Morphology of San Antonio submarine canyon on the central Chile forearc

A multibeam survey was conducted over San Antonio submarine canyon, near Valparaiso, Chile, in April and May 1993 using the SeaBeam 2000 system on the R/V Melville. The bathymetric data from this survey reveal a canyon with an overall sinuosity of 1.25, a broad, roughly U-shaped cross-section along most of its length, and an almost constant channel slope above the forearc structural high. The course of the canyon is deflected to the north by a prominent structural high opposite the town of San Antonio. SeaBeam 2000 side-scan sonar data reveal high backscatter material on the floor of the canyon with a longitudinal fabric, reminiscent of stream braiding, and point bars formed on the inside of channel bends. We interpret this high backscatter material to be coarse sediment, transported down the canyon as turbidity currents. The source of these turbidity currents is probably the Rio Maipo, which enters the ocean near the head of the canyon.