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Volatile emissions from the crater and flank of Oldoinyo Lengai volcano, Tanzania

January 1, 1996

As a comparison to airborne infrared (IR) flux measurements, ground-based sampling of fumarole and soil gases was used to characterize the quiescent degassing of CO2 from Oldoinyo Lengai volcano. Aerial and ground-based measurements are in good agreement: ∼75% of the aerially measured CO2 flux at Lengai (0.05–0.06 × 1012 mol yr−1 or 6000–7200 tonnes CO2 d−1) can be attributed to seven large crater vents. In contrast to Etna and Vulcano Island, where 15–50% of the total CO2 flux emanates diffusely through the volcanic flanks, diffuse emissions were measured only within 500 m of the crater rim at Lengai, contributing <2% of the total flux. The lack of extensive flank emissions may reflect the dimensions of the magma chamber and/or the lack of a shallow fluid flow system. Thermodynamic restoration of fumarole analyses shows that gases are the most CO2-rich and H2O-poor reported for any volcano, containing 64–74% CO2, 24–34% H2O, 0.88–1.0% H2, 0.1–0.4% CO and <0.1% H2S, HCl, HF, and CH4. Volatile emissions of S, Cl, and F at Oldoiyno Lengai are estimated as 4.5, 1.5, and 1.0 × 107 mol yr−1, respectively. Accuracy of the airborne technique was also assessed by measuring the C emission rate from a coal-burning power plant. CO2 fluxes were measured within ±10% near the plant; however, poor resolution at increased distances caused an underestimation of the flux by a factor of 2. The relatively large CO2 fluxes measured for alkaline volcanoes such as Oldoinyo Lengai or Etna may indicate that midplate volcanoes represent a large, yet relatively unknown, natural source of CO2.

Publication Year 1996
Title Volatile emissions from the crater and flank of Oldoinyo Lengai volcano, Tanzania
DOI 10.1029/96JB00173
Authors K.W. Koepenick, S.L. Brantley, J. M. Thompson, G.L. Rowe, A.A. Nyblade, C. Moshy
Publication Type Article
Publication Subtype Journal Article
Series Title Journal of Geophysical Research B: Solid Earth
Index ID 70018953
Record Source USGS Publications Warehouse
USGS Organization Volcano Hazards Program
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