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1. Magma Mixing During Conduit Flow is Reflected in Melt‐Inclusion Data From Persistently Degassing Volcanoes

   https://doi.org/10.1029/2021JB022799  

   Wei, Zihan; Qin, Zhipeng; Suckale, Jenny (February 2022, Journal of Geophysical Research: Solid Earth)

   Abstract Persistent volcanic activity is thought to be linked to degassing, but volatile transport at depth cannot be observed directly. Instead, we rely on indirect constraints, such as CO₂‐H₂O concentrations in melt inclusions trapped at different depth, but this data is rarely straight‐forward to interpret. In this study, we integrate a multiscale conduit‐flow model for non‐eruptive conditions and a volatile‐concentration model to compute synthetic profiles of volatile concentrations for different flow conditions and CO₂fluxing. We find that actively segregating bubbles in the flow enhance the mixing of volatile‐poor and volatile‐rich magma in vertical conduit segments, even if the radius of these bubbles is several orders of magnitude smaller than the width of the conduit. This finding suggests that magma mixing is common in volcanic systems when magma viscosities are low enough to allow for bubble segregation as born out by our comparison with melt‐inclusion data: Our simulations show that even a small degree of mixing leads to volatile concentration profiles that are much more comparable to observations than either open‐ or closed‐system degassing trends for both Stromboli and Mount Erebus. Our results also show that two of the main processes affecting observed volatile concentrations, magma mixing and CO₂fluxing, leave distinct observational signatures, suggesting that tracking them jointly could help better constrain changes in conduit flow. We argue that disaggregating melt‐inclusion data based on the eruptive behavior at the time could advance our understanding of how conduit flow changes with eruptive regimes. 

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2. Obsidian pyroclasts in the Yellowstone-Snake River Plain ignimbrites are dominantly juvenile in origin

   https://doi.org/10.1007/s00445-021-01448-1  

   Monnereau, L. R.; Ellis, B. S.; Szymanowski, D.; Bachmann, O.; Guillong, M. (April 2021, Bulletin of Volcanology)

   null (Ed.)

   Abstract Dense, glassy pyroclasts found in products of explosive eruptions are commonly employed to investigate volcanic conduit processes through measurement of their volatile inventories. This approach rests upon the tacit assumption that the obsidian clasts are juvenile, that is, genetically related to the erupting magma. Pyroclastic deposits within the Yellowstone-Snake River Plain province almost without exception contain dense, glassy clasts, previously interpreted as hyaloclastite, while other lithologies, including crystallised rhyolite, are extremely rare. We investigate the origin of these dense, glassy clasts from a coupled geochemical and textural perspective combining literature data and case studies from Cougar Point Tuff XIII, Wolverine Creek Tuff, and Mesa Falls Tuff spanning 10 My of silicic volcanism. These results indicate that the trace elemental compositions of the dense glasses mostly overlap with the vesiculated component of each deposit, while being distinct from nearby units, thus indicating that dense glasses are juvenile. Textural complexity of the dense clasts varies across our examples. Cougar Point Tuff XIII contains a remarkable diversity of clast appearances with the same glass composition including obsidian-within-obsidian clasts. Mesa Falls Tuff contains clasts with the same glass compositions but with stark variations in phenocryst content (0 to 45%). Cumulatively, our results support a model where most dense, glassy clasts reflect conduit material that passed through multiple cycles of fracturing and sintering with concurrent mixing of glass and various crystal components. This is in contrast to previous interpretations of these clasts as entrained hyaloclastite and relaxes the requirement for water-magma interaction within the eruptive centres of the Yellowstone-Snake River Plain province. 

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3. Reconciling petrologic magma ascent speedometers for the June 12th, 1991 eruption of Mt. Pinatubo, Philippines

   https://doi.org/10.30909/vol.07.01.117133  

   Harris, Megan; Hosseini, Behnaz; Myers, Madison; Bouley, Logan (January 2024, Volcanica)

   We investigate whether decompression rates derived from three often-disparate petrologic techniques (microlites, bubbles, and melt embayments) can be reconciled or integrated for a more complete understanding of magma ascent in the conduit. We focus on the well-studied and -documented earliest Plinian eruptions (June 12, 1991) of Mount Pinatubo. Using a newly developed two-stage decompression-diffusion model, volatile profiles in quartz-hosted embayments reveal an initial stage of decompression nearly two orders of magnitude slower than final rates. In applying time-integrated models of microlite and bubble nucleation and growth, initial decompression rates from embayments are supported by microlite modeling results, whereas final rates are in close agreement with bubble number densities. This consistency and continuity between speedometers supports the sensitivity of different petrologic recorders to specific regions of the conduit system and highlights the fidelity of embayments as recorders of decompression throughout the entire conduit. Ascent timescales derived from Pinatubo embayments range from hours to days, coinciding with the visual onset of lava effusion leading to explosive activity. 

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4. Crystal mush interaction controls eruptive style during the 2018 Kīlauea fissure eruption

   Soldati, Arianna; Weidendorfer, Daniel; Cimarelli, Corrado; Kueppers, Ulrich; Houghton, Bruce F; Tisdale, Caroline M; Dingwell, Donald B (September 2024, Journal of volcanology and geothermal research)

   We use new geochemical, petrological, and rheological data to constrain the formation and emplacement of the highly compositionally unusual(andesitic basalt) Kīlauea 2018 Fissure 17 (F17) eruptive products. Despite the restricted spatial and temporal distribution, F17 samples are texturally and geochemically diverse. The western samples are enriched in SiO2 by up to 10 wt%, relative to their eastern equivalents; additionally, the western samples contain microcrystalline enclaves, absent from the homogenous eastern samples. The compositions erupted along F17 suggest interaction between the basaltic 2018 juvenile magma and a crystal mush at depth, likely a left-over from the nearby 1955 eruption. Magma mingling caused heating and local melting of remnant mush, leading to melt hybridization and volatile exsolution. Rapid water exsolution likely caused overpressurization of the reservoir underneath the western side of F17, leading to Strombolian explosions of viscous magma, in contrast to sustained Hawaiian fountaining on the eastern side. Remelting of remnant crystal mush and melt hybridization in open-conduit systems may hence be an effective mechanism in inducing volatile saturation. 

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5. Coexisting Strombolian and Hawaiian activity during the 2018 fissure eruption of Kīlauea– Implications for processes of weak explosions

   https://doi.org/10.1016/j.jvolgeores.2023.107754  

   Walker, B.H.; Houghton, B.F.; Llewellin, E.W. (January 2023, Journal of volcanology and geothermal research)

   Mildly explosive eruptions—the most frequent manifestations of subaerial explosive volcanism on Earth—broadly group into two styles: Strombolian and Hawaiian. The former is characterized by sequences of intermittent discrete explosions, and the latter by sustained pyroclastic fountaining. Explosive activity during the 2018 fissure eruption of Kīlauea volcano (Hawaiʻi) provided an exceptional opportunity to record a wide range of Strombolian and Hawaiian behavior. We used high-resolution videography and image processing to quantify the frequency, duration, and steadiness (as seen by fluctuation in maximum clast height) of Hawaiian fountains and Strombolian jets. Combining these data with the currently published understanding of two-phase flow (melt + bubbles), we propose that the diversity in eruptive styles is related to melt viscosity, changing mass flux, and the extent of mechanical coupling versus decoupling of the exsolving volatile phases from the host magma. In particular, we single out the effects of the contrasts in abundance of a sub-population of the largest (meter-scale) bubbles that emerge intermittently and independently through the magma in the vent.. The coexistence of these styles—at vents often only meters apart—is a clear indication that the diversity in eruptive behavior is modulated at depths of probably no more than 100 m and perhaps as shallow as tens of meters. 

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