The coast of the U.S. Pacific Northwest (PNW), the ocean shores of Washington, Oregon and Northern California, experience property impacts ranging from the erosion and flooding that occur during the hours to days of an extreme winter storm, on a decadal time scale with the erosion processes enhanced by strong El Niños, and with the expectation of future increased hazards associated with the global rise in sea level and the possibility that storm intensities and their generated waves will continue in the future. The PNW is noted for its extreme waves, with measured significant wave heights during winter storms having reached 15 m, combining with tides elevated by a surge to erode both foredunes and sea cliffs. The beach morphology plays an important role, particularly rip current embayments that act to localize the sites of maximum property impacts. Of concern, wave buoy measurements have documented that the storm-generated wave heights have been increasing since at least the 1980s, and research underway has found climate controls on the levels of storm surges. The impacts of rising sea levels are variable along this shore, in that while the entire PNW coast is tectonically rising, the local rate of rise in the land varies in comparison with the eustatic rise in sea level, with some stretches of shore being submergent while others are emergent. Projections of accelerated rates of global sea-level rise indicate that by the end of this century the entire PNW coast will be submergent, experiencing significantly increased hazards from erosion and flooding. In recent decades the most extreme erosion impacts have occurred during strong El Niños, specifically those in 1982–1983 and 1997–1998 when measured tides were elevated by 25–50 cm throughout the winter, caused by warmer water temperatures and ocean currents. During those El Niños there was also a diversion of the storm tracks with waves arriving more from the southwest, producing northward displacements of sand on the beaches, resulting in extreme “hot-spot” erosion north of headlands and tidal inlets. With these multiple climate controls on the processes, it is certain that during this century there will be far more erosion and flooding problems along the U.S. PNW than in the past. The ultimate hazard, however, are the predictions by seismologists that there will be another major subduction earthquake like that which occurred on 26 January 1700, with the land along this coast abruptly dropping by 1–2 m, followed minutes later by the arrival of immense tsunami waves, producing devastating impacts comparable to those recently experienced in Sumatra and Japan.

Authors: 
Paul D. Komar et al
Short Description: 
The coast of the U.S. Pacific Northwest experience property impacts ranging from the erosion and flooding that occur during the hours to days of an extreme winter storm, on a decadal time scale with the erosion processes enhanced by strong El Niños, and w
Product Number: 
ORESU-BR-13-002
Entry Date: 
Tuesday, July 2, 2013
Miscellaneous: 
Source: Coastal Hazards, Coastal Research Library 6. Charles W. Finkl (ed.). DOI: 10.1007/978-94-007-5234-4_21
Year of Publication: 
2013
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