Skip to Main Content

Abstract

The areal distributions of active-beach widths, eolian-dune fields, coastal-terrace heights and beach grain size are examined along a 1,000-km open coastline in the convergent Cascadia margin of the northeast Pacific. Beaches range from 10 to over 500 m in width in a total of 42 continuous beach segments, which are considered proxies for littoral cells at least 2 km long. Tectonic upwarping has exposed coastal-terrace deposits (1–30 m thick) and/or underlying bedrock to elevations as much as 120 m above mean sea level. The regional distributions of short-beach segments (average of 8–12 km long) in northern Washington and northernmost California—southern Oregon correspond to areas of maximum variation in terrace height, reflecting relatively rapid rates of tectonic vertical deformation. The three largest beach segments, 65 to 165 km long, are associated with major dune fields, and correspond to three of the largest river sources, namely the Eel, Columbia and Umpqua Rivers. Tectonic downwarping of inner-shelf sediment sinks might account for narrow, short-beach segments associated with the Klamath and Rogue Rivers. Six beach segments in central Oregon are isolated from either major river or high-terrace sand sources, and are assumed to be derived from trasgressive shelf sands. However, the observed longshore variability in these beach deposits indicates that pre-existing distributions of offshore sands were not uniform along the coast. Finally, longshore trends in increasing beach width, increasing dune development and/or decreasing beach grain size to the north in about one-quarter of the analyzed beach segments suggest a small net northward transport. However, inconsistent trends of all three variables in the remaining segments confirm the occurrence of short-term conditions responsible for reversing longshore transport in littoral segments effectively bounded by prominant headlands.

You do not currently have access to this chapter.

Figures & Tables

Contents

GeoRef

References

Related

Citing Books via

Close Modal
This Feature Is Available To Subscribers Only

Sign In or Create an Account

Close Modal
Close Modal