The crater of Somma-Vesuvio is characterised by widespread fumarolic emissions accompanied by diffuse soil CO2 degassing. The fumaroles of Vesuvio crater bottom discharge vapors separated from a boiling hydrothermal system, which is mainly hosted in the volcanic conduits of Vesuvio. Gas equilibria indicate that high temperature (400-450°C) saline brines circulate in this hydrothermal system, whereas the stable isotopes of water suggest that this system is partially recharged by meteoric water and partly by magmatic water. Two field-surveys of soil CO2 fluxes have been performed in order to map and quantify the degassing process affecting the crater area. The results show that the whole inner crater and few spots located on the external slopes of the cone release deeply derived CO2. A rough estimation of the total CO2 output from the crater area gives 100-200 ton d-1. In addition to this ‘crater’ hydrothermal activity, several shallow warm wells discharging CO2-rich waters are present in the southern flanks of Vesuvio, and submarine gas emissions are situated along the southern coastline. This CO2 anomaly in the southern sector of the volcano may be originated by underground flow of CO2-rich groundwaters dissolving ‘volcanic-hydrothermal’ gases in the summital part of the volcano (depression of Somma). This area represents an important infiltration zone of meteoric waters due to its morphological features and the presence of permeable lavas. In order to test this hypothesis, the analytical compositions of gases dissolved in groundwaters and the isotopic composition of dissolved carbon have been compared with the calculated counterparts, obtained by theoretical models of interaction between local meteoric water, host-rocks and gases discharged by Vesuvio crater fumaroles. These models take into account different degassing pressures, from 1 bar to equilibrium pressure with respect to calcite. The good agreement between analytical and theoretical data supports the hypothesised conceptual geochemical model.
HYDROTHERMAL ACTIVITY AT VESUVIO
MORETTI, Roberto;
2001
Abstract
The crater of Somma-Vesuvio is characterised by widespread fumarolic emissions accompanied by diffuse soil CO2 degassing. The fumaroles of Vesuvio crater bottom discharge vapors separated from a boiling hydrothermal system, which is mainly hosted in the volcanic conduits of Vesuvio. Gas equilibria indicate that high temperature (400-450°C) saline brines circulate in this hydrothermal system, whereas the stable isotopes of water suggest that this system is partially recharged by meteoric water and partly by magmatic water. Two field-surveys of soil CO2 fluxes have been performed in order to map and quantify the degassing process affecting the crater area. The results show that the whole inner crater and few spots located on the external slopes of the cone release deeply derived CO2. A rough estimation of the total CO2 output from the crater area gives 100-200 ton d-1. In addition to this ‘crater’ hydrothermal activity, several shallow warm wells discharging CO2-rich waters are present in the southern flanks of Vesuvio, and submarine gas emissions are situated along the southern coastline. This CO2 anomaly in the southern sector of the volcano may be originated by underground flow of CO2-rich groundwaters dissolving ‘volcanic-hydrothermal’ gases in the summital part of the volcano (depression of Somma). This area represents an important infiltration zone of meteoric waters due to its morphological features and the presence of permeable lavas. In order to test this hypothesis, the analytical compositions of gases dissolved in groundwaters and the isotopic composition of dissolved carbon have been compared with the calculated counterparts, obtained by theoretical models of interaction between local meteoric water, host-rocks and gases discharged by Vesuvio crater fumaroles. These models take into account different degassing pressures, from 1 bar to equilibrium pressure with respect to calcite. The good agreement between analytical and theoretical data supports the hypothesised conceptual geochemical model.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
