Hugh Converse


Remarkable near-continuous examples of barrier beach features are found in many coastal areas, worldwide. The most notable North American examples are the margins of North America along the Atlantic and Gulf of Mexico, where barrier islands are found along more than 60 percent of the coastline. There are, in fact, 280 large-scale individual barrier features, 70 of which are highly developed and 100 more are being developed (Hobson, et al, 1980). These barriers have been built out of the enormous volumes of sediment available from the extensive watersheds of eastern and central North America and, through the ages, appear to have migrated long distances across a wide continental shelf in response to the interplay of waves and tidal currents, eustatic sea level fluctuations and sand supply. Barrier features are less in evidence on the west coast of North America though they are by no means absent. For example, along a 60-mile reach of the Oregon-Washington coast adjacent to the Columbia River mouth, impressive barrier spits have straightened the coast by blocking the bays and headlands. These are black-sand beaches, formed from the large sediment supply of the extensive inland basin of the Columbia (Bascom, 1980; Cooper, 1967), which has the 29thlargest discharge of the world's rivers (Inman and Nordstrom, 1971). The longest spit in this reach is about 19 miles long. The North Pacific coast is a high-energy wave environment, and these spits are continually shifting. Indeed, one of the most outstanding examples of continuing shore movement in North America is found at Cape Shoalwater at the north side of Willapa Bay, Washington where the inlet has migrated about 2.5 miles northward in the last 95 years across homesites, a cemetery and a lighthouse (Terich and Schwartz, 1981; US Corps of Engineers, 1971a).


barrier beach; California; beach features

Full Text: