V41B-0592
Volcanic Plume Chemistry: Formation of BrO, ClO and OClO
Reactive halogen species BrO, ClO and OClO have recently been observed at significant concentrations in volcanic plumes in the lower troposphere. To understand their formation, a more detailed knowledge of plume composition and its evolution via physical and chemical processing in the atmosphere is required. A volcanic chemical plume model has been developed for this purpose. Results from model runs in 0-D and 2-D are presented and the formation of BrO, ClO and OClO discussed. Experiments show that the plume chemistry depends on both the chemical initialization and how the plume disperses into the background atmosphere. The model runs cover a range of chemical initializations including recent crater rim measurements and high- temperature model outputs. A set of plume-air mixing scenarios are then used to explore the effect of plume dilution on the chemistry. In addition, the plume heterogeneity and its effects are also considered. The results are combined to give an overview of how BrO, ClO and OClO can be formed in volcanic plumes, what controls their chemistry, and the implications for the atmosphere on regional scales.
V41B-0593
Bromine, chlorine and sulfur emission into the free troposphere from a Rift volcano
In June 2007 spectroscopic measurements were carried out at the crater rim of the Niyragongo volcano located 15 km north of the city Goma, North Kivu region (DRC). Niyragongo volcano belongs to the Virunga volcanic chain and it is associated with the Western branch of the Great Rift Valley. The volcanism at Niyragongo is caused by the rifting of the Earth's crust where two parts of the African plates are breaking apart. Niyragongo is a 3470 m high stratovolcano, which a large summit crater usually containing a lava lake inside and it is considered one of the most active volcanoes in Africa. Satellite measurements show an extremely large sulphur dioxide plume since May 2002, and it is considered one of the biggest sulphur dioxide sources on Earth. The ground - based remote sensing technique - MAX-DOAS (Multi Axis Differential Optical Absorption Spectroscopy) using scattered sunlight has been applied during a one week field trip on top of the crater rim of Niyragongo volcano to measure nitrogen oxide, halogen oxides and sulphur dioxide. The used Mini-MAX-DOAS is a lightweight, compact, robust instrument and has very low power consumption which allows to be deployed over several days with some small lead batteries. The measurements provide valuable information of the chemical composition as well its variability within the volcanic plume of the lava lake and allowed also studying chemical transformation processes of the halogens inside the plume. Bromine-sulphur and chlorine-sulphur ratios were investigated and a minimal bromine and chlorine emission flux estimation will be presented.
V41B-0594
Ice in volcanic clouds and the implications for halogen transport to the stratosphere
Observations of ice in volcanic clouds and new understanding of the role of ice in the fallout of fine ash has led to a view of volcanic clouds with abundant ice nuclei, a feature that contrasts with pure water "meteorological" clouds. Mixed phase meteorological clouds in the temperature range -10°C to -30°C contain few ice nuclei (IN). This is significant because the saturation vapor pressure of water is greater than the saturation vapor pressure of ice: the few ice crystals that form on scarce IN experience rapid growth, and can subsequently trigger the precipitation formation process (Bergeron process). Volcanic ash is a highly effective at initiating ice nucleation in the liquid phase at temperatures below about -20°C. Abundant ash ice nuclei lead to a cloud with high ice particle numbers and competition for water vapor in the cloud is high. Consequently, hydrometeor growth is slowed, particles remain small and precipitation is inhibited. Thus volcanic clouds are unlikely to experience early washout of Cl and other halide volcanic gases. Observations of complete ozone destruction in the 26 March 2000 Hekla volcanic cloud strongly support these assumptions. It may be possible to test this hypothesis more extensively by modifying the TOMS ozone algorithm to correct for SO2 effects.
V41B-0595
Halogen and sulphur chemistry in volcanic plumes
Bromine oxide has been measured in the plumes of several slowly erupting volcanoes. We compared field measurements from Mt. Etna, Italy with results from a one-dimensional model that was initialised with volcanic plume compositions according to a thermodynamic model. Assuming an "effective source region" where plume air is being mixed with ambient air at still high temperatures we were able to reproduce the measurements for BrO and SO2 very well (Bobrowski et al., 2007). The model resolves the vertical dilution of the plume and includes a parameterisation for the horizontal entrainment of background air as well as a detailed set of gas-phase and aqueous-phase reactions. We will show details of the chemical plume evolution trying to understand previously underestimated mixing ratios of chlorine oxides under cloud-free conditions and under situations where clouds form in the volcanic plume. Furthermore we will present results of the speciation of sulphur compounds in the volcanic plume, with a critical evaluation of the evolution with time of H2S and SO2.
V41B-0596
Halogens in Mount Etna volcanic gas plume: insights into degassing processes
The passive and eruptive plume gas emissions from Mount Etna volcano, in Southern Italy, represent a persistent source of volcanic halogenidric acids (HCl, HF, HBr and HI) to the Earth's atmosphere. Etna's halogen source strength has been repeatedly characterized over the past few years [Francis et al., 1998; Caltabiano et al., 2004; Aiuppa et al., 2005], and the pre-eruptive Cl and F contents in Etna's basalts have been well constrained by measurements on both silicate melt inclusions and matrix glasses [Metrich et al., 2004; Spilliaert et al ., 2006a]. However, the mechanisms driving halogen degassing upon magma ascent and decompression are not entirely understood, and the significance of volatile ratios SO2/HCl and SO2/HF in the volcanic gas plume still a matter of debate [Aiuppa et al., 2002, 2004; Spilliaert et al., 2006b]. Here, we review a set of halogen measurements carried out in the Mount Etna volcanic gas plume during 2003-2007, and demonstrate that a large compositional range (e.g., SO2/HCl ratios from 0.4 to 12; CO2/HCl ratios from 0.1 to 52) characterize the sustained quiescent emissions from the volcano. By contrasting the volcanic gas data against model equilibrium compositions calculated by the Moretti et al. [2003] saturation model, we also attempt at a quantitative interpretation of the degassing process at Etna. The saturation models calculates the composition of a gas phase (in the H2O-CO2- SO2-HCl-HF system) at equilibrium with Etna's magmas at given set of P-T-X conditions, and takes into account halogen saturation by making use of the most recent experimental determinations of Cl and F partitioning between coexisting fluid and basaltic melt [Alletti et al., 2006, 2007]. Based on model calculations, we propose that the observed SO2/HCl and SO2/HF plume ratios at Etna derive from low pressure (P less than 10 MPa) open-system degassing of magmas feeding the upper conduit system of the volcano.
V41B-0597
Halogen Oxide Measurements at Masaya Volcano, Nicaragua
Sulphur dioxide (SO2) and halogen oxide emissions were measured at Masaya Volcano in Nicaragua in April 2007 using differential optical absorption spectroscopy (DOAS). Next to passive DOAS measurements using scattered sunlight, an active long-path DOAS system was operated for several days with the light beam crossing the crater of the volcano. These measurements for the first time give an insight into the night-time halogen chemistry occurring at volcanoes. While the passive DOAS instruments measured sulphur dioxide (SO2) and bromine monoxide (BrO) in various viewing geometries and distances from the crater during daytime, the active instrument additionally allowed a quantification of chlorine monoxide (ClO) and chlorine dioxide (OClO), as well as being able to measure round-the-clock. The results of the field measurements will be presented and their implications for halogen chemistry at volcanoes will be discussed.
V41B-0598
Origin of fluids from oil/gas fields and hot springs in the Green Tuff region of Japan: 129I results from halogen-rich fluids in the Akita and Niigata Basins
The Green Tuff region in the Akita and Niigata Basins, Japan, hosts major occurrences of oil and gas as well as of mineral deposits. We measured halogen concentrations and 129I/I ratios in oil and gas field brines and hot springs in order to determine the origin of iodine and, indirectly, of hydrocarbons in this area and their association with geological processes during the opening of the Japan Sea. Based on the concentration of iodine, the samples fall into three categories: Group A (I >200μM), Group B (200μM>I >100μM), and Group C (I <100μM). Samples in Groups A and B come predominantly from oil/gas fields and have 129I/I ratios below 350×10-15, corresponding to ages essentially in the Eocene period. In contrast, samples in Group C are generally from hot springs and have 129I/I ratios mostly above 400×10-15, corresponding to Miocene ages. These results indicate that source formations for Group C are associated with the active opening of the Japan Sea, but that those for Groups A and B are organic-rich segments of the late Eocene to Oligocene formations or of the older basement rocks accreted before the opening of the Japan Sea. Because the reservoir formations of oil and gas reservoirs are predominantly of Middle to Late Miocene age, mobilization of these brines could have been associated with the tectonic processes during the opening of the Japan Sea which also led to the formation of the hydrothermal sulfide-sulfate Kuroko Deposits in the same area. The hot springs of Group C probably reflect more directly these processes. Because of the close association of iodine with methane and other hydrocarbons, oil and gas in this area probably is derived also from sources of Eocene age, i.e. considerably older than the Green Tuff formations they currently are residing in.
V41B-0599
Volcanic Degassing of Halogens and Trace Metals at Mt Etna, Sicily – A Melt Inclusion Investigation
The process of volcanic degassing has important implications for eruption style, environmental impact of volcanic aerosols and economic mineralization processes at depth. Mt Etna, Sicily is persistently degassing, and responsible for 5-10% of global annual volcanic emissions of CO2, SO2 and volatile trace metals. We collected a suite of olivine hosted melt inclusions and matrix glasses in newly erupted products from Mt Etna, Sicily, spanning the major eruptions of the previous 6 years. These glasses have been measured for the concentrations of volatile (H, C, Cl, F) and trace elements (Li, Zr) by ion microprobe at the University of Edinburgh and for major and trace elements with a particular focus on the volatile trace metals by electron microprobe and laser ablation ICP-MS at the University of Cambridge. Volatile and trace element concentrations in melt inclusions allow us to constrain the storage, gas accumulation and degassing processes at Mt Etna over the past 6 years. The 2004-2007 melts were residual from the 2001- 2003 and were stored at a shallow depth where they evolved and equilibrated with a CO2-rich, H2O- poor flux of gas from depth. Because the life cycle of these melts is now well understood we can use new data of halogen and trace metal compositions from these same melt inclusions to determine the effect the shallow degassing process has on the behaviour of such environmentally and economically important elements. Trace metals and the halide forming elements are enriched in the volcanic plume of Etna partly because of their volatile behaviour and also due to the formation of stable complexes with the hard ligands Cl, F and S. Removal of metals from the melt by the process of shallow degassing will deplete the residual melt in trace metals and remove these elements from the volcanic system preventing ore formation, while enhancing the concentrations in the volcanic plume. We investigate the extent at which this has occurred on Mt Etna over the past 6 years.
V41B-0600
Non-volatile vs Volatile Behaviours of Halogens During the 79 AD Plinian Eruption of Vesuvius, Italy
Mte Somma-Vesuvius is one of the best studied active volcanoes on Earth primarily because of the variety of eruptive style and the related risk assessment in a densely populated region (700 000 to 3 millions people including Napoli). Determination of the pre-eruptive conditions and degassing behaviour during eruption of volatile species is fundamental for establishing the dynamics of the different eruption types. F and Cl behaviours during the 79AD plinian eruption were investigated through a detailed electron microprobe study of melt inclusions and matrix glass of pumice clasts from a complete sequence of the pumice-fallout deposits. These results highlight two different pre-eruptive states of the erupted magmas during the plinian phase. The white pumice (WP) magma, first emitted, and the upper part of the grey pumice (GP) magma were saturated relative to subcritical fluids (a Cl-rich H2O vapour phase and a brine) which buffered the Cl melt content at ~ 5300 ppm. Conversely, the major part of the GP magmas was not H2O-saturated and thus the Cl melt content was only controlled by the magma differentiation degree. These results and Cl solubility data for K- phonolitic melts allow to estimate the WP magma chamber was at a depth of ~ 7.5km and had a low vertical extent (<500 m). The GP magma reservoir was located just below but its vertical extent cannot be constrained. H2O and halogen degassing paths of silicic H2O-rich magmas during explosive plinian may be modelled using the residual volatile content of the melt and the vesicularity of representative pumice clasts. During the plinian phase of the 79AD eruption H2O is efficiently degassed, following different degassing modes, contrary to F and Cl which remain trapped in the melts. These new data demonstrate that the 79AD magma reservoir was only partially saturated in H2O (and Cl) prior eruption and provide new insights into the F and Cl behaviours in phonolitic melts. In H2O undersaturated phonolitic melts, both F and Cl behave as incompatible and non volatile elements. In H2O- saturated conditions Cl significantly partitions into the fluid phase. However Cl low diffusivity in K20-rich phonolitic melts may limit its extraction during rapid H2O degassing as in plinian eruptions. Keywords: Vesuvius; 79AD eruption; plinian eruption; halogen behaviour; magma degassing; magma differentiation.
V41B-0601
Halogens behaviours in Magma Degassing: Insights into Eruptive Dynamics, Hydrothermal Systems and Atmospheric Impact of Andesitic Volcanism
Shallow degassing of H2O in andesitic magmas determines the eruptive styles of volcanic eruptions and contributes to the hydrothermal systems developed around active volcanoes. Halogens behaviour during magma degassing primarily depends on their incompatible behaviour in the melts and on water solubility. Thus, residual contents of halogens in volcanic juvenile vitric clasts may be used as tracers of H2O degassing processes during explosive and effusive eruptions. Because of the large range of water-melt partition coefficients of halogens and their relatively low diffusion coefficients, a comparison of F, Cl, Br and I contents in volcanic clasts in function of their vesicularity and micro-cristallinity allows to precisely model the main degassing processes and to establish constraints on pre-eruptive conditions. Halogens acids (HCl, HBr and HI) extracted in the vapour phase have much more complex behaviours because of their high solubility in low temperature thermal waters, their variable condensation temperatures and their very high reactivity when mixed with low temperature and oxidizing atmospheric gases. A comparison of model compositions of high temperature gases with the composition of thermal waters, and gases from fumaroles or plumes of active volcanoes allows to characterise the shallow volcanic system and its evolutionary states. Variable halogen behaviours are discussed for a variety of eruption types (plinian, vulcanian and dome-forming) and active volcanic systems from the Lesser Antilles (Montagne Pelee, Soufrière of Guadeloupe, Soufriere Hills of Montserrat).
V41B-0602
F and Cl Diffusion in Phonolitic Melts
Halogens discharged into the atmosphere from magma degassing are highly variable from one volcano to another. The impact of their degassing on Earth's climate and their health hazards will mainly depend on initial volatile contents, eruptive style and degassing kinetics. In this study, fluorine and chlorine diffusion were measured in two natural phonolitic melts, one from Vesuvius and the other from Laacher See, at 0.5 and 1.0 GPa, between 1250 and 1450 ° C at anhydrous conditions and with about 2 and 5wt% of dissolved water. The two different starting materials allow us to investigate the alkali effect, Na vs. K, on halogen diffusion. One composition was a K2O-rich (~10wt%) phonolitic melt corresponding to the white pumice phase of the 79AD eruption of Vesuvius, and the other a Na2O-rich (~10wt%) phonolitic melt corresponding to most differentiated melt of the Laacher See (12 000 BC). The diffusion-couple technique in a piston cylinder was used. Experiments were performed both with only one halogen diffusing and with a mixture of halogens (F, Cl) diffusing in order to evaluate the interactions between the halogens during diffusion. Diffusion coefficients for fluorine range between 4*10-11 m2/s at 1250 ° C and 8*10-11 m2/s at 1450 ° C for the Na-rich melt and between 1*10-11 m2/s at 1250 ° C and 8*10- 11 m2/s at 1450 ° C for the K-rich melt at anhydrous conditions. Diffusion coefficients for chlorine range between 2*10-12 m2/s at 1250 ° C and 1*10-11 m2/s at 1450 ° C for the Na-rich melt and between 9*10-11 m2/s at 1250 ° C C and 7*10-11 m2/s at 1450 ° C for the K-rich melt at anhydrous conditions. Fluorine diffusivity is typically higher than chlorine in the Na-rich phonolitic melt by one order of magnitude, whereas in the K-rich phonolitic melt fluorine and chlorine diffusivity are similar. At low temperature fluorine diffusion is more rapid in the Na-rich phonolitic melt; conversely chlorine diffuses faster in the K-rich phonolitic melt. Compared to the results obtained for fluorine and chlorine in a basaltic melt and in a rhyolitic melt, chlorine diffusivity is similar in both rhyolitic and phonolitic melts, and significantly lower than in basaltic melt, contrary to F diffusion coefficients which are comparable and only weakly dependent on the melt composition. F and Cl diffusion depend upon the dominant alkali and always differ from one another in the same phonolitic melt composition. These results will help us to better understand the degassing or the lack of degassing of theses species during syn-eruptive melt decompression and vesiculation. The contrasting volatile diffusivities in magmatic melts during magma vesiculation may be a key controlling factor of the composition of the vapour phase (bubbles) produced.
V41B-0603
The Origin and Significance of F-rich Amphibole Rims in 2005 Mount St. Helens Dacite and Similar Eruptions
The ongoing (2004-present) eruption of dacite magma at Mount St. Helens contains amphibole along with plagioclase, low-Ca pyroxene, Ti-magnetite and ilmenite phenocrysts in a variably crystallized groundmass. Amphibole phenocrysts in the later part of the eruption, where the mass eruption rate was relatively low (1 vs. 6 cubic meters/sec), have a rim up to 40 microns thick that increases from low F (900 ppm) to 9000 ppm at the outer margin. The increase in F is accompanied by an increase in Si and Fe, and decreases in Mg and Al. These observations suggest the reaction to form the F-rich amphibole is the result of recrystallization rather than halogen diffusion exchange with pre-existing amphibole. The F- and SiO2-rich character of the overgrowth suggests that it developed as the rising dacitic magma passed beyond the stability of OH-rich amphibole in the slow erupting phase of the MSH eruption. The ability of the interstitial melt to crystallize additional amphibole beyond that in the existing phenocrysts is compositionally limited by the lack of Ca-pyroxene phenocrysts in the magma and the interstitial melt composition. It is postulated that the overgrowths was generated by decreases in pressure and abrasion-induced fining of some amphibole phenocryst material in the solidifying magma during its ascent. This model is being tested by hydrothermal experiments using finely ground with lightly crushed MSH 2005 dacite with and without additions of F.
V41B-0604
Fluid/Melt Partition Coefficients Of Halogens In Basaltic Melt
Despite the importance of halogens (F, Cl) in volcanic degassing, solubility and fluid/melt partitioning of these elements have not been comprehensively studied in natural basaltic melts. Experimental determinations of halogen solubility in Mount Etna melts are lacking, despite this volcano being one of the most active and intensively monitored on Earth with an estimated output of thousands tonnes of halogens per day. In order to better understand halogen degassing, we present the results of a series of halogen partitioning experiments performed at different pressures (1-200 MPa), redox conditions (from Δ NNO = + 2 to Δ NNO = – 0.3) and fluid compositions. Experiments used a hawaiitic, glassy, alkaline basalt with Mg# = 0.59, sampled during the July 2001 eruption of Mount Etna. A series of experiments were conducted using H2O-NaCl or H2O-NaF solutions. The effect of CO2 in multi-component fluid H2O-CO2-NaCl or H2O-CO2-NaF was also investigated. The experimental run products were mostly glasses, but a few run products contained less than 10% crystals. The concentration of halogens in the fluid phase after the experiment was calculated from mass balance, and the partition coefficients for both Cl and F at the studied conditions determined. Using these measurements and thermodynamical models, the dependence of these partition coefficients on the fugacities of various gaseous species was investigated.
V41B-0605
ANOMALOUS EMISSIONS OF SULFUR DIOXIDE AND SEISMICITY OF SAN MIGUEL VOLCANO, EL SALVADOR IN OCTOBER, 2006
San Miguel (also known as Chaparrastique) volcano in eastern El Salvador is located 15 km southwest of the city of San Miguel. This volcano has erupted more than 30 times since 1699, with the last gas and ash emission on January 16, 2002. During 2006, San Miguel presented anomalous gas emissions and seismicity. In this work, the seismic parameters reported by SNET (Servicio Nacional de Estudios Territoriales de El Salvador) and the crater gas emissions measured by researchers of the University of El Salvador are compared. For the gas efflux, two types of measurements were done using the Mini-DOAS system (Galle et al., 2002): transects around the crater perimeter (~100 m) and transects following roads located between 5 and 10 km from the crater. Several measurements between October 2005 and May 2006 indicate that the sulfur dioxide efflux during quiet periods is around 20 ton/day. From May to June 2006, a progressive increase in fumarolic activity and noise from gas emissions were observed. From May to August 2006, the sulfur dioxide emissions increased to 60 ton/day. A seismic crisis started on October 9, 2006, increasing the RSAM from 10-20 to 208 on October 10, 2006. During this time, the sulfur dioxide efflux reached a maximum of 492 ton/day. This increase in sulfur dioxide efflux represents 25 times the basic emissions during the previous quiet period and 8 times the values observed from May to August 2006. The correlation coefficient between sulfur dioxide efflux and RSAM values during this period of time was 0.81, which is statistically significant at a level higher than 99.9% . These anomalous changes in seismicity and sulfur dioxide emissions at San Miguel volcano suggest a magmatic reactivation with an increase in the exsolution of magma volatiles, long period seismic events, and volcanic tremor.
V41B-0606
Sulfur Dioxide Emissions from Bezymianny Volcano, Kamchatka: Results from the 2007 Field Season
Bezymianny volcano, Kamchakta, Russia, is one of the most active volcanoes in the Aleutian-Kamchatka-Kurile volcanic zone and has had over 48 explosive eruptions since it's paroxysmal eruption in 1956. In August 2007, volcanic sulfur dioxide (SO2) emissions were measured at Bezymianny using a FLYSPEC ultraviolet spectrometer system. Measurements were systematically collected on eleven days using both stationary scanning and aerial traverse modes. Flux rates (tonnes per day) of SO2 were calculated using measured column densities, wind speeds, and plume widths. These are the first ground and air based measurements collected from Bezymianny in over two decades. These data, as well as data collected in subsequent field seasons, will be used to generate a baseline emission dataset for the volcano to allow changes in activity to be detected. Secondary objectives of this project include validating remotely sensed data from satellite sensors including the Ozone Monitoring Instrument (OMI), the Moderate Resolution Imaging Spectroradiometer (MODIS) and the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER). Preliminary results from the 2007 field season and future work will be presented in this poster. http://www.gps.alaska.edu/PIRE
V41B-0607
UV Scanner DOAS Data Retrieved Using A Modelled Reference Spectrum
The difficulty of applying a real-time measured reference spectrum represents the main issue while using automatic Differential Optical Absorption Spectroscopy (DOAS) UV-Scanner networks for monitoring active volcanoes. Here we present the performance of a DOAS retrieval using a modelled reference spectrum derived from a high- resolution solar spectrum. Data analyzed were collected by the five UV scanners installed on Mt. Etna using three calibration cells (LC: low cell 3.2 e17; MC: middle cell 8.46 e17; and HC: high cell 9.98 e17 molecules/cm2) in order to collect calibrated clear-sky spectra (CCSS). We evaluated the errors affecting the CCSS retrievals examining the effects of seasonal variations, time of the day, changes of the telescope-viewing angle, and the modelled and real-measured instrumental line-shape function (ILS). For these purposes, between July 2006 and July 2007, 51 CCSS were recorded in different times of the day and different weather conditions using the LC and the MC, whereas the error associated with the variations of the telescope-viewing angle was evaluated on data collected in May 2007 using the LC and HC. This was estimated as the mean of each of 100 CCSS collected for every scanning angle. The modelled ILS function resolution was found empirically, while the real was measured experimentally using a mercury lamp. The absolute difference retrieved for the CCSS recorded in 12 months respect the true amounts of the calibration cells varied between ~ 1.15 e15 – 8.39 e16 molecules/cm2 for the LC and ~ 2.78 e15 – 1.75 e17 molecules/cm2 for the MC. These results revealed that the modelled reference spectrum did not affect significantly the DOAS performance. This was consistent with the absolute differences estimated for each scanning-angle variations (~ 1.15 e15 – 8.39 e16 molecules/cm2 for the LC and ~ 1.44 e15 – 2.52 e17 molecules/cm2 for the HC) respect to the true amounts. These results prove that UV-Scanner DOAS networks can work efficiently using a modelled reference spectrum. Additionally, they highlight that the modelled ILS could be a source of errors, since it could be not representative of the real ILS of the spectrometer. Errors are mostly dependent on the signal to noise ratio of the spectra and therefore can vary as a factor of the time of the day and viewing angle.
V41B-0608
BrO/SO2 studies at Mt. Etna during 2006 and 2007
In 2006 and 2007 during a series of different volcanic activities of Mt. Etna, including Lava flows strombolian explosions, Lava fountains, field studies, focusing on halogen oxides and sulphur dioxide emissions, were taking place with a scanning- as well as with a mobile-DOAS instrument. The Differential Optical Absorption Spectroscopy (DOAS) is an optical remote sensing technique and can simultaneously measure several trace gases. A BrO/SO2 time series from a fixed distance at 6 km from the emission source and gas emissions close to the different main craters and above lava flows were studied with the scanning DOAS instrument. In the same time period sulphur dioxide flux measurements were frequently carried out with a mobile-DOAS instrument at Mt. Etna during different states of volcanic activity. The SO2 fluxes varied between 194 t/d and 8800 t/d. The BrO/SO2 ratio showed peak three moth before the eruption started and the changes were not directly correlated to the changes in SO2 fluxes and therefore could provide additional information of the volcanic system. The BrO/SO2 ratio, a minimal bromine flux itself, which was calculated by using simultaneously measured SO2 fluxes, are presented in the context of the changing activity during the Mt. Etna 2006 eruption and the year 2007.
V41B-0609
Fluorine in Olivines from Plutonic, Extrusive, and Hypabyssal Suites
Fluorine contents in a wide range of naturally-occurring olivine grains were determined by secondary ion mass spectrometry (SIMS) using a Cs+ primary beam, detection of negative secondary ions and an auxiliary electron gun for charge neutralization. A range of minerals and glasses containing 3 to 1300 ppm F were used to calibrate the secondary ion signal. Matrix effects appear to be small, and because fluorine has a high electron affinity, sensitivity is high (sub-ppm). Olivines from the study by Simkin and Smith (J. Geol., 1970) were analyzed for their F contents and span a range of suites that include upper mantle xenoliths and kimberlites, plutonic intrusives, ophiolites, shallow hypabyssal picrites and teschenites, and extrusive alkaline and tholeiitic basalts. Overall, the olivines in this study show a range of F concentrations from 0.5 to 32 ppm. Olivines from high- pressure environments show the highest individual and average F values, however large variations are also observed in this suite. Mantle xenoliths from this sample collection show a maximum and average F value of 14 and 4.1 ppm, respectively, and one olivine from kimberlite contains 32 ppm F. Earlier analyses from our laboratory (Hervig and Bell, 2005 Fall AGU) show a larger range in F from mantle-derived olivines. Plutonic intrusives and ophiolites, including layered intrusives and cumulates, show a range of F contents from 0.5 to 15 ppm, with an average value of 4 ppm. Olivines from the Kiglapait layered intrusion, Labrador show F content increasing with degree of fractional crystallization until the P2O5 content of the rock begins to increase. At this point, F in olivine decreases, presumably indicating partitioning of F into apatite. In the Hawaiian suites studied, F in olivine was high (8-12 ppm) in evolved andesites and lower (1-8 ppm) in more primitive basalts. Hypabyssal suites include a peridotite dike from Skye, (F < 1 ppm), a chilled olivine dolerite from Bornaskitaig (F = 2 ppm), a picrite from Igdlorsuit, Greenland (F = 4 ppm), and a teschenite from Black Jack Sill, Australia (F = 1.5 ppm). Fluorine measurements on the Simkin and Smith olivines are consistent with earlier observations that F is highest in OH-rich olivines (i.e., upper mantle xenoliths in kimberlites; Hervig & Bell, AGU Fall Mtg 2005).
V41B-0610
Chlorine Isotope Ratios of Volcanic Glasses from Arc, Back-Arc and Mid-Ocean Ridges Settings - First Results of an Ion Microprobe Study
It has recently been demonstrated that chlorine isotopes ratios have a limited range in δ37Cl (~ -2 to +0.5‰) in Earth's crustal and mantle rocks which implies little or no isotopic fractionation by the solid- rock geochemical cycle during the differentiation of Earth (Sharp et al. Nature 2007; Bonifacie et al. Chem Geol 2007; Barnes et al. 2007 Goldschmidt). Here we report preliminary results of a study of Cl isotope by secondary ion mass spectrometry (SIMS) of volcanic glasses from arc, back-arc and mid-ocean ridge settings that conform to these results. The samples investigated comprise 7 samples of basaltic to rhyolitic glass shards and melt inclusions from the Izu Bonin volcanic front that comprise the last 13 million years of arc history. In addition, four basaltic and basaltic andesitic glasses from the Shikoku and Mariana backarc basins, and three basalts from mid ocean ridges (Juan de Fuca Ridge, East Pacific Rise) were analyzed with an Cameca IMS 1280 at WHOI during two sessions in August 2006 and May 2007, respectively. After correction for matrix-related and session-dependent instrumental mass fractionation, the samples investigated fall within an overall range of 3‰ in δ37Cl at an error of ±1.5‰ per sample (one standard deviation). Sample averages from the two sessions are comparable within 0.5‰ absolute. Within this error, the δ37Cl values of arc, backarc and MORB glasses are indistinguishable. Assuming that the MORB samples analyzed are within the range of δ37Cl of MORB determined by gas source isotope ratio mass spectrometry (IRMS; Sharp et al. Nature 2007; Bonifacie et al. Chem Geol 2007), the range of the glasses investigated completely overlaps with the range of the recently published high-precision data of MORB and arc volcanic rocks. While these first results agree with studies of bulk analyses, it is obvious that the large error associated with the SIMS method (~ ±1-1.5‰ versus ~ ± 0.12-0.26‰ obtained by IRMS) does not allow for using the δ37Cl obtained by SIMS as geochemical tracer within a single tectonic setting. However, from the data thus far collected, there appears to be potential for further reducing the systematic error and thus to improve the potential of the SIMS method as geoanalytical tool.
V41B-0611
Silicate Particles in the Mt Etna and Masaya Plumes
We present an overview of our work concerning the emission of fine silicate particles from active volcanoes. Size distributions of particles collected from the plumes of Mt Etna and Masaya were measured using automated scanning electron microscopy (QemSCAN). These size distributions were found to be lognormal and centred around 1 micron. These results were used to estimate emission fluxes of ~60 kg/day from Masaya and ~7000 kg/day from Mt Etna. These silicate particles are expected to have extended atmospheric lifetimes due to their small size and relative unreactivity. Fine silicate particles in ice-cores may therefore prove useful indicators of the extent of persistently active volcanism over time.