Shallow gas features in the Galician Rias Baixas (NW Spain)

Areas with gas accumulations and gas escapes have been mapped in two rias from Galicia (Ria de Pontevedra and Arousa) and compared with already published data from the Rias de Vigo (Garcia-Gil et al. 2002) and Muros-Noia (Magarinos-Alvarez et al. accepted). Calculations indicate different areas of gas-bearing sediments for each ria. Quantitative data from acoustic plume studies and pockmark densities in the seepage areas were also obtained. In terms of the area of gas-bearing sediment and seeping activity, the Ria de Arousa is found to be the most important from a quantitative point of view. Comparison of the locations of the gas accumulations with grain size distributions of sediments reveals a spatial coincidence with finer surface sediments that are mainly muds.