SEDIMENTOLOGICAL EVIDENCE FOR THE 1812 SANTA BARBARA TSUNAMI

On December 21, 1812, a magnitude ~7.2 earthquake struck the Santa Barbara basin. Contradictory historical accounts reference a coeval tsunami with runup heights of ~2m in Ventura, California. While deposits from the 3 week 1861-1862 storm that also flooded the coastline in this region have been identified in the geologic record, deposits from the 1812 Santa Barbara tsunami have not. We collected 6 cores from Alessandro Lagoon in Ventura to look for deposits from the 1812 tsunami. The cores were described and their grain size was measured. An age model was created using radiocarbon dating, charcoal, plutonium, exotic pollen, and spheroidal carbonaceous particles (SCPs). Two sand beds were found within the historical period. Both sand beds have a grain size and mineralogy similar to that of modern beach sand, but distinct from sand from the Santa Clara and Ventura rivers. The younger of the two sand beds is ~5-15 cm thick and likely represents the 1861-1862 storm identified in neighboring estuaries. The older of the two is ~3-7 cm thick and occurs within 20 cm of Spanish colonization in 1782. This sand bed likely represents the first recorded physical evidence of the 1812 tsunami. Our study improves our understanding for coastal hazards in southern California.