DESERT PAVEMENT PROCESSES AND FORM: INFLUENCES ON HYDROLOGIC PROCESSES AND LONG-TERM LANDSCAPE EVOLUTION IN ARID REGIONS

Desert pavements are ubiquitous, geologically persistent landforms in arid lands, whose formation typically is linked to deposition of eolian fines and development of underlying vesicular (Av) soil horizons. Surface exposure dating demonstrates that desert pavements are born and maintained at the land surface over geologic time. Clast size reduction in comparison to underlying parent material, along with armoring and packing of clasts in pavements contribute to their persistence, and studies of crack orientations in pavement clasts indicate physical weathering and diminution of particle size are driven by diurnal solar insolation. Over geologic time, cracks form and propagate from tensile stresses related to temporal and spatial gradients in temperature that evolve and rotate in alignment with the sun’s rays. Observed multimodal nature of crack orientations appear related to seasonally varying, latitude-dependent temperature fields resulting from solar angle and weather conditions. Properties of pavement surfaces and underlying soil profiles control surface hydrology, ecosystem function and the life-cycle of arid landscapes. Surface infiltration and soluble salt concentrations indicate saturated hydraulic conductivity of Av horizons declines on progressively older alluvial fan surfaces. Field observations and measurements from well-developed desert pavement surfaces on eolian mantled volcanic landforms also yield significantly lower infiltration rates, enhanced rates of overland flow characterized by high water: sediment ratios and reduced production of desert ecosystems. Consequently regionally extensive pavement and significantly decreased infiltration over geologic time have resulted in widespread overland flow, elaborate drainage networks on alluvial and eolian-mantled bedrock landscapes, and channel incision and regional dissection of the pavement-mantled landforms. However these once stable landscapes become progressively unstable with time, serving as sediment source areas for younger alluvial deposits (i.e., geologic life-cycle). Regional dissection of these desert landscapes appear to be controlled primarily by the intrinsic properties of pavement-mantled landscapes and not necessarily to external forces of climate change and tectonics.