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LondoƱo, John Makario
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- PublicationRestrictedThe hydrothermal system of Cerro MachĆn volcano (Colombia): New magmatic signals observed during 2011ā2013(2017)
; ; ; ; ; ; ; ; ;; ;Cerro MachĆn volcano in Colombia recently (2009ā2013) exhibited new seismic activity. A geochemical characterization of emitted fluids was carried out based on the chemical and isotopic compositions of fumaroles and thermal springs discharged in this volcanic area with the aim of improving the volcano monitoring program. The isotopic composition of fumaroles located in the upper part of the dome was characterized by depleted Ī“D and Ī“18O relative to the meteoric recharge fluids, which is due to a separation of the liquid phase in the lower part of the dome. A clear magmatic He signature was found in the fumaroles, with an increased magmatic contribution observed in the discharged fluids during 2011ā2013 corroborating the increase in recorded seismic activity. Coupling the geochemical and seismic information has highlighted a clear awakening of Cerro MachĆn volcanic activity, indicating that this volcano is still active deserve an improvement of volcanic monitoring activity by the scientific community.169 6 - PublicationOpen AccessVapour discharges on Nevado del Ruiz during the recent activity: Clues on the composition of the deep hydrothermal system and its effects on thermal springs(2017-04-08)
; ; ; ; ; ; ; ; ; ; ; The Nevado del Ruiz volcano is considered one of the most active volcanoes in Colombia, which can potentially threaten approximately 600,000 inhabitants. The existence of a glacier and several streams channelling in some main rivers, flowing downslope, increases the risk for the population living on the flank of the volcano in case of unrest, because of the generation of lahars and mudflows. Indeed, during the November 1985 subplinian eruption, a lahar generated by the sudden melting of the glacier killed twenty thousand people in the town of Armero. Moreover, the involvement of the local hydrothermal system has produced in the past phreatic and phreatomagmatic activity, as occurred in 1989. Therefore, the physico-chemical conditions of the hydrothermal system as well as its contribution to the shallow thermal groundwater and freshwater in terms of enthalpy and chemicals require a close monitoring. The phase of unrest occurred since 2010 and culminated with an eruption in 2012, after several years of relative stability, stillmaintains amoderate alert, as required by the high seismicity and SO2 degassing. In October 2013, a sampling campaign has been performed on thermal springs and stream water, located at 2600ā5000 m of elevation on the slope of Nevado del Ruiz, analyzed for water chemistry and stable isotopes. Some of these waters are typically steam-heated (low pH and high sulfate content) by the vapour probably separating from a zoned hydrothermal system. By applying a model of steam-heating, based on mass and enthalpy balances, we have estimated themass rate of hydrothermal steam discharging in the different springs. The composition of the hottest thermal spring (Botero Londono) is probably representative of a marginal part of the hydrothermal system, having a temperature of 250 Ā°C and low salinity (Cl ~1500 mg/l), which suggest, along with the retrieved isotope composition, a chiefly meteoric origin. The vapour discharged at the steam vent āNereidasā (3600 m asl) is hypothesized to be separated from a high temperature hydrothermal system. Based on its composition and on literature data on fluid inclusions, we have retrieved the P-T-X conditions of the deep hydrothermal system, aswell as its pH and fO2. The vapour feeding Nereidas would separate from a biphasic hydrothermal system characterized by the following parameters: t= 315 Ā°C, P= 15 MPa, NaCl = 10 wt%, CO2=5 wt%, and similar proportion between liquid and vapour. Considering also the equilibria involving S-bearing gases and HCl, pH would approach the value of 1.5 while fO2 would correspond to the FeO-Fe2O3 buffer. Chlorine content is estimated at 10,300mg/l. Changes in the magmatic input into the hydrothermal system couldmodify its degree of vapourization and/or P-T-X conditions, thus inducing corresponding variations in vapour discharges and thermal waters. These findings, paralleled by contemporary measurements of water flow rates, could give significant clues on risk evaluation.227 47 - PublicationRestrictedGeochemistry of REE, Zr and Hf in a wide range of pH and water composition: The Nevado del Ruiz volcano-hydrothermal system (Colombia)(2015-12-06)
; ; ; ; ; ; ; ; ;Inguaggiato, C.; UniversitĆ di Palermo ;Censi, P.; UniversitĆ di Palermo ;Zuddas, P.; Universites Sorbonne, Paris, France ;LondoƱo, J. M.; Servicio Geologico Colombiano, Manizales, Colombia ;ChacĆ³n, Z.; Servicio Geologico Colombiano, Manizales, Colombia ;Alzate, D.; Servicio Geologico Colombiano, Manizales, Colombia ;Brusca, L.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia ;D'Alessandro, W.; Istituto Nazionale di Geofisica e Vulcanologia, Sezione Palermo, Palermo, Italia; ; ; ; ; ; ; The geochemical behaviour of Rare Earth Elements, Zr and Hf was investigated in the thermal waters of Nevado del Ruiz volcano system. A wide range of pH, between 1.0 and 8.8, characterizes these fluids. The acidic waters are sulphate dominatedwith different Cl/SO4 ratios. The important role of the pH and the ionic complexes for the distribution of REE, Zr and Hf in the aqueous phase was evidenced. The pH rules the precipitation of authigenic Fe and Al oxyhydroxides producing changes in REE, Zr, Hf amounts and strong anomalies of Cerium. The precipitation of alunite and jarosite removes LREE from the solution, changing the REE distribution in acidic waters. YāHo and ZrāHf (twin pairs) have a different behaviour in strong acidic waterswith respect to the water with pH near-neutral. Yttrium and Ho behave as Zr and Hf in waters with pH near neutral-to-neutral, showing superchondritic ratios. The twin pairs showed to be sensitive to the co-precipitation and/or adsorption onto the surface of authigenic particulate (Fe-, Al-oxyhydroxides), suggesting an enhanced scavenging of Ho and Hf with respect to Y and Zr, leading to superchondritic values. In acidic waters, a different behaviour of twin pairs occurs with chondritic Y/Ho ratios and sub-chondritic Zr/Hf ratios. For the first time, Zr and Hf were investigated in natural acidic fluids to understand the behaviour of these elements in extreme acidic conditions and different major anion chemistry. Zr/Hf molar ratio changes from 4.75 to 49.29 in water with pH b 3.6. In strong acidic waters the fractionation of Zr and Hf was recognized as function of major anion contents (Cl and SO4), suggesting the formation of complexes leading to sub-chondritic Zr/Hf molar ratios.376 86