SAND MOVEMENT INTO CARMEL SUBMARINE CANYON, CALIFORNIA

J.R. Dingler, R.J. Anima

Abstract


Carmel Submarine Canyon heads in shallow water near Monastery Beach at the southeast corner of Carmel Bay, California, U.S.A. Very coarse sand, shaped into large oscillation ripples, covers the narrow shelf between the beach and the canyon; when this sand enters the canyon head, it lies at angles as great as the angle of repose. In some areas, these sand slopes show evidence of active grain flows in the form of downslope-coarsening, inversely graded deposits. The results of a dyed-sand tracer study adjacent to the canyon show that sand moved canyonward during the summer of 1979. Initially the dyed sand, which had been shaped into an oscillation ripple in the center of a 20-m by 60-m grid, moved offshore en ma sse. After a few days, though, the dyed sand dispersed with the center of mass moving canyonward. As wave-transported sand accumulates along the canyon rim, the upper slopes oversteepen, thereby causing some of the sand to avalanche downslope. Systematic changes in sand levels along three lines of rods over 15 months document preferential deposition of sand along the upper slopes; the greatest change occurred at the top of the lines (12-15 m depth) and the least at the bottom (30-40 m). Greater accretion during the spring months than during the summer months probably reflects the more energetic springtime wave climate. Between October 1981 and October 1982, 5.7 m3 of sand was deposited per meter alongslope on the middle line, which gives a calculated depositional rate of approximately 5 00 m /yr in the study area. Although we have monitored this area for over a year, we have not yet documented any large-scale events capable of flushing sand out of the canyon head. The only erosive event we have observed was a small grain flow we generated while digging on the slope.

Keywords


sediment transport; Carmel Canyon; California; submarine canyon

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