Large-scale cycles of Holocene deposition and erosion at the entrance to Willapa Bay, Washington: Implications for future land loss and coastal change

Abstract

quent and recent aerial photographs provides a basis for evaluating the morphological stability of each area and explaining some of the stratigraphic successions recorded in the vibracores. The oldest map of the area is a preliminary survey conducted in 1852 by the U.S. Coast Survey. The 1852 map was not included in the morphological analysis because it appears to be a generalized illustration of the area with limited horizontal control. In contrast, the 1871 map (Fig. 2) provides accurate details that can be judged of exceptionally high quality by its agreement with modern geographically controlled depictions of stable land features. The 1999 aerial photographs, representing the most recent geographically controlled depiction of the area, also served as a base for mapping depositional environments (Fig. 1), locating field observation sites (Figs. 3-5), and locating topographic transects (Fig. 6).

Forcing of large-scale cycles of coastal change at the entrance to Willapa Bay, Washington

“…Elevations decrease away from the axes of both features (Fig. 7), and elevations parallel to and perpendicular to their axes are relatively uniform (Morton et al, 2002). The relatively smooth surface morphologies suggest that eolian dunes are not a significant component of these features and the maximum surface elevations correspond to heights of wave runup and overwash on the beach rather than corresponding to the crests of sand dunes.…”

“…3). Explanations of the techniques and detailed descriptions of the geomorphic and stratigraphic data sets are presented in Morton et al (2002).…”

“…Historical morphological changes at the entrance to Willapa Bay were documented by comparing available charts, maps, and aerial photographs between 1852 and 2003 (Morton et al, 2002). The 1999 georeferenced aerial photographs served as a base for mapping depositional environments ( Fig.…”

“…Segments of Empire Spit were constructed or became emergent in the late 1920s. Since then, the spit has undergone substantial change including its landward migration, lateral elongation, and segmentation (Morton et al, 2002).…”

Tidal Flat Depositional Response to Neotectonic Cyclic Uplift and Subsidence (1–2 m) as Superimposed on Latest-Holocene Net Sea Level Rise (1.0 m/ka) in a Large Shallow Mesotidal Wave-Dominated Estuary, Willapa Bay, Washington, USA

“…are shown at sharp contacts between underlying laminated mud and overlying muddy sand, sand, or gravel lag (GL). Vibracore log KI11 was taken from Morton et al (2002). All four of the vibracores from the exposed northern tidal flats (W1-W4) grade up-section into sand or muddy sand layers ( Figure 8).…”