Oblique Dunes of Oregon Coast: ABSTRACT

Abstract

The oblique dunes of the Oregon coast are the largest (as high as 55 m) on the west coast of the United States. Where best developed, these perennial ridges have been migrating northeastward at an average rate of 4.4 m/year, as measured from aerial photographs dating from 1939 to 1975. The wind regime of the area can be characterized as obtuse bimodal, with sand-transporting winds from the north and northwest throughout the dry summers and between storms at other seasons, and from the south and southwest during fall, winter, and spring storms. Although the sand-transporting capacity of the southerly winds is reduced by accompanying rainfall, these winds are nevertheless strong enough to do more work than the northerly winds. Dune processes during the winter season of southerly storms include: (a) erosional smoothing of the south (stoss) slope; (b) erosion and formation of sawtooth remnants (yardangs) on the dune crest; (c) deposition by adhesion on the wet, low-angle north slope between the dune crest and the slip-face brink; (d) grainfall deposition on the west slip face, causing steepening to angles of 44° or more, followed by slumping; (e) local deposition by adhesion in wet interdune troughs; and (f) local subaqueous deposition in ephemeral interdune ponds and streams. Dune processes during the summer season of northerly winds include: (a) growth of small southeast-facing transverse dunes at the crests and on the south slopes of the oblique dunes, and in troughs between the oblique dunes; (b) pla tering of wind-rippled sand sheets against the base of the winter slip face, leading to the formation of a gently north-sloping apron; and (c) erosion of the upper part of the winter slip face, reducing the slope angle to 25° or less. End_of_Article - Last_Page 978------------