Soil gas methods to investigate geologic structures

Studies have shown that during significant proportion of the gases exsolved during the degassing of a magma body can diffuse through the surrounding rock. Carbon dioxide, being relatively inert, can migrate to the surface. The migration will follow fractures or other pathways, and the volatile may be in the liquid or gas phase. The mass gas flow may carry other inert gases with it, such as radon. Spatial variations in soil gas concentrations or gas fluxes can be indicate the underlying structure of the geology. It is an effective method for locating faults and fractures. A map is being produced of the diffuse degassing of Volcán de Colima. Radon, CO2 and additionally CH4 are being measured using an alpha scintillometer and infrared spectrometer. This map is revealing the location of some of the major faults associated with the volcano.