Figure 3. Example of an acoustic anomaly recorded by a 12 kHz echo sounder and interpreted to be from gas bubbles rising through the water column from a depth of about 90 m in between stations 24 and 77 (1.7 km SW of station 24 bearing 219°). Note that the gas bubble train extends as a straight line from a mound on the seafloor to the surface unlike the acoustic image of schooling fish that are typically seen as a near-spherical mass that does not extend from the seafloor to the sea surface.

http://geopubs.wr.usgs.gov/open-file/of03-122/figures/figure3
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