The Beer - Lambert Law

1. A COMPARISON OF VOLCANIC SO2 EMISSIONS FROM BEZYMIANNY, SHIVELUCH, AND MOUNT ST. HELENS VOLCANOES Taryn Lopez1, Sergey Ushakov2,3, Timothy Clark4 and Pavel Izbekov1 1Alaska Volcano Observatory, Geophysical Institute, UAF, Fairbanks, Alaska, U.S.A. 2Institute of Volcanology and Seismology, Petropavlovsk-Kamchatsky, Russia 3Kamchatka Volcano Eruption Response Team, Petropavlovsk-Kamchatsky, Russia 4United States Army Geospatial Center, Alexandria, Virginia, U.S.A. Figure 3a Introduction Description of Volcanic Activity Bezymianny (Kamchatka, Russia), Shiveluch (Kamchatka, Russia), and Mount St. Helens (Washington, U.S.A.) are three volcanoes that have undergone catastrophic directed-blast type eruptions in 1956, 1964, and 1980, respectively. These volcanoes are the targets of a five year, international, multidisciplinary, collaborative research project known as PIRE, aimed at investigating the response of magmatic systems to edifice collapse. Volcanic gas chemistry is one of the disciplines integral to the PIRE program. Herein, we present preliminary findings of sulfur dioxide (SO2) emissions from the target volcanoes measured during the 2007 and 2008 field seasons. Bezymianny (Figure 3a): Continuous activity since 1956 at Bezymianny volcano has consisted of dome growth and collapse; explosive activity; production of pyroclastic flows, lahars, and lava flows; and degassing. Annual to biannual explosive eruptions have occurred since 2001. The andesite to basaltic andesite dome mostly fills the 1956 crater though its exact size and extrusion rate is unknown (Pavel Izbekov, Pers. Comm.; Smithsonian GVP). Shiveluch (Figure 3b): Following the eruption of 1964, Shiveluch volcano underwent a period of relative quiescence until 1980. From 1980 through the present, activity has consisted of active dome growth and collapse; production of pyroclastic flows, lahars, and lava flows; explosive activity; and degassing (KVERT Website). The active dome is predominantly andesitic in composition (Shipman et al., 2009) and the estimated volume of dome material discharged from 1980-2004 is greater than 270*106 m3 (Dirksen et al., 2006). Mount St. Helens (Figure 3c): Since 1980, activity at Mount St. Helens volcano has consisted of intermittent periods (1980 - 1989 and 2004 - 2008) of dome growth accompanied by explosive activity, lahar production, and degassing. As of December, 2005, the recent eruptive period had produced a 73*106 m3 dacitic lava dome (Schilling et al., 2009). Lava dome growth ceased in January, 2008 and activity since then has remained quiet (CVO Website). Gorshkov, 1956 Figure 3b Figure 1: Location map of Washington, U.S.A., with Mount St. Helens volcano circled. Figure 2: Location map for Kamchatka Russia with Bezymianny and Shiveluch volcanoes circled. Belousov, 1994 Figure 3c Glicken, 1982 Figure 2 Figure 1 www.volcano.si.edu www.volcano.si.edu The Beer - Lambert Law Aλ = -ln(I λ/Io λ) = σλNL Volcanic Application of the Beer-Lambert Law Plume Width (m) Methods Where: A = Absorption λ = Wavelength Io = Incident light I = Transmitted light σ = Absorption X-section N = Concentration L = Path length Emission Rate Calculations Sample Spectrum = I Plume Velocity (m/s) Measurements of absorption of ultraviolet (UV) light by SO2 at the target volcanoes were collected in 2007 and 2008 using a FLYSPEC UV spectrometer system. These data were automatically converted to SO2 column densities (parts per million meter, ppmm) by the FLYSPEC operating software, according to the Beer-Lambert law (Figure 4). Measurements were collected in scanning mode, where a series of measurements were collected along a cross-section of the volcanic plume by rotating the FLYSPEC on a tripod. The resultant SO2 column density measurements (C in ppmm) were used along with the calculated plume width, (W in m), plume velocity (V in m/s), and a conversion factor (F = 0.0002302) to calculate SO2 emission rate in units of tonnes per day (t/d) according to the equation on the right (Figure 5). Reference Spectrum = Io Radiation Source SO2 Emission Rate (t/d) = VF∫C W Scan Angle (Degrees) Concentration of SO2 = N Pathlength through plume = L Plume Plume FLYSPEC SO2 Column Density (ppmm) θ FLYSPEC Edifice Edifice Figure 5 Figure 4 Results Discussion References The variability of SO2 emission rates seen among the target volcanoes may be attributed to volcanic activity at the time of sample collection, sampling limitations such as in the example of Shiveluch, and differences in the underlying magmatic systems, including magma composition, degassing state, and volume and depth of magma. Bezymianny: Higher relative SO2 emissions at Bezymianny may be attributed to a new or shallowing magma source. This agrees with the timing of sample collection between explosive eruptions in 2007 and 2008 (explosive eruptions occurred 5/2007, 10/2007 and 8/2008). Alternatively, recharge by a more mafic magma could explain the elevated SO2 emissions at Bezymianny relative to the other volcanoes. Shiveluch: The high measurement error at Shiveluch volcano make data interpretation difficult. Relatively high SO2 emissions corresponding with active magma recharge could be expected at Shiveluch to support the high level of eruptive activity. Alternatively, if the magma supply is shallow and volatile depleted, or more silicic in composition (lower S content), low SO2 emission rates would be expected. Mount St. Helens: The low SO2 emission rates measured at Mount St. Helens are consistent with a shallow, degassed magma. This agrees with the decrease in lava extrusion during the waning stages of the eruptive cycle at the time of sample collection. Future work involving collection of additional measurements and integration of the emission rate data with seismic, geodetic, and petrologic datasets from the target volcanoes may help to constrain the variables controlling the underlying magmatic systems of Bezymianny, Shiveluch, and Mount St. Helens volcanoes, and elucidate magmatic system response to edifice collapse. Cascades Volcano Observatory website: http://vulcan.wr.usgs.gov, accessed June, 2009. Dirksen, O., Humphreys, M., Pletchov, P., Melnik, O., Demyanchuk, Y., Sparks, R., and Mahony, S., 2006, The 2001-2004 dome-forming eruption of Shiveluch volcano, Kamchatka: Observation, petrologic investigation and numerical modeling, Journal of Volcanology and Geothermal Research, 155, 201-226. Izbekov, Pavel, Personal Communication, January, 2009. Kamchatka Volcano Eruption Response Team website: htp://www.kscnet.ru/ivs/kvert/index_eng.php, accessed June, 2009. Schilling, S., Thompson, R., Messerich, J., and Iwatsubo, E., 2008, Use of digital aerophotogrammetry to determine rates of lava dome growth, Mount St. Helens, Washington, 2004 – 2005; in Sherrod, D.R., Scott, W.E., and Stauffer, P.H., eds., A Volcano Rekindled; The renewed eruption of Mount St. Helens, 2004-2006: U.S. Geological Survey Professional Paper 1750. Shipman, J., Izbekov, P., and Eichelberger, J., 2009, Petrologic insight into the magmatic systems at Bezymianny and Shiveluch volcanoes, Kamchatka, Russia, Sixth Biennial Workshop on Subduction Processes emphasizing the Kurile-Kamchatka-Aleutian Arcs (JKASP 6), June 2009, Fairbanks, Alaska. Smithsonian Institute Global Volcanism Program website: www.volcano.si.edu, accessed June, 2009. Figure 6: Preliminary results find daily average SO2 emission rates ranging from ~80 - 390 (+/- 50%) t/d for Bezymianny; ~40 (+1000%) t/d for Shiveluch; and from below detection limit to ~10 (+/- 50%) t/d for Mount St. Helens. Poor plume viewing geometry at Shiveluch volcano prevented the entire plume cross-section from being measured and thus, the values presented here should be considered under-estimates. Acknowledgements This work has been supported by NSF PIRE Award # 0530278, the University of Alaska Fairbanks College of Natural Science and Mathematics, and the Alaska Volcano Observatory.