Somma-Vesuvius Volcanic Complex Research Articles

Soils on Recent Tephra of the Somma–Vesuvius Volcanic Complex, Italy

The Somma–Vesuvius volcanic complex emitted huge quantities of volcanic materials over a period from before 18,300 years BP to 1944. The activity during the last period, from post-AD 1631 to 1944, primarily produced lava and pyroclastics via effusive and strombolian eruptions. We investigated the pedogenesis on rocks formed from post-AD 1631 to 1944, occurring on the slopes of Mt. Vesuvius up to Gran Cono Vesuviano and in the northern valley separating Vesuvius from the older Mt. Somma edifice. Pertinent morphological, physical, chemical, and mineralogical (XRD and FT-IR) soil properties were studied. The results indicated the existence of thin and deep stratified soils on lava, as well as the presence of loose detritic covers formed via pyroclastic emplacement and redistribution. The soils showed minimal profile differentiation, frequently with layering recording the episodic addition of sediments. We found that the dominant coarse size of primary mineral particles was preserved, and there was a low level of clay production. The main mineralogical assemblage present in sands also persisted in clays, indicating the physical breaking of the parent material. Chemical weathering produced mineral modifications towards the active forms of Al and Fe and was also attested in selected soils by glass alteration, allophane production, and the presence of analcime in clay as a secondary product from leucite. The differences in glass alteration and analcime production found in the selected soils on lava were related to soil particle size and soil thickness. Concerning the youngest soil present on Gran Cono Vesuviano, other factors, such as the substratum’s age and site elevation, appeared to be implicated.

The geochemistry of leucite-bearing lavas from early stages of the Somma-Vesuvius volcanic complex: Feeder systems and mantle enrichment processes in the Neapolitan district of the Roman Magmatic Province

The lavas of the Mt. Somma volcanic epoch were erupted during the early stage of the Somma-Vesuvius volcanic complex. These lavas are mildly differentiated with the presence of plagioclase-clinopyroxene-olivine- ± leucite-bearing rocks (leucite tephrites, leucite-bearing shoshonites, latites), also characterized by low in MgO, Cr and Ni, with a Sr-Nd-isotope range (87Sr/86Sr = 0.706865–0.707861; 143Nd/144Nd = 0.51244–0.51258) that overlaps with lavas of the late stage Vesuvius erupted after 1631 CE (late stage of the Somma-Vesuvius volcanic complex). Differentiation is dominated by closed-system processes, with fractional crystallization of clinopyroxene, calcic plagioclase, olivine, magnetite, and leucite. Open-system differentiation processes are subordinate and associated with limited interaction with crustal rocks. Oxygen isotopes on clinopyroxene and olivine phenocrysts (δ18O = 6.5–7.9 ‰) are higher than typical uncontaminated mantle magmas, suggesting a crustal contribution to the melt. Although open-system assimilation + fractional crystallization certainly took place, this process alone does not adequately reproduce the chemical and isotopic composition of the Mt. Somma ultrapotassic magmas. Therefore, a contribution from a recycled crustal component in the mantle source is required, but probably dominated by sediment-derived fluids and melts. The Mt. Somma lavas are characterized by distinctly different geochemical features compared to the mafic products of the neighboring volcanic areas (i.e., Phlegrean, Procida and Ischia volcanic fields), where the recycled crustal component is less pronounced.

Crystal Chemistry, Thermal and Radiation-Induced Conversions and Indicatory Significance of S-Bearing Groups in Balliranoite

Crystal-chemical features of a sulfide-bearing variety of the cancrinite-group mineral balliranoite from the Tuluyskoe lapis lazuli deposit, Baikal Lake area, Siberia, Russia, have been investigated using a multimethodic approach based on infrared (IR), Raman, and electron spin resonance (ESR), as well as ultraviolet, visible and near infrared (UV–Vis–near IR) absorption spectroscopy methods, luminescence spectroscopy, electron microprobe analysis, selective sorption of CO2 and H2O from annealing products, and single-crystal X-ray structure analysis. Holotype balliranoite and its sulfate analogue, davyne, were studied for comparison. The crystal-chemical formula of the studied sample from Tultuyskoe is Na5.4K0.1Ca2.4(Si6Al6O24)Cl2[(CO3)0.7(SO4)0.18S*0.95Cl0.1(H2O)0.16], where the content of the wide zeolite channel is given in square brackets; S* is total sulfide sulfur occurring as disordered S2●−, cis- and trans-S4, S52−, minor S3●−, and HS− groups. The presence of S52− and HS− groups, the absence of CO2 molecules, and the association with pyrrhotite and Fe-free pargasite indicate that the studied sample crystallized under highly reducing, low-temperature conditions, unlike holotype balliranoite whose formation was related to the Somma-Vesuvius volcanic complex, Italy. Irradiation of balliranoite from Tultuyskoe with X-rays results in the transformations of polysulfide groups other than S3●− into S3●− in accordance with the scheme: S52− → S2●− + S3●−; 3S2●− → 2S3●− + e−; S4 + S2●− + e− → 2S3●−; S4 + S2●− + e− → 2S3●−; S4 + S52− + e− → 3S3●− (e− = electron).

The buried caldera boundary of the Vesuvius 1631 eruption revealed by present-day soil CO2 concentration

Volcanic risk at Vesuvius is one of the highest in the world due to the ~670,000 inhabitants living in the Red Zone, the area exposed to both pyroclastic flows and tephra fallout, to be evacuated before renewal of any eruptive activity. The national emergency plan for Vesuvius builds its risk zonation on a scenario similar to the last sub-Plinian eruption, which occurred in 1631. This study aims at providing new insights on the geometry of the caldera associated with this historical eruption. The impact of past Vesuvius eruptions on present-day soil CO2 concentration has been investigated by means of an extended geochemical survey carried out for identifying the circulation pathways of hydrothermal fluids inside the volcano. We performed 4018 soil CO2 concentration measurements over the whole Somma-Vesuvius volcanic complex, covering an area of 50 km2. Besides relatively low values, the results show a significant spatial CO2 concentration heterogeneity over Somma-Vesuvius ranging from the atmospheric value (~400 ppm) up to ~24,140 ppm. The summit of Vesuvius shows an area with anomalous CO2 concentrations well matching the crater rim of the 1906 eruption. Along the cone flanks, secondary CO2 anomalies highlight a roughly circular preferential pathway detected along 8 radial profiles at distances between ~840 m and ~1150 m from the bottom of the present-day crater resulting from the last eruption in 1944. In depth review of the available literature highlights an agreement between this circle-like shaped anomaly and the 1631 sub-Plinian eruption caldera boundary. Indeed, based on the historical chronicles the depression produced by the 1631 eruption had a diameter of 1686 m, whereas the CO2 circular anomaly indicates a diameter of 1956 m. Finally, the results were compared with a 3-D density model obtained from a recent gravity survey that corroborates both the literature and the CO2 data in terms of potential buried structure at the base of the Vesuvius cone.

MgO partition between olivine and K2O-rich silicate melt: Geothermometers applicable to high potassium magmas

Potassium and ultrapotassium magmas with potential origins in the upper mantle are common and widely distributed on the Earth. Previous experimental studies have suggested that K can significantly decrease the partial melting T of the peridotite. Since K has a strong effect on the melt composition, and on the molar partition coefficient of some cations such as Mg between the olivine and melt, DMgOl/liq, it can substantially affect the T estimation of the Ol geothermometers. However, none of the presently available geothermometers have critically considered the effect of K. In this paper, we have collected a large number of composition data of the Ol-melt equilibrium pairs covering a large range of K2O contents in the melts, and have successfully calibrated three K2O-dependent geothermometers on the basis of the MgO partition between the Ol and basaltic magma, two Ol geothermometers and one melt composition geothermometer. The database covers the P range from 1 atm to 7 GPa and T range of 1087–1950 °C. Compared to some other geothermometers, our Ol geothermometers reproduce the experimental T very well, with the average of the absolute differences between the calculated T and experimental T being only 14(15) °C at room P and 25(21) °C at high P, and with these differences showing no clear dependence on the P, T, and contents of K2O and any other oxides in the melts. Furthermore, our melt composition geothermometer allows excellent T estimate for the silicate magma coexisting with Ol by using the melt composition alone. The application of our melt composition geothermometer to the Somma-Vesuvius volcanic complex in Italy demonstrates that this geothermometer can lead to reasonable T estimates for the high potassium silicate magmas, even there are small amounts of volatiles such as H2O and CO2 in the melts.

Exploratory analysis of multi-element geochemical patterns in soil from the Sarno River Basin (Campania region, southern Italy) through compositional data analysis (CODA)

The Sarno River Basin (south-west Italy), nestled between the Somma–Vesuvius volcanic complex and the limestone formations of the Campania–Apennine Chain, is one of the most polluted river basins in Europe due to widespread industrialization and intensive agriculture. Water from the Sarno River, which is heavily contaminated by the discharge of human and industrial wastes, is partially used for irrigation on the agricultural fields surrounding it. We apply compositional data analysis to 319 soil samples, collected during two field campaigns along the river course and throughout the basin, to determine the concentration and possible origin (anthropogenic and/or geogenic) of the elemental anomalies, including potentially toxic elements (PTEs).The concentrations of 53 elements were determined using ICP-MS and, subsequently, log-transformed. Using hierarchical clustering, clr-biplot and a principal factor analysis, the variability and the correlations between a subset of extracted variables (26 elements) were identified. Factor score interpolated maps were then generated using both lognormal data (NDR) and clr-transformed data to better visualize the distribution and potential sources of the patterns in the Sarno Basin.The underlying geology substrata appear to be associated with raised levels of Na, K, P, Rb, Ba, V, Co, B, Zr, and Li, due to the presence of pyroclastic rocks from Mt. Somma–Vesuvius. Similarly, elevated Pb, Zn, Cd, and Hg concentrations are most likely related to the geological and anthropogenic sources, the underlying volcanic rocks, and contamination from fossil fuel combustion associated with nearby urban centers. Interpolated factor score maps and the clr-biplot show a clear correlation between Ni and Cr in samples taken along the Sarno River, and Ca and Mg near the Solofra district. After considering nearby anthropogenic sources, the Ni and Cr are PTEs most likely originating from the Solofra tannery industry, while Ca and Mg correlate to the underlying limestone-rich soils of the area.This study shows the applicability of the log-ratio transformations to these studies, as they clearly show relationships and dependencies between elements which can be lost when univariate and classical multivariate analyses are employed on raw and lognormal data.

Fluid Vents, Flank Instability, and Seafloor Processes along the Submarine Slopes of the Somma-Vesuvius Volcano, Eastern Tyrrhenian Margin

We report the geomorphological features of the continental shelf of the Gulf of Naples along the submarine slopes of the Somma-Vesuvius volcanic complex. This area is characterized by seafloor morphologies that are related to mantle degassing. Significant phenomena associated with this process occur. Doming of the seafloor has been detected in the area of Banco della Montagna, whereas a hole-like morphology has formed at Bocca dei Pescatori, likely as a result of a phreatic explosion. Outcropping or partially submerged volcanic bodies are also present as well as two main debris avalanche deposits arising from the main Somma-Vesuvius edifice. A large area characterized by an overall concave external profile and a global sediment wave morphology covers most of the southwestern area of the volcano.

The 3-D structure of the Somma-Vesuvius volcanic complex (Italy) inferred from new and historic gravimetric data

Existing 3-D density models of the Somma-Vesuvius volcanic complex (SVVC), Italy, largely disagree. Despite the scientific and socioeconomic importance of Vesuvius, there is no reliable 3-D density model of the SVVC. A considerable uncertainty prevails concerning the presence (or absence) of a dense body underlying the Vesuvius crater (1944 eruption) that is implied from extensive seismic investigations. We have acquired relative gravity measurements at 297 stations, including measurements in difficult-to-access areas (e.g., the first-ever measurements in the crater). In agreement with seismic investigations, the simultaneous inversion of these and historic data resolves a high-density body that extends from the surface of the Vesuvius crater down to depths that exceed 2 km. A 1.5-km radius horseshoe-shaped dense feature (open in the southwestern sector) enforces the existing model of groundwater circulation within the SVVC. Based on its volcano-tectonic evolution, we interpret volcanic structures that have never been imaged before.

The art of building in the Roman period (89 B.C. – 79 A.D.): Mortars, plasters and mosaic floors from ancient Stabiae (Naples, Italy)

This current research is focused on the mineralogical and petrographic characterisation of mortar-based materials from Villa San Marco in the ancient Stabiae (modern Castellammare di Stabia, Napoli), an outstanding example of Roman otium villae, and aims at recognising the technology used by the ancient skilled workers.Several analytical techniques were used such as digital videomicroscopy, optical microscopy, digital image analysis, scanning electron microscopy coupled with EDS analysis and Quantitative Powder X-ray Diffraction.A multi-layer technology characterised the plasters; the scratch coat was made with lime mortars mixed with a pozzolanic lightweight aggregate and cocciopesto, required ingredients providing a quick-setting and a better adhesion with the support. As far as the arriccio layer is concerned, the mix-design is a lime mortar with volcanic sand as the aggregate and a minor content of pozzolan and/or cocciopesto to enhance the workability of the mortar in order to correct any error due to the roughness of the scratch coat. The plaster s.s. was the removable support in case of mistakes, and gave a lighter colour to the preparation layer of the frescoes. The last thin layer, prepared with lime mortars and a carbonate aggregate, is characterised by low porosity in order to avoid pigment adsorption. The painting technique was a fresco with encaustication.In contrast, the mortars of the building structures were made with lime added to a pozzolanic aggregate (volcanics and cocciopesto), giving a quick setting during the implementation of the yellow tuff opus reticulatum.The rudera and nuclei of the mosaics were built with abundant volcanic sand and cocciopesto mixed with the lime, producing a more resistant surface, and finally the tesserae were fixed exclusively with lime. The white and black colours of the mosaics were produced by local limestone and tephritic lava.The results permitted an evaluation of the high level of specialization of both the workers and the artists that built and decorated these maritime villas. Moreover, the collected data highlighted the wide potentiality of the materials cropping out in the environs of the Somma-Vesuvius volcanic complex. This research aims at furnishing a useful reference for future restoration action in Villa San Marco and the other Roman villas in this area.

Fibrous minerals from Somma-Vesuvius volcanic complex

A survey on fibrous minerals coming from the densely populated area of Campania around the Somma-Vesuvius volcanic complex (Italy) was performed by means of a multi-methodological approach, based on morphological analyses, EMPA/WDS and SEM/EDS applications, and unit-cell determination through X-ray diffraction data. Such mineralogical investigation aims to provide suitable tools to the identification of fibrous natural phases, to improve the knowledge of both geochemical, petrogenetic and regional mineralogy of Somma-Vesuvius area, and to emphasize the presence of minerals with fibrous habit in all volcanic environments. The survey also fits well in the calls of health and environment of Horizon 2020 program of the European Commission (Climate Action, Environment, Resource Efficiency and Raw Materials).

Magnetic Theory and Applications in the Naples Bay (Southern Tyrrhenian Sea, Italy): Magnetic Anomaly Fields and Relationships with Morpho-Structural Lineaments

Magnetic theory and application to a complex volcanic area located in Southern Italy are here discussed showing the example of the Gulf of Naples, located at Southern Italy Tyrrhenian margin. A magnetic anomaly map of the Gulf of Naples has been constructed aimed at highlighting new knowledge on geophysics and volcanology of this area of the Eastern Tyrrhenian margin, characterized by a complex geophysical setting, strongly depending on sea bottom topography. The theoretical aspects of marine magnetometry and multibeam bathymetry have been discussed. Magnetic data processing included the correction of the data for the diurnal variation, the correction of the data for the offset and the leveling of the data as a function of the correction at the cross-points of the navigation lines. Multibeam and single-beam bathymetric data processing has been considered. Magnetic anomaly fields in the Naples Bay have been discussed through a detailed geological interpretation and correlated with main morpho-structural features recognized through morpho- bathymetric interpretation. Details of magnetic anomalies have been selected, represented and correlated with significant seismic profiles, recorded on the same navigation lines of magnetometry. They include the continental shelf offshore the Somma-Vesuvius volcanic complex, the outer shelf of the Gulf of Pozzuoli offshore the Phlegrean Fields volcanic complex, the relict volcanic banks of Pentapalummo, Nisida and Miseno, the Gaia volcanic bank on the Naples slope, the western slope of the Dohrn canyon, the Magnaghi canyon’s head and the magnetic anomalies among the Ischia and Procida islands.

Constraints on the origin of sub-effusive nodules from the Sarno (Pomici di Base) eruption of Mt. Somma-Vesuvius (Italy) based on compositions of silicate-melt inclusions and clinopyroxene

Major and trace element and volatile compositions of reheated melt inclusions (RMI) and their clinopyroxene hosts from a selected “sub-effusive” nodule from the uppermost layer of the Sarno (Pomici di Base; PB) plinian eruption of Mt. Somma-Vesuvius (Italy) have been determined. The Sarno eruption occurred during the first magmatic mega-cycle and is one of the oldest documented eruptions at Mt. Somma-Vesuvius. Based on RMI and clinopyroxene composition we constrain processes associated with the origin of the nodule, its formation depth, and hence the depth of the magma chamber associated with the Sarno (PB) eruption. The results contribute to a better understanding of the early stages of evolution of the long-lived Mt. Somma-Vesuvius volcanic complex. The crystallized MI were heated to produce a homogeneous glass phase prior to analysis. MI homogenized between 1202–1256 °C, and three types of RMI were distinguished based on their compositions and behavior during heating. Type I RMI is classified as phono-tephrite–tephri-phonolite–shoshonite, and is the most representative of the melt phase from which the clinopyroxenes crystallized. The second type, referred to as basaltic RMI, have compositions that have been modified by accidentally trapped An-rich feldspar and/or by overheating during homogenization of the MI. The third type, referred to as high-phosphorus (high-P) RMI, is classified as picro-basalt and has high-P content due to accidentally trapped apatite. Type I RMI are more representative of magmas associated with pre-Sarno eruptions than to magma associated with the Sarno (PB) eruption based on published bulk rock compositions for Mt. Somma-Vesuvius. Therefore, it is suggested that the studied nodule formed from a melt compositionally similar to that which was erupted during the early history of Mt. Somma. The clinopyroxene and clinopyroxene-silicate melt thermobarometer models suggest minimum pressures of 400 MPa (~11 km) for nodule formation, which is greater than pressures and depths commonly reported for the magmas associated with younger plinian eruptions of Mt. Somma-Vesuvius. Minimum pressures of formation based on volatile concentrations of MI interpreted using H 2 O-CO 2 -silicate melt solubility models indicate formation pressures ≤300 MPa.

Nephelines from the Somma-Vesuvius volcanic complex (Southern Italy): crystal-chemical, structural and genetic investigations

Sixteen nephelines from different geological occurrences were sampled at the type-locality, the Somma-Vesuvius volcanic complex (southern Italy), and investigated for their chemistry and crystal structure obtained by both single-crystal and powder X-ray diffraction. Nepheline-bearing samples are metamorphic or from magmatic ejecta and pumice deposits. The lower K contents characterize the pumice- and some metamorphic-derived nephelines, whereas the higher ones are found in some samples from magmatic nodules. The amount of the anorthite molecule, quite low on average, can be more variable in the metamorphic nephelines. The crystal-structure investigations on Somma-Vesuvius samples compare well with previous studies of natural nephelines. All 16 nepheline samples adopt space group P63. The observed lattice parameters vary between 9.9768–9.9946 A (for a) and 8.3614–8.3777 A (for c), respectively. Furthermore, chemical analysis revealed that all specimens exhibit an excess of Si relative the ideal Si:Al ratio of 1:1. The analysis of the T-O distances in our samples clearly indicates a distinct ordering process of aluminium and silicon on the tetrahedral sites which is an agreement with Loewenstein’s rule. A linear correlation between the distance of symmetry equivalent split atoms O(1)-O(1)’ and the T(1)-O(1)-T(2) tilt angle was observed. The average (B = Na) distances of all crystals are very similar which is consistent with the outcome of the site population refinement indicating full occupancy with sodium. Oriented precession-type sections of reciprocal space indicated the presence of at least the most intense family of satellite peaks, demonstrating that this group of satellite reflections can occur not only in nephelines from pegmatites and ijolites but also in rocks from completely different petrological settings.

Sodalite-group minerals from the Somma Vesuvius volcanic complex, Italy: a case study of K-feldspar-rich xenoliths

AbstractSodalites and sulfatic sodalites in holocrystalline K-feldspar-rich ejecta from the Somma Vesuvius volcanic complex, Italy, have been characterized by combined chemical, structural and spectroscopic analyses. Sodalite has a relatively homogeneous chemical composition, with the ubiquitous presence of CO32– and H2O/OH–. The sulfatic sodalites are isomorphous and have cage structures which can contain a wide variety of anions, molecular species and cations. Molecular CO2 and H2O/OH– are present in sulfatic sodalites, instead of the CO32– anions that are present in sodalite sensu stricto. The cell dimensions of the all of the studied sodalite samples are very similar, the sulfatic sodalite cell dimensions are more variable. Structure refinement of a distinctly green sample confirms the P3n space group. Metasomatic magma-derived fluids that are rich in H2O, CO2, Cl and S are believed to be responsible for the genesis of the relatively late-stage phases which form the ejecta containing the sodalite-group minerals.

On the fractal nature of volcano morphology detected via SAR image analysis: the case of Somma—Vesuvius Volcanic Complex

In this paper an innovative technique for the extraction of natural surfaces geomorphologic parameters from SAR data is presented and applied for volcano monitoring purposes. The observed surface is modeled as a fractal two-dimensional stochastic process. A theoretical framework for the analysis of the SAR imaging process is outlined. An algorithm founded on this imaging model is presented, allowing the retrieving of the point by point fractal dimension of the imaged surface. Significant results regarding the application of the proposed technique to the case study of the Somma-Vesuvius volcanic complex are shown, along with preliminary comments regarding the comparison with ground truth maps of the surface fractal dimension.

Crystal-chemical and structural characterization of fluorapatites in ejecta from Somma-Vesuvius volcanic complex

The mineralogy and crystal chemistry of apatites occurring in 14 ejecta of historical eruptions (1631 and 1872 A.D.) of the Somma-Vesuvius volcanic complex were investigated by a multi-methodological approach including polarized optical microscopy, scanning electron microscope, electron microprobe analysis in wavelength-dispersive mode, laser ablation inductively coupled plasma mass spectroscopy, and single-crystal X‑ray diffraction. Five different groups of apatite, with different mineralogical and crystal-chemical features, were identified. Apatite crystals occur with well-developed hexagonal prismatic habit and, more rarely, with skeletal acicular forms. The crystals are yellow (type 1), transparent and colorless (type 2 and type 3), green (type 4) and aquamarine colored (type 5), with different paragenesis: macro-crystalline aggregates of clinopyroxenes, phlogopite, and apatite (type 1; type 4); clusters of apatite with micro-crystalline clinopyroxene, minerals of the cancrinite group, feldspars, and opaque minerals (type 2); aggregates of apatite, sellaite, wagnerite, gypsum, and phlogopite (type 3); aggregates of davyne, nepheline, mica group minerals, and apatite (type 5). Chemical analyses of apatites show variable amounts of Na, REE, Mg, Sr, and Fe replacing Ca, not negligible amounts of Si and S substituting P, and a significant substitution of Cl and OH instead of F. Five crystals representative of each apatite-type were studied by single-crystal X‑ray diffraction. Their crystal structure was refined in the hexagonal P6 3/m space group. A significant variation of the unit-cell parameters with the composition was observed. A comparative crystal-chemical analysis between apatites from Somma-Vesuvius and those from other localities is carried out.

Crystal-chemical and structural characterization of fluorapatites from Somma-Vesuvius volcanic complex

Crystal-chemical and structural characterization of fluorapatites from Somma-Vesuvius volcanic complex

Geothermometric study of Mg-rich spinels from the Somma-Vesuvius volcanic complex (Naples, Italy)

The crystal chemistry of 13 spinel samples from the Somma-Vesuvius volcanic complex (Italy) was studied by crystal structural refinement and electron microprobe analysis, processing the data with a tested optimization model to obtain site populations. Five samples come from the volcanic xenoliths found in Pollena Quarry and belong to the deposits produced by the Pollena eruption of A.D. 472. All crystals are characterized by Fe 2+ ↔ Mg substitution and pertain to the Mg-rich portion of the spinel sensu stricto-hercynite join. The crystals show a partially inverted cation configuration with inversion degree ranging from 0.20–0.25. Aluminum contents characterize the crystal-chemistry: the unit-cell parameter decreases with increasing total Al and the M -O bond length decreases with increasing M Al. Using a well-tested geothermometer based on the M Al+ T Mg = T Al+ M Mg intracrystalline exchange, closure temperatures were calculated for the Pollena Quarry spinels. Results range from 694 to 809 °C. The latter value is assumed to be representative of the temperature of the Pollena eruption and is in excellent agreement with that reported in the literature (800 °C) and estimated by experimental phase equilibria.

Crystal structure and low-temperature behavior of "disordered" thomsonite

The crystal structure, crystal chemistry, and low-temperature structural evolution of natural thomsonite from Terzigno, Somma-Vesuvius volcanic complex, Naples Province, Italy, have been investigated by means of in situ single-crystal X-ray diffraction, electron microprobe analysis in the wavelength dispersive mode, and Raman spectroscopy. Six structure refinements have been obtained at different temperatures: 295.5, 248.0, 198.0, 148.0, 98.0, and 296.0 K (after the low-T experiments). The reflection conditions and the structure refinements prove that the crystal of thomsonite here investigated is orthorhombic with a = 13.0809(3), b = 13.0597(3), c = 6.6051(1) Å, V = 1128.37(14) Å 3 , and space group Pbmn, which differs from thomsonite from different localities reported in previous studies (with a ~ 13.1, b ~ 13.06, c ~ 13.2 Å, and space group Pncn). The refined bond distances suggest that the Si/Al-distribution in the tetrahedral framework is fully “disordered,” giving rise to the halving of the c axis relative to that found in “ordered” thomsonites. The extra-framework population consists of: (1) one site about 50% occupied by Ca (labeled as “Ca”); (2) one site occupied by Na (~70%) and Ca (~30%) (labeled as “Na”); and (3) three water molecule sites (“W1,” “W2,” “W3”). The structure refinements allowed the location of all the proton sites, and the hydrogen-bonding scheme in the structure is provided. The low-temperature refinements show no significant change in the structure within the T-range investigated. The evolution of the unit-cell volume with T exhibits a continuous and linear trend, without any evident thermo-elastic anomaly, with thermal expansion coefficients α V = V -1 ⋅∂V/∂T= 20(2)·10 -6 K -1 (between 98.0 and 295.5 K). A list with the principal Raman active modes is provided and a comparison with the vibrational modes previously found for “ordered” thomsonite is carried out.

Reconstructing the Roman topography and environmental features of the Sarno River Plain (Italy) before the AD 79 eruption of Somma–Vesuvius

A methodology was developed to reconstruct the Roman topography and environmental features of the Sarno River plain, Italy, before the AD 79 eruption of the Somma–Vesuvius volcanic complex. We collected, localized and digitized more than 1800 core drilling data to gain a representative network of stratigraphical information covering the entire plain. Besides other stratigraphical data including the characteristics of the pre-AD 79 stratum, the depth to the pre-AD 79 surface was identified from the available drilling documentations. Instead of a simple interpolation method, we used a machine based learning approach based on classification and regression trees to reconstruct the pre-AD 79 topography. We hypothesize that the present-day topography reflects the ancient topography and related surface processes, because volcanic deposits from the AD 79 eruption coated the ancient landscape. Thus, ancient physiographic elements of the Sarno River plain are still recognizable in the present-day topography. Therefore, a high-resolution, present-day digital elevation model (DEM) was generated. A detailed terrain analysis yielded 15 different primary and secondary topographic indices. Subsequently, a classification and regression model was applied to predict the depth of the pre-AD 79 surface combining present-day topographic indices with other physiographic data. This model was calibrated with the measured depth of the pre-AD 79 surface. The resulting pre-AD 79 DEM was compared with the classified characteristic of the pre-AD 79 stratum, identified from the drilling documentations. This allowed the reconstruction of pre-AD 79 environmental features of the Sarno River plain such as the ancient coastline, the paleo-course of the Sarno River and its floodplain. To the knowledge of the authors, it is the first time that the pre-AD 79 topography of the Sarno River plain was systematically reconstructed using a detailed database and sophisticated data mining technologies.