Rates of sulfur dioxide and particle emissions from White Island volcano,New Zealand,and an estimate of the total flux of major gaseous species

Airborne correlation spectrometry (COSPEC) was used to measure the rate of SO₂ emission at White Island on three dates, i.e., November 1983, 1230 ± 300 t/d; November 1984, 320 ± 120 t/d; and January 1985, 350 ± 150 t/d (t = metric tons). The lower emission rates are likely to reflect the long-term emission rates, whereas the November 1983 rate probably reflects conditions prior to the eruption of December 1983. The particle flux in the White Island plume, as determined with a quartz crystal microbalance/cascade in November 1983, was 1.3 t/d, unusually low for volcanic plumes. The observed plume particles, as shown from scanning electron microscopy, include halite, native sulfur, and silicates and are broadly similar to other volcanic plumes.Gas analyses from high-temperature volcanic fumaroles collected from June 1982 through November 1984 werde used together with the COSPEC data to estimate the flux of other gas species from White Island. The rates estimated are indicative of the long-term volcanic emission, i.e., 8000–9000 t/d H₂O, 900–1000 t/d CO₂, 70–80 t/d HCl, 1.5–2 t/d HF, and about 0.2 t/d NH₃. The long-term thermal power output at White Island is estimated at about 400 MW.     

Carbon-13 exchange between CO2 and CH4 under geothermal conditions

On the basis of recently reported data on the kinetics of carbon-13 exchange between CO₂ and CH₄ at temperatures above 500°C, first order rate constants $\text{log k = 11.16?10,190/T}$ were derived allowing variations in Δ, the difference in the isotopic composition of coexisting CO₂ and CH₄, to be evaluated as a function of initial composition and cooling rate of the rising geothermal fluid. Observed Δ-values in geothermal discharges are likely to represent frozen in compositions attained after minimum residence times of 20 ka at 400°C or 10 Ma at 300°C. The carbon-13 contents of any biogenic gases are unlikely to have been affected by thermal re-equilibration at temperatures below 200°C. The chemical equilibrium involving CO₂ and CH₄ can be expected to proceed about a hundred times faster than isotopic equilibration.     

“Geothermal mineral equilibria”. Reply to a comment by M. A. Grant

The dominant process limiting CO₂-contents of fluids in high temperature (>240°), liquid-dominated systems consists of the conversion of primary plagioclase by CO₂ to calcite and clay according to log P_CO2 = 15.26 ? 7850/(t + 273.2), temperature t in °C, with a likely error in log P_CO2 due to variations in the activities of the anorthite and kaolinite components of the mineral phases involved of around ± 1 log unit. Secondary processes such as adiabatic expansion, conductive cooling and mixing with cooler groundwaters are largely responsible for subsequent variations in P_CO2 at lower temperatures (>240°).     

A simple method for the collection and analysis of volcanic gas samples

Investigations into the chemistry of volcanic gases depend on the availability of complete and accurate analyses of volcanic exhalations. The wide variety of sampling and analysis methods hitherto used, often supplying only partial analyses of low precision, made intercomparison, and thus a systematic study of volcanic gases, difficult. With the method proposed here, complete volcanic gas samples are obtained permitting the accurate determination of all major species by standard analytical methods without the need for highly specialised ancillary equipment. The samples are collected in evacuated 300 ml pyrex flasks through titanium tubes deeply inserted into the gas vent. Two types of flask are used, a single compartment flask allowing the easy determination of the major constituents and containing 50 ml 4 N NaOH, and a double compartment flask for the separate analysis of the sulfur species and containing 25 ml 0.1 N As₂O₃ in 1 N HClO₄ in the first, and 50 ml 4 N NaOH in the second compartment. Non-absorbed gases are determined by gas chromatography, the rest by standard analytical procedures. The determination of H₂O, CO₂, SO₂, SO₂, S₂, H₂S, HCl, HF, H₂, N₂, O₂, CH₄, CO and NH₂ is described.     

Geothermal gas equilibria

Comparison of theoretical and analytical equilibrium constants based on the reactions CH₄ + 2H₂O = CO₂ + 4H₂, 2NH₃ = N₂ + 3H₂ and iron(II)-aluminium-silicate + 2H₂S = FeS₂ + H₂ + aluminium-silicate, shows that the composition of fluids discharged from geothermal areas in New Zealand (Wairakei, Kawerau, Broadlands) reflects close to complete attainment of chemical equilibrium within the system H₂O, CO₂, H₂S, NH₃, H₂, N₂ and CH₄. Under conditions prevailing in explored geothermal systems in New Zealand, the minerals graphite (elemental carbon), anhydrite, pyrrhotite, magnetite do not appear to take part in the overall equilibrium system. The three physical parameters required to evaluate geothermal gas reactions are temperature, pressure and vapor-liquid ratios within the gas equilibration zone.