Acoustic Reflexivity (Backscatter) Image: Sur Ridge & Sur Canyon, Monterey Bay, California, 1998

Sur Ridge, Platform, and Slope

Sur Slope is located south of the Monterey Canyon system and extends south to Sur Canyon. It has a broad half-cone shaped morphology and is capped by the Sur Platform or shelf, which separates Monterey Canyon from Sur Canyon. The Sur Platform projects seaward from Point Sur to a depth of 1,000 meters, the depth of the shelf break in this area. The upper part of the cone in the north and west has smooth topography and is relatively undissected compared to the southern part. Two prominent protrusions exist on Sur Slope and consist of Sur Ridge and Surveyor Knoll. At the northern end of Sur Ridge, a star-shaped head of a large gully is defined by the branching nature of the gully’s main channel, splitting into three distinct, evenly separated arms of approximately equal lengths.

A north-south lineation extends for over 50 kilometers across the lower Sur Slope. Where this lineation crosses the base of the slope, the Sur Canyon bends sharply to the south, and the western side of the canyon is comprised of a steep north-south trending cliff. This lineation is mapped as a fault and appears to control the east facing cliff and trough morphology of Sur Ridge. It appears to continue northward to the star-shaped head gully.

The western part of the Sur Slope steepens, and landslide scars are prominent from 1,500 to 3,000 meter depths. This major field of landsliding extends from Monterey Canyon to Sur Canyon and covers an area of more than 880 square kilometers. Within this field individual scars can be identified which range from less than 0.5 square kilometers to more than 11 square kilometers in area. Potential areas of composite slumping cover areas as big as 55 square kilometers. The largest scar was mapped and named Sur Slide by Normark and Gutmacher (1988).

Sur Canyon

Sur Canyon is located approximately 60 kilometers south of the head of Monterey Canyon. Its multiple heads notch the southern part of the Sur Platform. Sur Canyon is sinuous but generally trends west for more than 50 kilometers from its head to where its main channel sharply bends south and its floor broadens.

There are four major meanders—two near the head of the Sur Canyon main channel in approximately 1,000 meter water depth and two farther down canyon in approximately 1,500 meters of water. The floor of the canyon averages about 0.25 kilometers in width from the upper meanders to the down canyon bend, where the channel widens considerably to approximately 0.75 kilometers.

Four very straight, south-trending channels (or chutes) are present above and to the west of a fairly extensive (95 square kilometers) landslide field located just north of the upper meanders. One chute enters the head of the landslide field, and the others enter the main channel of Sur Canyon. All extend up to the flat shelf floor of the Sur Platform.

Landslides are prominent along the Sur Canyon, with well-defined slumps and flows concentrated along the northern wall of the canyon in the vicinity of the upper meanders as well as in the lower part of the canyon. Down canyon (at 1,500 meters), the Sur Canyon channel winds sinuously through steep walls. Several small slumps exist along this stretch of canyon, but mass failures appear considerably less prominent than elsewhere along the canyon.