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The southernmost thrust of the Himalayan orogenic wedge that separates the foreland from the orogen, the Main Frontal Thrust, is thought to accommodate most of the ongoing crustal shortening in the Sub-Himalaya. Steepened longitudinal river profile segments, terrace offsets, and back-tilted fluvial terraces within the Kangra reentrant of the NW Sub-Himalaya suggest Holocene activity of the Jwalamukhi Thrust (JMT) and other thrust faults that may be associated with strain partitioning along the toe of the Himalayan wedge. To assess the shortening accommodated by the JMT, we combine morphometric terrain analyses with in situ 10Be-based surface-exposure dating of the deformed terraces. Incision into upper Pleistocene sediments within the Kangra Basin created two late Pleistocene terrace levels (T1 and T2). Subsequent early Holocene aggradation shortly before ~10 ka was followed by episodic reincision, which created four cut-and-fill terrace levels, the oldest of which (T3) was formed at 10.1 ± 0.9 ka. A vertical offset of 44 ± 5 m of terrace T3 across the JMT indicates a shortening rate of 5.6 ± 0.8 to 7.5 ± 1.1 mm a−1 over the last ~10 ka. This result suggests that thrusting along the JMT accommodates 40-60% of the total Sub-Himalayan shortening in the Kangra reentrant over the Holocene. We speculate that this out-of-sequence shortening may have been triggered or at least enhanced by late Pleistocene and Holocene erosion of sediments from the Kangra Basin. [ABSTRACT FROM AUTHOR]

It has been proposed that at short timescales of 102–105 yr, climatic variability can explain variations in sediment flux, but in orogens with pronounced climatic gradients rate changes caused by the oscillating efficiency in rainfall, runoff, and/or sediment transport and deposition are still not well-constrained. To explore landscape responses under variable climatic forcing, we evaluate time windows of prevailing sediment aggradation and related paleo-erosion rates from the southern flanks of the Dhauladhar Range in the western Himalaya. We compare past and present 10Be-derived erosion rates of well-dated Late Pleistocene fluvial landforms and modern river sediments and reconstruct the sediment aggradation and incision history based on new luminescence data. Our results document significant variations in erosion rates ranging from 0.1 to 3.4 mm/yr over the Late Pleistocene. We find that, during times of weak monsoon intensity, the moderately steep areas (hillslope angles of 27 ± 13°) erode at lower rates of 0.1–0.4 mm/yr compared to steeper (>40°) crestal regions of the Dhauladhar Range that erode at 0.8−1.3 mm/yr. In contrast, during several millennia of stronger monsoon intensity, both the moderately steep and high slope areas record higher erosion rates (>1-3.4 mm/yr). Lithological clast-count analysis shows that this increase of erosion is focused in the moderately steep areas, where Lesser Himalayan rocks are exposed. Our data thus highlight the highly non-linear response of climatic forcing on landscape evolution and suggest complex depositional processes and sedimentary signals in downstream areas. • Paleo-erosion rates in the Himalaya are modulated by climate forcing. • Erosion rates are higher during episodes of strong monsoon. • Topographic response to climate change is non-linear. • Rapid erosion during short-lived strong monsoon phases result in valley aggradation. [ABSTRACT FROM AUTHOR]

The distribution of tectonic activity within the Himalaya is still disputed. For instance the tectonic processes that ultimately sustain Himalayan topography and the activity of major fault zones within the orogen at geological-timescales remain unknown. In our studies, we study landscape morphology and combine surface exposure,thermochronologic dating methods, thermokinematic modelsto address the spatial and temporal pattern of deformation in the western Himalaya. Of particular interest is a 30 to 40-km-wide orogen-parallel belt of rapid exhumation that extends from central Nepal to the western Himalaya. This belt has been linked to a mid-crustal ramp in the basal décollement, to out-of-sequence basement thrusts, and to the growth of Lesser Himalayan duplex structures. Further goals are constraining fault activity of the Main Boundary Thrust fault (MBT). From our results we conclude that all major deformation zones in western Himalaya are active and some portion of crustal shortening is accommodated by active out of sequence faulting sustaining topography. We have published several new studies containing new apatite fission-track (AFT) and zircon U-Th/He cooling ages from the western Himalayan region, particular in the vicinity of the transition from the central to the western Himalaya (~77°-78°E). We analyzed the spatial distribution of the relative change of river steepness using averaged basin wide river steepness indexes (ksn), both along and across strike to gain information about the regional distribution of differential uplift pattern and relate this to the activity of distinctive fault zones and orogenic segments. Our results recognize three orogenic segments with distinctive landscape morphology, structural architecture, and fault geometry exists along the western Himalaya: Garhwal-Sutlej, Beas-Lahul-Chamba, and Kashmir Himalaya (from east to west). We observe a positive correlation of averaged ksn values with long-term exhumation rates derived from recently published regional thermochronologic datasets combined with 1D and 2D-thermal modelling as well as with millennial timescale denudation rates based on cosmogenic nuclide dating. These results are in agreement with documented significant lateral changes in exhumation between the Dhauladar Range to the west, the Beas-Lahul region, and the Sutlej-Garhwal area to the east. Moreover, our data recognize distinctive fault segments suggesting varying differential uplift along strike of the Main Frontal Thrust (MFT), the Main Boundary Thrust (MBT), and in the vicinity of steep topographic transition between the Lesser and Greater Himalaya. In this region, we relate out-of-sequence deformation along major basement thrust ramps, such as the Munsiari Thrust (MT) combined with deformation along mid-crustal ramp along the basal décollement. Our results allow us to spatially correlate the termination of the rapid exhumation belt with a mid-crustal ramp to the west. In contrast to the Himalayan front farther to the east, exhumation in the far west is focused at the frontal parts of the mountain range, and associated with the hanging wall of the MBT. [ABSTRACT FROM AUTHOR]