UC Santa Barbara

Southern California is highly susceptible to hazards related to seismic activity and storms linked with El Niños and Atmospheric Rivers. These hazards are capable of incurring flooding, debris flow, coastal inundation, and rapid coastal erosion. Although much work has been done using lacustrine and deep marine sediment records to reconstruct the frequency of these past events, coastal records from lagoons and estuaries are less well documented. Here we present detailed sedimentologic and geochemical analysis of sediment cores, constrained by radiocarbon dates, from two estuarine/lagoon systems from coastal Southern California, Campus Lagoon and Las Salinas Lagoon. Our results record multiple occurrences of marine inundation thought to record storms of similar or greater magnitude as the catastrophic winter storms of 1861-1862. At least three of these events occurred pre 149 calibrated years before present (CYBP), one between 149 and 397 ± 22, two between 397 ± 22 and 617 ± 105 CYBP, and three between 1050 ± 200 and 3400 ±190 CYBP. These events establish a historic recurrence interval of ~660 years, and a post 2000 CYBP interval of 320 years, comparable to other California records. However, two of these pre-1 ka events may be the result of tsunami washover rather than storm washover as they correlate to large magnitude seismic earthquakes along the Pitas Point fault at 1050 ± 200 and 2250 ± 300 CYBP. A simultaneous environmental shift from an open lagoon to barrier-lagoon is observed in both lagoons at 4300 ± 250 CYBP that is interpreted to represent the onset of beach progradation in the Santa Barbara Channel in response to slowing sea-level rise.