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

Diffuse degassing of CO2, CH4 and H2 was investigated at the surface environment of Cañadas caldera, Canary Islands, during the gas survey carried out in the summer of 1995. Soil CO2 concentration varied significantly from atmospheric levels to 30%, while soil CH4 and H2 contents ranged from 5 to 851 ppm and from 0.5 to 620 ppm, respectively. Soil CO2, CH4 and H2 distribution suggests that high diffuse degassing at Cañadas caldera is volcanic-structurally controlled. Anomalous soil H2 concentrations were identified at the summit of Teide and outside caldera boundaries, where the most recent eruption of Tenerife Island occurred. δ13C–CO2 data showed a magmatic, mixed magmatic–biogenic, and biogenic origin while a biogenic origin is suggested for soil CH4 at Cañadas caldera and its surroundings. By coupling the CO2/3He ratio with the 3He/4He ratio of fumarolic gas samples from the summit of Teide, we propose three possible sources for carbon: MORB-type, organic carbon and carbonate.