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After a century of quiescence, Turrialba, a Quaternary stratovolcano in the Costa Rican Volcanic Front, started a new eruptive cycle in 2010 that is ongoing to this date (July 3rd, 2019). Violent eruptions began in 2014, producing columns of ash that reached 4 km above the summit of the volcano. Here we provide new major and trace element data from fresh, glassy fragments (basaltic to rhyolitic) and mineralogical data for feldspars, olivines, and pyroxenes from ash fallout collected from 2016 and 2017 eruptions. We investigate the composition of the magma replenishing the system as well as the different juvenile components involved in the latter phase of this renewed eruption cycle. We find a range of mafic to felsic compositions in every eruptive event sampled. Our new geochemical data, coupled with Monte Carlo binary mixing simulations, indicate that magmas at Turrialba volcano are influenced by the input of a back-arc-type, strongly high field strength element-enriched (20–60 ppm) component generated by decompression melting from subduction-driven corner-flow. Thermodynamic modeling using MELTS software suggests that fractional crystallization alone fails to explain the compositional range of Turrialba's eruptive products. We instead propose that a complex, multi-stage magma mixing process produced renewed activity at Turrialba based on the trace element variability, the dominant intermediate magmatic compositions observed, and the results of our multi-element mixing simulations. This mixing process occurs upon injection of new mantle-derived melts into Turrialba's fractionated magmatic reservoirs and is governed by chaotic dynamics induced by gradients in temperature and viscosity.

Mineral-hosted melt inclusions have become an important source of information on magmatic processes. As the number of melt inclusion studies increases, so does the need to establish recommended practice guidelines for collecting and reporting melt inclusion data. These guidelines are intended to ensure certain quality criteria are met and to achieve consistency among published melt inclusion data in order to maximize their utility in the future. Indeed, with the improvement of analytical techniques, new processes affecting melt inclusions are identified. It is thus critical to be able to reprocess any previously published data, such that reporting the raw data is one of the first “recommended practices” for authors and a publication-criteria that reviewers should be sensitive to. Our guidelines start with melt inclusion selection, which is a critical first step, and then continue on to melt inclusion preparation and analysis, covering the entire field of methods applicable to melt inclusions. Dedication In March of 2000, a melt inclusion workshop was held at the Chateau de Sassenage in Grenoble and a companion issue of Chemical Geology entitled “Melt Inclusions at the Millennium” was published. Erik Hauri was heavily involved with the meeting and contributed two landmark papers to the topical issue of Chemical Geology on the use of secondary ion mass spectrometry to analyze volatiles in melt inclusions. When the melt inclusion community re-convened at Woods Hole Oceanographic Institution (WHOI) in August of 2018, we were saddened that Erik was unable to join us due to his failing health. Less than a month later came the devastating news of his passing at only 52 years of age. In recognition of his incredible contributions to science in general and to the in situ analysis of melt inclusions in particular, the participants and organizers of the WHOI melt inclusion workshop dedicate this collegial paper to Erik Hauri, our colleague, mentor and friend. Thank you Erik.

Numerical modeling facilitates the exploration of geodynamic mechanisms that are inaccessible to direct geological sampling. However, quantitative comparison of geochemical signatures predicted by models with real petrological analyses remains restricted. On one hand, efficient melting parameterizations are limited in the information that they provide, on the other, thermodynamic models are not optimized for 3D geodynamic codes. In the Eastern Atlantic, several archipelagos are located near the continental margin, e.g. the Canaries, Cape Verde, Cameroon Volcanic Line, but the origin of this volcanic activity remains poorly understood. Suggested origins range from mantle-plume activity (deep origin) to Edge-Driven Convection (EDC, shallow origin), or an interaction of both mechanisms. To test and constrain these models, we use a recently developed parameterization, which can constrain major-element geochemistry of primary magmas in the form of wt% as a function of the P-T path, together with regional numerical models of EDC with or without plumes. In this work, using the finite-element code CITCOM, we explore 3D models with a step of lithospheric thickness (or “edge”) and with variable distances between an imposed plume and the edge. We predict characteristic compositional trends that depend on model parameters, such as plume temperature or distance of the plume from the continental edge, and compare them with actual melt-inclusion data from the Canary Islands and Cape Verde. We find geochemical trends ranging from alkalic – for the models without thermal anomalies or with weak plumes – to more tholeiitic – for the cases with vigorous plumes. In turn, EDC alone cannot explain the volcanic fluxes observed at the Canary Islands or Cape Verde, with predicted melting rates well below 1 km3 Myr-1. Comparison with melt inclusions points towards the importance of CO2, but a thermal anomaly (plume) is also needed. We use the obtained major elements together with the melt volumes and the plume buoyancy flux to constrain the most likely set of mantle properties that originate the aforementioned islands. Our preferred model is a weak, relatively cold plume (ΔT < 150 ˚C), moderately rich in volatiles, that is affected by the nearby EDC pattern.

Fluid and melt inclusions rich in CO2 are common in many geological environments and are a powerful tool to provide constraints on P-T-X conditions of fluids resulting in ore deposits as well as pressures of inclusions in volcanic systems. Raman spectroscopy is an in situ, non-destructive method capable of determining the CO2 densities of inclusions for most sample sizes (> 1 μm) and densities. However, significant discrepancies exist among published CO2 densimeters for Raman spectroscopic measurements, mainly due to inconsistent calibration procedures, hardware differences, and sparse measurements for fluid densities between 0.2 and 0.7 g/mL. In this study, we re-designed a Fluid Density Calibration Apparatus (FDCA) based on one originally described by Lin et al. (2007) with important structural changes such as high accuracy temperature measurements made directly inside the FDCA that significantly reduce the error for critical region measurements. We provide five highly precise new calibration equations for different temperatures and CO2 density ranges. Application of these equations to a set of melt inclusions from a Pico do Fogo eruption from Cabo Verde indicates that the total percent uncertainty in calculated CO2 contents of bubbles derived from our densimeter are always below 5% except for inclusions with densities in the most sensitive part of the critical region (~7.3% for a 0.425 g/mL bubble), while relative percent uncertainty for literature densimeters are always above 10% and up to 28% in the worst-case scenario. In this study, we include all of the new designs, diagrams, and operational procedures with the goal of providing the community a new high-precision and high-accuracy FDCA for Raman spectroscopy.

Volatile solubility in magmas depends on several factors, including composition and pressure. Mafic magmas with high concentrations of alkali elements are capable of dissolving larger quantities of H2O and CO2 than subalkaline basalt, which possibly contributes to large explosive eruptions. Existing volatile solubility models for alkali-rich mafic magmas are well calibrated below ~ 200 MPa, but at greater pressures the experimental data are sparse. To fill in this gap, we conducted a set of mixed H2O–CO2 volatile solubility experiments between 400 and 600 MPa at 1200 °C in six mafic compositions with variable alkali contents (Stromboli, Etna, Vesuvius, Erebus, Sunset Crater, and the San Francisco Volcanic Field). Results from our experiments indicate that existing volatile solubility models for alkali-rich mafic magmas, if extrapolated beyond their calibrated ranges, do not accurately describe CO2 solubility at mid-crustal pressures. We adapt an existing thermodynamic model to reflect our higher-pressure experimental data by determining model parameters $$\Delta {\text{V}}_{r}^{0,m}$$ (partial molar volume change of CO2 reaction) and K0 (equilibrium constant) for each studied composition. In these compositions, $$\Delta {\text{V}}_{r}^{0,m}$$ is found to vary between ~ 15 and ~ 25 cm3 mol−1, while ln K0 ranges from − 14.9 to − 14.0. The calculated solubility curves show good agreement with CO2 solubility data from the experiments and provide a more accurate description of CO2 solubility than purely empirical fits. These new experiments indicate while CO2 solubility is increased in alkali-rich mafic magmas, it is not simply controlled by total alkali content but rather the full multicomponent magma composition.

Sunset Crater volcano, located ~25 km northeast of downtown Flagstaff (Arizona, USA) in the San Francisco volcanic field, represents an interesting case of highly explosive monogenetic volcanism. Sunset Crater is a young (ca. 1085 CE) scoria cone, ~290 m high, that produced 0.52 km3 dense rock equivalent (DRE) of basaltic magma (0.16, 0.12, and 0.24 km3 DRE for the scoria cone, lava flows, and tephra deposit, respectively). The activity developed in three distinct phases: an initial fissure phase, followed by a highly explosive phase, and a final low-explosivity waning phase. The first phase was characterized by the opening of a 10-kmlong fissure, which produced the Gyp Crater spatter mounds and the Vent 512 lava flow ~10 km SE of the main scoria cone, followed by lava fountaining activity that produced the first tephra layer (unit 1, 0.01 km3 DRE). During the second highly explosive phase, the activity migrated to the northwest to evolve into a single-vent eruption, which formed the main scoria cone. The central vent activity was initially characterized by variable eruptive styles, which started the process of cone building, including deposition of a second tephra layer (unit 2, 0.01 km3 DRE), and the effusion of the two main lava flows (Bonito and Kana’a). Following the initiation of effusive activity, the eruption increased in explosivity to produce three subplinian tephra layers from the central vent (units 3, 4, and 5), which emitted more than 0.22 km3 DRE of basalt, with associated eruption columns >20 km high. By the end of this phase, the Kana’a lava flow was almost completely emplaced, but the Bonito flow continued to grow, forming a 3-km-diameter flow field. A final waning phase produced several tephra units, commonly discontinuous and reworked, with

Basaltic volcanoes produce a range of eruptive styles, from Strombolian to low-intensity fire fountaining to, much more rarely, highly explosive Plinian eruptions. Although the hazards posed by highly explosive eruptions are considerable, controlling mechanisms remain unclear, and thus improving our understanding of such mechanisms is an important research objective. To elucidate these mechanisms, we investigate the magma ascent dynamics of basaltic systems using a 1D numerical conduit model. We find that variations in magmatic pressure at depth play a key role in controlling modelled eruption characteristics. Our most significant result is that a decrease in pressure at depth, consistent with the emptying of a magma chamber, results in an enhanced volatile exsolution and in a deepening fragmentation depth. The corresponding decrease in conduit pressure ultimately produces a collapse of the conduit walls. This type of collapse may be a key mechanism responsible for the cessation of individual explosive eruptions, a notion previously explored for silicic eruptions, but never before for basaltic systems. Using previously published field and sample analysis to constrain model parameters, we simulate scenarios consistent with sub-Plinian eruptions, similar to those at Sunset Crater volcano in ~1085 CE in terms of mass eruption rates and duration. By combining these analyses with a chamber-emptying model, we constrain the size of the magma chamber at Sunset Crater to be on the order of tens of km3 in volume. During the 1085 CE Sunset Crater eruption, there were three main sub-Plinian events that erupted between 0.12 and 0.33 km3 of tephra, indicating that ~1% of the total chamber volume has been erupted during each sub-Plinian pulse, one order of magnitude higher than small basaltic eruptions.

[1] The Mojave Neovolcanic Province (MNVP), located in the Mojave block of southern California, comprises late Miocene to Quaternary small-volume basaltic centers. Geochemistry indicates an asthenospheric source for the MNVP beginning in the late Miocene, but no physical evidence of missing mantle lithosphere has been presented. We utilize receiver functions and ambient noise tomography to image the lithosphere beneath the Mojave block. Regionally, we find thin crust that thickens distal to sites of MNVP volcanism. Shear wave velocities between 40 and 75 km depth are consistent with the presence of mantle lithosphere in the southern Mojave block and very thin or missing mantle lithosphere to the north. With one exception, MNVP volcanoes lie along this sharp boundary. Our observations, together with the established geologic history and geochemistry of the MNVP, can be explained by small-scale edge-driven convection producing ongoing lithospheric removal within the Mojave block. Our results provide another example of lithospheric instability that occurs in response to rapid changes in mantle dynamics induced by major changes in tectonic plate geometry.

The SCDAP/RELAP5 code has been developed for best estimate transient simulation of Light Water Reactor coolant systems during a severe accident. The code models the coupled behavior of the reactor coolant system, the core, fission product released during a severe accident transient as well as large and small break loss of coolant accidents, operational transients such as anticipated transient without SCRAM, loss of offsite power, loss of feedwater, and loss of flow. A generic modeling approach is used that permits as much of a particular system to be modeled as necessary. Control system and secondary system components are included to permit modeling of plant controls, turbines, condensers, and secondary feedwater conditioning systems. This volume contains detailed code-to-data calculations performed using SCDAP/RELAP5/MOD3.1, as well as comparison calculations performed with earlier code versions. Results of full plant calculations which include Surry, TMI-2, and Browns Ferry are described. Results of a nodalization study, which accounted for both axial and radial nodalization of the core, are also reported.

The report describes the results of the first scoping test in the Irradiation Effects Test Series conducted by the Thermal Fuels Behavior Program, which is part of the Water Reactor Research Program of EG and G Idaho, Inc. The research is sponsored by the United States Nuclear Regulatory Commission. This test used an unirradiated, three-foot-long, PWR-type fuel rod. The objective of this test was to thoroughly evaluate the remote fabrication procedures to be used for irradiated rods in future tests, handling plans, and reactor operations. Additionally, selected fuel behavior data were obtained. The fuel rod was subjected to a series of preconditioning power cycles followed by a power increase which brought the fuel rod power to about 20.4 kW/ft peak linear heat rating at a coolant mass flux of 1.83 x 10/sup 6/ lb/hr-ft/sup 2/. Film boiling occurred for a period of 4.8 minutes following flow reductions to 9.6 x 10/sup 5/ and 7.5 x 10/sup 5/ lb/hr-ft/sup 2/. The test fuel rod failed following reactor shutdown as a result of heavy internal and external cladding oxidation and embrittlement which occurred during the film boiling operation.

The report describes the results of a test using four 0.97-m long PWR-type fuel rods with differences in diametral gap and cladding irradiation. The objective of this test was to provide information about the effects of these differences on fuel rod behavior during quasi-equilibrium and film boiling operation. The fuel rods were subjected to a series of preconditioning power cycles of less than 30 kW/m. Rod powers were then increased to 68 kW/m at a coolant mass flux of 4900 kg/s-m/sup 2/. After one hour at 68 kW/m, a power-cooling-mismatch sequence was initiated by a flow reduction at constant power. At a flow of 2550 kg/s-m/sup 2/, the onset of film boiling occurred on one rod, Rod IE-011. An additional flow reduction to 2245 kg/s-m/sup 2/ caused the onset of film boiling on the remaining three rods. Data are presented on the behavior of fuel rods during quasiequilibrium and during film boiling operation. The effects of initial gap size, cladding irradiation, rod power cycling, a rapid power increase, and sustained film boiling are discussed. These discussions are based on measured test data, preliminary postirradiation examination results, and comparisons of results with FRAP-T3 computer model calculations.