Investigation of the relationships between basin morphology, tectonic uplift, and denudation from the study of an active fold belt in the Siwalik Hills, central Nepal

The present study investigates correlations between an extensive range of g eomorphic properties that can be estimated from a digital elevation model a nd the uplift rate on geological timescales. The analysis focuses on an are a in the Siwalik Hills (central Nepal), where lithology and climate can be considered as uniform. This area undergoes rapid tectonic uplift at rates o f up to 15 mm yr(-1), which are derived from the geometric pattern of a fau lt-bend model of fold growth. The selected geomorphic properties can be div ided in two categories, depending on whether or not the vertical dimension is taken into account. None of the planar properties are significantly corr elated to uplift rate, unlike those that include the vertical dimension, su ch as the: mean elevation of basins, hypsometric curve, and hypsometric int egral, and relief defined by the amplitude factor of length scaling analysi s. Correlation between relief and uplift rate is observed for all length sc ales of topography shorter than 600 m, which suggests that all orders of th e streams are able to adjust to the tectonic signal. Simple mass balance co nsiderations imply that the average elevation is only 10% of surface uplift , suggesting that a dynamic equilibrium has been reached quite rapidly. Usi ng a simple two-process model for erosion, we find that fairly high diffusi on coefficients (order of 10 m(2) yr(-1)) and efficient transport of the ma terial by rivers are required. This unusually high value for mass diffusivi ty at small length scales may be obtained by either a very efficient linear diffusion or by landsliding. Actually, both processes may be active, which appears likely given the nature of the unconsolidated substratum and the f avorable climatic conditions. Local relief in the study area may therefore be used to predict either uplift or denudation, but the prediction is calib rated only for that specific climatic and lithologic conditions and cannot be systematically applied to other contexts.