Santa Cruz Island Reserve

27 May, 04 AM - 08 Jun, 08 AM

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 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 C-14 BP; Pinter et al., 1998) corresponds approximately in age to the 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, which would suggest 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 possibly reflect the ~5000-year average recurrence interval for rupture on the Santa Cruz Island Fault with most recent activity at 11.78 +/- 0.1 ka (Pinter and Sorlien, 1991). Field work will collect landslide samples and investigate the distributions and frequencies (multiple versus single event) of the landslides on Santa Cruz Island. Stratigraphy and sedimentology of latest Pleistocene landslides will also be examined on Santa Cruz Island to understand the depositional history and geomorphic processes that occurred which could determine the nature of the landslides. A good representative collection of landslide deposits will consist of 60-75 extracted samples from about twenty Quaternary landslide (Qls) locations. Post-field work analysis will include x-ray diffraction and x-ray microanalysis which will be used to identify the clay mineral and elemental composition of the landslide deposits to conduct a comparative analysis of bedrock geology as a factor of failure. Bulk samples will be sent to Wyoming Analytic, Inc. to analyze the percentage of total organic carbon (TOC) in order to separate acceptable and unacceptable samples for accelerated mass spectrometry (AMS) and vitrinite reflectance. Vitrinite reflectance will identify charred material and indicate relevant temperature regimes that could promote or dismiss influences of human activity (anthropogenic deposits, e.g. hearths). High-resolution dating of organic carbon within the samples of collected landslide deposits will be done using AMS radiocarbon dating or direct count 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. The trigger mechanism for the mass movement will allow accurate interpretation of the landscape disturbance history of Santa Cruz Island and possibly the surrounding islands of the Northern Channel Island chain.

Visit #21129 @Santa Cruz Island Reserve

Approved

Under Project # 21567 | Research

Landslide Chronology and Land Disturbance History of Santa Cruz Island, California

graduate_student - Southern Illinois University

Reservation Members(s)

Group of 3 Faculty May 27 - Jun 8, 2010 (13 days)

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Dorm 3 May 27 - Jun 8, 2010
Jeep 3 May 27 - Jun 8, 2010
Pickup Truck 3 May 27 - Jun 8, 2010