LANDSLIDE CHRONOLOGY AND LAND DISTURBANCE HISTORY OF SANTA CRUZ ISLAND, NORTHERN CHANNEL ISLANDS, CALIFORNIA

Mass movements such as shallow soil slips and large-scale deep-seated failures are common features found on Santa Cruz Island, (SCI). Triggering mechanisms of mass movements on Santa Cruz Island include heavy rainfall, vegetation and vegetation change, bedrock geology, seismic activity, or other mechanisms.

Large paleo-landslides have been mapped across Santa Cruz Island and have been dated or inferred to be of late Pleistocene age. These paleo-landslides are extremely large, some of them many orders-of-magnitude larger than any historical mass wasting feature. The one directly dated paleo-landslide (Valley Anchorage, 12,780 +/- 390 BP; Pinter et al., 1998) corresponds approximately in age to the earliest archeological features on these islands as well as a coeval and sweeping vegetation change from coniferous forest to mixed brush- and grasslands during the period of ~15,000-13,000 cal BP. This project will test the hypothesis that large, prehistoric landsliding on Santa Cruz Island are concentrated during that time interval, suggesting a causal link with vegetation change. Alternatively, landslide activity may occur earlier in the Pleistocene, which may suggest climatic control. A third alternative hypothesis is that the timing of prehistoric landsliding may reflect the ~5000-year average recurrence interval on the Santa Cruz Island Fault. .

Field work will collect landslide samples and map the areas, volumes, distributions and frequencies (multiple versus single event) of the landslides on Santa Cruz Island. Stratigraphy and sedimentology of the latest Pleistocene will also be examined on Santa Cruz Island to understand the geomorphic processes that occurred which could determine the nature of the landslides. High resolution dating of organic carbon within the samples of collected landslide deposits will be acquired using AMS radiocarbon dating. With a precise time range of slope failure, triggering mechanisms may be inferred, especially when correlating climate (pre-13-15,000 cal BP) human land use (post ~13-15,000 cal BP), vegetation change, and seismic activity.