Origin, composition and evolution of fumarolic fluids of subduction zone volcanoes in Nicaragua

During four field campaigns (2001-2003), fumarolic gases from the two Nicaraguan volcanoes Mombacho and Momotombo were repeatedly sampled with the objective of gaining a better understanding of processes occurring within their volcano-magma-systems. Mombacho is a highly dissected stratocone volcano that is generally considered extinct. The combined chemical and isotopic composition of the gases provide evidence for high-temperature conditions in the shallow subsurface. This suggests that Mombacho volcano should not be considered extinct, and could re-awaken and erupt in the future. Momotombo is an active volcano in persistent state of fumarolic activity since its last eruption in 1905 and discharges gases at high temperatures. The chemistry, isotopic compositions and trace element contents of the gases have changed considerably over the last 20 years. These changes appear to be related to degassing of different magma batches and major changes in the interaction between the magmatic and hydrothermal systems. Flux estimates for some highly volatile and potentially harmful trace elements of magmatic origin (e.g. Tl, Bi, As, Se, Sb, Hg, Cd) show that Momotombo is only a minor source of pollutants in the atmosphere