Mapping Program

Shepard Meander

Click on image for larger version.

Just below the base of the continental slope, directly offshore (west) of the Sur Platform, an oxbow meander occurs in the upper part of Monterey Seavalley. Northeast of this meander the floor of Monterey Seavalley is wide (3.5 kilometers), trending generally southwest. Prior to entering the meander, the seavalley trends almost due south, forming the upstream leg of the meander.

From the bend marking the start of the meander, the upstream leg is remarkably straight and trends nearly due south for over 12.5 kilometers, then sharply bends to the northwest (nearly a 110° bend). The active channel slips off a gentle, westerly dipping high along the eastern channel floor to occupy a thalweg that is located along the base of a 100 meter high erosional scarp. Just below the bend that denotes the beginning of the upstream leg, on the western or cut bank side of the channel, a pronounced 0.5-kilometer-wide by 1-kilometer-long re-entrant basin with a 50 meter headscarp and flat floor cuts into the neck of the meander. A short distance downstream from the re-entrant basin a landslide is also cutting into the neck of the meander.

Farther along the western wall of the upstream leg of the meander, several landslides occur. The elongation of the slides appear to align with a relic flow channel that curves along the distal margin of the meander.

The headward leg of the meander and the headward scarp of the spur are both 8 kilometers long. The drop in depth of the active channel floor here is from 3,420 meters to 3,460 meters, a total of 40 meters. The cut bank consists of a 150-100 meter scarp on the upstream (south) curve and a 300 meter scarp on the downstream (west) curve. These scarps are connected by a gentle 50 meter high scarplet that is cut into the toes of two landslides. The northern, or inside, wall of the channel is a 100 meter high, very gently dipping, headward slope of the meander curve. This slope steepens and increases to about 150 meters in height opposite the downstream cut bank.

The downstream leg of the meander bends back into the meander spur trending northeast for a distant of about 7 kilometers, where the channel makes its closest approach to the upstream leg. In this stretch the cut bank along the western side of the channel ranges from a 300 meter high steep cliff at the upstream curve to a gentle slopping 60 meter high bank near the downstream end of the leg. The inside bank (southeast side) is a gently dipping 100 meter bank that gives way to a flat 0.25-kilometer-wide channel terrace platform at the downstream bend or end of the leg. At the downstream edge of the terrace platform, a landslide occurs in the meander spur deposits.

The last bend in the meander changes the trend of the channel from northeast to northwest, a 90° turn. A point bar-like feature exists at this turn and bounds the channel on the southwest for about 8 kilometers of the 15 kilometer long stretch. The point bar is backed by a 100 meter high erosional scarp.

The northeastern wall of the northwesterly trending channel is a 200-meter-high, steep erosional cliff that extends from the terrace platform at the last meander bend for about 5.5 kilometers, to where the cliff becomes a very gently dipping bank prone to landsliding. Above this cliff and bank is a flat, older channel terrace platform.

At the end of the northwest trending channel, the seavalley takes another 90 degree turn to trend southwest. Here a point bar is again built out along the inside or southeastern margin of the channel. This bar continues back upstream around the bend to form the last 4 kilometers of channel bank along the southeastern side of the northwesterly trending channel.

MBARI provides these data "as is", with no warranty, express or implied, of the data quality or consistency. Data are provided without support and without obligation on the part of the Monterey Bay Aquarium Research Institute to assist in its use, correction, modification, or enhancement.

Entire survey area data—40 meter grid cell size
(geographic coordinates)

Grid Sun Illuminated Image Acoustic Reflectivity Image
at 1/2 grid cell size
Index Map Ascension
Sur Ridge/
Sur Canyon
Upper Lucia
Lower Lucia

Last updated: Oct. 08, 2013