WIND EROSION AND MICROBIAL BINDING AT THE WAVE, CENTRAL COLORADO PLATEAU, SOUTHWESTERN USA

At The Wave, a particularly photogenic landform along the Utah-Arizona border, modern southwesterly winds carrying sand abrade Jurassic Navajo Sandstone outcrops. Abundant cm-scale, transverse, upwind-facing, erosional steps cut sandstone sedimentary structures at a high angle. The small steps may be the erosional equivalent of wind ripples: high-energy impacts cut the steps, and each step shields a downwind flat from the low-angle approach of impacting grains. These step features resemble sastrugi, erosional forms cut into snow. Endolithic microbes lie just beneath the exposed sandstone surfaces, producing crusts necessary for formation of these erosional steps. The small steps are present on the walls of the smoothly-curved troughs at The Wave, on the walls of nearby circular alcoves, and on the bedrock domes at the centers of alcoves. Due to their locations and orientations, the large-scale curved troughs and alcoves could not have been formed by flowing water or by groundwater sapping; the small steps show they were sculpted by wind erosion. Microbial binding of the sandstone has three important effects: 1) reducing the effectiveness of wind erosion and the permeability of host rock, 2) acting as ecological engineers that reduce the amount of wind-blown sand covering the outcrop, and 3) reducing the habitat available for rooted plants, restricting them to sites where their roots can reach joints. Endolithic microbes dominate and maintain broad expanses of slickrock on the Colorado Plateau.