Figure 7. High-resolution sub-bottom profile images of gas plumes propagating through the centre of a submerged lake basin in 2008 and 2011.
(a) Column-like acoustic anomalies (blanked areas) interpreted as gas plumes are shown as areas with no colour and blue colour. Acoustic anomalies highlighted in blue correspond with the centre position of the submerged lake basin and interpreted as gas propagating through the submerged thaw-lake talik. In 2008, the top boundary of this acoustic anomaly was located ∼5 m below the seafloor; (b) in 2011, the position of the top boundary of this acoustic anomaly was reaching the seafloor, causing doming of the surface layer of sediments. During the survey in 2011, bubble plumes of CH4 releasing to the water column from the seafloor were observed at this site; multiple pockmarks in the seafloor were also documented within the site as shown in Fig. 6b.