A thermodynamic model to calculate the “Sulfide Content at Sulfide Saturation” or SCSS of basaltic and intermediate composition silicate melts has been built from four independently measurable thermodynamic entities, namely the standard state Gibbs free energy of the saturation reaction, the “sulfide capacity”, and the activities of FeO in the silicate melt and of FeS in the coexisting sulfide: ln [S2-]SCSS = ∆G(FeO-FeS)/RT + ln C(S2- )- ln a(FeO)(sil melt) + ln a(FeS)sulf The model was calibrated for silicate melts of basic and intermediate composition from published experimental results as a function of temperature, silicate melt composition, and sulfide matte composition in the system Fe-Ni-Cu-S-O at 1 bar. The likely effects of pressure and H2O content on SCSS were included in an exploratory way. The model was tuned against the large dataset of S contents in OFB glasses of Jenner and O’Neill (2012), giving it a precision comparable to that of the S analyses themselves, which is ~ 5%. All but 3% the OFB glasses were found to be sulfide saturated within uncertainty; these 3% have lost S by devolatization, revealed by their low S/Se. Applying the model to other OFB datasets suggests sulfide saturation is ubiquitous, including olivine-hosted melt inclusions proposed previously to be sulfide undersaturated. The sulfur fugacity (fS2) of undegassed Ocean Floor Basalts varies proportionally to fO2, with log10fS2 typically within the range -0.6 to +0.4.

In its three-dimensional (3-D) characterization, drought is approached as an event whose spatial extent changes over time. Each drought event has an onset and end time, a location, a magnitude, and a spatial trajectory. These characteristics help to analyze and describe how drought develops in space and time, i.e., drought dynamics. Methodologies for 3-D characterization of drought include a 3-D clustering technique to extract the drought events from the hydrometeorological data. The application of the clustering method yields small ‘artifact’ droughts. These small clusters are removed from the analysis with the use of a cluster size filter. However, according to the literature, the filter parameters are usually set arbitrarily, so this study concentrated on a method to calculate the optimal cluster size filter for the 3-D characterization of drought. The effect of different drought indicator thresholds to calculate drought is also analyzed. The approach was tested in South America with data from the Latin American Flood and Drought Monitor (LAFDM) for 1950–2017. Analysis of the spatial trajectories and characteristics of the most extreme droughts is also included. Calculated droughts are compared with information reported at a country scale and a reasonably good match is found.

Conceptual hydrological models imply a simplification of the complexity of the hydrological system; however, it lacks the flexibility in reproducing a wide range of the catchment responses. Usually, a trade-off is done to sacrifice the accuracy of a specific aspect of the system behavior in favor of the accuracy of other aspects. This study evaluates the benefit of using a modular approach, “The fuzzy committee model” of building specialized models (same structure associated with different parameter realization) to reproduce specific responses (high and low flow response) of the catchment. The study also assesses the applicability of using predicted runoff from both specialized models with certain weights based on a fuzzy membership function to form a fuzzy committee model. This research continues to explore the fuzzy committee models first presented by [Solomatine, 2006] and further developed by [Fenicia et al., 2007; Kayastha et al., 2013]. In this paper, weighting schemes with power parameter values are investigated. A thorough study is conducted on the relation between the fuzzy committee variables (the membership functions and the weighting schemes), and their effect on the model performance. Furthermore, the Fuzzy committee concept is applied on a conceptual distributed model with two cases, the first with lumped catchment parameters and the latter with distributed parameters. A comparison between different combinations of the fuzzy committee variables showed the superiority of all Fuzzy Committee models over single models. Fuzzy committee of distributed models performed well, especially in capturing the highest peak in the calibration data set; however, it needs further study of the effect of model parameterization on the model performance and uncertainty.

Cumulate rocks record the magmatic and cooling processes during formation of Earth’s igneous crust. Extracting the information of these two processes from mineral records, however, is often convoluted by various extents of diffusive resetting during cooling subsequent to main stages of crystallization. Accordingly, for cumulate rocks at diffusive closure, the apparent “equilibrium” temperatures derived from geothermometers are generally lower than the crystallization temperatures. Using analytical or numerical models, geospeedometers can extract cooling rates from the closure temperatures (or profiles) but only if the initial temperatures are determined independently. Here I summarize the general framework of geothermometry and geospeedometry from a trace element perspective. The Mg and REE-based exchange geothermometers for mafic cumulate rocks are reviewed as examples of the geothermometer design. Based on the observed differential diffusive closures of Mg and REE in oceanic gabbros, I outline a general resolution to uniquely determine the initial crystallization temperature and cooling rate of a cumulate rock. The basic idea is further demonstrated using the recently developed Mg-REE coupled geospeedometer for mafic cumulate rocks. Finally, I use the Hess Deep gabbros as a case study to show that this two-element coupled geospeedometer is particularly useful to delineate the igneous accretion and cooling styles during crust formation. This two-element (or multi-element) coupled approach outlined here can also be readily extended for decoding comprehensive thermal histories of other petrological systems at various geological settings or other rocky planetary bodies.

The mixing and mingling of magmas of different compositions are important geological processes. They produce various distinctive textures and geochemical signals in both plutonic and volcanic rocks and have implications for eruption triggering. Both processes are widely studied, with prior work focusing on field and textural observations, geochemical analysis of samples, theoretical and numerical modelling, and experiments. However, despite the vast amount of existing literature, there remain numerous unresolved questions. In particular, how does the presence of crystals and exsolved volatiles control the dynamics of mixing and mingling? Furthermore, to what extent can this dependence be parameterised through the effect of crystallinity and vesicularity on bulk magma properties such as viscosity and density? In this contribution, we review the state of the art for models of mixing and mingling processes and how they have been informed by field, analytical, experimental and numerical investigations. We then show how analytical observations of mixed and mingled lavas from four volcanoes (Chaos Crags, Lassen Peak, Mt. Unzen and Soufrière Hills) have been used to infer a conceptual model for mixing and mingling dynamics in magma storage regions. Finally, we review recent advances in incorporating multi-phase effects in numerical modelling of mixing and mingling, and highlight the challenges associated with bringing together empirical conceptual models and theoretically-based numerical simulations.

Experiment and observation have established the centrality of oxygen fugacity (fO2) to determining the course of igneous differentiation, and so the development and application of oxybarometers have proliferated for more than half a century. The compositions of mineral, melt, and vapor phases determine the fO2 that rocks record, and the activity models that underpin calculation of fO2 from phase compositions have evolved with time. Likewise, analytical method development has made new sample categories available to oxybarometric interrogation. Here we compile published analytical data from lithologies that constrain fO2 (n=860 volcanic rocks - lavas and tephras and n=326 mantle lithologies- the majority peridotites) from ridges, back-arc basins, forearcs, arcs, and plumes. Because calculated fO2 varies with choice of activity model, we re-calculate fO2 for each dataset from compositional data, applying the same set of activity models and methodologies for each data type. Additionally, we compile trace element concentrations (e.g. vanadium) which serve as an additional fO2-proxy. The compiled data show that, on average, volcanic rocks and mantle rocks from the same tectonic setting yield similar fO2s, but mantle lithologies span a much larger range in fO2 than volcanics. Multiple Fe-based oxybarometric methods and vanadium partitioning vary with statistical significance as a function of tectonic setting, with fO2 ridges < back arcs < arcs. Plume lithologies are more nuanced to interpret, but indicate fO2s  ridges. We discuss the processes that may shift fO2 after melts and mantle lithologies physically separate from one another. We show that the effects of crystal fractionation and degassing on the fO2 of volcanics are smaller than the differences in fO2 between tectonic settings and that effects of subsolidus metamorphism on the fO2 values recorded by mantle lithologies remain poorly understood. Finally, we lay out challenges and opportunities for future inquiry.

Magmas readily react with their surroundings, which may be other magmas or solid rocks. Such reactions are important in the chemical and physical evolution of magmatic systems and the crust, for example, in inducing volcanic eruptions and in the formation of ore deposits. In this contribution, we conceptually distinguish assimilation from other modes of magmatic interaction and discuss and review a range of geochemical (+/- thermodynamical) models used to model assimilation. We define assimilation in its simplest form as an end-member mode of magmatic interaction in which an initial state (t0) that includes a system of melt and solid wallrock evolves to a later state (tn) where the two entities have been homogenized. In complex natural systems, assimilation can refer more broadly to a process where a mass of magma wholly or partially homogenizes with materials derived from wallrock that initially behaves as a solid. The first geochemical models of assimilation used binary mixing equations and then evolved to incorporate mass balance between a constant-composition assimilant and magma undergoing simultaneous fractional crystallization. More recent tools incorporate energy and mass conservation in order to simulate changing magma composition as wallrock undergoes partial melting. For example, the Magma Chamber Simulator utilizes thermodynamic constraints to document the phase equilibria and major element, trace element, and isotopic evolution of an assimilating and crystallizing magma body. Such thermodynamic considerations are prerequisite for understanding the importance and thermochemical consequences of assimilation in nature, and confirm that bulk assimilation of large amounts of solid wallrock is limited by the enthalpy available from the crystallizing resident magma. Nevertheless, the geochemical signatures of magmatic systems-although dominated for some elements (particularly major elements) by crystallization processes-may be influenced by simultaneous assimilation of partial melts of compositionally distinct wallrock.

Changes in precipitation extremes remain a key uncertainty as the climate warms. Improved understanding of their evolution is crucial for effective water management. A number of studies have demonstrated various scaling relationships between precipitation extremes and several different environmental variables. In this chapter, we review recent important advances in two of these relationships primarily based on observations: The scaling of precipitation extremes with surface temperature (both air temperature and dew point temperature) and convective available potential energy (CAPE). Two up-to-date global daily datasets are also used to provide a further check on the generality of earlier findings. Known scaling relationships are used to quantify the impacts of these two factors on precipitation extremes. Results show that both of them play important roles, but their impacts vary over different regions on various time scales, highlighting the challenges of constructing global relationships to explain the changing nature of precipitation extremes.

Health outcomes attributable to wildfire smoke pollution exposure are an increasingly important global health issue especially as wildfires are increasing in frequency and intensity with climate change. In this chapter, we present an up-to-date overview of the literature regarding the health consequences of wildfire smoke pollution exposure experienced by adults, identify research gaps, and propose possible areas for future epidemiological studies. We also discuss existing interventions to reduce the negative health outcomes associated with wildfire smoke pollution exposure.

Xenoliths of plutonic rocks sporadically torn off by erupting magmas are known to carry valuable information about volcano plumbing systems and the lithosphere in which they emplace. One of the main steps to interpret such information is to quantify the pressure and temperature conditions at which the xenolith mineral assemblages last equilibrated. This chapter discusses some aspects of geothermobarometry of mafic and ultramafic rocks using the xenolith populations of Hualalai and Mauna Kea volcanoes, Hawaii, as case studies. Multiple- reaction geobarometry, recently revisited for olivine + clinopyroxene + plagioclase  spinel assemblages, provides the most precise pressure estimates (uncertainties as low as 1.0 kbar). An example is shown that integrates these estimates with calculated seismic velocities of the xenoliths and the available data from seismic tomography. The results allow to better constrain some km-scale horizontal and vertical heterogeneities in the magmatic system beneath Hawaii. Ultramafic xenoliths at Hualalai are the residuals of magma crystallization at 16–21 km depth, below the pre-Hawaiian oceanic crust. Few available gabbronorites and diorites record instead lower pressures and likely represent conduits or small magma reservoir crystallized at 0–8 km depth. At Mauna Kea, on the other hand, a significant portion of the xenolith record is composed by olivine-gabbros, which crystallized almost over the entire crustal thickness (3– 18 km). Ultramafic xenoliths are less abundant and might represent the bottom of the same magma reservoirs that crystallized in the deeper portion of the magmatic systems (11–18 km). Some unresolved issues remain in geothermometry of mafic and ultramafic rocks representing portions of magma reservoirs that cooled and recrystallized under subsolidus conditions. This suggests that further experimental and theoretical work is needed to better constrain the thermodynamics and kinetics of peridotitic and basaltic systems at low (< 1000 ̵̊C) temperatures.

The Himalayan orogen exposes a range of metamorphosed assemblages, from low-grade Indian shelf sediments of the Tethyan Formation to eclogite and ultra-high pressure rocks documented near the suture zone between the Indian craton and Asian subcontinent. Barrovian-grade pelites and mafic protoliths are exposed in the Himalayan core and include the Greater Himalayan Crystallines and Lesser Himalayan Formations. These units are separated by the Main Central Thrust (MCT). This fault system accommodated a significant amount of India-Asia convergence and is the focus of several models that explore ideas about the development of the range and collisional belts in general. These units provide critical information regarding the mechanisms of heat transfer within collisional belts. Garnets collected across the MCT record their growth history through changes in chemistry. These chemical changes can be extracted and modeled using a variety of thermodynamic approaches. This paper reviews the geological framework of the Himalayas with a focus on the protolith of its metamorphosed assemblages. It describes and applies particular thermobarometric techniques to decipher the metamorphic history of several garnet-bearing rocks collected across the MCT in central Nepal. Comparisons are made between the results of previously-reported conventional rim P-T conditions and P-T paths extracted using the Gibb’s method to isopleth thermobarometry and high-resolution P-T path modeling using the same data and assemblages. Predictions of the paths on garnet zoning are also presented for the high-resolution P-T path modeling and Gibb’s method using the program TheriaG. Although the approaches yield different absolute conditions and P-T path shapes, all are consistent with the development of the MCT shear zone due to imbrication of distinct rock packages. Greater Himalayan Crystalline garnets experienced higher-grade conditions that make extracting its P-T conditions and paths a challenge. Lesser Himalayan garnets appear to behave as closed systems and are ideally suited for thermodynamic approaches.

Coal fly ash has long been considered a potential resource for recovery of valuable elements, such as rare earth elements (REE), which are retained and concentrated upon combustion of coal feedstocks. Understanding REE occurrence within fly ash is a key to developing possible recovery methods. Recent results using modern analytical approaches shed light on the distribution REE in fly ash and the approaches required for their recovery. Some of the highest REE contents occur in fly ash derived from U.S. Appalachian Basin coals, and among these, coals influenced by input volcanic ash (Fire Clay coal, Kentucky) are especially enriched. Leaching studies of bulk fly ash show that, as a proportion of the total REE present, samples from eastern U.S. coals are generally less readily extractible than fly ash derived from western U.S. coals having lower REE contents. Direct determinations by ion microprobe show that REE in a range of fly ash samples are partitioned into aluminosilicate glasses formed during melting at boiler temperatures. These glasses comprise the largest mass fraction of coal fly ash. REE-enriched domains are present locally in fly ash at the nanometer scale (as shown by TEM), and these REE coexist with the glass phase. To enable systematic study of these REE, Ce has been proposed as a proxy for the trivalent lanthanides, as supported by speciation determinations demonstrating that Ce occurs in the trivalent form in fly ash. Despite a decreasing proportion of coal use for electric power generation in the U.S. and elsewhere, annual fly ash production, combined with coal ash already in storage, make up a large resource for potential recovery of rare earths and associated critical elements. Further developments in extraction technologies are needed to overcome difficulties in REE concentration and purification to produce REE materials of saleable purity derived from coal ash.

In karst environments, typically characterized by peculiar hydrogeological features and high heterogeneity and anisotropy, the connection between the recharge areas and the springs is often not straightforward. Rapid infiltration underground, and the resulting network of karst conduits, are frequently at the origin of a lack of correspondence among topographic divides and underground watersheds. As a consequence, in many karst areas there is still much work to do to fully understand the groundwater flow, with the only “underground truth” often being provided by cave data. In this contribution we start from general considerations about the difficulty in comprehending hydrogeology in karst, and use them to analyze one of the most important karst areas of southern Italy, the Alburni Massif in Campania (Italy). In detail, we present data about the main karst features at the surface (dolines, endorheic basins, etc.), the most important cave systems (reaching maximum depth of about 450 m below the surface), and the main basal springs coming out at the massif borders. Integration of the different sources of data allows to hypothesize the main directions of groundwater flows, and to perform the first attempts in correlating recharge and discharge data, but such hypothesis then often prove to be wrong by data from cave and diving explorations.

The solar corona, the outer atmosphere of the Sun, is heated to millions of degrees. This is several orders of magnitude hotter than the photosphere, the optical surface of the Sun, below, and a mystery that has baffled scientists for centuries. The answer to the question of how the solar corona is heated lies in the crucial magnetic connection through the atmosphere of the Sun. The magnetic field that threads the corona extends below the solar photosphere, where the convective motions drag the magnetic field footpoints, tangling and twisting them. The chromosphere is the atmospheric layer above the photosphere, below the corona, and the magnetic field provides an important connection between these layers. The exchange of mass and energy between the chromosphere and corona is an essential piece of this puzzle. The connection between the chromosphere and the corona is a challenging piece of the puzzle both observationally and computationally, as it is highly complex in space and time. We describe the history of the observations and theoretical understanding of the heating of the solar atmosphere, and end with future prospects of the coronal heating problem.

Iron is present in magmas at concentrations ranging from less than 1 wt% to more 8 than 10 wt% in two valence state. In general, Fe2+ is a network modifier in the melt structure while Fe3+ is a weak network former. The ratio Fe3+/(Fe3+ + Fe2+) depends on temperature, pressure, oxygen fugacity and melt composition. Parametric models allow its calculation, but the complex links between melt composition, iron oxidation state and coordination can be further rationalized using a ionic-polymeric model. Constraining concentration and oxidation state of iron is critical for determining magma density and viscosity, which drive exchanges of matter and heat in the Earth. At high pressures, changes in the coordination of elements, including iron, yield a stiffening and densification of magmas, potentially influencing dynamic and geochemical processes. Near surface, crystallization of Fe-bearing phases changes the residual melt composition, including iron content and oxidation state as well as volatile concentration, ultimately driving large changes in density and viscosity of magmas, and, hence, in the dynamic of fluid flow in volcanic systems. The complex interplay between magma iron content and oxidation state, major element chemistry, crystal and volatile content thus can play a large role on the dynamic of volcanic systems.

Time-related information of pre-eruptive magmatic processes is locked in the chemical profile of compositionally zoned minerals and can be retrieved by means of elemental diffusion chronometry. However, only the timescale of the outermost rim is commonly resolved, limiting our knowledge of timescales to those directly preceding the eruption. A major obstacle is the need to accurately constrain temperatures at which diffusion occurred. This is particular difficult for multiple zoned minerals where the different compositional boundaries indicate multiple physicochemical changes of melt environments during the lifetime of a crystal. Here, we argue that elemental diffusion chronostratigraphy can be fully resolved for crystals that have spent their lifetime in hot storage. Under this condition, crystals will be kept at the temperature of the eruptible magma(s), and diffusion timescales approximate the storage of the crystal in question in different melt environments. We further argue that hot storage conditions are typical of open-conduit systems in steady-state and are driven by the regular supply of fresh hot magmas determining the constant presence of eruptible magma. Fe-Mg interdiffusion in pyroxenes from Stromboli and Popocatepetl volcanoes are used as examples to reconstruct the time-dependent elemental diffusion chronostratigraphy of single crystals and discuss magma dynamics implications. Uncertainties introduced by temperature estimates and other input data, including experimentally derived values for the activation energy E and the pre-exponential factor D0, have large effects on the accuracy of modelled timescales, which need to be correctly evaluated and mitigated. Elemental diffusion chronostratigraphy is an extremely powerful tool to obtain time-related temporal information on the dynamics and histories of volcanic plumbing systems, which can lead to an in-depth knowledge of the magmatic system far beyond late-stage pre-eruptive processes. Combined with monitoring data and other petrological, geological and geophysical constraints at active volcanoes, they can greatly enhance our capability to inform volcanic hazard assessments.

Perhaps the least ambiguous signal that the mantle is convecting comes from observations of seismic anisotropy---the variation of wave speed with direction---which must arise due to the ordering of material as deformation occurs. Therefore significant effort has been made over many years to infer the direction and nature of mantle flow from these data. Observations have focussed on the boundary layers of the mantle, where deformation is expected to be strongest and where anisotropy is usually present. While prospects for mapping flow seem good, the lack of knowledge of several key issues currently holds progress back. These include the cause of anisotropy in the lowermost mantle, the causative material's response to shear, and the single-crystal or -phase seismic properties of the causative materials. In this chapter we review recent observations of lowermost mantle anisotropy, constraints on mineral elasticity and deformation mechanisms, and challenges in linking geodynamic modelling with seismic observations.

Due to the awareness of degrading groundwater quality in Florida’s freshwater 7 springs and beginning in the early 1990s, the state’s water management districts, the Florida 8 Department of Environmental Protection, and the U.S. Geological Survey began efforts to 9 coordinate monitoring of Florida’s first-and second-magnitude springs. This study investigates 10 changes in spring discharge and the concentrations of two saline indicators sodium (Na +) and 11 chloride (Cl-) from 1991 through 2020 (30 years) in the Floridan aquifer system (FAS). Data were 12 obtained from 32 major springs and three additional discharge gaging stations. Spring discharge 13 was observed to decrease, while concentrations of sodium and chloride increased. As a group, the 14 FAS springs experienced passive saline encroachment. Not only did encroachment occur along 15 Florida’s coasts, but also in the interior. Median concentrations of sodium and chloride increased 16 by an estimated range of 7 to 11% per decade. Evidence suggests the major driver is decreasing 17 rainfall and subsequent declines in recharge to the FAS, followed by sea-level rise. The sources 18 of the saline water are from salt water near Florida’s coasts and relict sea water from the deeper 19 portions of the FAS. The observed changes agree with those predicted by the Ghyben-Herzberg 20 principle for coastal, carbonate aquifers. 21