;2&lt;/sub&gt; and CO contents suggest increases in temperature and pressure in the upper parts of the hydrothermal system of Taal volcano. The &lt;sup&gt;3&lt;/sup&gt;He/&lt;sup&gt;4&lt;/sup&gt;He ratios corrected (Rc/Ra), and &amp;#948;&lt;sup&gt;13&lt;/sup&gt;C of fumarolic gases also increased during the periods 2010-2011 and 2017-2018 before the eruption onset. During this study, diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission values measured at TMCL showed a wide range of values from &gt;0.5&amp;#8201;g&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt; d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt; up to 84,902 g&amp;#8201;m&lt;sup&gt;&amp;#8722;2&lt;/sup&gt; d&lt;sup&gt;&amp;#8722;1&lt;/sup&gt;. The observed relatively high and anomalous diffuse CO&lt;sub&gt;2&lt;/sub&gt; emission rate across the ~12 years reached values of 4,670 &amp;#177; 159 t d&lt;sup&gt;-1 &lt;/sup&gt;on March 24, 2011, and 3,858 &amp;#177; 584 t d&lt;sup&gt;-1&lt;/sup&gt; on November 11, 2017. The average value of the soil CO&lt;sub&gt;2&lt;/sub&gt; efflux data measured by the geochemical station showed oscillations around background values until 14 March, 2017. Since then at 22:00 hours, a sharp increase of soil CO&lt;sub&gt;2&lt;/sub&gt; efflux from ~0.1 up to 1.1 kg m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt; was measured in 9 hours and continued to show a sustained increase in time up to 2.9 kg m&lt;sup&gt;-2&lt;/sup&gt; d&lt;sup&gt;-1&lt;/sup&gt; in 2 November, that represents the main long-term variation of the soil CO&lt;sub&gt;2&lt;/sub&gt; emission time series. All the above variations might be produced by two episodes of magmatic intrusion which favored degassing of a gas-rich magma at depth. During the 2010-2011 the magmatic intrusion of volatile-rich magma might have occurred from the mid-crustal storage region at shallower depths producing important changes in pressure and temperature conditions, whereas a new injection of more degassed magma into the deepest zone of the hydrothermal system occurring in 2017-2018 might have favored the accumulation of gases in the subsurface, promoting conditions leading to a phreatic eruption. These geochemical observations are most simply explained by magma recharge to the system, and represent the earliest warning precursor signals to the January 2020 eruptive activity.&lt;/p&gt;&lt;p&gt;Arpa, M.C., et al., 2013. Bull. Volcanol. 75, 747. https://doi.org/10.1007/s00445-013-0747-9.&lt;/p&gt;&lt;p&gt;Hern&amp;#225;ndez, P.A., et al.,&amp;#160; 2017. Geol. Soc. Lond. Spec. Publ. 437:131&amp;#8211;152. https://doi.org/10.1144/SP437.17.&lt;/p&gt;

Geochronology - a suitable tool to discern causality from temporal coincidence?

&lt;p&gt;Geoscientists tend to subdivide the system Earth into different subsystems (geosphere, hydrosphere, atmosphere, biosphere), which are interacting with each other in a non-linear way. The quantitative understanding of this interaction is essential to make reconstructions of the geological past. This is mostly done by a linear approach of establishing time-series of chemical and physical proxies, calibrating their contemporaneity through geochronology, and eventually invoke causality. A good example is the comparison of carbon or oxygen isotope time series to the paleo-biodiversity in ancient sedimentary sections, temporally correlated using astrochronology or high-precision U-Pb dating of volcanic zircon in interlayered ash beds. While highly accurate and precise data are necessary to form the basis for linear and non-linear models, we have to be aware that any analysis is the result of an experiment &amp;#8211; an isotope-chemical analysis in the U-Pb example - introducing random and non-random noise, which can mimic, disturb, distort or mask non-linear system behavior. High-precision/high-accuracy U-Pb age determination using the mineral zircon (ZrSiO4) and application of the techniques of isotope dilution, thermal ionization mass spectrometry is a good example of such an experiment we apply to the geological history of our planet.&lt;/p&gt;&lt;p&gt;Two examples where precise U-Pb dating methods are used to link disparate processes are (1) using the duration and the tempo of zircon growth in a magmatic system as a measure for modeling magma flux in space and time, and apply these to infer potential eruptibility and volcanic hazard of a plutonic-volcanic plumbing system; (2) establish absolute age and duration of magma emplacement in large igneous provinces, feed these data into models of volatile injection into and residence of volatile species in the atmosphere, estimate their influence on the inherent parameters of Earth&amp;#8217;s climate, and infer causality with climatic, environmental and biotic crises. Both of these are outstanding scientific questions that attract and deserve significant attention by a general as well as academic public. However, insufficient attention is drawn onto the questions of the nature and importance of the noise we add through isotopic age determination.&lt;/p&gt;&lt;p&gt;There are two prominent issues to be discussed in this context, (1) to what extent (at what precision) can we distinguish natural age variation among zircon grains from random scatter produced by analytical techniques and the complexity of the U-Pb isotopic system in zircon, and (2) how can we correlate the U-Pb dates established for crystallization of zircon in residual and/or assimilated melt portions of mafic magmatic rocks from large igneous provinces to the release and injection of magmatic and contact-metamorphic volatiles into the atmosphere? This contribution intends to demonstrate that analytical scatter and complex system behavior are often confounded with age variation (and vice versa) and will outline new approaches and insights how to quantify their respective contributions.&lt;/p&gt;

Gas emissions from the resumption of eruptive activity at Kīlauea Volcano’s summit in December 2020.

&lt;p&gt;K&amp;#299;lauea Volcano (Hawaii, USA) had been in a state of quiescence since the end of the historic 2018 eruption on its lower East Rift Zone. Tapping the volcanic plumbing system at elevations around 300 m well below the volcano&amp;#8217;s 1200 m summit, the 2018 eruption drained magma from the volcano&amp;#8217;s summit reservoir and East Rift Zone, causing the drainage of a decade-old subaerial lava lake followed by widespread caldera collapse. Two years later, on the evening of 20 December 2020, the Hawaiian Volcano Observatory (HVO) once again detected a glow within the now vastly deepened Halema&amp;#699;uma&amp;#699;u Crater at K&amp;#299;lauea&amp;#8217;s summit. A new eruption had begun. Observations over the next few days revealed lava flowing from three vents in the wall of the crater and into its base. A water lake, which had formed in 2019 &amp;#8211; 2020 from groundwater infiltration, boiled off within hours and the crater began rapidly filling with lava. Over the first 3 days of the eruption, the new lava lake filled the lowermost ~150 m of the summit crater, and sulfur dioxide (SO&lt;sub&gt;2&lt;/sub&gt;) emission rates sometimes exceeded 30,000 metric tons per day (t/d) as measured by Differential Optical Absorption Spectroscopy (DOAS) traverses recorded both from the ground and by helicopter. These vigorous SO&lt;sub&gt;2&lt;/sub&gt; emissions were also clearly detected by the Tropospheric Monitoring Instrument (TROPOMI) aboard the Sentinal-5 Precursor satellite, and comparisons of the ground-based data with those collected by TROPOMI are the topic of ongoing research. Lava effusion and gas emission rates then tailed off and, from 26 December to 2 January, DOAS measurements indicated SO&lt;sub&gt;2&lt;/sub&gt; emissions of ~5,000 t/d, similar to the average emission rate from K&amp;#299;lauea&amp;#8217;s summit lava lake throughout most of the volcano&amp;#8217;s 2008-2018 eruption. Data from a continuous Multiple Gas Analyzer System (MultiGAS) installed approximately 1.3 km downwind of the active vents indicate that the carbon dioxide (CO&lt;sub&gt;2&lt;/sub&gt;) to SO&lt;sub&gt;2&lt;/sub&gt; molar ratio of the emitted gas is low (0.3 &amp;#177; 0.1), consistent with a model in which the erupted lava has been previously degassed in carbon dioxide but is only now degassing the more soluble sulfur as it reaches the surface. Further MultiGAS measurements performed with an unoccupied aircraft system (UAS) show that the gas composition varies throughout the emitted plume, but that the primary constituents are water vapor (~80-90% molar), carbon dioxide (~3%), and sulfur dioxide (~7-16%), while hydrogen sulfide is below the detection limit of the instrumentation. As of 11 January 2021, lava effusion and gas emissions appear to be slowly decreasing in vigor, but it is as yet unclear whether the eruption will continue to weaken and end within the coming weeks, or whether K&amp;#299;lauea Volcano will once again harbor a sustained subaerial lava lake for months or years to come.&lt;/p&gt;

The Impact of Complex Volcanic Plumbing on the Nature of Seismicity in the Developing Magmatic Natron Rift, Tanzania

Constraining the architecture of complex 3D volcanic plumbing systems within active rifts, and their impact on rift processes, is critical for examining the interplay between faulting, magmatism and magmatic fluids in developing rift segments. The Natron basin of the East African Rift System provides an ideal location to study these processes, owing to its recent magmatic-tectonic activity and ongoing active carbonatite volcanism at Oldoinyo Lengai. Here, we report seismicity and fault plane solutions from a 10 month-long temporary seismic network spanning Oldoinyo Lengai, Naibor Soito volcanic field and Gelai volcano. We locate 6,827 earthquakes with ML −0.85 to 3.6, which are related to previous and ongoing magmatic and volcanic activity in the region, as well as regional tectonic extension. We observe seismicity down to ∼17 km depth north and south of Oldoinyo Lengai and shallow seismicity (3–10 km) beneath Gelai, including two swarms. The deepest seismicity (∼down to 20 km) occurs above a previously imaged magma body below Naibor Soito. These seismicity patterns reveal a detailed image of a complex volcanic plumbing system, supporting potential lateral and vertical connections between shallow- and deep-seated magmas, where fluid and melt transport to the surface is facilitated by intrusion of dikes and sills. Focal mechanisms vary spatially. T-axis trends reveal dominantly WNW-ESE extension near Gelai, while strike-slip mechanisms and a radial trend in P-axes are observed in the vicinity of Oldoinyo Lengai. These data support local variations in the state of stress, resulting from a combination of volcanic edifice loading and magma-driven stress changes imposed on a regional extensional stress field. Our results indicate that the southern Natron basin is a segmented rift system, in which fluids preferentially percolate vertically and laterally in a region where strain transfers from a border fault to a developing magmatic rift segment.

Inside the volcano: Three-dimensional magmatic architecture of a buried shield volcano

The nature and growth of magmatic plumbing systems are of fundamental importance to igneous geology. Traditionally, magma chambers have been viewed as rapidly emplaced bodies of molten rock or partially crystallized “magma mush” connected to the surface by a narrow cylindrical conduit (referred to as the “balloon-and-straw” model). Recent data suggest, however, that magma chambers beneath volcanoes are formed incrementally through amalgamation of smaller intrusions. Here we present the first high-resolution three-dimensional reconstruction of an ancient volcanic plumbing system as a large laccolithic complex. By integrating seismic reflection and gravity data, we show that the ~200 km3 laccolith appears to have formed through partial amalgamation of smaller intrusions. The complex appears to have fed both surface volcanism and an extensive sill network beneath the volcanic edifice. Numerous sills are imaged within the volcanic conduit, indicating that magma stalled at various levels during its ascent. Our results reveal for the first time the entire multicomponent plumbing system within a large ancient shield volcano.