Abstract
Gas-rich hydrothermal vents in crater lakes might pose an acute danger to people living nearby due to the risk of limnic eruptions as a result of gas accumulation in the water column. This phenomenon has been reported from several incidents, e.g., the catastrophic Lake Nyos limnic eruption. CO(2) accumulation has been determined from a variety of lakes worldwide, which does not always evolve in the same way as in Lake Nyos and consequently requires a site-specific hazard assessment. This paper discusses the current state of Lake Ngozi in Tanzania and presents an efficient approach how major gas-rich hydrothermal feed zones can be identified based on a multi-disciplinary concept. The concept combines bathymetry, thermal mapping of the lake floor and gas emission studies on the water surface. The approach is fully transferable to other volcanic lakes, and results will help to identify high-risk areas and develop suitable monitoring and risk mitigation measures. Due to the absence of a chemical and thermal stratification of Lake Ngozi the risk of limnic eruptions is rather unlikely at present, but an adapted monitoring concept is strongly advised as sudden CO(2) input into the lake could occur as a result of changes in the magmatic system.