Contrasting Effects of Propagating Versus Focused Uplift on Himalayan Erosion

Abstract

The Himalayas have undergone rapid uplift, intense orographic precipitation, and enhanced erosion since the Miocene. Observed correlations among deformation, precipitation, and erosion have motivated contrasting interpretations, ranging from long‐term feedbacks between denudation and ductile crustal extrusion to models dominated by brittle thrust accretion. Here, we distill these competing hypotheses into two end‐member uplift styles—spatially propagating uplift and focused uplift—and use a coupled numerical model of prescribed uplift, orographic precipitation, and surface processes to simulate landscape evolution in the Nepalese Himalaya. Both uplift models reproduce first‐order geomorphological observations, low‐temperature cooling ages, and transient correlation among uplift, precipitation, and erosion. Despite these similarities, the two uplift models yield systematically different long‐term behaviors. Propagating uplift model produces a nonsteady state landscape in which erosion does not balance uplift, whereas focused uplift model establishes a steady state. High‐temperature cooling ages increase gradually from the southern, presently tectonically active zone toward the northern suture under propagating uplift, but exhibit a sharp rise under focused uplift. In addition, propagating uplift model produces sufficient total rock uplift north of the tectonically active zone but underestimates uplift within the active zone, whereas focused uplift generates larger uplift within the active zone while underpredicting uplift farther north. Thus, rather than identifying a single preferred uplift mechanism, our results suggest that combining characteristics of propagating and focused uplift provides a plausible, but non‐unique, interpretation of Himalayan exhumation patterns. This study provides a comparative numerical framework for evaluating uplift‐erosion relationships in large orogenic systems.