Fisica

fisicaJournal of Volcanology and Geothermal Research 190 (2010) 325–336

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Journal of Volcanology and Geothermal Research
j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / j vo l g e o r e s

High temporal resolution SO2 flux measurements at Erebus volcano, Antarctica
Marie Boichu a,⁎, Clive Oppenheimer a, Vitchko Tsaneva, Philip R. Kyle b
a b

Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, United Kingdom Department of Earth and Environmental Science, New Mexico Institute of Mining and Technology, Socorro, NM 87801, USA

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The measurement of SO2 flux from volcanoes is of major importance for monitoring and hazard assessmentpurposes, and for evaluation of the environmental impact of volcanic emissions. We propose here a novel technique for accurate and high time resolution estimations of the gas flux. We use two wide field of view UV spectrometers capable of collecting, instantaneously, light from thin parallel cross-sections of the whole gas plume, obviating the need for either traversing, scanning or imaging. It enablestracking of inhomogeneities in the gas cloud from which accurate evaluation of the plume velocity can be made by correlation analysis. The method has been successfully applied on Mt. Erebus volcano (Antarctica). It yields estimations of the plume velocity and gas flux at unprecedented time resolution (1 Hz) and high accuracy (uncertainty of 33%). During a ∼ 2 h experiment on 26 December 2006, SO2 fluxvaried between 0.17 and 0.89 ± 0.2 kg s− 1 with a vertical plume velocity varying between 1 and 2.5 ± 0.1 m s− 1. These measurements provide insight into the short-term variations of the passive degassing of this volcano renowned for its active lava lake. A cyclicity in flux, ranging from about 11–24 min, is evident. We propose two physical mechanisms to explain this degassing pattern, associatedto periodic supply of either gas-rich magma or gas alone into the lake. The dual-wide field of view DOAS technique promises better integration of geochemical and geophysical observations and new insights into gas and magma dynamics, as well as processes of magma storage and gas segregation at active volcanoes. Crown Copyright © 2009 Published by Elsevier B.V. All rights reserved.

Article history:Received 10 August 2009 Accepted 21 November 2009 Available online 4 December 2009 Keywords: volcanic degassing DOAS spectroscopy high time resolution gas flux

1. Introduction Gas emissions from volcanoes are measured for several purposes, including monitoring, hazard assessment, and investigation of environmental impact. For over a century, fumarole chemistry has been studied using in-situcollection techniques. While these yield highly detailed analysis of fluid composition, field access can be limited and data streams are often discontinuous. However, since the first application of the correlation spectrometers (COSPEC), four decades ago (Moffat and Millan, 1971; Stoiber and Jepsen, 1973), numerous ground-based, airborne and spaceborne optical remote sensing instruments and methods haveemerged capable of measuring both volcanic gas fluxes and composition, for individual vents or an entire plume, and with improved temporal resolution (McGonigle and Oppenheimer, 2003). As a result, gas geochemistry has increasingly found its place among the operational techniques of volcano monitoring (Oppenheimer, 2003; Galle et al., 2003). Nevertheless, the time resolution of gas measurementsstill lags behind what is routinely achieved in geophysical studies, limiting progress in understanding the links between seismicity, deformation and degassing that are clearly of considerable relevance for understanding
⁎ Corresponding author. Tel.: +44 1223 766561. E-mail addresses: mb632@cam.ac.uk (M. Boichu), co200@cam.ac.uk (C. Oppenheimer), vip20@cam.ac.uk (V. Tsanev), kyle@nmt.edu (P.R....