Beschreibung: Here we present the data records (raw data) from 19 fragmentation experiments. In these runs silicic HVR254 dome rock (retrieved from the submarine Havre volcano) was crushed, remelted and fragmented using two different experimental settings: 1. dry runs (records labelled "D"): melt was fragmented by injection of pressurized Ar gas. 2. induced fuel-coolant interaction runs (records labelled "IFCI"): a water layer was established on top of the melt, before gas was injected from below. This caused fragmentation of the melt plug under IFCI conditions. Note that the runs D07, D08, D09, IFCI08 and IFCI09 used a reduced melt mass (100g instead of 250g). Files contain (separated by column) records of: time, trigger signal, force, pressure, microphone, electric field, seismic data. The units and amplification settings used are provided in the file headers. In addition, the results of morphometry analysis (t-tests) are provided in a pdf file. The morphometric analyses of natural ash focused exclusively on the curvi-planar grains dominant in Havre ash samples, labelled "Nat1" - "Nat6". Four types of experimental grains were compared with them: • “DG”: particles from dry runs, from the lab floor • “IG”: grains from open IFCI runs, from the lab floor • “IW”: very small particles from open IFCI runs deposited in water droplets on the walls and ceiling around the experimental area • “IU”: particles from IFCI runs with U-tube, from the water bowl

Beschreibung: The most recent eruptive activity of Turrialba volcano began on the 5th of January 2010, after more than a century of dormancy. The fragmentation process and aerodynamic behavior of the ash from Turrialba’s vulcanian eruptions were investigated by combining grain-size, petrography, mineralogy, Scanning Electron Microscopy (SEM) and Energy Dispersive System (EDS) analyses. The ash components include variable percentages of accessory fresh (no necessary juvenile) to hydrothermally altered lithics (15 - 50 % vol.) with hydrothermal minerals (≤ 12 % vol.: anhydrite, gypsum, bassanite, alunite, hexahydrite, pyrite, heulandite, native sulfur), clay minerals (8 - 17 % vol.: montmorillonite, halloysite, allophane), and a smaller quantity of fresh glassy ashes (5 - 49 % vol.) as fragments and shards (3 - 20 % vol. tackylite and 2 - 26 % vol. sideromelane), as well as primary and eroded/recycled phenocrysts (3 - 13 % vol.: 1 - 5% vol. plagioclase, 1 - 7 % vol. pyroxene, 0 - 1 % vol. olivine, 0 - 6 % vol. opaques, cristobalite and tridimite), and xenocrysts (≤ 1 % vol.: riebeckite and biotite). The secondary minerals were sourced from the deeper to surficial hydrothermal system. Textural features identified in ash particles (90 - 350 μm) suggest that they were formed by brittle fragmentation of vesicle-poor magma/water interaction; molten structures seems to be related to the ductile behavior of some fragments, probably due to the high temperature (〉 600 °C) of the fumarolic/magmatic system. The percentage of juvenile components was low (1 - 2 % vol.) at the first opening eruptive phase in January 2010, and it increased steadily until the end of 2016 (ca. 12 - 25 % vol.) . The ash eruptions in the Western Crater from 2014 to 2016 were related to one and later two or three simultaneously active vents fed by distinct conduit branches. The alternation of volcanic explosions (VEI: 0 - 2), from closed conduit and the formation of new craters, to open system with phreatomagmatic events, and the repose intervals (inter-eruptive exhalative degassing), were controlled by the rate at which magma ascended and remained in the volcanic edifice. The recent tephra sequence consists of a complex succession of layers generated by contrasting fragmentation and transportation dynamics. They resulted from fully diluted, low temperature (〈 300 °C), pyroclastic density currents (wet surge deposits), originated by short-lived, singlepulse, column collapse of phreatomagmatic columns, which traveled short distances (〈 1000 m) from the vent area and surmounted topographic obstacles, and simultaneous fallout and ballistic ejecta. The fine material, in continuous suspension within the uppermost part of the convective plume, was dispersed into the atmosphere and finally settled down on the Valle Central. The quiescent phases could be related to a temporal cooling of the magmatic dike system or to a waning of magmatic activity at depth. Sequential fragmentation/transport theory (SFT) was used to decompose grain-size distributions into five different sub-populations. A new way of using the resultant fragmentation coefficient to assign sub-populations to different fragmentation mechanisms, even in cases when modes overlapped, is presented. For the first time the corresponding results are consistent with the phreatomagmatic eruptions, as well as with those derived from ab initio fractal model.

Beschreibung: Published

Beschreibung: 7-60

Beschreibung: 6V. Pericolosità vulcanica e contributi alla stima del rischio

Beschreibung: N/A or not JCR

Beschreibung: In this paper, we present results of the reconstruction of the total grain size distribution (TGSD) of the material erupted during explosive volcanic eruptions at Campi Flegrei (Italy) considering all components (juvenile, lithic and crystal clasts). To date, the few TGSDs made available have been mostly reconstructed by assuming that the tephra deposits consisted of only one component. This simplification can introduce substantial bias in the interpretation of magma fragmentation mechanisms and significantly affect ash dispersion forecasts, since each tephra component has specific aerodynamic characteristics. By means of field investigations and laboratory analyses on samples collected from deposits of the Agnano-Monte Spina and Astroni eruptions, we reconstructed the TGSDs of juvenile, lithic and crystal components via the Voronoi tessellation method. Our results show how the systematic reconstruction of a TGSD, from the component-specific to the bulk TGSD, can provide important information on magma fragmentation mechanisms and wall-rock erosion processes. Results confirm that the bulk TGSD is the combination of the merging of different component subpopulations, according to their own TGSD, density and relative mass proportions. In addition, the integration of component analysis, TGSD and settling velocity data allowed characterization of the aerodynamic behaviour of each component at variable distances from the vent, which can be related to their own parent grain size distribution. The integration of new data from distal tephra deposits for the considered eruptions has thus allowed a reassessment of the erupted volumes of eruptions considered in this research, which are now 3.17 and 0.63 km3, for Agnano-Monte Spina and Astroni, respectively.

Beschreibung: Published

Beschreibung: id 31

Beschreibung: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Beschreibung: JCR Journal

Beschreibung: In this paper we illustrate the stratigraphy, geochronology, and geochemistry (major, minor, trace elements and Sr-isotopes) of a Holocene tephra layer found within coastal sedimentary deposits north of Caleta Olivia (Santa Cruz Province, Argentina). The stratigraphic succession comprises beach deposits with basal erosive surface resting on the local substrate (“Formación Patagonia”) followed by a poorly developed paleosoil. The paleosoil is covered by a lenticular finegrained (Mdφ: 5.2, 0.027 mm), well sorted (σφ: 1.2) volcanic ash layer and aeolian sands. The geochemical composition of shard fragments points to an origin from the Hudson volcano, located in the southern Andes, ca. 400 km to the west. The geochemistry, Sr-isotopes and the radiometric constraints (younger than the age of the underlying marine layer dated at ca. 4,100 a cal BP) further allow correlating this tephra with the so-called H2 eruption (ca. 3,900 a cal BP). This finding is of interest owing to the poor preservation potential of tephra within the Late Holocene sedimentary deposits of the Atlantic coast of Patagonia and represents the first finding of H2 eruption in this area, improving our knowledge of the dispersion of the fine-grained distal deposit of the Hudson volcanic explosive activity, thus allowing a better estimate of the eruptive dynamics and the risks associated with the Hudson volcano.

Beschreibung: Published

Beschreibung: 276-280

Beschreibung: 6A. Geochimica per l'ambiente e geologia medica

Beschreibung: JCR Journal

Beschreibung: Southern Tuscany (Italy) is an important metallogenic district that hosts relevant S-polymetallic deposits that have intensely been exploited for centuries. Consequently, potential toxic elements, such as Hg and As, are widely distributed in the surrounding environment. In this paper, an extensive sedimentological, mineralogical and geochemical study of two Late Quaternary sediment profiles, partially outcropping along the coast of southern Tuscany (Ansedonia area), was carried out to evaluate the contents and mobility of Hg and As with the aims to contribute to the definition of the geochemical baseline of southern Tuscany before the human intervention and evaluate the potential dispersion of these harmful elements. The sedimentological, mineralogical and geochemical (major elements) features revealed that the studied profiles are mostly related to the local geological characteristics and the Quaternary geological history of the area. The concentrations and the normalized patterns of trace and rare earth elements highlighted the absence of any anthropogenic activity. This implies that the studied samples are to be regarded as good proxies for evaluating the geochemical baseline of southern Tuscany before the intense mining activity. The enrichment factors (EF) of most trace elements were indeed lower or close to 2, indicating a variability close to the average concentration of the Upper Continental Crust (UCC), while other elements slightly enriched, such as Pb, were in agreement with the natural baseline reported for southern Tuscany. Mercury and As displayed EF values 〉40 when compared to the average contents of UCC, although they decrease down to 4 when compared to the suggested baseline for southern Tuscany. The higher Hg and As contents detected in this study, inferred to natural sources, evidenced (i) the great natural variability occurring in largely mineralized areas and (ii) the importance of estimating reference environmental parameters in order to avoid misleading interpretations of the detected anomalies. Moreover, the results of leaching test on sediment samples denoted a relatively low mobility of Hg and As, suggesting that these elements are preferentially mobilized by transport of clastic sediments and such anomalies may be preserved for relatively long times in Quaternary sediments. However, leachable Hg (0.6–9.7 μg/L) and As (2.1–42.2 μg/L) concentrations are significantly high when compared to those of the Italian limit for groundwater (1 µg/L for Hg and 10 µg/L for As). Quaternary sediments from southern Tuscany could then be a potential, though natural, source of Hg and As to groundwater systems

Beschreibung: Published

Beschreibung: 1998

Beschreibung: 5A. Ricerche polari e paleoclima

Beschreibung: JCR Journal

Beschreibung: Acknowledging the grain size dependency of shape is important in volcanology, in particular when dealing with tephra produced and emplaced during and after explosive volcanic eruptions. A systematicmeasurement of the tridimensional shape of vesicular pyroclasts of Campi Flegrei fallout deposits (Agnano-Monte Spina, Astroni 6 and Averno 2 eruptions) varying in size from 8.00 to 0.016 mm has been carried out by means of X-Ray Microtomography. Data show that particle shape changes with size, especially for juvenile vesicular clasts, since it is dependent on the distribution and size of vesicles that contour the external clast outline. Two drag laws that include sphericity in the formula were used for estimating the dependency of settling velocity on shape. Results demonstrate that it is not appropriate to assume a size-independent shape for vesicular particles, in contrast with the approach commonly employed when simulating the ash dispersion in the atmosphere.

Beschreibung: Published

Beschreibung: 18-24

Beschreibung: 3V. Proprietà chimico-fisiche dei magmi e dei prodotti vulcanici

Beschreibung: JCR Journal

Beschreibung: Among the active volcanoes worldwide, Somma-Vesuvius is one with the highest volcanic risk as the surrounding areas are highly populated. Somma-Vesuvius is quiescent since 1944, but geological and historical records reveal a frequent violent explosive activity in the last 4000 years, representing a severe risk for the ~700000 inhabitants currently living in the area having a high probability for being impacted by pyroclastic density currents (“red zone”) and more than one million people who can be potentially affected by tephra fallout. This study aims to analyze the distribution and grain-size of tephra fallout deposits from several Somma-Vesuvius eruptions of different styles, ranging from Violent Strombolian to sub-Plinian and Plinian, for characterizing the associated magmatic fragmentation through the assessment of their total grain-size distribution (TGSD). Chronologically, we focus on the Avellino (4365 BP) and Pompeii (A.D. 79) Plinian eruptions, the Pollena (A.D. 472) sub-Plinian eruption, and the 1906 and 1944 Violent Strombolian eruptions. The related TGSDs were estimated by means of the Voronoi tessellation method, which requires a suitable number of local grain-size distributions and estimation of the area of minimum tephra loading (zero-line contour). However, field-derived TGSDs can be biased towards the coarse and fine grain-size populations due to the typical paucity of available field outcrops of fallout deposits. To encompass this issue, we performed a sensitivity study on the assumption behind TGSD reconstructions and described TGSDs through analytical grain-size distributions that best fit the field TGSDs. Our main objective is a more robust estimation of the TGSDs associated with the different eruptive styles, which is crucial, together with the other eruption source parameters, for robustly predicting tephra loading and airborne ash dispersal of future eruptions at Somma-Vesuvius.

Beschreibung: Published

Beschreibung: id 106683

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: JCR Journal

Beschreibung: Pyroclastic density currents are ground hugging gas-particle flows that originate from the collapse of an eruption column or lava dome. They move away from the volcano at high speed, causing devastation. The impact is generally associated with flow dynamic pressure and temperature. Little emphasis has yet been given to flow duration, although it is emerging that the survival of people engulfed in a current strongly depends on the exposure time. The AD 79 event of Somma-Vesuvius is used here to demonstrate the impact of pyroclastic density currents on humans during an historical eruption. At Herculaneum, at the foot of the volcano, the temperature and strength of the flow were so high that survival was impossible. At Pompeii, in the distal area, we use a new model indicating that the current had low strength and low temperature, which is confirmed by the absence of signs of trauma on corpses. Under such conditions, survival should have been possible if the current lasted a few minutes or less. Instead, our calculations demonstrate a flow duration of 17 min, long enough to make lethal the breathing of ash suspended in the current. We conclude that in distal areas where the mechanical and thermal effects of a pyroclastic density currents are diminished, flow duration is the key for survival.

Beschreibung: Published

Beschreibung: 4959

Beschreibung: 5V. Processi eruttivi e post-eruttivi

Beschreibung: JCR Journal

Beschreibung: The alluvial plain of the Ceyhan River (SE Turkey) has been populated since the Neolithic. In 1954, Marjory Veronica Seton-Williams described for this area several archeological mounds (höyük), which are the remains of ancient settlements. Today, according to the archeological research carried out in the area, some of these mounds result to have been leveled by agricultural activities. In this work, we identified many color anomalies by low-cost remote-sensing analyses of satellite images. We checked the nature of these anomalies in a dedicated survey and we found a good correspondence between color anomalies and archeological remains consistent with leveled höyük. We compared the grain size and chemical characteristics of the soil collected inside the color anomalies with the soil collected in other areas of the alluvial plain. We found irrelevant differences in grain-size characteristics, but a higher content of CaCO3 in soils collected inside the anomalies with respect to those collected outside. Therefore, the content of CaCO3 could be considered the feature that makes the color anomalies visible. The reason for this higher content of CaCO3 is related to the anthropogenic material used in the different phases of höyük growth. This work suggests a low-cost analysis useful for rapid identification and preservation of archeological information on the history of Mediterranean settlement

Beschreibung: Published

Beschreibung: Article 241

Beschreibung: 5A. Paleoclima e ricerche polari

Beschreibung: JCR Journal

Beschreibung: The interaction of magma and wall-rocks is inevitable when magma is moving through Earth's crust. These interactions happen on different timescales and especially the short-term interactions (seconds to days) during the final ascent of the magma can induce changes in eruption dynamics. However, information on this matter is scarce and scattered in different scientific fields. We conducted this review in order to present a full picture of the state of the art for short-timescale magma–wall-rock interactions. According to the three existing studies on short-term magma–carbonate interactions, magma viscosity is the most important controlling factor for carbonate assimilation. Lower viscosity magmas enhance CO2-bubble migration away from the reaction site, resulting in a higher carbonate assimilation rate. The released CO2 plays an important role regarding eruption dynamics since a higher CO2 release rate would result in accelerated magma ascent and may increase eruption intensity. Despite the importance for hazard assessment, important factors (pressure, magma composition, vapour phase solubilities, carbonate clast properties) for carbonate assimilation in general and CO2 release rate in particular are not or only poorly constrained. This review presents the present-day knowledge of short-term magma–carbonate interaction that is relevant to establish the basis for future work concerning magma–wall-rock interactions.

Beschreibung: Published

Beschreibung: 4V. Processi pre-eruttivi