A striking characteristic of the southeastern part of the remarkably linear northwest-southeast Algodones Dunes chain is a succession of regularly spaced, wholly enclosed flats exposing the alluvial substrate. Each flat is bounded on the northwest by a high active slip face of sand and on the southeast by a more gently inclined deflated sand slope, suggesting that the flats are moving southeasterly along the chain axis. Measurements over a 12-yr interval confirm this movement and indicate an average southeasterly movement of 35 to 40 cm/yr.

Development of alluvium-floored intradune flats is presaged by formation of ridge-and-hollow couplets farther to the northwest. Embryonic ridge-and-hollow forms extend almost to the northwestern tip of the chain. Development of long, linear transverse, sand-trapping ridges, which are instrumental in creating downwind hollows, appears to be an inherent characteristic of eolian transport under conditions of relatively smooth terrain, scanty vegetation, and a limited flux of sand supplied approximately orthogonally to a dominant resultant direction of drift.

Principal resultant sand drift produced by a multidirectional wind regime over the dunes is southeast; northeast is the next most favored direction. Secondary influences of faulting may account for the unusual linearity of the chain, which is probably a belt of shoreline dunes about 37,000 yr old. Intradune flats are large enough to be resolved on orbiter photos of Mars, and some of the patterns on the martian surface attributed to eolian processes may involve intradune flats.

First Page Preview

First page PDF preview
You do not currently have access to this article.