Eos, Transactions American Geophysical Union

Plume 1400 Meters High Discovered at the Seafloor off the Northern California Margin



On 17 May 2009, the Kongsberg EM302 multibeam echo sounder on board the U.S. National Oceanic and Atmospheric Administration's (NOAA) Okeanos Explorer was collecting bathymetry and water column acoustic data offshore of northern California when it suddenly imaged a previously undiscovered 1400-meter-high plume (Figure 1) rising from the seafloor at 40°32.13′N, 124°47.01′W. The ship was mapping in water depths of approximately 1830 meters and heading east up the northern California continental margin 20 kilometers north of the Gorda escarpment. The continental shelf in this area is known to have subsurface and water column thermogenic and methane gas, although no plumes from this area previously have been reported from deeper than the continental shelf.