Tectonic control on ¹⁰Be‐derived erosion rates in the Garhwal Himalaya, India

Abstract

[1] 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 10 Be-derived catchment-averaged erosion rates from the Yamuna catchment in the Garhwal Himalaya, northern India. Tributary erosion rates range between~0.1 and 0.5 mm yr À1 in the Lesser Himalaya and~1 and 2 mm yr À1 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 10 Be-derived erosion rates, possibly related to nonproportional sediment supply from different tributaries and incomplete mixing in main stem channels.

Tectonic controls of Holocene erosion in a glaciated orogen

“…While it is difficult to assess our snow shielding estimates, we note the relative effect on erosion rates is similar to those based on snow-depth measurements within other snowy orogens (Wittmann et al, 2007;Norton et al, 2010;Scherler et al, 2013). 280…”

“…6). In tectonically active and previously glaciated mountain ranges there are three common orogenic processes that are most often suggested to dominate Holocene erosion rate patterns: climate gradients (Carretier et al, 365 2013;Olen et al, 2016), glacial modification of the landscape (Moon et al, 2011;Glotzbach et al, 2013), and patterns of tectonic rock uplift (Adams et al, 2016;Scherler et al, 2013;Godard et al, 2014). In the following we explore the relevance and applicability of these explanations to our data set.…”

“…Instead, we implemented a least-squares power function regression to explore possible connections between erosion and channel steepness, similar to other recent studies (Scherler et al, 2013):…”

Tectonic controls of Holocene erosion in a glaciated orogen

“…However, using a model based solely on fluvial incision in the Olympic Mountains would be misleading as the modern river channel likely still reflects the preferred geometry of PlioPleistocene glaciers (Adams and Ehlers, 2017). Instead, we implemented a least-squares power function regression to explore possible connections between erosion and normalized channel steepness, similar to other recent studies (Scherler et al, 2013):…”

Sensitivity analysis and implications for surface processes from a hydrological modelling approach in the Gunt catchment, high Pamir Mountains

“…Milliman and Syvitski, 1992;Galy and France-Lanord, 2001) and plays a crucial role in the global carbon cycle (Maher and Chamberlain, 2014), sound estimates of the hydrological water balance and water components are also of fundamental importance for Earth surface processes. The primary control of tectonically driven topographic steepness on erosion suggests that changes in water availability are balanced by complex interactions between channel steepness and width, as well as concentrated sediment transport (Burbank et al, 2003;Scherler et al, 2014). But hydrology-related surface processes are manifold, including frost cracking intensities based on available water content (e.g.…”