WIND STREAKS - GEOLOGICAL AND BOTANICAL EFFECTS ON SURFACE ALBEDO CONTRAST

Two wind streaks in the eastern Mojave Desert of California were exami ned to gain insight into the origin of the surface brightness contrast that makes them visible, both on the ground and in remote sensing dat a. The two localities are: a 4-km-long dark streak oriented S43E from the Amboy cinder cone (34 degrees 32'N, 115 degrees 46'W), located on a Quaternary basalt flow covered with aeolian sand, and a 2-km-long da rk streak oriented S22E from a low hill near the southwestern base of Sleeping Beauty Mountain (34 degrees 48'N, 116 degrees 20'W), located on a sand-covered alluvial surface. in both cases, the dark streaks ha ve enhanced rock abundances on the streak surface, relative to the sur roundings. At the Amboy streak, slope wash likely contributed to the r ock concentration on the streak surface, shielded from burial under ae olian sand by the cinder cone. Ar the Sleeping Beauty streak, the rela tive albedo contrast is strongly emphasized by the presence of Big Gal leta grass only outside of the streak. The albedo contrast of the Slee ping Beauty streak can be effectively eliminated by the seasonal prese nce of annual grass preferentially within the streak. Some plants may have reflectances that are strongly dependent upon viewing and illumin ation geometry, raising the possibility that certain terrestrial aeoli an features may appear variable on a diurnal basis. Alluvial processes appear to have been important at both localities for redistributing s urface materials, even given the infrequent rain conditions present in the Mojave Desert.