Sea-Cliff Erosion Along the Oregon Coastby Paul D. Komar, Oregon State Univ, Corvallis, United States,
Shuyer-Ming Shih, Oregon State Univ, Corvallis, United States,
Abstract: Sea-cliff erosion is a problem along the coast of Oregon in that many communities have been built on terraces affected by bluff retreat. There is considerable coast-wide variability in the rates of cliff erosion that are not explainable in terms of ocean processes. This variability is likely due to tectonic activity that is causing differential uplift rates along the coast. In areas where sea-cliff erosion is significant, there are marked differences in the nature of the erosion processes. In the Newport area the cliffs consist mainly of seaward-dipping Tertiary mudstones that are susceptible to landsliding, and this process dominates cliff retreat. In the Lincoln City littoral cell the cliffs are entirely Pleistocene sands that tend to erode uniformly with minimal development of landsliding. In that littoral cell there is a longshore variation in beach-sediment grain sizes, ranging from a coarse-sand reflective beach to a fine-sand dissipative beach. Rip-current embayments are more important to cliff erosion on the reflective portion of the beach, producing bluff retreat that has a high degree of spatial variability and is extremely episodic. Wave run-up during extreme storms is more important on the dissipative portion of the beach, but the waves generally act to remove only the accumulated talus brought down by subaerial processes. Excluding the landslide areas, cliff retreat along the Oregon coast is occurring at a low rate, probably because of its tectonic setting that produces coastal uplift.
Subject Headings: Erosion | Cliffs | Coastal environment | Beaches | Landslides | Littoral drift | Uplifting behavior | Oregon
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