27 research outputs found

    Rischi Naturali e Protezione Civile in Campania

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    Terra Pericolosa

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    Active degassing structures of Stromboli and variations in diffuse CO 2 output related to the volcanic activity

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    The main CO2 diffuse degassing structures (DDS) of Stromboli were identified through extensive CO2 soil flux investigations, with 3600 measurements by an accumulation chamber. These DDS extend from the nearby crater area of Pizzo sopra la Fossa (Pizzo) to the coastal area of Pizzillo and are all associated with NE–SW deep fractures, corresponding to the main volcano-tectonic axis of the island, some of which produced flank eruptions in prehistoric times. In each of the four main DDS, a target area was defined covering the zone with the highest CO2 soil flux, where periodic CO2 flux surveys were carried out. The highest CO2 release was observed during the 2007 eruption and high flux values were recorded at both Pizzo and Pizzillo also in moments of high prolonged Strombolian activity (high number of daily explosions observed from the craters and/or high frequency of VLP seismic events). In order to better investigate the rate of diffuse CO2 degassing in relation to volcanic activity, an automatic station hourly measuring CO2 soil flux and environmental parameters (atmospheric T, P and humidity, soil moisture and T, wind speed and direction) was installed in March 2007 at Nel Cannestrà and Rina Grande DDS. Unusual positive correlations were found at Nel Cannestrà between gas flux and SE wind speed and at Rina Grande between gas flux and soil moisture, which are explained by the local conditions, which favour respectively a Venturi effect and the increase in gas flux toward the station during rains. Ten months of continuous recording confirmed the strong influence of environmental conditions on the CO2 soil flux, but statistical data processing made it possible to recognize clear positive anomalies expressing high rates of deep magmatic CO2 degassing. Comparison with seismic data indicates that high CO2 fluxes are apparently correlated with increases in volcanic activity, such as higher explosion frequency and VLP amplitude. Particularly promising is the temporal coincidence of highest recorded flux anomaly with a major explosion that occurred during the observation period. Data confirm that the two continuously monitored DDS are preferentially deep degassing sites, where anomalous increases of CO2 release could represent a geochemical precursor for either high energy explosions from the craters or the opening of flank eruptive fissures that might threaten the village of Stromboli

    L’acquifero nelle ghiaie di base del Tevere: una risorsa geotermica per la città di Roma

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    Significativi risparmi di combustibili fossili e di elettricità e una forte riduzione dell’inquinamento atmosferico possono essere realizzati utilizzando risorse geotermiche di entalpia molto bassa, con temperature intorno o anche inferiori a 20 °C, per il riscaldamento invernale e il condizionamento estivo di ambienti. I risultati di questo studio mostrano che l’acquifero contenuto nelle ghiaie di base del Tevere rappresenta una importante risorsa geotermica per la città di Roma per questi tipi di impieghi termici. Il processa mento dei dati stratigrafici di 216 pozzi perforati negli anni scorsi nelle alluvioni del Tevere hanno consentito di elaborare mappe del tetto, del letto e quindi dello spessore delle ghiaie di base. L’acquifero si incontra a profondità tra 30 e 60 m dal piano campagna, più alta verso sud, nelle zone dell’Eur e meno a nord di Monte Mario. Questi dati indicano che la risorsa geotermica può essere estratta con pozzi di costo limitato. Lo spessore dell’acquifero di base è in genere intorno a 10 m, ma cresce a 30-40 m nel tratto nord del fiume e vi sono varie zone con spessori di 15-20 m. la continuità è ottima lungo l’asse del fiume e assicura una buona alimentazione longitudinale accresciuta da contributi laterali nelle zone dove le ghiaie vengono a contatto con livelli permeabili, con le ghiaie del Fosso della Crescenza a nord e le vulcaniti dei Colli Albani nella parte centro meridionale. L’acquifero è confinato verso il basso dalle argille dalle argille di Monte Vaticano e verso l’alto dai depositi limosi impermeabili del Tevere che impedendo la percolazione verticale delle piogge e dell’acqua del fiume, lo proteggono da fattori inquinanti e da effetti termici stagionali. I parametri chimico-fisici misurati su 17 pozzi, indicano una temperatura dell’acqua che varia da 16 a 21 °C, ma con una prevalenza di valori intorno a 18-19 °C che appaiono ideali per usi termici sia estivi che invernali. Il pH è per lo più neutro o leggermente acido in alcune zone. La conducibilità elettrica è localmente abbastanza elevata con valori di poco superiori a 5000μS/cm. È stato stimato un fabbisogno intorno a 20 l/s di acqua geotermica con T 17-18 °C per riscaldare e condizionare un grosso condominio di 40.000 m3. L’acquifero di base del Tevere può facilmente fornire tali quantitativi di acqua in vari punti della città, considerato che comunque l’acqua, dopo la sua utilizzazione dovrà essere re iniettata nell’acquifero di provenienza.Significant saving in the fossil fuel and electric energy consumption and a strong reduction of the atmospheric pollution can be obtained by using low enthalpy geothermal resources., with temperature around or even below 20°C for space heating and conditioning. The results of this study indicate that the aquifer contained in the basal gravels of Tiber River represents an important geothermal resource for this kind of direct heat utilization in the city of Rome. Maps describing the variation along the river course of the top, bed and hence thickness of the base gravels have been obtained by processing the stratigraphic data of 216 wells drilled in the past in the Tiber alluvional deposits. The aquifer top is found at 30-60m depth from the ground, higher depths being found in the southern Eur zone and the shallower once in the zone Nord of Monte Mario. This values indicate that the geothermal water can be easily extracted with low-cost wells. The thickness of the base aquifer is usually around 10m, but is rises to 30-40m in the northern river sector and to 15-30m in several other zones. There is an excellent continuity of the aquifer along the river course, that ensures a good longitudinal water recharge, that is increased by lateral contribution from the zones where the gravels are in contact with permeable rocks, such as the Fosso della Crescenza gravels, to the North and the Colli Albano volcanic in the central-southern sector. The aquifer is confined downward by the Monte Vaticano Pleocenic shales and upward by impervious Tiber silt deposit. The latters prevent vertical percolation of rain and river waters protect the base aquifer from both pollution and seasonal thermal effects. Physic-chemical parameters measured in 17 wells indicated a water temperature (T) ranging from 16 to 21,6 °C, but usually around 18-19 °C, values that appear as ideal for direct heat utilization. The pH is mostly neutral and slightly acid in some zones, whereas electrical conductivity is locally rather high with values slightly exceeding 5000µS/cm. it has been stimated that 20 l/s of a geothermal water with a T of 17-18°C are needed for winter heating and summer cooling of a 40,000 m3 space. The base Tiber aquifer can easily provide such a resource in several zone of Rome city considering that the water, after its utilization will have to be reinjected into the provenance aquifer
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