GEOPHYSICAL MAPPING OF SUBMERGED LANDSCAPES IN OREGON RESERVOIRS AS AN ANALOG FOR COASTAL ENVIRONMENTS

Coastal environments are impacted by sea-level change on glacial cycles lasting about 100,000 yrs. The most recent global sea-level rise (22 ka to present) submerged vast terrestrial paleolandscapes and archaeological sites along the Earth’s continental shelves. The search for these sites is typically conducted using various geophysical methods, which are ground-truthed through direct sampling. However, sampling in submerged environments can be prohibitive in terms of cost and logistics (e.g., submersibles, diving, and coring from vessels).

Inland reservoirs represent a novel analog for studying submerged terrestrial landscapes and archaeological sites. The same scale and time-independent processes that impact coastal environments through sea level changes are also produced through a reservoir’s annual infilling and drawdown cycle. Within these reservoirs, geophysical data collected during high water levels can be ground-truthed with terrestrial methods during drawdown, all at an overall lower cost than offshore research. Here, we present geophysical data collected within reservoirs of Oregon’s Willamette Valley to investigate the suitability of these methods for identification of paleolandforms in drowned river valleys known to contain archaeological sites of variable ages and materials. These settings allow the opportunity to observe characteristic geophysical signals of known landforms and archaeological sites and apply those observations to various other submerged environments. Additionally, these data can be used to monitor and manage changes to landforms and sites caused by repeated inundation and exposure.