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Sulfur, heat, and magma budget of Erta ‘Ale lava lake, Ethiopia

¹ Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, UK
² Laboratoire Pierre Süe, Centre National de la Recherche Scientifique, CEA, CE-Saclay, 91191 Gif/Yvette, France
³ Department of Geography, King's College London, Strand, London WC2R 2LS, UK
⁴ Department of Geography, University of Cambridge, Downing Place, Cambridge CB2 3EN, UK

We report here the first measurements of the SO₂ flux from Erta ‘Ale volcano (Ethiopia); the measurements were obtained in March 2003 with a portable ultraviolet spectrometer. Emission rates averaged 0.7 kg·s^–1 from the active lava lake and 1.3 kg·s^–1 from the whole volcano (including fumarolic emissions in the north part of the caldera). This modest output combined with an estimate of the melt sulfur content indicates a magma-supply rate of 350–650 kg·s^–1 (0.13–0.25 m³·s^–1). Radiant heat power from the lava lake, measured by infrared thermography, was found to vary between 5 and 30 MW according to activity of the lake surface and time elapsed since resurfacing events. We show that 8%–14% crystallization and/or 30–60 °C cooling of the upwelling magma reaching the lake, as well as degassing, are sufficient to increase magma density in the upper conduit and drive convection between the surface and a feeding reservoir. Fluctuations in the system, such as degree of vesiculation and magma supply rate, can be buffered by ascent or descent of the magma level within a flared vent region whose geometry directly controls lake surface area and hence heat loss.

Key Words: lava lake • Erta ‘Ale • SO₂ flux • heat loss • magma convection • differential optical absorption spectroscopy