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Moretti R., Arienzo I., Civetta L, Orsi, Papale P. 

  

Multiple magma degassing sources at an explosive volcano.

 
Earth and Planetary Science Letters, 367: 95–104,(2013)
 
Abstract 
Chronograms of relevant geochemical and geophysical observablesPersistent degassing of closed-conduit explosive volcanoes may be used to inspect and monitor magmatic processes. After interaction with shallow hydrothermal fluids, volcanic gases collected at surface can differ substantially from those exsolved from magma. We report here on an innovative approach to identify and separate the contribution of variable magmatic components from fumarolic gases, by processing the 30-year-long geochemical dataset from the Campi Flegrei caldera, Southern Italy. The geochemical record shows periodic variations, which are well correlated with geophysical signals. Such variations are interpreted as due to the time-varying interplay of two magma degassing sources, each differing in size, depth, composition, and cooling/crystallization histories. Similar multiple degassing sources are common at explosive volcanoes, with frequent ascent and intrusion of small magma batches. Our innovative method permits the identification of those magma batches, which contributes to the interpretation of unrest signals, forecasting and assessment of volcanic hazards.
 

Fig. 1. Chronograms of relevant geochemical and geophysical observables. Molar H2O(f)/CO2(f) (panel a), CH4(f)/CO2(f) (panel b),H2S(f)/CO2(f) (panel c) ratios and δ18OH2O,f values (panel d) have been determined on Solfatara fumarolic discharges (Caliro et al., 2007; Chiodini et al., 2011, 2010a) (FC: Fumarola Centrale; BG: Bocca Grande; BN: Bocca Nuova; P: Pisciarelli). Panels (e) and (f) show chronograms of ground elevation residuals (computed after addition of the secular subsidence and subtraction of a first-order exponential decay in time; Chiodini etal., 2010a), and seismicity (D’Auria etal., 2011), respectively. Note that ground elevation residuals are shown on a reversed axis to remark the strong correlation with CH4(f)/CO2(f), the minima of which are anticipated by seismicity.

 

Keywords: magmatic degassing, hydrothermal systems, explosive volcanism, unrest, isotopic inversion, fluxing