Carpinteria Salt Marsh Reserve

20 Oct, 01 AM - 28 Oct, 10 AM

Recent tsunamis, including the devastating tsunamis that occurred in Sumatra and across the Indian Ocean (December 26, 2004), Samoa (September 29, 2009), Chile (February 27, 2010), and the Japan (March 11, 2011), have heightened our awareness of the need for a more accurate assessment of tsunami hazards in Southern California. An active area of tsunami hazard research focuses on the identification and interpretation of ‘tsunami deposits’ – sediments entrained by a tsunami, transported, and then deposited in coastal environments. Tsunami deposits are most often found in beach and lagoon environments that lie in seismically active regions where tsunamis are common. Lagoon and marsh environments are particularly useful because relatively low energy coupled with relatively high sedimentation rates increase the potential to preserve deposits. Also, the tsunami-deposited sand makes a sharp contrast with the mud and peat often characterize the sediments from these environments, facilitating identification of tsunami sediments. In locations where the recorded history is short relative to the geological record (i.e. Southern California), tsunami deposits are a way to investigate the magnitude and frequency of potentially destructive tsunamis. Minor tsunamis have impacted the Santa Barbara County coastline in the historic past (for example, the 1812 tsunami) but little is known of the potential for large tsunamis along this stretch of coastline. Carpinteria is an important location to explore for tsunami deposits because of its proximity to offshore fault systems and offshore landslides, both potential causes of tsunamis, and because human impacts on the marsh are small relative to other marshes in southern California. Our preliminary reconnaissance, on May 7, 2004 showed the presence of sand layers in cores taken at the marsh that may have been deposited by tsunamis. The results of our initial reconnaissance warranted further investigation to determine an origin for the sand layers. Further investigations identified four groupings of cores that contained candidate tsunami deposits. Final results of this investigation are still pending. Recent work by Tom Rockwell and others on Holocene marine terraces between Ventura and Carpenteria has demonstrated that the Ventura Avenue Anticline (VAA) and associated Pitas Point – Ventura thrust have produced large uplift events. The amount of inferred uplift, on the order of 6-9 m per event, could produce a sizeable tsunami along the Santa Barbara – Ventura County coastline. Radiocarbon dates suggest uplift events at about 0.8 ka and 1.9 ka and suggest that the recurrence of such events is in the range of a thousand years. Gouge cores taken during the initial investigation were not sufficiently deep to provide the age resolution necessary to capture tsunami deposits from these uplift events. We propose to take several deeper cores within the marsh to look for evidence fro tsunami inundation from these large uplift events. Our primary method of investigation will uses a portable hydraulic corer that can take cores several meters depth. The coring unit can be used with little impact to the marsh. The coring unit is a small tripod, about 1.2 m base, that has screw anchors at the three corners. On the tripod is mounted a hydraulic system that works off of a foot pump. The core barrel and core stem fit through the middle and are pumped into the ground in about 80-90 cm drives, and then the core is extracted the same way. Core depths in ideal sediments can reach up to 9 m. Cores from Carpinteria may be considerably less. The advantage of this system is that whole cores are preserved for examination in the lab and the depths sufficient to capture tsunamis deposits from the uplift events, and possibly expand on the record of uplifts. We expect to take deep cores at from 8-10 sites throughout the marsh. While at the marsh, we may also attempt top recover some more gouge cores (30 and 60 mm barrels) and source sediment samples similar to what was done on our previous investigations. We will take great care to be ecologically sensitive and to refrain from disturbing plants and animals, or the work of other researchers.

Visit #29659 @Carpinteria Salt Marsh Reserve

Approved

Under Project # 8843 | Research

Carpinteria Marsh Tsunami Deposit Investigation

research_scientist - US Geological Survey

Reservation Members(s)

Group of 2 Graduate Student Oct 20 - 28, 2012 (9 days)
Robert Peters Oct 20 - 28, 2012 (9 days)
Group of 4 Research Scientist/Post Doc Oct 20 - 28, 2012 (9 days)

Reserve Resources(s) | Create Invoice

Day Use Only 7 Oct 20 - 28, 2012