YARDANG EVOLUTION IN MESQUITE LAKE PLAYA, MOJAVE DESERT, CALIFORNIA

Yardangs, streamlined landforms sculpted by desert winds, are found along the northeast edge of the Mesquite Lake playa in the Mojave Desert. Historical aerial and ground photographs and lithology indicate that these yardangs are not the remnants of a former playa surface, but are the wind-eroded remnants of gypsum dunes and small sand sheets. Mesquite Lake yardangs recorded in 1906 and 1916 photographs no longer exist and the present yardang field is absent on 1952 aerial photographs. Yardangs were sculpted from cross-bedded, gypsum sands that originated from the southern and central playa and accumulated along the northeast edge of the playa. Most dunes became semi-stabilized by woody shrubs (nebkhas). Wetting and drying of the gypsum sands resulted in light cementation and increased cohesiveness of the sands. Wind abrasion from southerly winds streamlined nebkhas into typical yardang forms and carved yardangs from the sand sheet by exploiting variations in surface topography and sand cohesiveness. Initial measurements from repeat photography and erosion pins on and adjacent to 0.5–2.2-m-high yardangs indicate wind erosion is greatest at the yardang base and top, and on the surface of the cohesive sand sheet. In the first six months of measurement, surface erosion values ranged from 1 cm to 14 cm. Erosion above the yardang base was enhanced by wetting and drying, which resulted in easily deflated, thin crusts of gypsum. Also, desiccation cracks on the tops of some yardangs facilitated accelerated erosion by both wind and water. Yardangs at Mesquite Lake playa are short-lived landforms. They form and degrade over a few decades. Several cycles of yardang formation have occurred on the playa during the past century: new yardangs evolve shortly after new dunes are emplaced and stabilized along the edge of this dynamic playa.