Pedro A. Hernández

Diffuse emission of CO2 from Miyakejima volcano, Japan

Abstract Two soil gas surveys were carried out in May and September 1998 at Miyakejima volcano, in the Izu Mariana arc, Japan. CO 2 flux values for May and September surveys ranged from 0.1 to 18,150 g m −2 day −1 and from 0.1 to 9685 g m −2 day −1 , respectively. Statistical graphical analysis showed three overlapping populations. The spatial distribution of these emissions correlated quite closely with the geothermal and geological characteristics of the studied area. The structure releasing higher CO 2 is the summit cone Oyama and surrounding areas, where the most obvious geothermal features occur. A total output about 100–150 t day −1 is estimated from this area. A good correlation was observed between soil CO 2 flux and soil temperature at the summit caldera indicating extensive condensation of fumarolic steam within the upper part of Miyakejima. Carbon isotopic analysis of selected samples inside the summit caldera ( δ 13 C–CO 2 =−0.90‰ to −5.70‰) suggests a mixing of carbon derived from marine limestone and magmatic CO 2 while a clear biogenic origin ( δ 13 C–CO 2 =−14.76‰ to −25.52‰) is observed for the diffuse degassing of CO 2 outside summit caldera.

Diffuse emission of carbon dioxide from Cerro Negro Volcano, Nicaragua, Central America

We report the first detailed soil CO2 efflux survey carried out at Cerro Negro volcano, Nicaragua, Central America. Soil CO2 efflux values ranged from 0.5 to 35,000 g m−2 d−1. Spatial distribution of CO2 efflux shows that volcanic gas is mainly released from the summit crater and the fissures opened during the August 1999 eruption. The total CO2 output of Cerro Negro is conservatively estimated to be 2,800 t d−1, based on a study area of 0.58 Km². Contour maps of soil CO2 efflux, ground temperature, and δ13C(CO2) distributions support an important magmatic contribution for the total output of CO2 at Cerro Negro volcano.

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

Abstract The theory of an in situ method to measure CO 2 flux from hydrothermal fumarolic 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 tracer gas into the vent at known flux and by measuring CO 2 to the tracer gas ratio in situ. In Izu-Oshima, we carried out flux measurements at a low-temperature steam well (90°C) with three different tracer gas species (H 2 , CH 4 and SF 6 ) and three methods (GC, portable analyzers, FTIR) to evaluate this method. The calculated CO 2 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 ( 2 fluxes were 9×10 −2 and 2×10 0 kg/day, respectively. The total CO 2 flux from the cone including both fumarolic and ground CO 2 discharges was estimated to be less than several tons per day. In Teide volcano, CO 2 flux measurements were performed in the fumarolic system of the summit crater (85°C). CO 2 flux from one fumarole reached levels up to 30.2 kg/day. We estimated that the CO 2 discharge from all fumaroles is roughly 30 t/day or less at maximum. These results imply that the total output of CO 2 flux from Teides fumarolic activity is much lower than the observed levels of CO 2 diffuse degassing from the summit crater.

Pressure gradient measurements in volcanic diffuse gas emanations

We describe a differential pressure measurement device which allows one to estimate fluid pressure gradients ranging from 6.3 × 10−6 to 3.15 × 10−3 atm/m in soil diffuse volcanic gas emanations. The lower limit roughly corresponds to the atmospheric (static) pressure gradient due to gravity, and should represent the minimum required value for volcanic gases to reach the Earths surface by viscous flow. In the study of diffuse gas emanations, such as for the purpose of volcanic surveillance, such physical data supplements the geochemical monitoring of concentrations and fluxes of specific substances constituting the flowing gaseous mixture and may be used to infer volcanic mechanical states. We describe laboratory experiments with the device and report on a successful preliminary test with diffuse gas emanations on the Miharayama cone of the Izu-Oshima volcano (Japan), where the highest fluid pressure gradients have been found to be associated with the highest CO2 fluxes and lowest CO2 concentration gradients.