ASPECT-DEPENDENT FEEDBACKS BETWEEN REGOLITH PRODUCTION AND TRANSPORT AT THE SHALE HILLS CRITICAL ZONE OBSERVATORY

Understanding how regolith production and transport respond to perturbations in climate and/or tectonic forcing remains a first-order question in Earth science. Recent studies integrating geochemical and geophysical techniques in near surface studies of Earth’s weathered zone reveal a previously under-appreciated coupling between chemical and mechanical breakdown of rock during regolith formation. First order observations of the Susquehanna Shale Hills Critical Zone Observatory (SSHO), using high resolution LiDAR-derived topographic data and depths to hand auger refusal, reveal a systematic asymmetry in hillslope gradient and mobile regolith thicknesses; both are greater on north-facing hillslopes. Hydrologic and geochemical studies of at the SSHO also suggest asymmetric sediment transport, fluid flow, and mineral weathering with respect to hillslope aspect. Here, we investigate the role of (micro)climate in inducing fracturing and priming the development of the observed asymmetry. Shallow p-wave velocity profiles suggest differences in thickness for both the mobile and immobile regolith material with respect to aspect and are consistent with patterns of fracture densities observed in boreholes and with predictive cracking intensity models related to frost action. Similarly, p-wave velocity profiles correspond with chemical depletion profiles measured in the SSHO subsurface. This combination of data suggests that the feedbacks between chemical weathering and the physical structure of the SSHO subsurface may be driven by aspect-dependent microclimate asymmetry over geologic time.