Soil gas CO2, CH4, and H-2 distribution in and around Las Canadas Caldera,Tenerife, Canary Islands, Spain

Diffuse degassing of CO2, CH4 and H-2 was investigated at the surface envir onment of Canadas caldera, Canary Islands, during the gas survey carried ou t in the summer of 1995. Soil CO2 concentration varied significantly from a tmospheric levels to 30%, while soil CH4 and H-2 contents ranged from 5 to 851 ppm and from 0.5 to 620 ppm, respectively. Soil CO2, CH4 and H-2 distri bution suggests that high diffuse degassing at Canadas caldera is volcanic- structurally controlled. Anomalous soil H-2 concentrations were identified at the summit of Teidei and outside caldera boundaries, where the most rece nt eruption of Tenerife island occurred. delta C-13-CO2 data showed a magma tic, mixed magmatic-biogenic, and biogenic origin while a biogenic origin i s suggested For soil CH4 at Canadas caldera and its surroundings. By coupli ng the CO2/He-3 ratio with the He-3/He-4 ratio of fumarolic gas samples fro m the summit of Teide, we propose three possible sources for carbon: MORB-t ype, organic carbon and carbonate. (C) 2000 Elsevier Science B.V. All right s reserved.