Abstract
Volcanic eruptions are often preceded by precursory increases in the volcanic carbon dioxide (CO2) flux. Unfortunately, the traditional techniques used to measure volcanic CO2 require near-vent, in situ plume measurements that are potentially hazardous for operators and expose instruments to extreme conditions. To overcome these limitations, the project BRIDGE (BRIDging the gap between Gas Emissions and geophysical observations at active volcanoes) received funding from the European Research Council, with the objective to develop a new generation of volcanic gas sensing instruments, including a novel DIAL-Lidar (Differential Absorption Light Detection and Ranging) for remote (e.g., distal) CO2 observations. Here we report on the results of a field campaign carried out at Mt. Etna from 28 July 2016 to 1 August 2016, during which we used this novel DIAL-Lidar to retrieve spatially and temporally resolved profiles of excess CO2 concentrations inside the volcanic plume. By vertically scanning the volcanic plume at different elevation angles and distances, an excess CO2 concentration of tens of ppm (up to 30% above the atmospheric background of 400 ppm) was resolved from up to a 4 km distance from the plume itself. From this, the first remotely sensed volcanic CO2 flux estimation from Etna’s northeast crater was derived at ≈2850–3900 tons/day. This Lidar-based CO2 flux is in fair agreement with that (≈2750 tons/day) obtained using conventional techniques requiring the in situ measurement of volcanic gas composition.
Highlights
In the last two decades, there have been major advances in the instrumental monitoring of volcanic gas plume composition and fluxes [1]
Attempts to remotely sense the volcanic CO2 flux from distal locations have been limited in number [9,10], while the majority of the observations have involved in situ measurements in the proximity of hazardous active volcanic vents [3]
For example, one of the largest volcanic CO2 point sources on Earth [11], the volcanic CO2 flux has systematically been measured since the mid-2000s by combining in situ measurement of the volcanic CO2 /SO2 ratio
Summary
In the last two decades, there have been major advances in the instrumental monitoring of volcanic gas plume composition and fluxes [1] These have included the first instrumental networks of scanning Differential Optical Absorption Spectrometers (DOAS) for volcanic SO2 flux monitoring, the implementation of satellite-based volcanic gas observations, and the advent of sensor units for in situ gas monitoring [1,2,3,4,5,6]. It has been shown that, at open-vent persistently degassing volcanoes, volcanic eruptions are often preceded by anomalous increases of the volcanic CO2 flux [7] These initial observations have motivated attempts to systematically monitor the volcanic CO2 flux, and to identify novel measurement strategies [8]. For example, one of the largest volcanic CO2 point sources on Earth [11], the volcanic CO2 flux has systematically been measured since the mid-2000s by combining in situ measurement of the volcanic CO2 /SO2 ratio
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