Optical sensing of volcanic gas and aerosol emissions

Abstract

Volcanic gas and aerosol surveillance yield important insights into magmatic, hydrothermal, and atmospheric processes. A range of optical sensing and sampling techniques has been applied to measurements of the composition and fluxes of volcanic emissions. In particular, the 30-year worldwide volcanological service record of the Correlation Spectrometer (COSPEC) illustrates the point that robust, reliable, straightforward optical techniques are of tremendous interest to the volcano observatory and research community. This chapter reviews the field, in particular the newer and more versatile instruments capable of augmenting or superseding COSPEC, with the aim of stimulating their rapid adoption by the volcanological community. It focuses on sensors that can be operated from the ground, since they generally offer the most flexibility and sensitivity. The success of COSPEC underlines the point, however, that such devices should be comparatively cheap, and easy to use and maintain, if they are to be widely used.

Fractal degassing from Erebus and Mayon volcanoes revealed by a new method to monitor H2O emission cycles

“…Monitoring degassing cycles and gas puffing at active volcanoes is valuable for volcanic surveillance because they are a proxy for the physical processes occurring within magma conduits and reservoirs [e.g., Ripepe et al , ; Allard et al , ; Tamburello et al , ]. Degassing cycles are currently monitored using remote methods as they allow obtaining time series at high sampling rates and are safer than in situ direct collection of volcanic gases [ McGonigle and Oppenheimer , ]. For instance, Harris and Ripepe [] and Branan et al [] analyzed gas puffing activity at Stromboli and Masaya by measuring temperature changes of the vent with thermal infrared thermometers and thermal imagers; Oppenheimer et al [] and Boichu et al [] registered SO 2 cycles at Erebus volcano with spectroscopic techniques, and more recently, Tamburello et al [] monitored SO 2 pulsations at Etna with UV cameras.…”

Passive vs. active degassing modes at an open-vent volcano (Stromboli, Italy)

“…Over the last few decades, remote sensing techniques working in the UV region of the electromagnetic spectrum have increasingly been applied to explore the long-term (years) to mediumterm (days) trends in the rate of SO 2 release from active subaerial volcanoes (McGonigle and Oppenheimer, 2003;Oppenheimer et al, 2011;Tamburello et al, 2011a). From these observations, the time-averaged budgets of SO 2 release for a number of individual volcanoes have been obtained, leading to assessments of the global volcanic SO 2 flux (Andres and Kasgnoc, 1998).…”

Real‐time measurement of volcanic H2S and SO2 concentrations by UV spectroscopy

“…One reason for this is that while open‐path spectroscopic determinations of SO 2 columns are comparatively easy due to the position of electronic and rotational‐vibrational absorption lines in the ultraviolet (UV) and infrared (IR), H 2 S is much more challenging to measure in the IR because its absorption spectrum lies in a region of strong water vapour absorption, and in the UV because its electronic spectrum is at shorter wavelengths at which molecular scattering is much stronger. In the published work on Fourier transform IR spectroscopy of volcanic gases in the field, there are no reports of detection or quantification of H 2 S [ McGonigle and Oppenheimer , 2003]. The only prior optical detection of volcanic H 2 S was achieved (with CO 2 and H 2 O) by direct fumarole sampling at Solfatara using an evanescent fibre laser sensor [ Willer et al , 2002].…”