Design and experimental development of a portable instrument for measuring diffuse helium efflux in active volcanic systems

Among the actions to be taken by any community threatened by volcanic activity to reduce the risk associated with volcanic hazards, a multidisciplinary approach to volcano monitoring is mandatory to optimize the early warning system for future volcanic eruptions. Such a multidisciplinary approach must be constantly updated with technological development. As part of this multidisciplinary approach to volcanic monitoring, attention to volcanic gases is one of the most important volcanic monitoring tool. The chemical composition of the gases emanating from a volcano, whether visible (through fumaroles and/or plumes) or non-visible (diffuse emissions), provides vital information on the degree of activity of a volcano. Monitoring and studying the behavior of volcanic gases as precursors of volcanic activity has attracted increasing interest from the scientific community. Portable instruments developed in the last 20 years allow measurement of larger gaseous species such as CO2, but in situ estimation of the emission of trace gases such as He is not possible to date, as the flux of this species is too low and would require too long accumulation times to distinguish changes in concentration inside the collection chamber. Among volcanic gases, helium (He) has unique characteristics as a geochemical tracer, as it is chemically inert and radioactively stable, non-biogenic, highly mobile and relatively insoluble in water. He flux is traditionally estimated following theoretical simulations, with strong limitations in the precision and accuracy of the He flux estimation. In this work we present a project that aims to overcome the technological limitations and develop a prototype to measure diffuse He emissions in situ in volcanic areas. “Portable” in this project is a key term, because the instrument must be suitable to be transported easily on the back of the volcanologist to complete surveys with tens of measurements each day. The project will take advantage of recent technological advances in two different technologies: (1) the miniaturization of quadrupole mass spectrometers (QMS), which have managed to drastically reduce their dimensions and weight; and (2) the possible spectrophotometric detection of He in trace levels.