Pulsating turbidity currents with relationship to high swell and high tides

Abstract

THE Rio Balsas of Mexico has built a delta into the Pacific at latitude 18°N, virtually covering the narrow shelf, where the seaward slope is cut by numerous valleys. In 1967, during a period of large swell, Reimnitz¹ made a SCUBA dive to 18 m in a tributary of the Rio Balsas Canyon (Fig. 1) and encountered downcanyon current pulses estimated at more than 1 m s⁻¹. We visited the area on the RV Ellen B. Scripps in April 1975 and placed a current meter in Rio Balsas Canyon at a depth of 285 m. During the 5-d recording, a period of rather heavy swell occurred. This was indicated on our tide record (taken ∼ 0.5 km inside the river estuary) by wave-induced oscillations with amplitudes up to 20 cm at periods of about 3 or 4 min. These persisted for approximately 36 h (Fig. 2). High swell was also observed on our fathometer records during traverses nearshore, and wave heights up to ∼ 5 m were seen, considerably larger than during the rest of our study.