Figure 4—Pediment Development Cartoon.
Cartoon illustrations of pediment development for both open- and closed-basin conditions, from numerical modeling experiments in Strudley et al. (2006). Bare-bedrock uplands lack topographic detail because of simplified initial conditions and the absence of bedrock incision by stream flow in the model. Time steps (t) are arbitrary and are used for illustration only; subscripts n, m, and p are used to denote large advances in model time (103-106 yr), while numeric changes in subscripts (0 to 1) indicate consecutive model time steps. Dashed lines illustrate bedrock surface for previous time step, t. Figures not drawn to scale; sediment thickness on pediments exaggerated for clarity. (A) Initial condition for open- and closed-basin models. (B-D) Open-basin pediment development: pediment and piedmont junction form as soon as the foot of the mountain mass retreats from the position of the fixed base level (time steps t0 to t1). Headward extension of pediment and piedmont junction continue through time step tn. (E-G) Alluvial fan and pediment development under closed-basin conditions. Following upslope migration of a piedmont junction, the mountain mass has eroded completely, leaving a pediment surface upslope and alluvial fan downslope (G). (H) Weathering rates an order of magnitude higher, combined with slightly higher rainfall rates (intensity or duration increased by a factor of ~2.5), produce faster growing pediments and, a ‘pediment association’ (downslope fan deposit, midslope pediment, and remnant mountain mass).
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Jan5 10
