Extract from related chapter 5.5.2 in reference: The Orca Seamount was discovered in the central basin of the Bransfield Strait around the posit 62°26'S and 58°24'W on the west side of the Antarctic Peninsula, the most western area of the south polar continent. Through the discovery was made known in 1987, it was only during three bathymetric surveys with high resolution fan echosounders between 1993 and 1995 that the character and complete shape of a remarkable volcano seamount became evident. The data acquisition and processing revealed a spectacular crater of 350 m depth. The relative hight of this 3 km wide "caldera" rim is 550 m with a basal diameter of the seamount cone of 11 km. Its flanks are about 15° steep but in some places the slope reaches up to 36°. The nearly circular shape of the Orca edifice spreads outh with several pronounced spurs, trending parallel to the basin axis in a northeast-southwest direction.The Bransfield Strait is a trough-shaped basin of 400 km length and 2 km depth between the South Shetland Island Arc and the Antarctic Peninsula, formed by rifting behind the islands. The separation of the South Shetland island chain from the peninsula began possibly several million years ago. The active rifting is still going on however, and has caused recent earthquakes and volcanism along the Bransfield Strait. The Strait hosts a chain of submerged seamounts of volcanic origin with the presently inactive Ora Seamount as the most spectacular one. The South Shelfand Island owe their existence to a subduction related volcanism which is perhaps 5-10 times older than the age of Orca and the other seamounts along the central basin of the Bransfield Strait.

Image 5.5.2-1 (various views): Orca Seamount, Antarctica. Close up multibeam echosound image. The color coded 3D-image reveals details of the inner crater and the partially irregular rim of the Orca volcano, being on of the largest known in the Antarctica region.Image 5.5.2-2 (orca_pos1.tif): Environment of the Orca Seamount. Multibeam echosounder image. The arrow indicates the Orca position inside the Bransfield Strait along the Antarctic Peninsula. Despite the coarser resolution by the standard grid of 1 km the trench on the western side of 5000 m depth is clearly visible.Image 5.5.2-3 (orca_pos2.tif): Environment of the Orca Seamount. Multibeam echosounder Image. The arrow indicates the Orca as one of a chain of seamounts inside the Bransfield Strait. The standard grid of the depiction of 1 km, which cannot resolve the crater of the Orca volcano, demonstrates the peerless diagnostic capability of the best high resolution multibeam imaging shown in the close-up.