Mountain mass denudation and piedmont formation in the Mojave and Sonoran deserts

Abstract

Map analysis of 45 mountain masses. Migration of the piedmont junction in embayments extends the piedmont by removing the divides between the embayments, whereas migration of the piedmont junction along the mountain front causes the piedmont to be extended by mountain front retreat. In the mountain masses studied, the percentage of the total piedmont junction occurring in embayments (% EPJ) is directly related to the area (A) of a mountain mass and inversely related to its relief (R), and A and R together account for 81 percent of the variation in % EPJ. Inasmuch as the former relationship dominates the latter, it is evident that as a mountain mass diminishes in size there is a tendency for % EPJ to decrease and hence for divide removal to become progressively less important relative to mountain front retreat. Field data suggest (1) that channels are capable of turning abruptly after issuing from a mountain mass and of eroding more than half the mountain front in some mountain masses; (2) that, nevertheless, hillslope processes usually affect a greater part of the mountain front than channel processes; and (3) that even in embayments, hillslope processes usually play an important role in piedmont junction migration.--Modified journal abstract.