We provide empirical evidence for the impact of surface processes on the structure of the present-day foreland fold-and-thrust belt of the Himalaya. We have reconstructed and analyzed ten balanced cross sections distributed along the entire length of the Himalayan arc. Here, we focus on the Siwalik Group, which represents the deformed part of the foreland basin and consists of synorogenic Middle Miocene to Pleistocene sediments that form the youngest and frontal part of the Himalayan orogen. We make two important observations: (1) a distinct west-to-east increase in strain and strain rate correlates with plate convergence rates, and (2) belt morphology is inversely correlated with rainfall amount. According to the predictions of the critical taper model, an eastward increase in convergence rate would induce higher rates of material accretion. Thus, the Himalayan fold-and-thrust belt should widen eastward, yet we have observed the opposite. However, higher annual rainfall amounts and specific stream power appear to favor a narrower belt. Thus, we suggest that the morphology of the Himalayan foreland fold-and-thrust belt is controlled primarily by surface processes, in accordance with the critical taper model.

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