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1. The radius of the umbrella cloud helps characterize large explosive volcanic eruptions

   https://doi.org/https://doi.org/10.1038/s43247-020-00078-3  

   Constantinescu, Robert; Hopulele-Gligor, Aurelian; Connor, Charles B.; Bonadonna, Costanza; Connor, Laura J.; Lindsay, Jan M.; Charbonnier, Sylvain; Volentik, Alain C. (January 2021, Communications earth environment)

   null (Ed.)

   Eruption source parameters (in particular erupted volume and column height) are used by volcanologists to inform volcanic hazard assessments and to classify explosive volcanic eruptions. Estimations of source parameters are associated with large uncertainties due to various factors, including complex tephra sedimentation patterns from gravitationally spreading umbrella clouds. We modify an advection-diffusion model to investigate this effect. Using this model, source parameters for the climactic phase of the 2450 BP eruption of Pululagua, Ecuador, are different with respect to previous estimates (erupted mass: 1.5–5 × 1011 kg, umbrella cloud radius: 10–14 km, plume height: 20–30 km). We suggest large explosive eruptions are better classified by volume and umbrella cloud radius instead of volume or column height alone. Volume and umbrella cloud radius can be successfully estimated from deposit data using one numerical model when direct observations (e.g., satellite images) are not available. 

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2. Dynamics of one of the largest Quaternary explosive eruptions in the Andes: The ca. 29 ka Campo de la Piedra Pómez VEI ≥ 6 caldera-forming eruption, NW Argentina

   https://doi.org/10.1007/s00445-025-01858-5  

   Báez, Walter; de_Silva, Shanaka; Cirer, Mercedes; Bertea, Esteban; Constantinescu, Robert; Danišík, Martin; Schmitt, Axel K; Ramos, Frank C (September 2025, Bulletin of Volcanology)

   MEdmonds (Ed.)

   Large explosive volcanic eruptions (Volcanic Explosivity Index ≥ 6) have the potential to profoundly impact modern society. Databases that encompass information on age, size, dynamics, and geological context of large eruptions are essential for devising effective long-term strategies for hazard and risk assessment. A critical limitation of these databases is the underreporting of events, particularly of those that occurred in remote regions like the southern edge of the Central Volcanic Zone of the Andes (24–27°S). In this study, we provide the first lithofacies description of the proximal and distal fall deposits linked to a previously overlooked eruption in this region, the Campo de la Piedra Pómez caldera-forming eruption from the Cerro Blanco Volcanic Complex (NW Argentina). Importantly, a zircon double-dating age of 28.9 ± 3.2 ka (2σ) for the Campo de la Piedra Pómez eruption is significantly younger than a previously reported 40Ar/39Ar sanidine age. In addition, a new (U-Th)/He age for the Barranca Blanca Ignimbrite indicates that it is significantly older and unrelated to the Cerro Blanco Volcanic Complex, clarifying a long-standing stratigraphic question. Major and trace element compositions of bulk rock and glass allow for a reliable regional correlation of proximal and distal fall deposits, and a clear geochemical distinction of the Campo de la Piedra Pómez eruption from other potential sources with similar compositions. Using inverse modeling of tephra dispersion, we estimate a minimum fall deposit volume of ~ 25.6 ± 5.6 km3. Adding this to the previous estimate of 17.2 km3 for the ignimbrite, the minimum bulk tephra erupted during the Campo de la Piedra Pómez eruption is now estimated at 42.7 km3 (~ 17.5 km3 Dense Rock Equivalent). The dynamics of the Campo de la Piedra Pómez eruption have been reconstructed from field-based data including facies analysis, componentry, and maximum size distribution of lithic clasts. The eruption started with a sustained Plinian phase characterized by a high discharge rate ( 108 – 109 kg/s) and an eruptive plume of ~ 35–40 km above the vent. Partial plume collapse then generated high-mobility pyroclastic density currents. The onset of caldera collapse triggered the transition to a mixed eruptive style, including the development of pyroclastic fountaining (boiling-over) from fissure-like vents accompanied by substantial pyroclastic density currents, and coeval convective Plinian plume activity from a spatially separated narrow vent. As the eruption progressed, fissure-like vents expanded, entirely halting the convective Plinian plume. Despite the huge volume erupted, the Campo de la Piedra Pómez eruption produced only an incipient collapse structure with limited subsidence. 

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3. Airfall volume of the 15 January 2022 eruption of Hunga volcano estimated from ocean color changes

   https://doi.org/10.1007/s00445-024-01744-6  

   Kelly, Liam J; Fauria, Kristen E; Manga, Michael; Cronin, Shane J; Latu’ila, Folauhola Helina; Paredes-Mariño, Joali; Mittal, Tushar; Bennartz, Ralf (June 2024, Bulletin of Volcanology)

   Abstract On 15 January 2022, Hunga volcano erupted, creating an extensive and high-reaching umbrella cloud over the open ocean, hindering traditional isopach mapping and fallout volume estimation. In MODIS satellite imagery, ocean surface water was discolored around Hunga following the eruption, which we attribute to ash fallout from the umbrella cloud. By relating intensity of ocean discoloration to fall deposit thicknesses in the Kingdom of Tonga, we develop a methodology for estimating airfall volume over the open ocean. Ash thickness measurements from 41 locations are used to fit a linear relationship between ash thickness and ocean reflectance. This produces a minimum airfall volume estimate of$${1.8}_{-0.4}^{+0.3}$$ ${1.8}_{-0.4}^{+0.3}$ km³. The whole eruption produced > 6.3 km³of uncompacted pyroclastic material on the seafloor and a caldera volume change of 6 km³DRE. Our fall estimates are consistent with the interpretation that most of the seafloor deposits were emplaced by gravity currents rather than fall deposits. Our proposed method does not account for the largest grain sizes, so is thus a minimum estimate. However, this new ocean-discoloration method provides an airfall volume estimate consistent with other independent measures of the plume and is thus effective for rapidly estimating fallout volumes in future volcanic eruptions over oceans. 

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4. Volcanic Ash Affected by Lightning During the Hunga 2022 Eruption

   https://doi.org/10.1029/2025JD044700  

   Genareau, Kimberly; Paredes‐Mariño, Joali; Cronin, Shane J; Harkema, Sebastian S; Schultz, Christopher J; Murphy, Kelley M; Naeger, Aaron R (March 2026, Journal of Geophysical Research: Atmospheres)

   Abstract The 15 January 2022 eruption of Hunga volcano (Kingdom of Tonga) produced the most lightning ever documented during an explosive eruption to date. This study estimates the mass of erupted tephra that may be structurally or electromagnetically affected by the lightning, based upon lightning peak current, channel length, and ash plume particle concentration. The lightning channels totaled 1.67 million m³in volume and contained 548 kg of volcanic ash at a calculated plume concentration of 0.328 g/m³. From this total, 54.8 kg of ash may display physical evidence in the form of lightning‐induced textures, such as lightning‐induced volcanic spherules, but this is an insignificant fraction of the total airfall deposit (10⁻⁸%). However, the total mass of ash exposed to magnetic flux densities exceeding Earth's ambient surface values is 2.24 × 10¹⁴ g, corresponding to just over a third (34.9%) of the calculated mass of total airfall (5.21 × 10¹⁴ g). This study reveals that even though physical evidence of volcanic lightning may be limited, ash particles will still be affected by the electromagnetic fields generated by the lightning discharge. The extent of these effects will be a function of lightning properties, ash properties, and location of the ash in relation to the discharge channel. 

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5. From the ashes of VEI: Decoding explosivity, mass eruption rate and hazards in real time

   https://doi.org/10.22541/essoar.176967627.71453176/v1  

   Sahagian, Dork (January 2026, AGU)

   Ash-producing volcanic eruptions are a major natural hazard. The explosivity of these eruptions has been described for decades by a semi-quantitative “Volcanic Explosivity Index (VEI)” based on a number of interdependent factors (eruption duration, volume of ejected material, eruptive column height, tropospheric and stratospheric injection, and many qualitative descriptors), most of which could only be assessed after eruption had ceased. The utility of this semi-quantitative index has been questioned since then, yet its common usage persists. We suggest that if VEI is to be used in the future, it may as well be an index that can be determined in real time during an eruption, and one that strictly reflects eruption intensity. We find that the same value for the “traditional” Volcanic Explosivity Index of past eruptions can be estimated in real time during an eruption, based solely on eruption column height. This approach is not intended to replace the traditional VEI scale or supplant more detailed mechanistic approaches to mass eruption rate (MER); rather it can be used to provide a more immediate way of calculating the VEI and linking to MER, in real time while an eruption is taking place. As such, if the easily observed height can be measured, both MER and VEI can be estimated. This may facilitate emergency response by aviation, hazard management, and others to mitigate societal impact of hazardous eruptions. This scheme can be inverted to use volume-based VEI of ancient eruptions to roughly retrodict unobserved column height for key historic and pre-historic eruptions. Further, ash particle morphology reflects explosivity in terms of decompression rate at the vent of unobserved eruptions. With sufficiently rapid decompression, this could result in an observable bi-modal bubble size distribution. The morphology of ash particles reveals a threshold between VEI 3 and 4, above which there is sufficiently rapid decompression to trigger a second nucleation event near the vent. 

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