Many submarine canyon walls consist of unconsolidated sand sitting at the angle of repose (~ 31°). The sand walls commonly maintain this slope for many tens of meters before leveling out at the canyon bottom. Where such angle-of-repose sand slopes occur within scuba diving depth, they present an opportunity to study subaqueous grain flows in situ. Such a study has been conducted in the head of Carmel submarine canyon, Carmel Bay, California.

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The object of the study was to determine the depositional pattern associated with subaqueous, gravity-driven grain flows. In particular, we attempted to determine whether the resulting deposits would exhibit inverse grading, as has been observed on the foresets of eolian dunes and in beach foreshore laminations. The experiments consisted of dumping dyed sand onto the slope, which generated a grain flow approximately 25 m long, and taking undisturbed cores both across and down the flow. The cores were dissected and the distribution of dyed grains determined.

Because the sand was divided into three size fractions that were each dyed a different color, grading and sorting patterns were readily discernible. In addition to inverse grading, we found sorting both down and across the flow, and the largest grains traveled the greatest distances. Because samples from natural, angle-to-repose sand slopes of Carmel Canyon show a downslope increase in grain size, we conclude that similar processes operate there. Once the slopes begin to level out, deposition of fine material from suspension becomes important and coarse material is no longer found in surficial samples.

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