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Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement.
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- PublicationRestrictedMeasuring volcanic degassing of SO2 in the lower troposphere with ASTER band ratios(2010)
; ; ; ; ; ; ; ; ; ; ;Campion, R.; Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement. ;Salerno, G. G.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Coheur, P. F.; Université Libre de Bruxelles, Chimie Quantique et Photophysique, ;Hurtmans, D.; Université Libre de Bruxelles, Chimie Quantique et Photophysique ;Clarisse, L.; Université Libre de Bruxelles, Chimie Quantique et Photophysique ;Kazahaya, K.; Geological Survey of Japan, Institute of Advanced Science and Technology, ;Burton, M.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Pisa, Pisa, Italia ;Caltabiano, T.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Catania, Catania, Italia ;Clerbaux, C.; Université Libre de Bruxelles, Chimie Quantique et Photophysique, ;Bernard, A.; Université Libre de Bruxelles, Département des Sciences de la Terre et de l'Environnement.; ; ; ; ; ; ; ; ; We present a new method for measuring SO2 with the data from the ASTER (Advanced Spaceborne Thermal Emission and Reflectance radiometer) orbital sensor. The method consists of adjusting the SO2 column amount until the ratios of radiance simulated on several ASTER bands match the observations. We present a sensitivity analysis for this method, and two case studies. The sensitivity analysis shows that the selected band ratios depend much less on atmospheric humidity, sulfate aerosols, surface altitude and emissivity than the raw radiances. Measurements with b25% relative precision are achieved, but only when the thermal contrast between the plume and the underlying surface is higher than 10 K. For the case studies we focused on Miyakejima and Etna, two volcanoes where SO2 is measured regularly by COSPEC or scanning DOAS. The SO2 fluxes computed from a series of ten images of Miyakejima over the period 2000–2002 is in agreement with the long term trend of measurement for this volcano. On Etna, we compared SO2 column amounts measured by ASTER with those acquired simultaneously by ground-based automated scanning DOAS. The column amounts compare quite well, providing a more rigorous validation of the method. The SO2 maps retrieved with ASTER can provide quantitative insights into the 2D structure of non-eruptive volcanic plumes, their dispersion and their progressive depletion in SO2.185 28 - PublicationRestrictedVolcano-hydrothermal system and activity of Sirung volcano (Pantar Island, Indonesia)Sirung is a frequently active volcano located in the remote parts of Western Timor (Indonesia). Sirung has a crater with several hydrothermal features including a crater lake. We present a timeseries of satellite images of the lake and chemical and isotope data from the hyperacid hydrothermal system. The fluids sampled in the crater present the typical features of hyperacidic systems with high TDS, low pH and d34SHSO4 –d34SS0 among the highest for such lakes. The cations concentrations are predominantly controlled by the precipitation of alunite, jarosite, silica phases, native sulfur and pyrite which dominate the shallow portions of the hydrothermal system. These minerals may control shallow sealing processes thought to trigger phreatic eruptions elsewhere. Sparse Mg/Cl and SO4/Cl ratios and lake parameters derived from satellite images suggest gradual increase in heat and gas flux, most likely SO2-rich, prior to the 2012 phreatic eruption. An acidic river was sampled 8 km far from the crater and is genetically linked with the fluids rising toward the active crater. This river would therefore be a relevant target for future remote monitoring purposes. Finally, several wells and springs largely exceeded the World Health Organization toxicity limits in total arsenic and fluoride.
161 4 - PublicationRestrictedChemical evolution of thermal waters and changes in the hydrothermal system of Papandayan volcano (West Java, Indonesia) after the November 2002 eruption(2008-06-27)
; ; ; ; ; ;Mazot, A.; Department of Earth and Environmental Sciences, CP 160/02, Université Libre de Bruxelles, 50 Ave. Roosevelt, 1050 Brussels, Belgium ;Bernard, A.; Department of Earth and Environmental Sciences, CP 160/02, Université Libre de Bruxelles, 50 Ave. Roosevelt, 1050 Brussels, Belgium ;Fischer, T.; Department of Earth and Planetary Sciences, University of New Mexico, Albuquerque, NM 87131-0001, USA ;Inguaggiato, S.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;Sutawidjaja, I. S.; Directorate of Volcanology and Geological Hazard Mitigation, Jalan Diponegoro 57, Bandung 40122, Indonesia; ; ; ; Papandayan is a stratovolcano situated in West Java, Indonesia. Since the last magmatic eruption in 1772,only few hydrothermal explosions have occurred. An explosive eruption occurred in November 2002 and ejected ash and altered rocks. The altered rocks show that an advanced argillic alteration took place in the hydrothermal system by interaction between acid fluids and rocks. Four zones of alteration have been defined and are limited in extension and shape along faults or across permeable structures at different levels beneath the active crater of the volcano. At the present time, the activity is centered in the northeast crater with discharge of low temperature fumaroles and acid hot springs. Two types of acid fluids are emitted in the crater of Papandayan volcano: (1) acid sulfate-chloride waters with pH between 1.6 and 4.6 and (2) acid sulfate waters with pH between 1.2 and 2.5. The water samples collected after the eruption on January 2003 reveal an increase in the SO4/Cl and Mg/Cl ratios. This evolution is likely explained by an increase in the neutralization of acid fluids and tends to show that water–rock interactions were more significant after the eruption. The evolution in the chemistry observed since 2003 is the consequence of the opening of new fractures at depth where unaltered (or less altered) volcanic rocks were in contact with the ascending acid waters. The high δ34S values (9–17‰) observed in acid sulfatechloride waters before the November 2002 eruption suggest that a significant fraction of dissolved sulfates was formed by the disproportionation of magmatic SO2. On the other hand, the low δ34S (−0.3–7‰) observed in hot spring waters sampled after the eruption suggest that the hydrothermal contribution (i.e. the surficial oxidation of hydrogen sulfide) has increased.242 25 - PublicationRestrictedStratification at the Earth's largest hyperacidic lake and its consequencesVolcanic lakes provide windows into the interior of volcanoes as they integrate the heat flux discharged by a magma body and condense volcanic gases. Volcanic lake temperatures and geochemical compositions therefore typically serve as warnings for resumed unrest or prior to eruptions. If acidic and hot, these lakes are usually considered to be too convective to allow any stratification within their waters. Kawah Ijen volcano, featuring the largest hyperacidic lake on Earth (volume of 27 millionm3), is less homogeneous than previously thought. Hourly temperature measurements reveal the development of a stagnant layer of cold waters (<30◦C), overlying warmer and denser water (generally above 30◦C and density ∼1.083 kg/m3). Examination of 20yrs of historical records and temporary measurements show a systematic thermal stratification during rainy seasons. The yearly rupture of stratification at the end of the rainy season causes a sudden release of dissolved gases below the cold water layer which appears to generate a lake overturn, i.e. limnic eruption, and a resonance of the lake, i.e. a seiche, highlighting a new hazard for these extreme reservoirs. A minor non-volcanic event, such as a heavy rainfall or an earthquake, may act as a trigger. The density driven overturn requires specific salinity-temperature conditions for the colder and less saline top water layer to sink into the hot saline water. Spectacular degassing occurs when the dissolved gases, progressively stored during the rainy season due to a weakened diffusion of carbon dioxide in the top layer, are suddenly released. These findings challenge the homogenization assumption at acidic lakes and stress the need to develop appropriate monitoring setups.
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