Volcanic Degassing

Objectives:

·        To develop novel remote sensing techniques for surveillance of volcanic gases and aerosols

·        To develop comprehensive models for volcanic degassing

·        To understand the atmospheric chemistry and transport of volcanic plumes

·        To understand the impacts of volcanic gases and aerosols on human health and terrestrial ecosystems

Fourier transform infrared spectroscopy (FTS) & geochemical modelling of volcanic degassing

Volcanoes emit gases both during and between eruptions. Surveillance of gas composition and flux is essential for interpretation of volcanic activity, since degassing exerts a fundamental control on magma dynamics and eruption style.  It also supports assessment of the role of volcanic gases in atmospheric chemistry and dynamics. We have played a key role in the development of the application of Fourier transform infrared spectroscopy to field measurement of volcanic gases.   The technique is now used by several observatory and university-based scientists worldwide, including application to routine monitoring of Mount Etna by a former research associate now at the Italian National Geophysical and Volcanological Institute.  We designed and conducted the first volcanological experiments using solar occultation FTS, and have played a significant role in the geochemical surveillance of Soufričre Hills Volcano, Montserrat, since 1996.  Work there has led to a detailed interpretation of volatile sources and fluxes, contributing to overall understanding of the eruption. 

 

Contact: Clive Oppenheimer, Hayley Duffell, for final reports on NERC projects click here.

Sponsors: NERC, EC

Horrocks, L.A., Oppenheimer, C., Burton, M.R., Duffell, H.R., Davies, N.M., Martin, N.A., and Bell, W., 2001, Open-path Fourier transform infrared spectroscopy of SO2: an empirical error budget analysis, with implications for volcano monitoring, Journal of Geophysical Research-Atmospheres, 106, 27647-27659.

Oppenheimer C, Francis P, Burton M, Maciejewski A, Boardman L, 1998, Remote measurement of volcanic gases by Fourier transform infrared spectroscopy, Applied Physics B, 67, 505-515.

Differential Optical Absorption Spectroscopy (DOAS)

In collaboration with Bo Galle (Chalmers University of Technology, Gothenburg), we have recently established the potential of a new miniature ultraviolet spectrometer for measuring the sulfur dioxide flux from volcanoes.  Tests with the compact and easy-to-operate device at Masaya volcano (Nicaragua) and Soufričre Hills Volcano (Montserrat) have proved extremely encouraging and the “mini-DOAS” is sure to be rapidly adopted by volcano observatories and university-based groups for measurements of this key volcanic gas.

Contact: Andrew McGonigle

Sponsors: EC, GNV

McGonigle, A., & Oppenheimer, C., Optical sensing of volcanic gas and aerosol emissions, in Volcanic degassing, Geological Society Special Publication, accepted.

Galle, B., Oppenheimer, C., Geyer, A., McGonigle, A., Edmonds, M., and Horrocks, L.A., 2002, A miniaturised ultraviolet spectrometer for remote sensing of SO2 fluxes: a new tool for volcano surveillance, Journal of Volcanology and Geothermal Research, in press.

Laser spectroscopy

Volcanic volatiles observed at the surface can be derived, in varying proportions, from mantle, slab or groundwater sources. One approach to probing these sources is the measurement of isotopic signatures.  We are working in collaboration with Frank Tittel (Rice University, Houston) and Paolo de Natale (LENS, Firenze) in the development and application of novel laser spectrometers for volcanic gas detection and measurement.  Preliminary tests of two Difference Frequency Generation lasers were carried out at Masaya volcano in 2000. 

Contact: Clive Oppenheimer

Sponsors: NERC, GNV

Richter, D., Erdelyi, M., Curl, R.F., Tittel, F.K., Oppenheimer, C., Duffell, H.J., and Burton, M., 2002, Field measurement of volcanic gases using tunable diode laser based mid-infrared and Fourier transform infrared spectrometers, Optics and Lasers in Engineering, 37, 171-186.

Sun photometry

Portable Sun photometers provide an attractive means to measure volcanic aerosol remotely.  Preliminary investigations into the technique were carried out at Mount Etna using the Cimel Sun photometer on loan from the NERC Equipment Pool for Spectroscopy.  Measurements obtained under, and outside the plume permit subtraction of background atmospheric aerosol and modelling of the resulting spectra yields particle concentration and size distributions.

Contact: Matt Watson, Clive Oppenheimer

Sponsors: NERC

Watson, I.M., and Oppenheimer, C., 2001, Particle-size distributions of ash-rich volcanic plumes determined by sun photometry, Atmospheric Environment, 35, 3561-3572..

Watson, I.M., and Oppenheimer, C., 2000, Particle size distributions of Mt. Etna’s aerosol plume constrained by sun-photometry, Journal of Geophysical Research-Atmospheres, 105, 9823-9830.

Measurements and modelling of the atmospheric chemistry and transport of volcanic plumes and their environmental and health impacts

We have been applying FTS, Sun-photometry, and direct sampling methods to investigate gas and aerosol composition, aerosol size distribution, and chemistry of tropospheric volcanic plumes.  Our recent observations have highlighted meteorological controls on particle size distributions, and on removal of gaseous HCl, HF and SO2.  Measurements carried out at Masaya volcano in 2001 revealed for the first time the importance of very low pH, submicron-sized sulfate particles as a primary emission (or possibly combustion product) of magmatic degassing.  This work has important implications for the environmental and health impacts of volcanic emissions, and their long range transport. 

A key long-term aim of this work is to build a set of linked physical, chemical and statistical models to investigate the chemistry and transport of (primarily tropospheric) volcanic clouds and, to quantify their atmospheric, environmental and health impacts, especially with regard to the threat of major pollution events arising from Icelandic volcanism. This will lead to a detailed understanding of Britain’s and continental Europe’s vulnerability to a range of potential Icelandic eruptions, and to development of new methods for risk mitigation, and will have wide application in modelling other types of pollution, and their implications for respiratory morbidity and cardiovascular mortality.  Such models will also permit new studies of global scale volcano-climate interaction. 

Contact: Tamsin Mather Clive Oppenheimer, Claire Witham

Sponsors: NERC

Burton, M.R., Oppenheimer, C., Horrocks, L.A., Francis, P.W., 2001, Diurnal changes in volcanic plume chemistry observed by lunar and solar occultation spectroscopy, Geophysical Research Letters, 28, 843-846.

Oppenheimer C, Francis P and Stix J, 1998, Depletion rates of SO2 in tropospheric volcanic plumes, Geophsyical Research Letters, 25, 2671-2674.

 

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