Abstract

A dune field of uniform 6-m-high barchan ridges, about 40 square km in area, has blown inland from a barrier beach and has formed a partition of sand across the lagoon. The partition connects the barrier beach with the Baja California mainland. During 3.5 years of observation, the dunes advanced with a mean velocity of 18 m/year. This is equivalent to a discharge of 23 cu m of sand/m width/year. This discharge acting over the 1800-year life of the barrier beach, as dated by Carbon-14, is shown to be compatible with total volume of sand required to extend the dune field across the lagoon to the mainland. Observed travel rate of dunes was about twice that predicted from wind measurements.

During high water accompanying spring tides, the floor of the interdune areas is inundated by water from the lagoons; thus, the windward margins of the dunes are subjected to the action of small waves generated by wind. The waves form miniature barrier beaches that are preserved as the dune migrates and serve as fortnightly and monthly time markers in the sediments. Avalanche bedding is the most common small-scale internal structure in the dune field. Gently sloping laminations associated with wind-blown ripples and with wave swash on the miniature barrier beaches are also common.

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