USE OF RADIOCARBON DATING AND DENDROCHRONOLOGY TO INVESTIGATE A POSSIBLE SUBMERGED FOREST IN ELD INLET—A TEACHER-RESEARCHER PARTNERSHIP

We test evidence for, and possibly date subsidence in Mud Bay (Eld Inlet), 5 mi west-northwest of Olympia, Washington, by evaluation of historic maps and photographs, field investigations, and a combination of radiocarbon dating and tree-ring analysis of intertidally exposed snags.

Previous studies of submerged forests in Puget Sound show evidence of subsidence, possibly caused by movement along shallow crustal faults that intersect the south Puget Lowland (Gower et al, 1985; Sherrod, 2001). The discovery of a submerged Squaxin Island tribal village site called Qwu?gwes in Mud Bay provided early evidence of submergence at Mud Bay (Croes and others, 2005). Carolyn Garrison-Laney turned up additional evidence of subsidence there (Garrison-Laney, 2003).

Investigations in Mud Bay are challenging because of numerous pilings and intense historical use of the area. To look for possible in-situ subfossil trees, we have sampled submerged snags using hand saws and increment borers, have mapped them geographically using GPS (global positioning system) to within several meters, and have noted certain characteristics of each snag such as size and geologic/stratigraphic environment.

Two submerged (> 2m), bark-bearing Douglas fir snags have yielded calibrated calendric radiocarbon age ranges of A.D. 1420 – 1690 and A.D. 1710 – 1940 respectively at 95.4 percent probability (k=1.6), and thus these snags are not correlative. In our future investigations we will complete the reconnaissance mapping and sample collection of submerged snags and use dendrochronology to test for correlations of the samples with nearby tree-ring chronologies.

This proposed research will assist in the interpretation of the paleoseismic and environmental history of Eld Inlet as well as provide an important link for local high school students to recent geologic history. The project has been greatly assisted by a Partners-in-Science grant from the M.J. Murdock Charitable Trust.