A simple model for pediment formation.
Résumé
Pediments are very flat and smooth erosive surfaces, connected to higher relief by a scarp, that covers up totwo thirds of the Earth’s surface. A physical mechanism to explain their formation remains elusive. Commonlyaccepted hypotheses include: (1) the widening of an incised river network (lateral corrasion of Gilbert, 1877), (2)sheetflow erosion, (3) subsurface weathering and exhumation (Strudley et al, 2006) and (4) slope retreat, usuallyat the base of an escarpment (King, 1949), potentially helped by flexural isostatic rebound (Pelletier, 2010). Herewe explore the third hypothesis, which we believe applies mostly in regions characterised by intense rainfall wheredeep weathering profiles are commonly observed.In this study, using a new coupled model of groundwater flow and surface erosion, we highlight the criticalimpact of the geometry of the water table and of the unsaturated zone within a weathering profile to explain itsevolution through time. The model is calibrated and used to explain the formation of pediments as the product ofa dynamical balance between weathering front propagation and surface erosion. We also explore the effects ofabrupt changes in rainfall intensity and base level drop on the geometry of the predicted pediments.