Auv Multibeam Bathymetry and Sidescan Survey of the SS Montebello wreck Offshore Cambria CA

An MBARI Mapping AUV survey of the SS Montebello wreck offshore Cambria, CA collected high-resolution multibeam bathymetry and sidescan imagery of the vessel and the surrounding seafloor. The Montebello was an oil tanker that was torpedoed and sunk about 11 km offshore in 275 m water depth by a Japanese submarine on December 23, 1941. The Montebello was loaded with 3,000,000 gallons of crude oil, and there is no evidence that significant leakage of that cargo occurred at the time of the sinking or in the 69 years since. The California Department of Fish and Game’s Office of Spill Prevention and Response (OSPR) commissioned the AUV survey as part of a multi-agency Montebello Task Force effort to assess the potential pollution threat. The survey data will be used to determine the extent and general character of the wreckage for a pending Task Force report and to guide any future ROV dive or assessment activity . The AUV surveyed the wreck site from altitudes of 75 and 25 m; the low-altitude high-resolution survey consists of a grid with a 50 m line spacing both parallel and orthogonal to the ship. The 200 kHz multibeam bathymetry images the wreck from both above and from the sides with an 0.5 m lateral resolution. The combination of soundings from all of the survey lines results in a three-dimensional distribution of soundings that delineates the external morphology and some of the internal structure of the wreck. 410 kHz chirp sidescan sonar data also image the site from both directions. The bathymetry data indicate that the Montebello was pitched forward down when it impacted the bottom, crushing and breaking off the bow section. Both forward and aft deckhouses are largely intact, and in fact the multibeam images the individual decks within those structures. About half of the forward mast remains, both amidships masts and the smokestack are missing. A good deal of the deck piping and equipment appears intact, and aside from the bow, the ship’s sides appear intact. The rudder is intact but leaning to port. The multibeam also imaged a considerable fish population above and around the wreck site.