THE HOLOCENE RECORD OF TSUNAMI ACROSS THE CALIFORNIA COAST (Invited Presentation)

Tsunami threaten coastlines worldwide and California is no exception. The sources for tsunami across the California coast range from distant sources (e.g. Alaska) and large subduction zones (e.g. Cascadia) to more localized offshore structures such as thrust faults, landslides, and slumps. In this study we review a few of the incidences of tsunami with a focus on the Holocene record of overwash deposits within marshes and shallow estuaries and erosion of sandy beaches recorded in ground-penetrating radar profiles. Records of past tsunami are plentiful across the northern California coast due to its proximity to the Cascadia Subduction Zone. Near Crescent City the penultimate Cascadia rupture around 900 BP lead to significant erosion along a large sandy coastal plain. This erosion removed over 225,000±28,000 m³ of sand from a 1.7 km stretch of the coast. The identification of potential tsunami deposits across southern California remains more elusive with several potential local tsunami sources. One such potential source is a major rupture of the Pitas Point thrust (PPT) and folding along the associated Ventura Avenue Anticline (VAA) between the cities of Santa Barbara and Ventura. Cores collected in several estuaries along the Santa Barbara Coast including Devereux Slough, Goleta Slough, Carpinteria Slough, Dune Pond, and Campus Lagoon have failed to find evidence for significant overwash at the same time as reconstructed earthquakes across the PPT-VAA despite recording other periods of significant overwash likely due to historically recorded storms and other events. However, a record from a sixth site in a small coastal pond does seem to suggest evidence of major overwash at time periods coincident with earthquakes on the PPT-VAA. We discuss potential reasons why the overwash may have been recorded in this small coastal pond but not the other 5 sites. These studies highlight the potential risks of tsunami and other overwash events (e.g. storms) to the California Coast.