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Authors: Chiodini, G.* 
Granieri, D.* 
Avino, R.* 
Caliro, S.* 
Costa, A.* 
Werner, C.* 
Title: Carbon dioxide diffuse degassing and estimation of heat release from volcanic and hydrothermal systems
Journal: Journal of geophysical research. B, Solid planets 
Series/Report no.: 11, B08204
Publisher: American geophysical union
Issue Date: 2005
DOI: 10.1029/2004JB003542
Keywords: Carbon dioxide
Thermal gradient
Energy released
Subject Classification04. Solid Earth::04.02. Exploration geophysics::04.02.01. Geochemical exploration 
04. Solid Earth::04.02. Exploration geophysics::04.02.03. Heat flow 
04. Solid Earth::04.04. Geology::04.04.12. Fluid Geochemistry 
04. Solid Earth::04.08. Volcanology::04.08.01. Gases 
04. Solid Earth::04.08. Volcanology::04.08.07. Instruments and techniques 
05. General::05.06. Methods::05.06.99. General or miscellaneous 
Abstract: We present a reliable methodology to estimate the energy associated with the subaerial diffuse degassing of volcanic-hydrothermal fluids. The fumaroles of 15 diffuse degassing structures (DDSs) located in eight volcanic systems in the world were sampled and analyzed. Furthermore, each area was measured for soil temperature gradients and for soil CO2 fluxes. The results show that each hydrothermal or volcanic system is characterized by a typical source fluid which feeds both the fumaroles and diffuse degassing through the soil. Experimental data and the results of physical numerical modeling of the process demonstrate that the heat released by condensation of steam at depth is almost totally transferred by conduction in the uppermost part of the soil. A linear relationship is observed between the log of the steam/gas ratio measured in the fumaroles and the log of the ratio between soil thermal gradient and soil-gas flux. The main parameter controlling this relation is the thermal conductivity of the soil (Kc). For each area, we computed the values of Kc which range from 0.4 to 2.3 W m 1 C 1. Using the CO2 soil fluxes as a tracer of the deep fluids, we estimated that the total heat released by steam condensation in the systems considered varies from 1 to 100 MW.
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