Soil gas CO2, CH4, and H2 distribution in and around Las Cañadas caldera, Tenerife, Canary Islands, Spain

Abstract Diffuse degassing of CO 2 , CH 4 and H 2 was investigated at the surface environment of Canadas caldera, Canary Islands, during the gas survey carried out in the summer of 1995. Soil CO 2 concentration varied significantly from atmospheric levels to 30%, while soil CH 4 and H 2 contents ranged from 5 to 851 ppm and from 0.5 to 620 ppm, respectively. Soil CO 2 , CH 4 and H 2 distribution suggests that high diffuse degassing at Canadas caldera is volcanic-structurally controlled. Anomalous soil H 2 concentrations were identified at the summit of Teide and outside caldera boundaries, where the most recent eruption of Tenerife Island occurred. δ 13 C–CO 2 data showed a magmatic, mixed magmatic–biogenic, and biogenic origin while a biogenic origin is suggested for soil CH 4 at Canadas caldera and its surroundings. By coupling the CO 2 / 3 He ratio with the 3 He/ 4 He ratio of fumarolic gas samples from the summit of Teide, we propose three possible sources for carbon: MORB-type, organic carbon and carbonate.

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