Assessing Coastal Landscape Change for Archaeological Purposes: Integrating Shallow Geophysics, Historical Archives and Geomorphology at Port Angeles, Washington, USA

摘要

To mitigate saltwater flooding, the waterfront and downtown areas of Port Angeles, Washington were built-up with up to 8m of anthropogenic fill beginning in 1913. Shoreline modification continued into the present as this important natural deep-water harbour along the Strait of Juan de Fuca was developed for maritime industries. This and other historical activities obscured at least two historically occupied villages and burial sites of the indigenous Coast Salish Klallam people. Since these archaeological sites remain buried beneath the modern Port Angeles waterfront knowledge of the distribution of buried landforms, coastal zone processes, and estimates of site preservation and modern disturbance potential is needed for archaeological identification and preservation efforts. We created a model of the fill thickness by combining data from: (i) field observations, where the thickness of the fill could be observed directly in the landscape; (ii) topographic differences between pre-fill sounding maps and present-day LIDAR-determined elevations; and (iii) ground-penetrating radar (GPR) surveys. The GPR surveys also helped to reconstruct the now buried palaeoenvironment by identifying tidal lagoons, beach berms and stream channel features beneath the fill layer. The history of post-glacial sea-level change, here impacted by global eustasy, glacio-isostatic and tectonic factors is the first control on the development of quasi-stable coastal landforms suitable for long-term human occupation. Knowledge of past landscapes is a critical component in the development of future archaeological site catchment 'predictive' models based upon the spatial distribution and stability of landforms and resource accessibility prior to the Euro-American historic period of intensive shoreline modification. The geophysical and geomorphic identification and spatial reconstruction of buried landforms also provides needed insight into the geology of the subsurface and its control on the flow of groundwater and contaminants across the nearshore environment.