EXAMINING PALEODRAINAGE EVOLUTION SINCE THE LAST GLACIAL MAXIMUM, NORTHERN CHANNEL ISLANDS, CALIFORNIA, USA

Newly collected, high resolution, sub-bottom CHIRP and side-scan sonar data from the Northern Channel Islands (NCI) platform were used to analyze the evolution of fluvial systems and paleochannel geomorphology since the Last Glacial Maximum (LGM). Sea level and drainage basin size and shape have changed greatly since the LGM (~20 kya and eustatic sea level ~120 m below present), during which, modern drainage networks extended to the paleoshoreline located near the continental shelf edge. Several paleodrainage networks were imaged in the acoustic data from the NCI platform. They exhibit variable morphology, ranging from single, well-defined narrow valleys to wider valleys with multiple channels. Regional climate and tectonics are consistent between these drainage systems, suggesting more localized controls on paleodrainage morphology. We examined drainage basin characteristics, including basin area, channel gradient, surficial geology, and shelf morphology to assess the relative importance of these variables on NCI paleodrainage evolution. These results could be used in future modeling to predict paleodrainage morphology offshore other modern river systems, with implications for natural and archaeological resources associated with these environments.