Geology

PRISM and GeoMapNW (http://geomapnw.ess.washington.edu) are currently developing detailed geologic maps of the Hood Canal Area. This southwestern portion of the Lowland, lacks new geologic maps that can be compared with recent mapping efforts in the central and northern Puget Lowland. Like much of the Puget Lowland, this area has been shaped by multiple glaciations, as well as, active fluvial, coastal, and hill-slope processes. The area is the likely westward projection of a recently identified (and potentially seismogenic) structure, the Tacoma fault, which is of concern to growing populations in the region. Previous maps of the proposed area are either small scale (1:200,000) and/or predate the last two decades of significant advancement in our understanding of the stratigraphy and processes that shaped the Puget Lowland.

One of the primary benefits of the continued mapping in this area is to address growing social issues associated with rapid suburban development. The unconsolidated sediments in the area are a source for aquifers that provide drinking water to many residents. Without a clear understanding of the nature and extent of deposits in the area, there are no means for assessing the long-term availability and potential contamination problems with the local groundwater resources. The many lakes and coastal bluffs of the area have residential communities and the surrounding areas are being rapidly developed for the infrastructure necessary to accommodate the growing population. Due to the nature of the thick unconsolidated sediments throughout the area, slumping and landslides are frequent along Hood Canal and episodically prove to be a severe hazard to the residents living along the coast. Their occurrence has been demonstrated in other parts of the lowland to be well-correlated with particular stratigraphic sequences.