SEEING THE WIND THROUGH THE TREES: AEOLIAN LANDFORMS IN NORTHWEST OREGON

Most of our understanding of the Quaternary geomorphology of northwest Oregon relates to fluvial and hillslope processes. Recent LiDAR surveys have brought the geomorphology of this region into focus and shed light on a greater diversity of landforms than previously recognized. Through the analysis of this data, I recognize three regions that are characterized by distinct, although inactive, aeolian landforms. A large (>30 sq. km) region of transverse dunes occurs along a ridge crest that forms the divide between the Nehalem and Columbia rivers. These dunes are characterized by gently sloping, convex-up, south-facing slopes and steep, north-facing, concave-up slip faces. The dune crests are sinuous in plan view, but overall define a prevailing wind direction from the south. No cross-cutting relations exist with features of a known age, but these duneforms exist on top of several large stabilized landslide complexes. On the west flank of the Portland Hills occurs a region of blowouts with associated parabolic dunes. Cross-cutting relations and differences in blowout morphology suggest at least two generations of these landforms are present. The orientation of blowouts and parabolic dunes indicate winds from the east-northeast, from the direction of the Columbia River Gorge. The lowest elevations of the blowouts are below the maximum inundation height for the late Pleistocene Missoula floods, suggesting at least the younger generation postdates the floods. Finally, near the town of Sandy are several small complexes of blowouts and parabolic dunes. The orientations of these landforms indicate winds from the east, likely funneled down the large glacial valleys on the southwest slopes of Mount Hood. Blowouts and parabolic dunes indicate the presence of vegetation and very localized sediment deflation-deposition coupling, whereas the large region of transverse dunes suggests a lack of vegetation and significant sediment supply when these were active. Altogether, these aeolian landforms provide information for climatic and environmental reconstructions and controls on the rates and timing of landscape evolution in northwest Oregon.