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Protracted interseismic locking of the low‐angle décollement of the Himalaya causes strain accumulation and results in growing slip deficit with time. Unlocking the frontal splay of the décollement during high‐magnitude earthquakes (Mw ≥6.5) may cause surface ruptures along the Himalayan Frontal Thrust (HFT). According to Paleoseismic investigations and observations on undeformed fluvial strath surfaces, the HFT in Nahan Salient has not experienced coseismic slip at least for the last six to seven centuries. Our new observations and chronological assessments on folded and faulted fluvial strath surfaces on the hanging wall of the HFT indicates a maximum slip rate of 10.4 ± 0.8–12.2 ± 0.8 mm/a (averaged over the last 7–8 ka). Seismic quiescence of 600–700 a results in a ~6.2–8.5 m slip deficit on the HFT which could trigger a Mw ≥7.7 earthquake. Our findings underline an enormous seismic risk prevailing in the Nahan area. [ABSTRACT FROM AUTHOR]

Sediment transfer from the interiors of the Himalaya is complex because the archives are influenced by both glacial and monsoonal cycles. To deconvolve the coupling of glacial and monsoonal effects on sediment transfer processes, we investigate the Late Pleistocene–Holocene sediment archive in the Upper Chenab valley. Optically stimulated luminescence (OSL) ages from the archive indicate major aggradation during ca. 20–10 ka. Isotopic fingerprinting using Sr-Nd isotopes in silt fractions together with clast counts in boulder-pebble fractions indicate a decreasing Higher Himalayan sediment flux in the archive with time. Decreasing clast size, increasing clast roundness, increasing matrix to clast ratio, and dominance of the Higher Himalayan sourcing unequivocally suggest strong glacial influence during the initial stages of the archive formation. This evidence also agrees with the existing retreat ages of glaciers in the Upper Chenab valley. Results of our study also show that the upper parts of the archive contain significant fluvial sediment contribution from the Lesser Himalaya, which suggests an active role of the stronger Indian Summer Monsoon (ISM) in the region during the Early Holocene. The apparent decrease in sediment supply from the Higher Himalayan sources could have been due to longer source-to-sink transport in the Early Holocene and/or increased hillslope flux from Lesser Himalayan sources. [ABSTRACT FROM AUTHOR]

Understanding millennial‐scale fault activity and related structural architecture from seismic gaps in active orogens is important for assessment of future seismic risks. Here, we present new Late Pleistocene–Holocene shortening rates across a segment of the 600‐km‐long Medlicott‐Wadia Thrust (MWT) system in the Sub‐Himalaya (SH) from the far‐western Himalayan sector of Jammu. OSL‐dated offset and folded fluvial strath terraces provide a measure for the intra‐wedge convergence and document strain partitioning within the SH, among which the MWT is the most active. Estimated differential uplift rates across the frontal and rear splay of the MWT is 3.2 ± 0.8 mm/a and 3.1 ± 0.4 which translates into a cumulative Late Pleistocene–Holocene shortening rate of 5.5 ± 0.5–5.8 ± 0.5 mm/a on the MWT. Previously published balanced cross‐sections proposed deformation pattern and in range of ~1 mm/a. Our study reaffirms deformation rates from neighbouring MWT fault segments; moreover, it provides independent constraints to the structural architecture of the frontal fold‐and‐thrust belt and implies changes in fault displacement rates on Quaternary time‐scales. [ABSTRACT FROM AUTHOR]

The Lesser Himalaya exposed in the Kishtwar Window (KW) of the Kashmir Himalaya exhibits rapid rock uplift and exhumation (∼3 mm yr-1) at least since the late Miocene. However, it has remained unclear if it is still actively deforming. Here, we combine new field, morphometric and structural analyses with dating of geomorphic markers to discuss the spatial pattern of deformation across the window. We found two steep stream segments, one at the core and the other along the western margin of the KW, which strongly suggest ongoing differential uplift and may possibly be linked to either crustal ramps on the Main Himalayan Thrust (MHT) or active surface-breaking faults. High bedrock incision rates (>3 mm yr-1) on Holocene–Pleistocene timescales are deduced from dated strath terraces along the deeply incised Chenab River valley. In contrast, farther downstream on the hanging wall of the MCT, fluvial bedrock incision rates are lower (<0.8 mm yr-1) and are in the range of long-term exhumation rates. Bedrock incision rates largely correlate with previously published thermochronologic data. In summary, our study highlights a structural and tectonic control on landscape evolution over millennial timescales in the Himalaya. [ABSTRACT FROM AUTHOR]

The interplay of tectonics, climate and erosion has been proposed as the driving factor behind the growth and evolution of the Himalaya. In this review paper, we focus on the neotectonic deformation history within the southernmost morphotectonic sector of the Himalaya (the Sub-Himalaya) through synthesis of geomorphic data. The Sub-Himalaya is arguably consuming ∼100% of the total Himalayan shortening since early Quaternary. We compiled geodetic shortening rates, paleoseismic events (historical earthquakes), shortening rates deduced from uplifted strath/fill terraces and shortening rates from balanced cross-sections from the north-western, central and eastern Himalayan compartments to obtain an orogen-wide perspective of Quaternary deformation. We supported the compiled data with topographic swath, longitudinal river-profile analysis and ks n plots of the existing drainage in those compartments. Review of the existing data shows a mismatch of the trend of the geodetic shortening rates with those of the millennial or longer timescales; however, Holocene and modern day-shortening rates are of same range (∼14–21 mm a−1). Quaternary shortening rates are much lower, probably due to a longer time-averaging. Except central Nepal, the other sectors show significant out-of-sequence thrusting (∼50% of the total) within the Sub-Himalaya since the Holocene. Paleoseismic data show variable recurrence intervals of large earthquakes along-strike (∼100–600 years) and large seismic gaps or slip-deficit sectors, which could potentially cause surface-rupture earthquakes in the future. [ABSTRACT FROM AUTHOR]

Deciphering the response of sediment routing systems to climatic forcing is fundamental for understanding the impacts of climate change on landscape evolution. In the Kangra Basin (northwest Sub-Himalaya, India), upper Pleistocene to Holocene alluvial fills and fluvial terraces record periodic fluctuations of sediment supply and transport capacity on timescales of 10 3 to 10 5 yr. To evaluate the potential influence of climate change on these fluctuations, we compare the timing of aggradation and incision phases recorded within remnant alluvial fans and terraces with climate archives. New surface-exposure dating of six terrace levels with in-situ cosmogenic 10 Be indicates the onset of incision phases. Two terrace surfaces from the highest level (T1) sculpted into the oldest preserved alluvial fan (AF1) date back to 53.4 ± 3.2 ka and 43.0 ± 2.7 ka (1 σ ). T2 surfaces sculpted into the remnants of AF1 have exposure ages of 18.6 ± 1.2 ka and 15.3 ± 0.9 ka , while terraces sculpted into the upper Pleistocene–Holocene fan (AF2) provide ages of 9.3 ± 0.4 ka (T3), 7.1 ± 0.4 ka (T4), 5.2 ± 0.4 ka (T5) and 3.6 ± 0.2 ka (T6). Together with previously published OSL ages yielding the timing of aggradation, we find a correlation between variations in sediment transport with oxygen-isotope records from regions affected by the Indian Summer Monsoon. During periods of increased monsoon intensity and post-Last Glacial Maximum glacial retreat, aggradation occurred in the Kangra Basin, likely due to high sediment flux, whereas periods of weakened monsoon intensity or lower sediment supply coincide with incision. [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]

Two end‐member kinematic models of crustal shortening across the Himalaya are still debated: one assumes localized thrusting along a single major thrust fault, the Main Himalayan Thrust (MHT) with non-uniform underplating due to duplexing, and the second one advocates for out‐of‐sequence thrusting in addition to thrusting along the MHT and under-plating. Furthermore, several studies argue that all crustal shorting during the Quaternary is accommodated within Sub-Himalayan fold and thrust belt. In this study, we combined tectonogeomorphic field observations, topographic analysis and luminescence dating of the Quaternary alluvium from the Kishtwar region in NW Himalaya. We have used 30m SRTM data to analyze the regional geomorphic parameters of the area and found that the river Chenab shows, as previously reported, significant changes in the longitudinal river profile, hypsometric integral, valley width and normalized steepness indices across the Kishtwar window situated ~ 150 km inside the Himalayan front. Unadjusted hypsometry, high ksn values, and several non-lithological knickpoint zones in the Chenab river profile hints towards possible ongoing neotectonic activity especially at the western margin of the window. We combined our morphometric analysis with field observation and field data on rock strength and observed tilted Quaternary deposits along the Chenab valley. We have observed faults disrupting Quaternary fluvial sequences and ~20֯ NE-tilted fluvial sequence of pebble conglomerate and coarse sand layers in the vicinity the town of Kishtwar. Even, the observed knickpoints within the window do not correspond to significant changes in the substrate rock strength and therefore hint about their non-lithologic origin. We also observed changes in the drainage pattern of Chenab, as it was frequented by large landslides (despite being located in a fairly-low rainfall region) and landslide-dammed lakes throughout the Kishtwar window and downstream. Previously published young (<3 Ma) apatite fission track ages from the Lesser Himalayan duplex in the Kishtwar Window suggest higher exhumation over million-year timescale. Therefore, our findings possibly hint towards a protracted tectonic uplift process – and the quaternary tilted deposits suggests that this deformation is active until today or very recent. Moreover, frequent low-magnitude mid-crustal (8-30 km) seismic events, steep channel gradients, high angle bedrock foliations of the Lesser Himalayan duplex, multiple knickpoints and young AFT ages within the Kishtwar window hints about active shortening accommodated due to movement along a mid-crustal ramp of the MHT.We are processing the OSL samples obtained from the deformed sand and silt layers within the alluvium. We are hopeful that we will be able to chronologically constrain the late Quaternary deformation with the new luminescence ages. [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]