A seeping sea-floor in a Ria environment: Ria de Vigo (NW Spain)

 The occurrence of gas accumulations in the Ría de Vigo (NW Spain) have been characterized by the authors in previous research. Pockmarks frequently appear on seismic and sonar records, covering ca. 45% of the sea-floor of the study area, which indicates that gas expulsion is not an uncommon phenomena in the coastal Ría environment. Here we report the occurrence of gas seepage for the first time along the coast of NW Spain. Side-scan sonar, echo-sounder and high-resolution seismic techniques, were used for mapping gas-expulsion features. Some expulsion pockmarks sit over elongated features that represent bottom marks created by anthropogenic activity. Thus, these anthropogenic sites may act as preferential venting zones for gas, as well as being potential hazards on a muddy sea-bed such as that of the Ría where gas accumulates just below the surface of the sea-floor. Received: 25 May 1998 · Accepted: 20 November 1998