SEDIMENTARY RECORD OF RECENT FLOOD EVENTS FROM SAUCES CANYON, SANTA CRUZ ISLAND, CALIFORNIA

The coastline of Santa Cruz Island, Ventura County, California, has a long history of environmental change due to anthropogenic modification, tectonic events, climate changes, and impacts from short-duration natural hazards such as storms and wildfires. While past studies have addressed the environmental history recorded in sediments preserved in lakes, estuaries, and offshore environments of the other Channel Islands, no sediment cores, to our knowledge, have been taken from the small estuaries that often exist at the mouths of coastal canyons along Santa Cruz Island. Here we show preliminary results from a transect of 7 vibracores up to 1.5 m in length taken from the estuary located at the mouth of Sauces Canyon (Cañada de los Sauces), along the southwest coast of Santa Cruz Island. These cores show 4 distinct, correlative, fining-upward packages above bedrock. Each 10-50 cm package has a sharp or erosional base and fines upward from gravel and pebbles to organic-rich clay. Charcoal fragments counted at the 125-250µ and >250µ size fractions vary regularly throughout the mud units, without distinct peaks commonly associated with fire or erosional events. Two radiocarbon dates of plant fragments taken at 30 and 80 cm depths in core SCI14-03 returned modern ages (calibrated using CALIBOMB (Reimer et al., 2004) to 1956-2006 A.D.), while one radiocarbon date (microscopic charcoal, likely reworked) returned an age of ~5000 yrs BP. Preliminary Pb-210 data provides support for the younger radiocarbon ages, suggesting the top three packages are less than 150 years old. Therefore, we hypothesize that each of these fining upward packages represents a high-intensity terrestrially derived flood event separated by clay accumulation and re-establishment of wetland vegetation during periods of quiescence. The present geochronological data indicate at least 3 such events have occurred in the last 150 years, but higher-resolution geochronology is necessary before a recurrence interval and mechanism can be established with confidence.