Volcano Type Research Articles

Effect of different Ga species in Ga-ZSM-5 on dehydrogenation performance of cyclohexane to benzene

Ga-containing ZSM-5 can effectively promote the dehydrogenation process in the methanol-to-aromatics (MTA) process. However, the forms of gallium species are diversity. It remains elusive which active gallium species has the best dehydrogenation activity. The catalytic activity of dehydrogenation of eight different Ga species (GaH2+, GaO+, Ga2O22+, GaH2+, Ga(OH)2+, Ga(OH)2+, GaH(OH)+, Ga+) in Ga-ZSM-5 was investigated by using DFT calculations in the dehydrogenation of cyclohexane to produce benzene as a model reaction. The DFT results combined with microkinetic calculation results suggested that GaH2+, Ga(OH)2+ and Ga2O22+, especially Ga2O22+, are the most likely species responsible for dehydrogenation. Interaction forces between metal ions and reactants and reactant activation energies show an inverted volcano type relationship. Enthalpy and entropy effects analysis indicate that the dehydrogenation of cyclohexane to benzene on Ga species is dominated by the enthalpy barrier. This opens up the prospect of better understanding the effect of dehydrogenating active species in Ga-doped ZSM-5 on the catalytic reaction.

Hydrogen adsorption on fcc metal surfaces towards the rational design of electrode materials

The successful large-scale implementation of hydrogen as an energy vector requires high performance electrodes and catalysts made of abundant materials. Rational materials design strategies are the most efficient means of reaching this goal. Here we present a study on the adsorption of H-atoms onto fcc transition metal surfaces and propose descriptors for the rational design of electrodes and catalysts by means of correlations between fundamental properties of the materials and among other properties, their experimentally measured performance as hydrogen evolution electrodes (HEE). A large set of quantum mechanical modelling data at the DFT level was produced, covering the adsorption of H-atoms onto the most stable surfaces (100), (110) and (111) of: Ag, Au, Co, Cu, Ir, Ni, Pd, Pt and Rh. For each material and surface, a coverage dependent set of minimum energy structures was produced and chemical potentials for adsorption of H-atoms were obtained. Averaging procedures are here proposed to approach modelling to the experiments. Several correlations between the computed data and experimentally measured quantities are done to validate our methodology: surface plane dependent adsorption energies, chemical potentials and experimentally determined surface energies and work functions. We search for descriptors of catalytic activity by testing correlations between the DFT data obtained from our averaging procedures and experimental data on HEE performance. Our methodology allows us to obtain linear correlations between the adsorption energy of H-atoms and the exchange current density (i0) in a HEE, avoiding the volcano-like plots. We show that the chemical potential has limitations as a descriptor of i0 because it reaches an early plateau in terms of i0. Simple quantities obtained from database data such as the first stage electronegativity (χ) as devised by Mulliken has a strong linear correlation i0. With a quantity we denominate modified second-stage electronegativity (χ2m) we can reproduce the typical volcano plot in a correlation with i0. A theoretical and conceptual framework is presented. It shows that both χ and χ2m, that depend on the first ionization potential, second ionization potential and electron affinity of the elements can be used as descriptors in rational design of electrodes or of catalysts for hydrogen systems.

Pressure dependence of electrochemical CO2 reduction to ethanol in flow cell

The electroreduction of carbon dioxide (CO2RR) to ethanol is an ideal approach for using released CO2 and producing fuel. The impact of CO2 partial pressure (PCO2) on ethanol synthesis was significant but was not well understood. The present study investigates the pressure dependence of ethanol formation from 0.25 bar to 15 bar in a high-pressure flow cell. It displayed a volcano type. The PCO2 associated with the peak Faradaic efficiency (FE) of ethanol increased as the current density increased. The pressure peak values were 0.5 bar, 0.75 bar at 100, 200, and 300 mA cm−2, respectively. Ethanol formation kinetics was affected by adsorbate-adsorbate interactions and the physical blocking of active sites on catalysts with excess CO2. Besides, ethanol synthesis using the configured flue gas, i.e., low-concentration CO2 (VCO2 = 5–30%), was realized via system pressurization from 5 to 20 bar at 200 mA cm−2. By optimizing the combination of CO2 concentration and total pressure (Ptot), the fuel efficiency (FE) of ethanol was maximized to 26.5%. This study uncovers the ideal CO2 partial pressure for ethanol synthesis under industrial current densities, hence presenting potential industrial applications for utilizing flue gas directly in ethanol production.

Variable controlling factors lead to contrasting patterns of volcanism in the Changbaishan volcanic area (Tianchi-Longgang), China-North Korea: Insights from morphometry and spatial-temporal analyses

The coexistence of monogenetic and polygenetic volcanoes is a common phenomenon in volcanic areas. However, the genetic relationship between monogenetic and polygenetic systems and the factors controlling their distinct eruptive styles are not well understood. In active volcanic areas, analysing the clustering and vent alignment of monogenetic volcanoes, as well as examining the geomorphology and relative ages of scoria cones, offers quantitative insights into magma supply rates, volcano type distribution, and volcanic development trends. Our study presents geomorphological and spatio-temporal analyses of the co-existing monogenetic volcanoes in the Longgang Volcanic Field (LVF) and those associated with a polygenetic volcano (Tianchi) in the Changbaishan Volcanic Area, China. The distance between the two volcanic areas is around 150 km. Monogenetic vents in the LVF exhibit greater density compared to the dispersed system associated with Tianchi. The LVF vents also show better alignment, particularly in the direction of pre-existing basement faults (NE-SW, NW-SE and EW). By using scoria cone morphometric parameters and features, we estimated the relative ages and erupted volumes of monogenetic volcanoes in the LVF and the Tianchi area. We classified the cones of the two volcanic systems into five eruptive periods and found that, despite similar magma sources and output rates over approximately 870 kyr, differing numbers of scoria cones across age classes suggest that Tianchi's magma system influences its associated monogenetic volcanic plumbing. Furthermore, the continuous rise in output rates of monogenetic volcanoes in the Tianchi area highlights the increasing magma supply sustaining Tianchi volcano. Together, these interpretations are consistent with the two systems being controlled by different factors: the Tianchi monogenetic volcanic system is more controlled by magmatism, whereas the LVF is more strongly controlled by local tectonic structures, alongside an increasing magma supply causing the formation of progressively larger individual volcanoes. In volcanic areas, analysing monogenetic volcanoes' spatial-temporal distribution, volumes and recurrence rate provides a framework to evaluate magma supply rates and tectonic associations, which are key to the development of different volcano types.

Revealing the role of a bridging oxygen in a carbon shell coated Ni interface for enhanced alkaline hydrogen oxidation reaction.

Encapsulating metal nanoparticles inside carbon layers is a promising approach to simultaneously improving the activity and stability of electrocatalysts. The role of carbon layer shells, however, is not fully understood. Herein, we report a study of boron doped carbon layers coated on nickel nanoparticles (Ni@BC), which were used as a model catalyst to understand the role of a bridging oxygen in a carbon shell coated Ni interface for the improvement of the hydrogen oxidation reaction (HOR) activity using an alkaline electrolyte. Combining experimental results and density functional theory (DFT) calculations, we find that the electronic structure of Ni can be precisely tailored by Ni-O-C and Ni-O-B coordinated environments, leading to a volcano type correlation between the binding ability of the OH* adsorbate and HOR activity. The obtained Ni@BC with a optimized d-band center displays a remarkable HOR performance with a mass activity of 34.91 mA mgNi-1, as well as superior stability and CO tolerance. The findings reported in this work not only highlight the role of the OH* binding strength in alkaline HOR but also provide guidelines for the rational design of advanced carbon layers used to coat metal electrocatalysts.

Tectonics and evolution of the Palmeiras and Xai-Xai Grabens, offshore southern Mozambique

The tectonic evolution of the Mozambique Basin was controlled by the break-up of Gondwana which led to the development of extensional domains along the East African margin. As a result, multiple grabens systems were formed both onshore and offshore southern Mozambique. Two of them are the Palmeiras and Xai-Xai grabens, which are discussed in greater details in this study using an extensive seismic dataset, together with regional gravity and magnetic data. The data show that the Palmeiras Graben evolved from a single extensional phase in the Middle to Late Jurassic (Kimmeridgian?). In contrast, the Xai-Xai Graben records three extensional phases. The first extensional phase occurred in the Late Jurassic (Tithonian?) to Early Cretaceous (Berriasian), the second during the Aptian-Albian and the third in the Late Miocene. The tectonic evolution of these grabens strongly controlled their sedimentary infill during Late Jurassic and Early Cretaceous rifting.Volcanism associated to these tectonic events is documented by onshore and offshore boreholes, as well as by the presence of buried volcanic bodies, lava extruded along fault planes and intrusions of Mesozoic age. Furthermore, a volcano-sedimentary sequence and dome type volcanoes were imaged in seismic data.Differences in tectonic activity impacted the oil and gas potential of both the Palmeiras and Xai-Xai grabens. The sedimentary sequences deposited in the Palmeiras Graben were preserved due to a period of relative tectonic stability predominating from the Aptian to the present day. The burial of the Palmeiras Graben during this period of tectonic stability under a thermal subsidence favoured the generation and preservation of hydrocarbons. In contrast, the Xai-Xai Graben was impacted by intense tectonics, which led to a limited or restricted deposition of strata since the Late Cretaceous to the Paleocene – Early Eocene. As a consequence of a long lasting tectonic activity in the Xai-Xai Graben, uplifting and erosion of potential reservoirs and destruction of existing traps, impacted on the prospectivity for hydrocarbons.

PALEOVOLCANIC KARING RECONSTRUCTION IN THE MERANGIN JAMBI UNESCO GLOBAL GEOPARK TERRITORY BASED ON PETROLOGICAL AND GEOCHEMICAL APPROACH

The presence of lava and pyroclastic sequences in the Karing River on the Merangin Jambi UNESCO Global Geopark territory provides information about the existence of ancient volcanoes. The absence of confirmed rock formations from the distribution of volcanic rock products that have been mapped nationally and also the shape of this ancient volcanic body, is an important reason for this research to be carried out using a petrological approach using petrography and XRF gochemical methods. Petrographic analysis is an appropriate method to determine the mineralogy consist, textures and particular textures, rock structures that are confirmed from field data. Meanwhile, a geochemical approach is used to determine rock oxide compounds. This method aims to reconstruct the shape and type of volcanoes. Research data shows that there are four lava sequences, with Sequence 1 having an entablature structure, Sequence 2 and Sequence 3 having a flow structure, and Sequence 4 having a vesicular-flow structure. The petrography results show that Sequence 1 and Sequence 2 are composed of phenocrysts and microliths of plagioclase, olivine, clinopyroxene, orthopyroxene. Meanwhile, in Sequence 3, hornblende is present, and in Sequence 4, the mineral olivine is absent. The results of geochemical analysis from the four lava sequences are in basalt rocks with 40%-50% Silica content, Calk-alkali basalt magma series, petrogenesis interpreted from the convergence of oceanic subduction beneath continent. The pyroclastic rocks found at the bottom of the lava sequence are evidence of the stratigraphic structure that makes up a volcano originating from the Karing Paleovolcanic, while the pyroclastic rocks found at the top of the lava sequence are believed to originate from other ancient volcanic eruptions. With the stratigraphy composed of lava and pyroclastic sequences, it can be concluded that this ancient volcano is a strato volcano type which is relatively sloping and almost resembles a shield volcano.

Tidal modulation of the seismic activity related to the 2021 La Palma volcanic eruption

The volcanic eruption at La Palma started on September 19, 2021. The eruption was preceded by a seismic swarm that began on September 11, although anomalous seismicity has been observed on the island since 2017. During the co-eruptive phase of the seismic activity, hypocenters depth was generally less than 15 km, save for the period between November 10 and November 27, when hypocenters ranged in the depth from 15 to 40 km. The eruption ended on December 13, 2021. We compute tidal stress for each earthquake at the hypocenter depth and find statistically significant correlations between the occurrence times of the earthquakes and the confining tidal stress values and stress rates. The correlation is depth-dependent, and ocean-loading tides have a stronger effect than body tides. We find that tidal stress variations contribute to the eruption onset and that certain explosive events, typical in Strombolian type volcanoes, seem to occur preferentially when the tidal stress rate is high. Our analysis supports the hypothesis that tides may modulate earthquake activity in volcanic areas, specifically during magma migration at shallow depths. A conceptual model is proposed, which could have a general application in the Canary Islands archipelago and other volcanic islands.

Integrating global geochemical volcano rock composition with eruption history datasets

The major element composition of volcanic rocks carries important information about the source and differentiation processes affecting the magma, the physical properties that allow it to erupt, and its eruptive style. Although global rock geochemical databases exist, these are not linked to volcanic eruption history which hampers our global understanding of the relationship between magma composition and eruption dynamics. Here, we integrate two global databases, the Geochemistry of Rocks of the Oceans and Continents (GEOROC) and the Holocene volcanoes of the world of the Global Volcanism Program (VOTW-GVP). The integration is based on matching the location name, geographic position and eruption time, which is automated by a tool called DashVolcano. The tool is open-source, accessible at https://github.com/feog/DashVolcano, and gives access to the integrated datasets via an interactive dashboard. DashVolcano is based on more than 138,000 volcanic rock samples and provides the basis for the identification of global relationships between eruption styles, volcano types, and rock composition for more than 700 volcanoes and their eruptions for the last 10,000 years. The combined record of the eruptive history and its corresponding geochemical rock composition that DashVolcano provides can be used for characterizing global geochemical differences between volcanoes, and should also prove useful for improved long-term hazard and risk evaluations.

Giant Martian Volcano-Tectonic Megamorphic Structures of the Central Type and Their Probable Small Terrestrial Analogues

The article shows that neither on the ground nor on the bottom of the seas there are no today topographical volcano-tectonical megamorphic structures similar in size, composition and origin to those giant morphic structures with volume of their building up rocks of 1–2.4 × 106 km3 revealed on Mars (patera Alba, Mount Olympus, Arsia, Askrian, Pavlina, Elysium). Fragments and traces of such formations have not been unambiguously revealed and described in geological strata of both Meso-Cenozoic and Paleozoic. The same applies to the older epochs of the Earth. The components of the relief of the Martian megamorphic structures are roughly similar in their form to very strongly enlarged copies of long-known and repeatedly described terrestrial volcanic structures – large shield, shield-like, and substantially lava volcanoes, lava domes, as well as calderas of different types. Although the structures of the listed types of volcanoes are not morphologically identical to their Martian analogues, they are smaller in height of their structures, and their slopes are steeper. Calderas are many times shallower. The age of Martian volcanic forms is much older. A unique formation is the megamorphic structure of Mount Olympus, which was formed in a large glacial cover, and in the formation of which the glacial processes also took a significant part. It is attributed to megamorphic structures of the giant tyuya type. Its small analogues are different in age and parameters glacial-subarctic tuyas, which suffered glaciation in the volcanic regions of the Earth.

Pitted-Ground Volcanoes on Mercury

On the planet Mercury, pyroclastic deposits formed by explosive volcanism are developed around rimless volcanic pits that are up to dozens of kilometers in diameters. Some pyroclastic deposits on Mercury, however, host no discernable main eruption centers but feature pitted-ground terrains that each consists of many similar sized and irregularly shaped pits. Individual pits are usually much smaller and shallower than typical volcanoes on Mercury. The origin of these landforms is unknown, but it is indicative of styles of volcanism on Mercury and/or post-volcanic modifications. Here, we investigate the possible origin of these peculiar landforms based on their geological context, morphology, geometry, reflectance spectra, and geophysical background. Reflectance spectra of pyroclastic deposits around such volcanoes are comparable with those erupted from typical volcanic pits on Mercury, suggesting a genetic relation between these pitted-ground terrains with explosive volcanism, and the source magma might have similar compositions. Pitted-ground volcanoes are mainly observed in impact structures, and two cases were formed in high-reflectance smooth plains and channeled lava flows. Most pitted-ground volcanoes are relatively degraded compared with typical volcanoes on Mercury, and some might have been formed in geological recent times judged by both their pristine preservation and crosscutting relationship with impact rays. All pitted-ground volcanoes have unconfined morphology boundaries, and each case is composed by dozens of rimless pits that have similar preservation states and interconnected edges. Such morphological characteristics are unique among volcanic landforms on terrestrial bodies, and they cannot be explained by multiple post-eruption collapses of a main explosive volcano. Pitted-ground volcanoes that are developed in lava flows with the same age have different preservation states, suggesting that the pits were not formed by escape of thermally destabilized volatiles from substrate and subsequent roof collapses. The largest pitted-ground volcano (~3700 km2) is located on the Borealis Planitia, and Bouguer gravity data reveal no larger mass concentration in the subsurface than surrounding terrains, consistent with a paucity of shallow intrusions in the crust of Mercury. Short-term and spatially-clustered explosive eruptions could explain the peculiar morphology and geometry of the pits, suggesting that pits in a given pitted-ground volcano are akin to swarms of monogenetic volcanoes. However, possible magma dynamics for the formation of pitted-ground volcanoes cannot be confirmed until future high-resolution gravity mapping could reveal detailed interior structures beneath these volcanoes. Based on comparative studies with spatially-clustered and similarly aged volcanoes on Earth, we interpret that a combination of pervasive crustal fractures and regional thermal anomaly in the thin mantle of Mercury might have caused such short-term and spatially-clustered explosive eruptions. If this interpretation was true, the heavy degradation state of most pitted-ground volcanoes and the few well-preserved cases are consistent with an overall cooling trend of the mantle, indicating the existence of longstanding heterogeneous thermal structures in the mantle.

Effusive and explosive volcanism on the northern Futuna Ridge, Lau Basin: A combined bathymetric, magnetic and seismic investigation

The Utu Uli Hill, located on the northern Futuna Ridge in the Lau Basin (Southwestern Pacific Ocean), displays recent volcanism in a complex area, possibly the boundary of one of many intermediate platelets between the Pacific and Australian plates or the result of progressive melting and dismantling of the Vitiaz subduction slab. The combination of bathymetric, magnetic and 3D reflection seismic data allows us to recognize and describe several types of submarine volcanoes, namely clustered small volcanoes, flat-topped volcanoes, elongated volcanic ridges, and volcaniclastic domes, and to unravel the geological evolution of the area. Sea-surface magnetic anomalies reveal that the area formed during the last 780 ka, whereas the large variations of amplitude in the near-seafloor, high-resolution magnetic anomalies suggest scattered ages for individual edifices and widespread volcanism within the whole Futuna Ridge. The spectacular volcaniclastic domes initiate only at depth shallower that 1150–1200 m. They show feeder dyke systems and evidence of hydrothermalism at their summit, and are locally affected by collapse structures.

Tuning Catalytic Activity in Ultrathin Bimetallic Nanowires Via Surface Segregation: Application in Electrochemical Methanol Oxidation

The reaction kinetics and efficiency in any catalytic process is controlled by the adsorption and desorption of reactant and intermediates on the surface of catalyst. As a consequence, the surface properties, composition and geometry of the catalyst dictates the mechanism of reactions. The surface electronic structure is modulated by variations in surface and subsurface atomic configurations, e.g., ordering and surface segregation, which in turn can vividly affects catalytic properties.1,2 A great deal of efforts are being devoted to develop efficient heterogenous catalyst by critically controlling the surface structure and chemistry. Here, I would like to present results on two different strategies for controlling the surface composition in ultrathin bimetallic AuPd nanowires. Au nanowire template-based method was used to grow AuPd wires by gradually increasing the amount of Pd.3 Percentage of composition of Au and Pd in AuPd nanowires gave either alloy nanowires with Au-rich compositions or core-shell structure at higher Pd compositions with Au-rich core and Pd-rich shell. Surface morphology of alloyed nanowires were induced through segregation of Pd to the surface by annealing under controlled CO atmosphere. High resolution microscopic imaging was possible due to the fact of substantial difference in the atomic number between Au and Pd. Electrocatalytic methanol oxidation reaction (MOR) in alkaline medium is important for energy conversion and was selected to study the catalytic activity of AuPd nanowires. A nearly monotonic increase of MOR potential was observed with increase in Pd content. Interestingly, a typical volcano type behavior of the specific activity was observed with different composition and with 40 and 50% Pd samples showed the optimum values in terms of current, potential and If/Ib values. Owing to a higher Pd content of CO-annealed nanowires, a lowering of potential was observed though the specific activity was maintained. These findings provide clear strategies to independently control the reaction potential and the activities of nanocatalysts with smaller amounts of the expensive active metal. The compositional effects on the electronic structure of the AuPd nanowires (catalyst surface) as well as binding energy of intermediates involved in the MOR was investigated using DFT calculations. d-band center analysis was employed to check interaction of CO* which a major intermediate of MOR with the catalyst surface. The theoretical investigation align well with the experimental results where it was found that the MOR potential increases with increasing amount of Pd and for the Au rich case the reaction does not reach up to CO2 but yields HCHO as a product at lower potentials. From our experimental finding it was evident that it is possible to lower the MOR potential to attain comparable or better activity through enrichment with the precious metal on the surface while essentially dropping the real quantity used.

(Keynote) Interpretation of Oxygen Reduction Activity Volcano Correlations for MN4 Molecular Catalysts Compared to Those for Metallic Electrodes

A classical well-known reactivity index in electrocatalysis is the binding energy of key intermediates to the active sites. For example, this is well documented for the catalytic activity of metal electrodes for the oxygen reduction reaction (ORR)[1], alloys and metal oxides and less studied for molecular catalysts [2]. The activity at constant potential (log(i)E) plotted versus the M-O2 binding energy has the shape of a volcano. This is well documented in several papers, especially by the group of Norksov for metallic electrodes [1] and can be applied to many electrochemical reactions. This has been extended to MN4 molecular catalysts. In contrast to metallic electrodes MN4 molecular catalysts have discrete energy levels and the active site is the central metal, surrounded by an organic ligand with an MN4 central moiety. Essentially one of the key intermediates is the binding of the reacting O2 molecule to the active sites at the rate determining step as: [MN4]ad + O2(aq) + e- ↔ [RMN4O2 -]ad where MN4 is a surface confined macrocyclic complex or a pyrolyzed catalysts bearing a MN4 active moiety embedded in a graphene or graphitic structure. As the ORR reaction involves the transfer of several electrons ( 2, 2+2 or 4 electrons), several adsorbed intermediates can be involved. If the controlling step is the first step, it is expected that for the binding step when DGad = 0 a maximum activity should be observed and the partial coverage of adsorbed intermediate is = 0.5. On thermodynamic ground this corresponds to a thermoneutral condition for the best catalyst. In this work we have tested this hypothesis by studying ORR in alkaline media using several iron porphyrins and iron phthalocyanines as catalysts immobilized on graphite and carbon nanotubes. The trends in reactivity versus the Fe(III)/(II) redox potential for ORR describe a typical volcano correlation. However if the currents are divided by the θFe(II), the fraction of active sites calculated at E=-0.24 V vs SCE using the Nernst equation, log(i/ θFe(II),)E vs. E°Fe(III)/(II) gives a straight line of slope -0.120V/decade. The maximum corresponds to θFe(II) = 0.5 and occurs at a potential close to that used for comparing the activities. A similar behaviour is observed for the oxidation of hydrazine but the continuation of the straight line is observed at potentials more positive than that of the maximum. Again the maximum is observed at the potential chosen for comparison. Those catalysts having Eº’ Fe(III)/(II) >> θFe(II) higher than -0.56V (for hydrazine oxidation) are in the Fe(III) state as predicted by the Nernst equation. That oxidation state Fe(III) is inactive for both reactions studied as OH- ions are strongly bound to Fe(III), especially in alkaline media. So the falling of the activities in the strong binding side of the volcano can be attributed preferentially to a gradual decline in the number of Fe(II) active sites and not to gradual decrease of the fraction (1-θ ) of empty or available active sites due to occupancy by intermediates. Schmickler and Santos [3] have shown that some volcano correlations for HER on metals that are in an oxidized form, and then inactive for this reason.We conclude that even though there are similarities between the volcano correlations for metallic and molecular catalysts, there some differences in the interpretation of the activity maximum that might not correspond to a thermoneutral condition. Acknowledgements: This work was supported by ANID, Anillo Project ACT 192175 and Fondecyt, Project 1181037

Disasters and Hazards: Risk Reduction, Mitigation and Management

Disasters and Hazards: Risk Reduction, Mitigation and Management

Reconstructing the Linear Relations by Designing Bi-Atom Sites on NbS2 for the Efficient Nitrogen Reduction Reaction

Tremendous enthusiasm for bi-atom catalysts (BACs) for the nitrogen reduction reaction (NRR) has been aroused due to the insufficient activation of N2 in single-atom catalysts (SACs). Herein, using density functional theory (DFT) calculations, the catalytic activities toward NRR of the NbS2-based SACs and BACs have been investigated. Our results reveal that there are typical volcano relationships between catalytic activities (limiting potentials) and the adsorption free energies of NNH* (∆G(NNH)*) on SACs, but the peak limiting potential is only −0.57 V. Interestingly, this volcano relationship can be reconstructed by supporting bi-atoms sites on NbS2, in which ∆G(NH2)* can serve as the descriptor to predict the catalytic performance of BACs. Most importantly, the optimal limiting potential of Mn2 BAC can reach a significant −0.26 V via an enzymatic pathway. These results compare catalytic activities between SACs and BACs and provide a theoretical basis for exploring novel, highly efficient electrocatalysts for NRR.

Induced polarization images alteration in stratovolcanoes

We investigate the complex conductivity of 32 volcanic rock samples from two stratovolcanoes, La Soufrière Volcano (Guadeloupe Island, Caribbean) and Papandayan volcano (Java Island, Indonesia). These stratovolcanoes are characterized by high degrees of kaolinite-related alteration associated with the upwelling of acidic ground waters as well as the formation of smectite-rich clay caps. Our goal is to assess the dependence of two geoelectrical properties, the electrical conductivity and normalized chargeability, on the conductivity of the pore water and the Cation Exchange Capacity (CEC) for volcanic rocks at near-neutral pH conditions. An alteration index based on CEC is built for both smectite- and kaolinite-rich zones. The data are discussed in the context of a previously acquired experimental dataset based on samples collected from shield volcanoes in Hawaii. We show that all the core samples display the same trends in their petrophysical geoelectrical properties whatever the type of volcanoes. Surface conductivity and normalized chargeability are strongly controlled by the CEC of the material and the bulk tortuosity of the pore space (product of the formation factor by the porosity). This implies in turn that the conductivity and the normalized chargeability are controlled by rock alteration in the same way as long as surface conductivity dominates the bulk conductivity contribution, which is salinity and pH dependent (both being interrelated in acidic pore waters). These petrophysical results are then applied to the interpretation of a 3D induced polarization survey performed at Papandayan stratovolcano in Indonesia. The tomograms are used to image the alteration of the volcanic edifice and we conclude that surface conduction is non-negligible in these volcanoes. Only above a pore water conductivity higher than 10 S m−1 at 25 °C) the bulk conductivity dominates the surface conductivity associated with alteration.

How big will the next eruption be?

Anticipating the size of the next volcanic eruption in long-term forecasts is a major problem in both basic and applied volcanology. In this study, we investigate the extent to which eruption size is predictable based on historical and other attribute data. Data from the Smithsonian Global Volcanism Program (GVP) Catalog is used to determine the predictability of volcanic eruption size as quantified through the reported VEI (Volcano Explosivity Index). The numerical and categorical attributes from the global volcanic catalog were classified with trained random forest and simple prediction models to make a forecast of VEI that can be tested against the most recent eruption of each volcano. We compare these results to two different baseline predictability levels by: (a) selecting randomly from the global distribution of VEIs for the most recent eruptions to calculate a cohort baseline and (b) selecting the most frequent VEI for a given population to calculate a zero-rule baseline. We found that: (1) nearly any method that incorporates prior information on a specific volcano improves the prediction accuracy of the succeeding eruption VEI by at least 10 percentage points relative to the cohort baseline case, (2) incorporating attributes beyond previous VEIs can provide better accuracy and achieve up to 30 percentage point accuracy gains, (3) total accuracy of the VEI forecasting by these methods can be up to nearly 80% and (4) the zero-rule is an effective prediction method that is modestly outperformed (~ 5 percentage point gain) by random forest methods with multiple attributes on most datasets. We find no notable preference in accuracy based on volcano type. The results quantify the importance of volcano-specific information in long-term forecasting and may help practitioners assess their expected performance when anticipating future eruption size.

Defining the Pre-Eruptive States of Active Volcanoes for Improving Eruption Forecasting

A crucial feature to manage a volcanic crisis is the ability of volcanologists to promptly detect an impending eruption. This is often affected by significant uncertainty, mainly for the difficulty in interpreting the monitoring signals in terms of the exact timing of a possible eruption. Here we contribute to this problem, focusing on the states of active volcanoes with closed conduit, as deduced from monitoring data. Four main states can be identified. In the quiescence state 1) the monitoring data lie on a baseline, suggesting the lack of shallow magma/fluid movement. The unrest state is highlighted by minor 2) to major 3) variations in the intensity and rate of monitoring data; in both cases, radial ground deformation pattern and non-migrating seismicity imply shallow magma and/or fluid accumulation. The state of impending eruption 4) is characterised by non-radial, asymmetric ground deformation pattern and migrating seismicity, which suggest that magma approaches the surface through a propagating dyke. As early recognition of this distinctive state is crucial for timely eruption forecast, monitoring activity should be aimed at its prompt detection. The application of this rationale to two types of active volcanoes in densely inhabited areas, a restless caldera (Campi Flegrei) and a quiescent stratovolcano (Vesuvio), highlights its feasibility and importance in eruption forecasting. This rationale may foster a general reference framework to be adopted in case of unrest, supporting in interpreting the monitoring data, as well as more effective: 1) operationally-oriented, monitoring system; 2) probabilistic forecast; 3) use of volcanic alert levels.

Integrated on‐land‐offshore stratigraphy of the Campi Flegrei caldera: New insights into the volcano‐tectonic evolution in the last 15 kyr

AbstractSilicic calderas are volcanic systems whose unrest evolution is more unpredictable than other volcano types because they often do not culminate in an eruption. Their complex structure strongly influences the post‐collapse volcano‐tectonic evolution, usually coupling volcanism and ground deformation. Among such volcanoes, the Campi Flegrei caldera (southern Italy) is one of the most studied. Significant long‐ and short‐term ground deformations characterise this restless volcano. Several studies performed on the marine‐continental succession exposed in the central sector of the Campi Flegrei caldera provided a reconstruction of ground deformation during the last 15 kyr. However, considering that over one‐third of the caldera is presently submerged beneath the Pozzuoli Gulf, a comprehensive stratigraphic on‐land‐offshore framework is still lacking. This study aims at reconstructing the offshore succession through analysis of high‐resolution single and multichannel reflection seismic profiles and correlates the resulting seismic stratigraphic framework with the stratigraphy reconstructed on‐land. Results provide new clues on the causative relations between the intra‐caldera marine and volcaniclastic sedimentation and the alternating phases of marine transgressions and regressions originated by the interplay between ground deformation and sea‐level rise. The volcano‐tectonic reconstruction, provided in this work, connects the major caldera floor movements to the large Plinian eruptions of Pomici Principali (12 ka) and Agnano Monte Spina (4.55 ka), with the onset of the first post‐caldera doming at ca. 10.5 ka. We emphasise that ground deformation is usually coupled with volcanic activity, which shows a self‐similar pattern, regardless of its scale. Thus, characterising the long‐term deformation history becomes of particular interest and relevance for hazard assessment and definition of future unrest scenarios.