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1. CO2 emissions during the 2023 Litli Hrútur eruption in Reykjanes, Iceland: ẟ13C tracks magma degassing

   https://doi.org/10.1007/s00445-024-01751-7  

   Fischer, Tobias P; Mandon, Céline L; Nowicki, Scott; Ericksen, John; Vilches, Felipe Rojas; Pfeffer, Melissa A; Aiuppa, Alessandro; Bitetto, Marcello; Vitale, Angelo; Fricke, G Matthew; et al (June 2024, Bulletin of Volcanology)

   We report CO2 emission rates and plume δ13C during the July 2023 eruption at Litli Hrútur in the Fagradalsfjall region of the Reykjanes Peninsula. The CO2 emission rates were measured by UAV utilizing a new method of data extrapolation that enables obtaining rapid flux results of dynamic eruption plumes. The δ13C values are consistent with degassing-induced isotopic fractionation of the magma during and after the eruption. Our results show that rapid, real-time CO2 flux measurements coupled with isotopic values of samples collected at the same time provide key insights into the dynamics of volcanic eruptions and have the potential of forecasting the termination of activity. 

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2. Extent and Volume of Lava Flows Erupted at 9°50′N, East Pacific Rise in 2005–2006 From Autonomous Underwater Vehicle Surveys

   https://doi.org/10.1029/2021GC010213  

   Wu, Jyun‐Nai; Parnell‐Turner, Ross; Fornari, Daniel_J; Kurras, Gregory; Berrios‐Rivera, Natalia; Barreyre, Thibaut; McDermott, Jill_M (March 2022, Geochemistry, Geophysics, Geosystems)

   Abstract Seafloor volcanic eruptions are difficult to directly observe due to lengthy eruption cycles and the remote location of mid‐ocean ridges. Volcanic eruptions in 2005–2006 at 9°50′N on the East Pacific Rise have been well documented, but the lava volume and flow extent remain uncertain because of the limited near‐bottom bathymetric data. We present near‐bottom data collected during 19 autonomous underwater vehicle (AUV)Sentrydives at 9°50′N in 2018, 2019, and 2021. The resulting 1 m‐resolution bathymetric grid and 20 cm‐resolution sidescan sonar images cover 115 km², and span the entire area of the 2005–2006 eruptions, including an 8 km²pre‐eruption survey collected with AUVABEin 2001. Pre‐ and post‐eruption surveys, combined with sidescan sonar images and seismo‐acoustic impulsive events recorded during the eruptions, are used to quantify the lava flow extent and to estimate changes in seafloor depth caused by lava emplacement. During the 2005–2006 eruptions, lava flowed up to ∼3 km away from the axial summit trough, covering an area of ∼20.8 km²; ∼50% larger than previously thought. Where pre‐ and post‐eruption surveys overlap, individual flow lobes can be resolved, confirming that lava thickness varies from ∼1 to 10 m, and increases with distance from eruptive fissures. The resulting lava volume estimate indicates that ∼57% of the melt extracted from the axial melt lens probably remained in the subsurface as dikes. These observations provide insights into recharge cycles in the subsurface magma system, and are a baseline for studying future eruptions at the 9°50′N area. 

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3. Determining the umbrella cloud geometry of unwitnessed silicic explosive eruptions: A case study from Mount Mazama (Oregon, United States)

   Wiejaczka, J; Giachetti, T (February 2024, Journal of volcanology and geothermal research)

   Volcanic Ash Transport and Dispersal Models (VATDMs) make real-time forecasts of tephra fall resulting from explosive eruptions possible. However, these predictions still mainly rely on eruption source parameters, such as erupted mass, total grain-size distribution, and plume height, gathered via thorough studies of past eruptions similar in nature. This dependency of eruption source parameters to analogous eruptions becomes particularly challenging when there are limited instances of similar events. An example is rhyodacitic to rhyolitic eruptions. This type of volcanic eruption has only been witnessed twice, at Chait´ en (2008–2009) and Cord´ on Caulle (2011− 2012), both in Chile. Here, we examine the 7.7 ka Cleetwood eruption of Mount Mazama (Oregon, USA), as a case study. This rhyodacitic eruption started explosively with two initial VEI 4, subplinian phases, and ended effusively with the emplacement of a rhyodacitic flow. We use the results of a detailed study of the proximal and medial tephra deposits as input in a VATDM to investigate the geometry and dimensions of the main plume formed during the Cleetwood eruption. We 1) constrain the erupted mass and calculate a detailed total grain-size distribution, 2) explore the Reanalysis 2 wind database to determine the direction and velocity of the local wind at the time of the eruption, and 3) use the VATDM Tephra2 with a grid-search method to estimate plume height, mass distribution within the plume, and the characteristics of tephra diffusion. We find that a vertical release of the erupted mass along a single line above the vent adequately replicates the measured mass loads but fails to simultaneously fit measured grain-size distributions at the same locations. We thus devise a method that not only accounts for a customized total grain-size distribution, real 1D wind patterns, and variable mass distribution within the plume, but also allows for adjustments to the size and location of an elliptical umbrella cloud. Using this method, we successfully replicate both local mass loads and high-resolution grain-size distributions and show that particles ≥0.125 mm from the lower Cleetwood unit were likely deposited from a 5 ×45 km2 umbrella reaching 16 km a.s.l., elongated in the direction of main wind intensity. This research contributes to enhancing the accuracy of predicting tephra transport from silicic volcanic eruptions. Moreover, it underscores the importance of utilizing grain-size data in combination with mass loads at specific locations to gain insights into the characteristics of the eruption plume, especially for eruptions that have not been directly observed. 

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4. Sulfur isotopes of sulfate measurements from a Greenland ice core (1200-1850) and volcanic gas measurements from various volcanoes and hot springs in Iceland

   https://doi.org/10.18739/A2N873162  

   Jongebloed, Ursula; Alexander, Becky; Cole-Dai, Jihong; Schauer, Andrew; Larrick, Carleigh; Wood, Robert; Fischer, Tobias; Carn, Simon; Salimi, Sara; Edouard, Shana; et al (January 2022, NSF Arctic Data Center)

   The Arctic is warming at almost four times the global rate. Cooling caused by anthropogenic aerosols has been estimated to offset sixty percent of greenhouse-gas-induced Arctic warming, but the contribution of aerosols to radiative forcing (RF) represents the largest uncertainty in estimating total RF, largely due to unknown preindustrial aerosol abundance. Here, sulfur isotope measurements in a Greenland ice core show that passive volcanic degassing contributes up to 66 ± 10% of preindustrial ice core sulfate in years without major eruptions. A state-of-the-art model indicates passive volcanic sulfur emissions influencing the Arctic are underestimated by up to a factor of three, possibly because many volcanic inventories do not include hydrogen sulfide emissions. Higher preindustrial volcanic sulfur emissions reduce modeled anthropogenic Arctic aerosol cooling by up to a factor of two (+0.11 to +0.29 W m-2 (watts per square meter)), suggesting that underestimating passive volcanic sulfur emissions has significant implications for anthropogenic-induced Arctic climate change. These data include sulfur isotopes of sulfate measurements from a Greenland ice core and volcanic gas measurements (CO2:S (carbon dioxide:sulfur) ratios) from various volcanoes and hot springs in Iceland. 

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5. Ultra-High Resolution Stable Isotope Analysis of a Nepal Stalagmite Reveals Short-Term Summer Monsoon Rainfall Changes Associated with the 1257 CE Mount Samalas Eruption

   Methe, Anna E. (April 2024, Cornell College)

   The eruption of Mount Samalas in Indonesia ~1257 CE has been argued to be one of the largest eruptions of the last two millennia. It released a monumental amount of volcanic aerosols, and reduced incoming solar energy by more than 30 W/m² (Sigl et al., 2015). Large volcanic eruptions can cause short term (generally 5 years for tropical eruptions like Samalas) regional or global climate shifts, which include changes to monsoon rainfall (Ridley et al, 2015; Sigl et al., 2015). In order to investigate the impact of this eruption on the Indian summer monsoon in Nepal, I analyzed at ultra-high resolution the carbon and oxygen isotopes of a fast growing, precisely dated aragonite stalagmite from Siddha cave (28.26689°, 83.96851°, 820m), located in the Pokhara valley in central Nepal, leading up to and through the period spanned by the Mount Samalas eruption. Each micro milled sample was ~40 µm wide and the area sampled was ~1 cm , for a total of 261 analyses. Stalagmites are composed of calcium carbonate, with the oxygen coming primarily from precipitation dripping into the cave. Studies of oxygen isotopes in precipitation, both near Siddha cave and in Kathmandu (130 km to the southeast), reveal that the amount effects in oxygen isotopes are weak in this region. The amount effect, a relationship saying that the precipitation amount has a negative relationship with oxygen isotope values, is very weak in this region. Therefore, I relied on carbon isotopes as a proxy for site-specific rainfall. Carbon isotopes in stalagmite carbonate originate from the soil and bedrock around, and as the drip water infiltrates the earth, it begins to dissolve CO2. This process continues until the drip water is supersaturated and the pressure differential forces calcite (or aragonite) to precipitate out of the drip water and crystalize. The carbon isotopes define sinusoids that appear to represent annual cycles of rainfall associated with the summer monsoon and the winter dry season. While some outliers exist, the total number of season cycles (18-21) is within error of the number of years of growth as determined by U/Th dating (1 cm = 26 ± 8 years). To investigate the impact of the eruption on the regional climate, we detrended the carbon isotope data and then calculated anomaly values in the wet and dry season relative to the mean of those values. The most prominent feature of the time series is two large positive isotope anomalies, separated by a moderate negative isotope anomaly. I interpret these to reflect disruptions to both the wet and dry season precipitation cycles from aerosol forcing from Mount Samalas. If correct, then this data reveals, somewhat surprisingly, an anomalously wet monsoon season in the first year after the eruption and only 1 year of reduced summer monsoon rainfall following the eruption before a return to pre-eruption summer monsoon rainfall activity. References Ridley, H. E. et al. (2015). Aerosol forcing of the position of the intertropical convergence zone since ad 1550. Nature Geoscience, 8(3), 195–200. Sigl, M. et al. (2015). Timing and climate forcing of volcanic eruptions for the past 2,500 years. Nature, 523(7562), 543–549. 

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