EVALUATING HOODOO FORM AND PROCESS USING TLS LIDAR POINT CLOUD DATA, BLACK MESA, NE ARIZONA

The advent of back-pack portable, high-resolution, precise, terrestrial LiDAR scanners (TLS) has opened a new dimension of scale in which we can make quantitative field observations. Specifically, TLS technology provides a unique platform to gather the 3D structure of entire outcrops or landforms at relatively high resolution (1-3 cm). Data collected using these instruments are particularly useful when the understanding of geomorphic processes requires precise measurements of form and/or change. We have introduced TLS techniques in on-going investigations of semiarid landscapes associated with weakly cemented sandstones along part of the Black Mesa escarpment of NE Arizona. Jurassic sandstones exposed along this escarpment are sensitive to moisture, thus climate, via hydration-expansion weathering of clay cements. Abundant sediment shed from weathered slopes has caused locally rapid valley floor aggradation and upper basin slope vertical denudation rates of 2-3 mm/year, as indicated by dendrochronology over 10-100 yr timescales, and cosmogenic radionuclide concentrations in hoodoo-capping concretions over 1000 yr timescales. These rates suggest rapid hoodoo formation. Employing the UNM LiDAR Laboratory Optech Ilris 3D terrestrial LiDAR scanner, we have constructed a high-resolution model of several hoodoos located on a treeless, east-facing slope of the escarpment. We are extracting profile and sectional information directly from the point cloud data, and generating partial models of hoodoo topography and slope to consider key processes in the formation of erosional hoodoos. To date, no detailed dimensional analysis of erosional hoodoos has been reported. Our data products also serve as inputs into highly detailed models of slope drainage networks that can provide insight to the details of convergent and divergent flow and other key hillslope erosion processes within the study area. Repeat scans can provide direct measurement of modern erosion rates and patterns. Continued investigation of this site will provide insight to the key processes of escarpment retreat and the delivery of sediment from these steep slopes to the nearby basin floor, which in turn may further elucidate the impacts of Holocene climate change on this rapidly evolving landscape.