Search Results (4)

One of the most intriguing questions of modern volcanology is the inception of an eruption. Despite efforts to detect premonitory signals, numerous unpredicted eruptions have occurred recently. It has been suggested that these unpredicted eruptions might be explained by viscosity variations in elemental sulfur accumulated within the hydrothermal systems present in several volcanic settings under the influence of organics, hydrocarbons, hydrogen sulfide, halogens, and ammonia. Changes in impure sulfur viscosity are more complex than those in pure S, invoked decades ago to trigger eruptions by system sealing in volcanoes hosting a crater lake. Growing evidence suggests that sulfur accumulation is a common process, not restricted to crater lakes. Moreover, both types and amounts of gas species released at the surface, critical for volcano monitoring, would be altered, following chemical reactions involving impure S, invalidating signals used to issue alerts. Impure sulfur behavior may explain puzzling degassing and contrasting signals reported at volcanoes and restless calderas worldwide, with implications for hazard assessment and volcanic-risk-mitigation strategies. Full article

Lake Tazawa, the deepest lake (423.4 m depth at maximum) in Japan underwent drastically changed water quality in 1940, because volcanic water from two active volcanos was then drawn into the lake for power generation and irrigation. Thereby, the pH of lake water decreased from 6.7 to 4.2, which exterminated a land-locked type of sockeye salmon, Oncorhynchus nerkakawamurae (locally called Kunimasu trout). Additionally, the mean residence time of lake water changed from 195 years to 8.9 years by rapidly increasing the outflow for power generation and irrigation. In this study, long-term chemical fluxes controlling lake water chemistry were obtained, and a groundwater water cycle system between the lake and the volcano was explored by estimating hydrological and chemical budgets of the lake. In the chemical budget estimate, two ionic species, SO₄²⁻ and Cl⁻, in volcanic fluids were chosen and each mass conservation equation was yielded. The hydrological budget estimate gave us the net groundwater inflow at −1.36 m³/s on average over three periods in 2020–2021, and then the simultaneous equation coupled with the chemical budget equation allowed us to separate into groundwater inflow and outflow at 6.01 m³/s and 7.37 m³/s, averaged over the three periods, respectively. The evaluated groundwater inflow and outflow were compared with those of the other crater or caldera lakes. The linear relationship between the lake volume and the magnitude of groundwater inflow or outflow suggests that the groundwater cycle scale in such a lake increases with the magnitude of the volcanic eruption to have formed the lake. Full article

In order to assess the sustainability and impact of production from geothermal reservoirs on hydrological systems, a thorough understanding of local and regional hydrogeological systematics is a prerequisite. The Menengai Caldera in the Kenya Great Rift Valley is one of the largest explored geothermal fields in the country. This paper presents a hydrochemical investigation of the Menengai Caldera geothermal field and the ground and surface waters of the surrounding Nakuru County. Our results demonstrated a similar, sodium-alkaline dominated, ionic composition across all water types. Geothermal wells return the highest cation/anion concentrations and largely demonstrate a meteoric source from their δ¹⁸O and δ²H signature. Wells MW-09 (central part of the caldera), MW-18 (eastern part) and MW-20 (central part) showed a more evaporitic signature, closely matching with our own calculated Lake Evaporation Line, suggesting an increased mixing influence of Lake Nakuru waters. MW-09 also showed evidence of high-temperature oxygen isotopic exchange and significant water-rock interaction. Lake samples largely demonstrated seasonal shifts in ionic and isotopic values. Lake Nakuru ionic composition and isotopic values increased throughout the 12-month wet–dry–wet season sampling period. This correlated with a decrease in area which suggests a lessening of water inflow and facilitates increased evaporation. Groundwaters demonstrated clear evidence of mixing between meteoric, irrigation and lake waters. These observations enhanced the understanding of the hydrological system surrounding the Menengai Caldera and, when combined with future studies, will provide a powerful tool to assess the sustainability and impact of soon-to-be completed geothermal power production operations. Full article

This paper is a preliminary attempt to assess the composition of pollutants in two different caldera lakes situated in the Indonesian Archipelago: Batur and Bratan. Both lakes are characterized by largely different physico-chemical regimes; Batur Lake is located in an area that is currently volcanically active, unlike Bratan Lake. The latter is much smaller and shallower than Batur Lake. The concentration of pollutants in the Indonesian equatorial lakes is largely unknown, and the impact of both biological and geothermal processes on their distribution requires attention. This study shows that the concentrations of cations (Na⁺, K⁺, Mg²⁺, Ca²⁺), anions (SO₄²⁻, F⁻, Cl⁻, Br⁻) and trace elements (Li, B, Al, V, Cr, Mn, Co, Ni, Cu, Zn, As, Se, Rb, Sr, Mo, Cd, Sn, Cs, Ba, Pb, U, Be, Ag, Sb, Tl, Bi) differ greatly between both lakes. Most chemical parameters determined in volcanically influenced Batur Lake were tens to hundreds times higher than in Bratan Lake, and in the case of trace metals, the ratios of the two lakes’ concentrations reached several hundreds. This study also compared the composition and concentration levels of organic compounds in both lakes, such as fatty acids, halocarbons and esters. On the other hand, the content of organic chemicals in the lakes also results from biological activity by phytoplankton, zooplankton and bacteria. Full article