Automated, high time-resolution measurements of SO2 flux at Soufri�re Hills Volcano, Montserrat

Abstract

We report here the first results from an automated, telemetered UV scanning spectrometer system for monitoring SO 2 emission rates at Soufrire Hills Volcano, Montserrat. Two spectrometers receive light by way of a motor-driven stepping prism and telescope in order to make vertical scans of the volcanic plume. Spectral data from these spectrometers, situated 2,800 m apart and 4,500 m from the volcano, are relayed back to the observatory every 4-5 s via radio modems. A full scan of the plume is accomplished every 1-6 min by the (timesynchronised) spectrometers and a SO 2 emission rate is calculated using the SO 2 slant concentrations, scan angles and plume speeds estimated from the wind speed from a telemetered weather station near to the volcano. The plume's position and dimensions are calculated using the angular data from the two spectrometers. The plume height varies significantly diurnally and seasonally and is important in order to minimise the error on SO 2 emission rates. The new scanning system (Scanspec) provides SO 2 emission rates from 08:00 to 16:00 h local time every day. Preliminary results highlight a number of features of the SO 2 time series and plume dynamics and give our first indications of the errors and limits of detection of this system. SO 2 emission rates vary widely on all time scales (minutes, days, months). This new system has already provided the first real and consistent indication that SO 2 emission rates vary on a minutes to hours basis, which can be correlated with volcanic activity (for example, rockfall and pyroclastic flow activity). It is anticipated that this system at Soufrire Hills will yield information on shallow processes occurring on short time scales (periods of minutes to hours) as well as deep processes relating to magma supply rates, which will be associated with longer wavelength SO 2 signals of weeks to months.

Volcano remote sensing with ground-based spectroscopy

“…Such a system was automated at the Soufrière Hills volcano, Montserrat, and has been collecting data autonomously since 2002. This is an outstanding example of the value added to volcanological monitoring by rapid capitalization upon new technological opportunities (Edmonds et al 2003a). While SO 2 fluxes are the most ubiquitous of all ground-based remotely sensed volcanic data, and have provided many valuable scientific insights, they are limited in their utility by large errors (potentially greater than 100%).…”

Ultraviolet Imaging of Volcanic Plumes: A New Paradigm in Volcanology

“…Since the turn of the century, these units have been replaced with low cost USB-coupled linear array spectrometers, costing only a few thousand dollars, an order of magnitude less than COSPEC [8,9]. Data analysis to deliver SO 2 column amounts is achieved using DOAS routines, and the units have been applied from mobile platforms, e.g., on cars and airplanes, whilst traversing beneath a plume, as well as in fixed position deployments involving scanning optics [10,11]. These scanning spectrometers are now in routine operation on numerous volcanoes worldwide [12,13].…”

Heat and SO2 Emission Rates at Active Volcanoes - The Case Study of Masaya, Nicaragua

“…In particular, the combination of Ultraviolet (UV) spectrometers with the Differential Optical Absorption Spectroscopy (DOAS) analytical method (Noxon, 1975;Platt, 1994;Platt & Stutz, 2008) improved significantly data collection, offering a number of advantages such as the possibility of obtaining measurements in the challenging environments typical of volcanic areas, detection of other plume species (Bobrowski et al, 2003;O'Dwyer et al, 2003;Oppenheimer et al, 2005), and collection of high-resolution SO 2 flux by permanent scanner networks (e.g. Arellano et al, 2008;Edmonds et al, 2003;Salerno et al, 2009aSalerno et al, , 2009b.…”