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Ramírez-Umaña, Carlos
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Ramírez-Umaña, Carlos
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- PublicationOpen AccessFluid-mineral dynamics at the Rincón de la Vieja volcano—hydrothermal system (Costa Rica) inferred by the study of major, minor and rare earth elements in the hyperacid crater lake(2023-10)
; ; ; ; ; ; ; ; ; ; ; ; ;; ; ; ; ; ; ; ; ; ;Volcanic lakes are complex natural systems and their chemical composition is related to a myriad of processes. The chemical composition of major, minor, Rare Earth Elements (REE) and physico-chemical parameters at the hyperacid crater lake of Rincón de la Vieja volcano (Costa Rica) are here investigated during February 2013–August 2014. The study of the lake chemical composition allows to identify the main geochemical processes occurring in the lake and to track the changes in the volcanic activity, both important for active volcanoes monitoring. The total REE concentration ( REE) dissolved in the crater lake varies from 2.7 to 3.6 mg kg−1 during the period of observation. REE in the water lake samples normalized to the average volcanic local rock (REEN-local rock) are depleted in light REE (LREE). On the contrary REEN-local rock in the solids precipitated (mainly gypsum/anhydrite), from lake water samples in laboratory at 22°C, are enriched in LREE. The low variability of (La/Pr)N-local rock and (LREE/ HREE)N-local rock ratios (0.92–1.07 and 0.66–0.81, respectively) in crater lake waters is consistent with the low phreatic activity (less than 10 phreatic eruptions in 2 years) observed during the period of observation. This period of low activity precedes the unrest started in 2015, thus, it could be considered as a pre-unrest, characterized by infrequent phreatic eruptions. No clear changes in the REE chemistry are associated with the phreatic eruption occurred at mid- 2013. The results obtained investigating water-rock interaction processes at theRincón de la Vieja crater lake show that rock dissolution and mineral precipitation/ dissolution are the main processes that control the variability of cations composition over time. In particular, precipitation and dissolution of gypsum and alunite are responsible for the variations of REE in the waters. Despite the low variations of (La/Pr)N-local rock and (LREE/HREE)N-local rock ratios, this study allows to suggest that REE can be used, together with major elements, as practical tracers of water-rock interaction processes and mineral precipitation/ dissolution at active hyperacid crater lakes over time, also during periods of quiescence and low phreatic activity.70 10 - PublicationRestricted39 Years of Geochemical Monitoring of Laguna Caliente Crater Lake, Poás: Patterns from the Past as Keys for the Future(2019)
; ; ; ; ; ; ; ; ; ; ; ; ; Since 1978 water chemistry of the Laguna Caliente crater lake has been used to monitor volcanic activity at Poás, Costa Rica, making it arguably the best studied hyper-acidic crater lake on Earth. During these 39 years, three of water of Laguna Caliente, independent on previous deterministic research and resulting conceptual models. Common patterns of chemical parameters in relation with phreatic eruptive activity for the period 1978–Septem- ber 2014 are sought, applying the objective statistical method of Pattern Recognition. This resulted in the definition of the strongest precursory signals and their respective thresh- olds. Numerical outcomes often confirm find- ings based on geochemical models (e.g. SO4, SO4/Cl and pH are strong monitoring param- eters). However, some surprising parameters (opposite behavior of Mg/Cl ratios, decreases in Ca and Mg concentrations, increasing Al/Mg ratios) still need a geochemical expla- nation and should be a focus for future research strategies. The obtained parameters and thresholds were retrospectively applied for the “test period” of the Pattern Recognition method (November 2014–February 2016). This test provided hints that suggested that eruptive activity at Poás was not yet over, despite apparent quiescence in early 2016. Indeed, after new phreatic eruptions since May 2016, the 2006–2016 phreatic eruptive cycle culminated in phreatomagmatic activity in April 2017. We conclude that evaluating time series of chemical composition of crater lakes framed in the Pattern Recognition method can be a useful monitoring approach. Moreover, increased sampling frequency can provide more details and more adequate phases of unrest occurred, manifested through frequent phreatic eruptions, with each a dura- tion of several years to over a decade (1978– 1980, 1986–1996, 2006–2016). We here present a novel technique to deal with the long time series of the chemical composition93 - PublicationOpen AccessRare Earth Elements Variations in a Hyperacid Crater Lake and Their Relations With Changes in Phreatic Activity, Physico-Chemical Parameters, and Chemical Composition: The Case of Poás Volcano (Costa Rica)(2022-01-03)
; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; ; Decades of geochemical monitoring at active crater lakes worldwide have confirmed that variations in major elements and physico-chemical parameters are useful to detect changes in volcanic activity. However, it is still arduous to identify precursors of single phreatic eruptions. During the unrest phase of 2009–2016, at least 679 phreatic eruptions occurred at the hyperacid and hypersaline crater lake Laguna Caliente of Poás volcano (Costa Rica). In this study, we investigate the temporal variations of Rare Earth Elements (REE) dissolved in Laguna Caliente in order to 1) scrutinize if they can be used as a new geochemical tool to monitor changes of phreatic activity at hyperacid crater lakes and 2) identify the geochemical processes responsible for the variations of REE concentrations in the lake. The total concentration of REE varies from 950 to 2,773 μg kg−1. (La/Pr)N-local rock ratios range from 0.93 to 1.35, and Light REE over Heavy REE (LREE/HREE)N-local rock ratios vary from 0.71 to 0.95. These same parameters vary in relation to significant changes in phreatic activity; in particular, the (La/Pr)N-local rock ratio increases as phreatic activity increases, while that of (LREE/HREE)N-local rock decreases when phreatic activity increases. REE concentrations and their ratios were compared with the variations of major elements and physico-chemical parameters of the lake. Calcium versus (La/Pr)N-local rock and versus (LREE/HREE)N-local rock ratios show different trends compared to the other major elements (Na, K, Mg, Al, Fe, SO4, and Cl). Moreover, a higher loss of Ca (up to 2,835 ppm) in lake water was found with respect to the loss of Al, K, and Na. This loss of Ca is argued to be due to gypsum precipitation, a process corroborated by the mass balance calculation simulating the precipitation of gypsum and the contemporaneous removal of REE from the lake water. The observed relations between REE, changes in phreatic activity, and the parameters commonly used for the monitoring of hyperacid volcanic lakes encourage investigating more on the temporal and cause-effect relationship between REE dynamics and changes in phreatic activity at crater lake-bearing volcanoes.560 44