B. Ardouin

Volcanic emission of radionuclides and magma dynamics

210Pb,210Bi and210Po, the last decay products of the238U series, are highly enriched in volcanic plumes, relative to the magma composition. Moreover this enrichment varies over time and from volcano to volcano. A model is proposed to describe 8 years of measurements of Mt. Etna gaseous emissions. The lead and bismuth coefficients of partition between gaseous and condensed phases in the magma are determined by comparing their concentrations in lava flows and condensated volatiles. In the case of volatile radionuclides, an escaping time is calculated which appears to be related to the volcanic activity. Finally, it is shown that that magma which is degassing can already be partly degassed; it should be considered as a mixture of a few to 50% of deep non-degassed magma with a well degassed superficial magma cell.

Radioactive isotopes and trace elements in gaseous emissions from White Island, New Zealand

Abstract Measurements of the radioactivity of gases released by White Island volcano show variations in 210 Po-concentrations with temperature in fumarolic gases, and this is interpreted to be due to dilution of magmatic gases with vapours derived from an envelope of acid brines surrounding the vent system. The degassing model derived for Mount Etna emissions is tested on White Island magmatic gases. The results are a short degassing time (2 days), small degassing magma volume ( 5 × 10 6 m 3 ), and the following estimations of emanation coefficients: Pb= 1% , Bi= 2.7% , Cd= 0.05% and Cu= 0.07/%. The initial content of S in the magma is estimated to be within the range 300–600 mg/kg. Fluxes of trace metals (kg/day) emitted by the volcano are estimated to be Pb= 125 , Bi= 6 , Cu= 300 and Cd= 9 .

Source strength assessment of volcanic trace elements emitted from the Indonesian arc

Abstract We have for the first time estimated volcanic emission of volatile metals for a large regional volcanic source showing permanent activity, namely the Indonesian Arc. We have done this by normalizing concentrations of metals ratios in volcanic plumes to SO 2 emission rates. Metal/SO 2 ratios measured in magmatic gases are used to estimate emissions from eruptive activity, whereas those measured in fumarolic gases are used to estimate emissions from non-eruptive activity. The SO 2 emission rate obtained is 3.5 × 10 6 tons per year, which represents about 20% of the annual worldwide volcanic flux of SO 2 . The obtained trace metal ( 210 Po, Pb, Bi, Cd, Zn and Cu) fluxes account for only about 5 to 30% of their global volcanic flux. These relatively low values for trace metal emissions (relative to the volcanic activity and the number of active volcanoes of the region) appear to reflect the andesitic magma composition of the volcanoes of the arc.

Origins of 210Po in the atmosphere at lamto, ivory coast: Biomass burning and saharan dusts

Abstract Measurements of 210 Po and 210 Pb activities in surface air at Lamto (Ivory Coast) during 18 months are presented and discussed in relation to the regional sources of 210 Po. High seasonal variation is observed with maximum in winter, reaching an activity of 210 Po as high as I Bq per 10 3 m 3 . Our estimation shows that the high 210 Po activity in winter is not closely related to the local biomass burning emissions but rather due to the particular atmospheric circulation patterns and geographical location of this region: in winter, surface winds having continental origin bring soil dusts, enriched in 210 Po and 210 Pb, from Sahara desert. However, biomass burning and the growth from 222Rn within the atmosphere appear to be the major sources of unsupported 210 Po in the other seasons.

210Po in savanna burning plumes

During the FOS-DECAFE experiment at Lamto (Ivory Coast) in January 1991 aerosols samples were collected at ground level above fires in order to investigate the possibility of using210Po as a tracer of biomass burning. The concentration of this radionuclide in plants is studied as a function of its content in soils and in the atmospheric background. It is shown that it depends strongly on the atmospheric content in210Po, due to dry deposition of the aerosols. The mean concentration of plants at Lamto is found to be about 4.4 pCi of210Po/gC during the fire season and falls down to less than 1pCi/gC outside this period. The budget of210Po is evaluated taking into account its complete volatilization during the flaming phase, the (210Po)ash/(210Po)plants ratio, which is measured to be about 14% and the percentage of submicron particles in the plume, about 91%. The inferred flux of210Po is 3850 Ci/yr for the African savanna, and 5800 Ci/yr for the global savanna. From this flux, fluxes of Ct and Cs are estimated to be 8.4 and 1.1 Tg of C/yr for the worldwide savanna.

Long-lived radon decay products in Mount St. Helens emissions: An estimation of the magma reservoir volume

Abstract The size of the Mount St. Helens magma reservoir is estimated from long-lived radon decay products in fumarole emissions. Samples were collected in September 1981 on filters and by a new sampling technique developed for fumarole condensate. The Po-210/Pb-210 activity ratios were significantly higher in the condensate than on the filters. The difference is attributed to Po-210 losses from the filters by a variety of processes and to trapping of Po-210 in sulfur precipitate that prevents detection of alpha particles. Model calculations based on Po-210, Pb-210, and Bi-210 activities give volume estimates for the degassing magma of about either 1 × 10 8 m 3 or 4 × 10 5 m 3 /d according to the model utilized.

An international intercomparison of marine atmospheric radon 222 measurements in Bermuda

As part of an international measurement intercomparison of instruments used to measure atmospheric 222Rn, four participating laboratories made nearly simultaneous measurements of 222Rn activity concentration in commonly sampled, ambient air over approximately a 2-week period, and three of these four laboratories participated in the measurement comparison of 14 introduced samples with known, but undisclosed (“blind”) 222Rn activity concentrations that could be related to U.S. national standards. The standardized sample additions were obtained with a calibrated 226Ra source and a specially designed manifold used to obtain well-known dilution factors from simultaneous flow rate measurements. The exercise was conducted in Bermuda in October 1991. The 222Rn activity concentrations in ambient Bermudian air over the course of the intercomparison ranged from a few hundredths to about 2 Bq m−3, while the standardized sample additions covered a range from approximately 2.5 to 35 Bq m−3. The overall uncertainty in the latter concentrations was in the general range of 10% at a 3 standard deviation uncertainty interval. The results of the intercomparison indicated that two of the laboratories were within very good agreement with the standard additions and almost within expected statistical variations. These same two laboratories, however, at lower ambient concentrations, exhibited a systematic difference with an averaged offset of roughly 0.3 Bq m−3. The third laboratory participating in the measurement of standardized sample additions was systematically low by about 65–70%, which was also confirmed in their ambient air concentration measurements. The fourth laboratory, participating in only the ambient measurement part of the intercomparison, was also systematically low by at least 40% with respect to the first two aforementioned laboratories.