Water and dissolved gas geochemistry at Coatepeque, Ilopango and Chanmico volcanic lakes (El Salvador, Central America)

Abstract

Coatepeque (on the E slope of Santa Ana Volcano), Ilopango (inside Ilopango Caldera) and Chanmico (associated with San Salvador Volcano) are volcanic lakes in El Salvador, showing a thermocline at a relatively shallow depth (from 30 to 40 m, from 20 to 40 m and from 5 to 15 m depth, respectively) and anoxic conditions below 33, 24 and 4 m depth, respectively. The Na +-Cl − composition of the Coatepeque and Ilopango lakes, displaying TDS values up to 1226 and 1216 mg/L, respectively, is likely due to hydrothermal fluids that feed these two lakes, as also confirmed by Cl − /Br − molar ratios ≤ 650, high As, B, Li and Si contents and Cl − /SO 4 2− ratio N 1. The Mg 2 +-HCO 3 − water composition of Lake Chanmico, whose TDS values were between 566 and 856 mg/L, suggests water-rock interaction processes with mafic/ultramafic rocks variably affected by serpentinization processes, which produced high Mg 2+ , Si and B concentrations. Waters at depth were characterized by the presence of CO 2 from an extra-lacustrine source, as suggested by δ 13 C-CO 2 values significantly less negative than those typically related to biogenic processes, albeit this gas was found in smaller quantities when compared to those recorded in other meromictic lakes hosted in quiescent volcanic systems (e.g. Lake Kivu in DRC, Monticchio, Albano and Averno lakes in Italy, Hule and Rio Cuarto lakes in Costa Rica, Lake Pavin in France). The occurrence of CH 4 , whose concentrations in Lake Chanmico were up to two orders of magnitude higher than those recorded in Coatepeque and Ilopango lakes, suggests bacterial methanogenesis.

Volcanic Lakes in Africa: The VOLADA_Africa 2.0 Database, and Implications for Volcanic Hazard

“…The irregular shape of the 3 km-wide collapse caldera and its crater lake is in agreement with the presumed young age of the crater and the latest magmatic eruption (<1 ka; Fontijn et al, 2010). A pioneering study on the water chemistry of Lake Ngozi (Delalande-Le Mouëllic et al, 2015) hypothesizes that the lake is affected by geothermal input (Na-Cl-rich, Mg-poor) and hydrothermal activity (pH 6.4-6.9, SO 4 -rich steam heated waters), similar to the caldera lakes in El Salvador (Cabassi et al, 2019;Rouwet, 2021). Dominant CO 2 degassing (δ13C-DIC from +2.8 to +5.8‰, Delalande-Le Mouëllic et al, 2015) is probably of magmatic origin as also suggested by the high 3 He/ 4 He ratios (7-8.3 Ra, de Moor et al, 2013).…”

Detecting gas-rich hydrothermal vents in Ngozi Crater Lake using integrated exploration tools

“…Therefore, limited risk of limnic eruptions is assumed, though monitoring measures are advised as sudden CO 2 recharge 12 due to renewed or increased gas input cannot be excluded. In that context Lake Ngozi is rather comparable to the geothermally heated Kelud crater lake (Indonesia) 13 or volcanic lakes in El Salvador 14 , than Lake Nyos, Lake Kivu or Lake Monoun.…”

Monitoreo de microplásticos superficiales en el lago de Coatepeque, 2021-2022

“…El lago de Coatepeque (13º 51' 48.0" N, -89º 32' 45.9" W) abarca 25.3 km 2 de superficie acuática y su origen está asociado al colapso de un antiguo volcán (Cabassi et al, 2019). La cuenca de este cuerpo de agua es endorreica (Quiñonez-Basagoitia, 2019) y se ubica entre los departamentos de Sonsonate y Santa Ana en la zona oeste del país, aproximadamente a 740 metros sobre el nivel del mar.…”