169 research outputs found
Runout modelling of gravity-induced pyroclastic density currents at Stromboli volcano (Italy)
No full textGravity-induced pyroclastic density currents (PDCs) at Stromboli volcano were investigated by means numerical and empirical modelling. With the aim of testing the suitability of landslide numerical model DAN- 3D and empirical models are used related to gravity-induced PDCs, in particular this work presents the results of the back analysis of three events occurred on 1906, 1930 and 1944 at Stromboli volcano. These two methods were able to reproduce the extension and the order of magnitude of the thickness of the PDCs reported in the literature. The best results of DAN-3D models were obtained using a Voellmy model with frictional coefficient of f = 0.19 and a turbulence parameter ξ = 1000 m/s. The mobility terms, find with the numerical model, are compared with empirical data of literature of the similar events
Growth and erosion: The volcanic geology and morphological evolution of La Fossa (Island of Vulcano, Southern Italy) in the last 1000 years
No full textThe Island of Vulcano (Aeolian Islands, Southern Italy) consists of several volcanic edifices whose formation overlapped in time and space beginning 120 ka ago. The most recent volcano is the La Fossa cone, a 391 m-high active composite cone that began to erupt 5.5 ka ago. Eruptive activity at the La Fossa cone occurred in several cyclic phases separated by prolonged periods of erosion.
The last 1000 years of eruptive activity and morphological variations in the cone and its surrounding area were investigated through a stratigraphic reconstruction. This was based on 139 natural cuts, 26 machine- excavated and 5 hand-dug trenches in the volcaniclastic succession. The revised stratigraphy of the volcanic and volcaniclastic sequence was compared with geological maps based on the Unconformity-bounded Stratigraphic Units criteria compiled in 2006–2010. It was found that the last 1000-year period can be divided into (in hierarchical order) Eruptive Clusters and Units. Several unconformities of different hierarchical order were also identified (erosional surfaces and/or palaeosols). Stratigraphic relationships with the Vulcanello products and with rhyolitic tephras related to the eruptions of Mt. Pilato (the last-formed volcanic edifice of the Island of Lipari) were fundamental in assigning a calen- dar age to most of the tephra units in the studied sequence. The morphological evolution of the upper part of the cone was also reconstructed in order to assess the average cone growth rate. This work suggests a new stratigraphic and chronological interpretation of the evolution and “cyclic” activity of the La Fossa cone in the last 1000 years. Several eruptions occurred in two main clusters. The stratigraphic record and morpho- logical features reveal that the areas around the cone were affected by the deposition of reworked materials, with large amounts of tephra deposited on the steep slopes and within the major streams
Magmatic sulfide immiscibility at an active magmatic-hydrothermal system: The case of La Fossa (Vulcano, Italy)
No full textMagmatic sulfide minerals preserved in fresh volcanic rocks can be used to trace sulfur and chalcophile element evolution in magmatic systems and to constrain the potential magmatic contribution to ore-forming fluids. In this work, we present a petrographic and microanalytical study of magmatic sulfides in the products of La Fossa (Vulcano, southern Italy), an active arc-related volcano currently with a shallow acidic hydrothermal system, and discuss the results with petrological data obtained from melt inclusions. While the sulfur-rich basalts feeding the plumbing system were oxidized and sulfide-undersaturated, as common in arc-basalts, a major event of sulfide melt separation from the silicate melt occurred at the trachytic stage, in the shallow reservoir (minimum depth based on H2O content of melt inclusions is 1200-2200 m), promoted by the lowering of fO2. Sulfide immiscibility was unrelated to magnetite fractionation and was encountered after a notable sulfur loss at the transition from mafic to intermediate magma composition. The late sulfide saturation implies that the silicate melt became enriched in Cu with differentiation. This is indicated by the relatively high Cu concentration in the analyzed sulfide blebs, comparable to the composition of sulfides found in other active arc volcanoes as well as in magmatic systems associated with porphyry copper mineralization. The newly reported occurrence of sulfide immiscibility in the La Fossa shallow reservoir has implications for the evolution of sulfur in the plumbing system and for the contribution of magmatic sulfur and metals to surface fumaroles, as well as to the deep hydrothermal fluids during non-eruptive periods. The results indicate that La Fossa volcano is a possible active analogue of mineralizing magmatic-hydrothermal systems
The last 1100 years of activity of La Fossa caldera, Vulcano Island (Italy): new insights into stratigraphy, chronology, and landscape evolution
No full textA detailed study of past eruptive activity is crucial to understanding volcanic systems and associated hazards. We present a meticulous stratigraphic analysis, a comprehensive chronological reconstruction, thorough tephra mapping, and a detailed analysis of the interplay between primary and secondary volcanic processes of the post-900 AD activity of La Fossa caldera, including the two main systems of La Fossa volcano and Vulcanello cones (Vulcano Island, Italy). Our analyses demonstrate how the recent volcanic activity of La Fossa caldera is primarily characterized by effusive and Strombolian activity and Vulcanian eruptions, combined with sporadic sub-Plinian events and both impulsive and long-lasting phreatic explosions, all of which have the capacity to severely impact the entire northern sector of Vulcano island. We document a total of 30 eruptions, 25 from the La Fossa volcano and 5 from Vulcanello cones, consisting of ash to lapilli deposits and fields of ballistic bombs and blocks. Volcanic activity alternated with significant erosional phases and volcaniclastic re-sedimentation. Large-scale secondary erosion processes occur in response to the widespread deposition of fine-grained ash blankets, both onto the active cone of La Fossa and the watersheds conveying their waters into the La Fossa caldera. The continuous increase in ground height above sea level, particularly in the western sector of the caldera depression where key infrastructure is situated, is primarily attributed to long-term alluvial processes. We demonstrate how a specific methodological approach is key to the characterization and hazard assessment of low-to-high intensity volcanic activity, where tephra is emitted over long time periods and is intercalated with phases of erosion and re-sedimentation
Campionamento di acqua potabile per la determinazione di virus
No full textL'articolo illustra i criteri statistici per la misura della qualità delle acque al fine di ottenere informazioni sulla presenza di viru
Modelling Erosion and Floods in Volcanic Environment: The Case Study of the Island of Vulcano (Aeolian Archipelago, Italy)
No full textThe re-mobilization of volcaniclastic material poses a hazard factor which, although it decreases with time since the last eruption, remains present in the hydrographic basins of volcanic areas. Herein, we present the results of the numerical modelling of erosive phenomena of volcanic deposits, as well as of flooding in the volcanic area. The proposed approach includes runoff estimation, land use analysis, and the application of hydraulic and erosion modelling. It exploits the Iber software, a widely used and validated model for rainfall-runoff, river flooding, and erosion and sediment transport modelling. The methodology was applied to the Island of Vulcano (Italy), known for the erosion phenomena that affect the slopes of one of its volcanic cones (La Fossa cone). The rainfall excess was calculated using a 19-year dataset of hourly precipitations, and the curve number expressed by the information on soil cover in the area, derived from the land cover and land use analysis. The erosion and flow models were performed considering different rainfall scenarios. Results show a particularly strong erosion, with thicknesses greater than 0.4 m. This is consistent with field observations, in particular with some detailed data collected both after intense events and by long-term observation. Results of the hydraulic simulations show that moderate and torrential rainfall scenarios can lead to flood levels between 0.2 and 0.6 m, which mostly affect the harbours located in the island’s inhabited area
Editorial. Synthetic aperture radar and natural hazards. Applications and outlooks
No full textThe ability of Synthetic Aperture Radar (SAR) to image the Earth’s surface, even through dense cloud cover and in night-and-day conditions, can facilitate the evaluation and monitoring of
natural hazards and the management of natural disasters. The family of SAR satellite sensors orbits the Earth at an altitude ranging from 500 to 800 km, following sun-synchronous, near-polar orbits, slightly inclined with respect to Earth meridians. The most commonly used bands in SAR applications are the C-band (5–6 GHz, 5, 6 cm wavelength), the X-band (8–12 GHz, 3, 1 cm wavelength), and the L-band (1–2 GHz 23 cm wavelength) with a temporal resolution depending on the satellite revisiting time. The availability of SAR has made a new spectrum of measurements possible on a global and spatial scale not attainable by ground-based studies, revealing critical insights into remote or poorly understood areas (e.g., Biggs et al., 2014). This Research Topics presents a review of articles on the state-of-art in the application of SAR sensors to study surface deformation in different geologic environments and triggered by a variety of processes. The topics discussed range from the analysis of co-seismic deformation (Merryman Boncori) to studies of volcanic unrest (Dzurisin et al.; Garthwaite et al.), monitoring of landslides (Bianchini et al.) and ground subsidence in urban areas (Solari et al.)
Variations of the blood gas levels and thermodilutional parameters during ICP monitoring after severe head trauma in children
No full textPurpose: The purpose of this study was to define, in children following head trauma and GSC ≤ 8, at which level of intracranial pressure (ICP), the thermodilutional, and gas analytic parameters implicated in secondary cerebral insults shows initial changes. Methods: We enrolled in the study 56 patients: 30 males and 26 females, mean age 71 ± 52 months. In all children, volumetric hemodynamic and blood gas parameters were monitored following initial resuscitation and every 4 h thereafter or whenever a hemodynamic deterioration was suspected. During the cumulative hospital stay, a total of 1050 sets of measurements were done. All parameters were stratified in seven groups according to ICP (group A1 = 0–5 mmHg, group A2 = 6–10 mmHg, group A3 = 11–15 mmHg, group A4 16–20 mmHg, group A5 21–25 mmHg, group A6 26–30 mmHg, group A7 >31 mmHg). Results: Mean values of jugular oxygen saturation (SJO2), jugular oxygen partial pressure (PJO2), extravascular lung water (EVLWi), pulmonary vascular permeability (PVPi), fluid overload (FO), and cerebral extraction of oxygen (CEO2) vary significantly from A3 (11–15 mmHg) to A4 (16–20 mmHg). They relate to ICP in a four-parameter sigmoidal function (4PS function with: r2 = 0.90), inflection point of 15 mmHg of ICP, and a maximum curvature point on the left horizontal asymptote at 13 mmHg of ICP. Conclusions: Mean values of SJO2, PJO2, EVLWi, PVPi, FO, and CEO2 become pathologic at 15 mmHg of ICP; however, the curve turns steeper at 13 mmHg, possibly a warning level in children for the development of post head trauma secondary insult
Analisi spaziale della copertura vegetale in zone a differente grado di antropizzazione.
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