A CUESTA STORY: DECIPHERING THE ROLE OF A MIGRATING TRANSVERSE ESCARPMENT USING GEOCHRONOLOGICAL DATING AND REMOTE MONITORING SENSORS

Migrating Transverse Escarpments (MTEs) are small bedrock escarpments acting as local drainage divides within strike valleys between larger, parallel cuesta escarpments. These features are ubiquitous in the Mancos Shale of central Utah, where erosion is mostly accomplished by shallow, precipitation-induced mass wasting. Surficial mapping suggests a rudimentary theory of a MTE’s life cycle: formation by local baselevel lowering, propagation by hillslope processes, and a final equilibrium position set by erosional conditions on either side of the divide. MTEs may be of particular relevance for several areas of geomorphic research, namely due to their water-dependent processes operating in highly erodible rocks, role in creating and maintaining relief along regional-scale cuestas, and expression of divide migration processes. However, our current understanding of MTEs is limited by a lack of quantitative data concerning the specific geomorphic processes that set propagation timescales. We address this issue by establishing a long-term monitoring laboratory at a single MTE (TNNK-1a) to serve as a control site for future investigations. Our goals are: A. Constrain TNNK-1a’s age and sediment flux, B. Investigate the relationship between mass wasting and various modes of water delivery.

The age of TNNK-1a is constrained by dating a correlated set of fluvial sediments and terrace surfaces using OSL, radiocarbon, and TCN techniques. Multiple sets of erosion pins and regolith creep markers measure sediment flux via changes in surface elevation and downslope translation. Flux measurements are complemented by high-resolution DEMs constructed semi-annually using structure-from-motion photogrammetry. A remote weather station continuously records rainfall, air temperature, relative humidity, and volumetric soil moisture. Morphological changes are recorded by three accelerometers and a trail camera that photographs the hillslope every six hours; mass wasting events observed by these devices are compared with weather station data to evaluate the moisture content required to initiate slope failure and the capacity of different weather events to wet the regolith. Data from these experiments are used to calibrate numerical models designed to evaluate MTE propagation under various climatic conditions.