12 research outputs found
Mercury emissions from soils and fumaroles of Nea Kameni volcanic centre, Santorini (Greece)
There have been limited studies to date targeting mercury emissions from volcanic fumarolic systems, and no mercury flux data exist for soil or fumarolic emissions at Santorini volcanic complex, Greece. We present results from the first geochemical survey of Hg and major volatile (CO2, H2S, H2O and H2) concentrations and fluxes in the fumarolic gases released by the volcanic/hydrothermal system of Nea Kameni islet; the active volcanic center of Santorini. These data were obtained using a portable mercury spectrometer (Lumex 915+) for gaseous elemental mercury (GEM) determination, and a Multi-component Gas Analyzer System (Multi-GAS) for major volatiles. Gaseous Elemental Mercury (GEM) concentrations in the fumarole atmospheric plumes were systematically above background levels (~4 ng GEM m-3), ranging from ~4.5 to 121 ng GEM m-3. Variability in the measured mercury concentrations may result from changes in atmospheric conditions and/or unsteady gas release from the fumaroles. We estimate an average GEM/CO2 mass ratio in the fumarolic gases of Nea Kameni of approximately 10-9, which falls in the range of values obtained at other low-T (100°C) volcanic/hydrothermal systems (~10-8); our measured GEM/H2S mass ratio (10-5) also lies within the accepted representative range (10-4 to 10-6) of non-explosive volcanic degassing. Our estimated mercury flux from Nea Kameni's fumarolic field (2.56 × 10-7 t yr-1), while making up a marginal contribution to the global volcanic non-eruptive GEM emissions from closed-conduit degassing volcanoes, represents the first available assessment of mercury emissions at Santorini volcano, and will contribute to the evaluation of future episodes of unrest at this renowned volcanic complex
Active hydrothermal fluids circulation triggering small-scale collapse events: the case of the 2001–2002 fissure in the Lakki Plain (Nisyros Island, Aegean Sea, Greece)
In 2001–2002, two ground collapses occurred in the island of Nisyros (Aegean
Sea, Greece), which formed a 600 m long and up to 5 m wide fissure in the vegetated
central part of the Lakki Plain caldera. The fissure was alternatively ascribed to tensional
stress release and hydrothermal alteration. In this study, we present original data of diffuse
CO2 soil fluxes, soil temperatures, mineralogical and chemical composition of the calderafilling
deposits exposed on the fissure walls, and chemical and isotopic composition of
interstitial soil gases collected from: the bottom of the fissure, the adjacent vegetated areas, the hydrothermal craters, and selected sites outside the caldera. The occurrence of intense
hydrothermal alteration was shown by both mineralogical and chemical analyses of the
fissure walls material. Typical mineral assemblage and enrichments in incompatible elements
related to advanced argillic alteration, characterizing steam-heated hydrothermal
environments, were recognized. Although the low-permeable sediment cover in the Lakki
Plain concealed the underneath hydrothermal gas flow, preventing anomalous soil temperatures
and CO2 fluxes, the chemical and isotopic composition of the interstitial soil
gases revealed an active hydrothermal fluids circulation below the collapsed area, likely
controlled by buried structural lineaments. Hydrothermal alteration can then be invoked as
the most likely trigger mechanism for the 2001–2002 collapse event