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Erosion in the Himalaya is responsible for one of the greatest mass redistributions on Earth and has fueled models of feedback loops between climate and tectonics. Although the general trends of erosion across the Himalaya are reasonably well known, the relative importance of factors controlling erosion is less well constrained. Here we present 25 Be-10-derived catchment-averaged erosion rates from the Yamuna catchment in the Garhwal Himalaya, northern India. Tributary erosion rates range between similar to 0.1 and 0.5mmyr(-1) in the Lesser Himalaya and similar to 1 and 2mmyr(-1) in the High Himalaya, despite uniform hillslope angles. The erosion-rate data correlate with catchment-averaged values of 5 km radius relief, channel steepness indices, and specific stream power but to varying degrees of nonlinearity. Similar nonlinear relationships and coefficients of determination suggest that topographic steepness is the major control on the spatial variability of erosion and that twofold to threefold differences in annual runoff are of minor importance in this area. Instead, the spatial distribution of erosion in the study area is consistent with a tectonic model in which the rock uplift pattern is largely controlled by the shortening rate and the geometry of the Main Himalayan Thrust fault (MHT). Our data support a shallow dip of the MHT underneath the Lesser Himalaya, followed by a midcrustal ramp underneath the High Himalaya, as indicated by geophysical data. Finally, analysis of sample results from larger main stem rivers indicates significant variability of Be-10-derived erosion rates, possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels.
The Greater and Lesser Caucasus mountains and their associated foreland basins contain similar rock types, experience a similar two-fold, along-strike variation in mean annual precipitation, and were affected by extreme base-level drops of the neighboring Caspian Sea. However, the two Caucasus ranges are characterized by decidedly different tectonic regimes and rates of deformation that are subject to moderate (less than an order of magnitude) gradients in climate, and thus allow for a unique opportunity to isolate the effects of climate and tectonics in the evolution of topography within active orogens. There is an apparent disconnect between modern climate, shortening rates, and topography of both the Greater Caucasus and Lesser Caucasus which exhibit remarkably similar topography along-strike despite the gradients in forcing. By combining multiple datasets, we examine plausible causes for this disconnect by presenting a detailed analysis of the topography of both ranges utilizing established relationships between catchment-mean erosion rates and topography (local relief, hillslope gradients, and channel steepness) and combining it with a synthesis of previously published low-temperature thermochronologic data. Modern climate of the Caucasus region is assessed through an analysis of remotely-sensed data (TRMM and MODIS) and historical streamflow data. Because along-strike variation in either erosional efficiency or thickness of accreted material fail to explain our observations, we suggest that the topography of both the western Lesser and Greater Caucasus are partially supported by different geodynamic forces. In the western Lesser Caucasus, high relief portions of the landscape likely reflect uplift related to ongoing mantle lithosphere delamination beneath the neighboring East Anatolian Plateau. In the Greater Caucasus, maintenance of high topography in the western portion of the range despite extremely low (<2-4 mm/y) modern convergence rates may be related to dynamic topography from detachment of the north-directed Greater Caucasus slab or to a recent slowing of convergence rates. Large-scale spatial gradients in climate are not reflected in the topography of the Caucasus and do not seem to exert any significant control on the tectonics or structure of either range. (C) 2016 Elsevier B.V. All rights reserved.