Direct Summary of "Cobb Seamount", contibution number 415, Department of Oceanography, University of Washington. Deep-Sea Research, 1967, Vol. 14, pp. 191 to 201.)

Cobb Seamount

Cobb Seamount is an ancient volcano located in the northeast Pacific Ocean, 500 km (270 nautical miles) west of Gray's Harbor, Washington. Investigations of this feature, which commenced with its discovery in 1950 by the M.V. John N. Cobb, consist of over 927 kilometers of soundings, 34 bottom samples, 25 hydrographic stations, underwater photography, and 2 current time studies. This is an ancient volcano which rises from a base of 1500 fathoms (2743 meters) to within 18.5 fathoms (34 meters) of the surface and comprises an area of 824 kilometers sqared (240 square nautical miles). Slopes averaging twelve degrees are indented by four terraces at 500,100,80 and 45 fathoms. From the "45-fathom (82-meter) terrace" rises a basalt pinnacle 26 fathoms high 0with 45 degree slopes and a flat fissured top 200 meters by 400 meters. The mountain morphology and 27 + or - 6 million-year potassium-argon date of the basalt suggests that this was an Oligocene volcano which was terraced by wave abrasion. Subsequent subsidence to 500 fathoms (914 meters) was accompanied by terracing and near truncation by sea stillstands during Quaternary glacio-eustatic oscillations.