Onyeali, Mazi-Mathias CÌý1Ìý;ÌýJoseph, Erouscilla PÌý2Ìý;ÌýFrey, HolliÌý3
1ÌýCU Boulder
2ÌýThe University of Trinidad and Tobago
3ÌýUnion College
Dominica has an abundance of volcanic activity, with nine (9) potentially active volcanoes, many of which have highly active volcanic-hydrothermal systems. The waters are predominantly acid-sulphate in character (SO4=100–4200 mg/L, pH?4), and likely formed because of dilution of acidic gases in near surface oxygenated groundwater. The waters are of primarily meteoric origin with ?18O ranging from ?1.75 to 10.67‰, and ?D from ?6.1 to 14.5‰, however are affected by evaporation effects at/near the surface. With updated water chemistry data from five (5) hydrothermal areas (Boiling Lake, Valley of Desolation, Sulphur Springs, Watten Waven, Cold Soufriere) for the period 2014 to 2017, we will re-evaluate the characteristics of these systems, which were last reported in 201. We will present updated reservoir temperatures using a variety of geothermometers and provide insight into water-rock interactions taking place in the reservoirs.
Recent changes in chemistry of the waters have indicated that while the origin of the hydrothermal systems are still dominantly meteoric (?18O = -3‰ to 8 and ?D = -5 to 18‰), surface evaporation effects and variable amounts of mixing with shallow ground waters play an important role. Fumaroles appear to reflect a deeper source contribution as compared to thermal waters with differences in chemistry (acidity, temperature, higher TDS, ?13C) observed. The general composition of the waters for most of the hydrothermal systems studied indicate no significant changes with the exception of the Boiling Lake, which experienced a draining event in November 2016, which lasted for 6 weeks. Decreases in Na, K, and Cl were seen post draining, while SO4 remained relatively low (66 ppm) but showed a small increase. The chemistry of the Boiling Lake appears to show significant changes in response to changes in the groundwater system. Changes in the groundwater system at the lake observed during the 2004/2005 draining, which lasted for 6 months was attributed to strain release from a nearby regional seismic event. Based on the changes observed during the recent draining events there are likely a number of other factors affecting the ground water system at the Boiling Lake. Of particular note is the drastic change in SO4 concentrations in the Boiling Lake, which went from 1830 ppm in 2003 to <100 ppm presently.
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