Possible rip current origin for bottom ripple zones, to 30-m depth

Side-scan sonar records along the moderate- to high-energy Pacific Coast of Mexico show ripple-marked bands normal to the surf. These bands have been traced as far seaward as 1,500 m from the beach in water as deep as 30 m. There is strong evidence that these ripple bands are produced by rip currents. Earlier studies suggested that rip currents do not extend to the bottom beyond the breaker zone. Our interpretations indicate that rip currents—probably those that develop under severe wave conditions—transport sediment, shape the bottom, and produce internal sedimentary structures much farther seaward than was previously believed.