[You are receiving this message because your address came up in a specific literature search; it was not included in any mailing lists, and is used for a single advice. The information in this e-mail and in any attachments is confidential and intended solely for the attention and use of the named addressee(s). This information may be subject to legal, professional or other privilege and further distribution of it is strictly prohibited without our authority. If you are not the intended recipient, you are not authorised to and must not disclose, copy, distribute, or retain this message or any part of it, and should notify us immediately. This footnote also confirms that this email has been automatically scanned for the presence of computer viruses, profanities and certain file types].
Morphological and geochemical features of crater lakes in Costa Rica: an overview
Franco TASSI, Orlando VASELLI, Erik FERNANDEZ, Eliecer DUARTE, Maria MARTINEZ, Antonio DELGADO HUERTAS, Francesco BERGAMASCHI
This paper describes the compositional and morphological features of the crater lakes found in the volcanoes of Rincón de La Vieja, Poás, Irazú, Congo and Tenorio volcanoes (Costa Rica). As evidenced by the distribution of the water and dissolved gas chemistry along vertical profiles, the different fluid sources feeding the lakes reflect the present status of each of the volcanic systems. The chemical features of the Caliente (Poás volcano) and Rincón crater (Rincón de la Vieja volcano) lakes are mainly dependent on i) inputs of magmatic fluids from sub-lacustrine fumaroles and ii) water-rock interaction processes. Conversely, the Irazú lake is mainly affected by the presence of CO2(H2S)-rich fluids discharged from a hydrothermal system, which masked possible magmatic fluid contributions. Rainfall and organic activity are the main factors responsible for the chemical composition of Hule, Botos, Congo and Tenorio lakes. The chemical and isotopic water composition of Botos, Irazú and Hule lakes have displayed no significant variations along the vertical profiles. In contrast, Caliente lake shows a distinctive chemical stratification, mainly involving F-, Cl- and SO4 2-. The behaviour of these compounds seems to be governed by both dissolution of highly acidic species, i.e. HF, HCl and SO2 released from the magmatic environment, and microbial activity. Despite the significant increases with depth of dissolved CO2 at Caliente and Irazú lakes, the hazard for Nyos-type gas eruptions can be considered negligible, since i) the water volumes are too small and ii) the convective heat transfer limits the CO2 recharge rate. The relatively high concentrations of dissolved CO2 measured at the maximum depth of the Hule lake are likely produced by both degradation of organic material and degassing from a deep source. The sporadic episodes of fish deaths recently observed in this lake can be associated with lake overturn processes that have favoured the rise up to the lake surface of deep, oxygen-depleted waters.
lake stratification, limnic eruptions, hyperacidic lake