INVESTIGATION OF SUBFOSSIL TREES AT IRELY LAKE, OLYMPIC NATIONAL PARK, WASHINGTON, USA

Submergence or burial of trees can allow their preservation. Measuring the age of these subfossil trees can help determine geologic events or climate changes such as earthquakes, drought, mass movements, and volcanic activity that occurred hundreds of years ago and that caused tree mortality. Irely Lake (20–4 acres) on the Olympic Peninsula is 15 km northeast of Lake Quinault. Irely Creek feeds the lake from the northeast and has built a small delta into the lake, which drains to Quinault River via Big Creek along its west margin. The lake contains numerous submerged and standing subfossil snags that were drowned after the lake formed. The standing snags consist mostly of western redcedar (Thuja plicata Donn ex D. Don), along with mostly submerged stumps of other species. We took several core samples and small wedge cuts from two of the western redcedar snags in the lake and scanned the polished samples at 0.01mm resolution. The scanned images were measured using ImageJ image analysis software. We are using analysis of the ring measurements with program Cofecha and visual examination of the samples to compare the subfossil trees, and are comparing this data with a master chronology of coastal western redcedar and with cores from old trees in the vicinity. The measurements of annual growth rings of these snags could help determine when the trees died and the age of the lake. Several mapped faults bound or run through the lake, but further assessments of the geology of the site are needed to further determine what formed Irely Lake, which submerged these trees, killing them.