An in situ method for measuring CO2 flux from volcanic-hydrothermal fumaroles

The theory of an in situ method to measure CO2 flux from hydrothermal fumar olic vents using a tracer gas technique is established and applied to vents and wells at three sites: Izu-Oshima (Japan), Kirishima (Japan) and Teide (Canary Islands, Spain) volcanoes. The method is done by releasing the trac er gas into the vent at known flux and by measuring CO2 to the tracer gas r atio in situ. In Izu-Oshima, we carried out flux measurements at a low-temp erature steam well (90 degreesC) with three different tracer gas species (H -2, CH4 and SF6) and three methods (GC, portable analyzers, FTIR) to evalua te this method. The calculated CO2 flux showed an average of 2.3 t/day. In the case of Kirishima volcanic area, the flux measurement was tested at two low-temperature fumaroles on Iwoyama cone(< 100 degreesC). The CO2 fluxes were 9 x 10(-2) and 2 x 10(0) kg/day, respectively. The total CO2 flux from the cone including both fumarolic and ground CO2 discharges was estimated to be less than several tons per day. In Teide volcano, CO2 flux measuremen ts were performed in the fumarolic system of the summit crater (85 degreesC ). CO2 flux from one fumarole reached levels up to 30.2 kg/day. We estimate d that the CO2 discharge from all fumaroles is roughly 30 t/day or less at maximum. These results imply that the total output of CO2 flux from Teide's fumarolic activity is much lower than the observed levels of CO2 diffuse d egassing from the summit crater. (C) 2001 Elsevier Science B.V. All rights reserved.