Contribution of fine ash to the atmosphere from plumes associated with pyroclastic density currents

A co-pyroclastic density current (co-PDC) plume forms as a mixture of fine-grained (<90 μm) particles and hot gas lofts from the top of a pyroclastic density current. Such plumes can rise tens of kilometers and inject substantial volumes of fine ash into the atmosphere with significant implications for airspace disruption, populations, livestock, and agriculture in downwind areas. Co-PDC deposits have a remarkably consistent grain size that remains constant with distance from source, regardless of eruption style, highlighting the complex sedimentation mechanisms that control deposition of co-PDC ash due to its fine grain size. Observations and numerical simulations of co-PDC onset emphasize the role played by the dynamics of PDCs in the development of co-PDC columns and plumes. The key differences between co-PDC and vent-derived plume source conditions and dispersion dynamics have important implications for application of remote sensing and numerical modeling methods

A Novel approach to reconstruct the plinian and co-ignimbrite phases of large eruptions - Campanian Ignimbrite

Reconstructing the volume and tephra dispersal from volcanic super-eruptions is necessary to assess the widespread impact of these massive events on climate, ecosystems and humans. Recent studies have demonstrated that volcanic ash transport and dispersion models are unrivaled in accurately constraining the volume of material ejected and provide further insight about the eruption dynamics during these gigantic events. However, the conventional simplified characterization of caldera-forming supereruptions as a single-phase event can lead to inaccurate estimations of the eruption dynamics and its impacts. Here, we apply a novel computational inversion method to reconstruct, for the first time, the two phases of the largest eruption of the last 200 ky in Europe, the Campanian Ignimbrite (CI) super-eruption. Additionally, we discuss the eruption’s contribution to the Middle to Upper Paleolithic transition by evaluating its environmental and climate implications

Reconstructing the Plinian and co-ignimbrite sources of large volcanic eruptions: a novel approach for the Campanian Ignimbrite

The 39 ka Campanian Ignimbrite (CI) super-eruption was the largest volcanic eruption of the past 200 ka in Europe. Tephra deposits indicate two distinct plume forming phases, Plinian and co-ignimbrite, characteristic of many caldera-forming eruptions. Previous numerical studies have characterized the eruption as a single-phase event, potentially leading to inaccurate assessment of eruption dynamics. To reconstruct the volume, intensity, and duration of the tephra dispersal, we applied a computational inversion method that explicitly accounts for the Plinian and co-ignimbrite phases and for gravitational spreading of the umbrella cloud. To verify the consistency of our results, we performed an additional single-phase inversion using an independent thickness dataset. Our better-fitting two-phase model suggests a higher mass eruption rate than previous studies, and estimates that 3/4 of the total fallout volume is co-ignimbrite in origin. Gravitational spreading of the umbrella cloud dominates tephra transport only within the first hundred kilometres due to strong stratospheric winds in our best-fit wind model. Finally, tephra fallout impacts would have interrupted the westward migration of modern hominid groups in Europe, possibly supporting the hypothesis of prolonged Neanderthal survival in South-Western Europe during the Middle to Upper Palaeolithic transition

Uncertainty quantification and sensitivity analysis of volcanic columns models: results from the integral model PLUME-MoM

The behavior of plumes associated with explosive volcanic eruptions is complex and dependent on eruptive source parameters (e.g. exit velocity, gas fraction, temperature and grain-size distribution). It is also well known that the atmospheric environment interacts with volcanic plumes produced by explosive eruptions in a number of ways. The wind field can bend the plume but also affect atmospheric air entrainment into the column, enhancing its buoyancy and in some cases, preventing column collapse. In recent years, several numerical simulation tools and observational systems have investigated the action of eruption parameters and wind field on volcanic column height and column trajectory, revealing an important influence of these variables on plume behavior. In this study, we assess these dependencies using the integral model PLUME-MoM, whereby the continuous polydispersity of pyroclastic particles is described using a quadrature-based moment method, an innovative approach in volcanology well-suited for the description of the multiphase nature of magmatic mixtures. Application of formalized uncertainty quantification and sensitivity analysis techniques enables statistical exploration of the model, providing information on the extent to which uncertainty in the input or model parameters propagates to model output uncertainty. In particular, in the framework of the IAVCEI Commission on tephra hazard modeling inter-comparison study, PLUME-MoM is used to investigate the parameters exerting a major control on plume height, applying it to a weak plume scenario based on 26 January 2011 Shinmoe-dake eruptive conditions and a strong plume scenario based on the climatic phase of the 15 June 1991 Pinatubo eruption

A Novel approach to reconstruct the plinian and co-ignimbrite phases of large eruptions - Campanian Ignimbrite

Reconstructing the volume and tephra dispersal from volcanic super-eruptions is necessary to assess the widespread impact of these massive events on climate, ecosystems and humans. Recent studies have demonstrated that volcanic ash transport and dispersion models are unrivaled in accurately constraining the volume of material ejected and provide further insight about the eruption dynamics during these gigantic events. However, the conventional simplified characterization of caldera-forming supereruptions as a single-phase event can lead to inaccurate estimations of the eruption dynamics and its impacts. Here, we apply a novel computational inversion method to reconstruct, for the first time, the two phases of the largest eruption of the last 200 ky in Europe, the Campanian Ignimbrite (CI) super-eruption. Additionally, we discuss the eruption’s contribution to the Middle to Upper Paleolithic transition by evaluating its environmental and climate implications

Molecular and genetic characterization of Rhizobium japonicum strain USDA191

R. japonicum nodulates and fixes nitrogen on soybeans. Recently, R. japonicum was reclassified in the genus Bradyrhizobium. In 1982, several unusual fast-growing R. japonicum strains were discovered in the People\u27s Republic of China. Most of these strains will nodulate but do not fix nitrogen on North American soybean cultivars. However, one exception is R. japonicum strain USDA191 which will effectively fix nitrogen on several North American soybean cultivars. The goal of this study was the identification and isolation of the genes responsible for nodulation and nitrogen fixation in strain USDA191 and also to determine if these symbiosis genes could function in other bacteria.;R. japonicum strain USDA191 was mutagenized with ultraviolet light, nitrosoquanidine and the transposon Tn5. In this manner, several auxotrophic mutants of R. japonicum USDA191 were generated. Tn5 was also used to label a plasmid in strain USDA191 that carries the symbiotic genes. A helper plasmid was used to mobilize Tn5-labeled pSym191 to other strains of Rhizobium to determine if these genes were expressed in a foreign background. When pSym191 was transferred to Agrobacterium tumefaciens, ineffective nodules were formed on soybean plants. However, when pSym191 was transferred to a Sym plasmid cured strain of R. leguminosarum, no nodules were formed.;pSym191 was also transferred to E. coli strains, where cointegrate plasmids were identified containing deleted regions of pSym191 and the helper pRL180. When these R-prime plasmids were transferred back to a Nod(\u27-) Nif(\u27-) strain of R. japonicum USDA191, only some of the deleted plasmids were able to form nodules on soybeans. It was determined that only two out of four HindIII fragments from strain USDA191 that hybridized with nod genes from R. meliloti were necessary for nodulation. A cosmid clone bank of plasmid DNA was constructed in the broad host-range vector pVK102 and the nodulation fragments isolated and subcloned in pVK102. The two HindIII fragments were subcloned together and transferred to Sym plasmid cured strains of R. trifolii, R. leguminosarum, and R. phaseoli. Only the R. trifolii transconjugants that contained the two R. japonicum USDA191 HindIII nod fragments were able to form nodules on soybeans

Insights into the formation and dynamics of coignimbrite plumes from one-dimensional models

Coignimbrite plumes provide a common and effective mechanism by which large volumes of fine-grained ash are injected into the atmosphere. Nevertheless, controls on formation of these plumes as a function of eruptive conditions are still poorly constrained. Herein, two 1-D axysymmetric steady state models were coupled, the first describing the parent pyroclastic density current and the second describing plume rise. Global sensitivity analysis is applied to investigate controls on coignimbrite plume formation and describe coignimbrite source and the maximum plume height attained. For a range of initial mass flow rates between 108 and 1010 kg/s, modeled liftoff distance (the distance at which neutral buoyancy is attained), assuming radial supercritical flow, is controlled by the initial flow radius, gas mass fraction, flow thickness, and temperature. The predicted decrease in median grain size between flow initiation and plume liftoff is negligible. Calculated initial plume vertical velocities, assuming uniform liftoff velocity over the pyroclastic density current invasion area, are much greater (several tens of m/s) than those previously used in modeling coignimbrite plumes (1 m/s). Such velocities are inconsistent with the fine grain size of particles lofted into coignimbrite plumes, highlighting an unavailability of large clasts, possibly due to particle segregation within the flow, prior to plume formation. Source radius and initial vertical velocity have the largest effect on maximum plume height, closely followed by initial temperature. Modeled plume heights are between 25 and 47 km, comparable with Plinian eruption columns, highlighting the potential of such events for distributing fine-grained ash over significant areas

Sources of uncertainty in the Mazama isopachs and the implications for interpreting distal tephra deposits from large magnitude eruptions

Estimating the area of tephra fallout and volume of large magnitude eruptions is fundamental to interpretations of the hazards posed by eruptions of this scale. This study uses the tephra from the caldera forming eruption of Mount Mazama (Crater Lake, OR, USA) to demonstrate the challenges faced when working with large prehistoric tephra deposits and outlines the methodologies required to determine eruption volume and magnitude. We combine > 250 Mazama tephra occurrences, reported by a range of disciplines (including archaeology, paleoclimatology and volcanology), with new field studies to better understand the extent of the distal tephra. We find that the Mazama tephra has been remobilised to varying degrees over the past 7000 years, so each tephra locality was appraised for the likelihood that it records primary tephra fallout. We designated 45 of the distal (> 100 km from source) tephra sites as suitable for use in the production of isopachs using a spline fitting method. The new distal isopachs were then integrated with proximal fallout data and estimates of the ignimbrite volume from previous studies to revise the estimated bulk erupted volume from the climactic Mazama eruption to ~ 176 km3 (~ 61 km3 dense-rock equivalent; DRE). This study demonstrates the importance of collating tephra localities from a range of disciplines and that even remobilised deposits provide valuable information about the extent of the deposit. Interpreting remobilised deposits can provide insight into post-eruptive processes that could potentially pose secondary hazards following large magnitude eruptions. We also show that in some circumstances, remobilised deposits preserve important physical properties such as grain size

Investigating Source Conditions and Controlling Parameters of Explosive Eruptions: Some Experimental-Observational- Modelling Case Studies

Explosive volcanic eruptions are complex systems that can generate a variety of hazardous phenomena, for example, the injection of volcanic ash into the atmosphere or the generation of pyroclastic density currents. Explosive eruptions occur when a turbulent multiphase mixture, initially predominantly composedf of fragmented magma and gases, is injected from the volcanic vent into the atmosphere. For plume modelling purposes, a specific volcanic eruption scenario based on eruption type, style or magnitude is strictly linked to magmatic and vent conditions, despite the subsequent evolution of the plume being influenced by the interaction of the erupted material with the atmosphere. In this chapter, different methodologies for investigating eruptive source conditions and the subsequent evolution of the eruptive plumes are presented. The methodologies range from observational techniques to large-scale experiments and numerical models. Results confirm the relevance of measuring and observing source conditions, as such studies can improve predictions of the hazards of eruptive columns. The results also demonstrate the need for fundamental future research specifically tailored to answer some of the still open questions: the effect of unsteady flow conditions at the source on the eruptive column dynamics and the interaction between a convective plume and wind

A review of laboratory and numerical modelling in volcanology

Modelling has been used in the study of volcanic systems for more than 100 years, building upon the approach first applied by Sir James Hall in 1815. Informed by observations of volcanological phenomena in nature, including eye-witness accounts of eruptions, geophysical or geodetic monitoring of active volcanoes, and geological analysis of ancient deposits, laboratory and numerical models have been used to describe and quantify volcanic and magmatic processes that span orders of magnitudes of time and space. We review the use of laboratory and numerical modelling in volcanological research, focussing on sub-surface and eruptive processes including the accretion and evolution of magma chambers, the propagation of sheet intrusions, the development of volcanic flows (lava flows, pyroclastic density currents, and lahars), volcanic plume formation, and ash dispersal. When first introduced into volcanology, laboratory experiments and numerical simulations marked a transition in approach from broadly qualitative to increasingly quantitative research. These methods are now widely used in volcanology to describe the physical and chemical behaviours that govern volcanic and magmatic systems. Creating simplified models of highly dynamical systems enables volcanologists to simulate and potentially predict the nature and impact of future eruptions. These tools have provided significant insights into many aspects of the volcanic plumbing system and eruptive processes. The largest scientific advances in volcanology have come from a multidisciplinary approach, applying developments in diverse fields such as engineering and computer science to study magmatic and volcanic phenomena. A global effort in the integration of laboratory and numerical volcano modelling is now required to tackle key problems in volcanology and points towards the importance of benchmarking exercises and the need for protocols to be developed so that models are routinely tested against real world data