Twenty-nine months of geomorphic change in upper Monterey Canyon (2002-2005)

Time serial multibeam bathymetry is used to evaluate geomorphic trends and submarine processes in the upper 4 km of Monterey Canyon, California. Seven high-resolution bathymetric surveys conducted between September 2002 to February 2005 show that the upper canyon axis and head grew in volume 1 000 000 m3 ± 700 000 m3, at an average annual rate of 400 000 m3/a ± 300 000 m3/a through lateral erosion and vertical incision. This net loss of substrate during the 29-month period is parsed between local erosion of 1 400 000 m3 and local deposition of 350 000 m3. A submarine landslide with a scar void volume of 70 000 m3 and debris pile of 52 000 m3 occurred between March 2003 and September 2004. During the subsequent months until February 2005, the slide scar grew 40% in volume while the debris pile shrank by 80%. The canyon-head rim adjacent to Moss Landing Harbor prograded seaward and retreated shoreward significantly (up to 50 m) during the study suggesting frequent episodes of sediment build up and subsequent down-canyon failure. A large field of sand waves located in the channel axis was completely reworked in each time series except for a 24 h period where no wave crest movement was noted, and a 32 day period where up-canyon migration of approximately 7 m was recorded in the northern tributary.