| 20 May 2026
Late Pleistocene Aggradation and Holocene Surface Reworking of Fluvial Terraces in the glacially overprinted Western Higher Himalaya
Abstract. Himalayan rivers are thought to undergo continuous adjustment in response to climatic variability, with changes in monsoon intensity and glacial extent playing a particularly important role in the Higher Himalaya. At the same time, short-term processes such as landslides, debris flows, and floods exert significant influence on both river dynamics and landscape morphology. We study a ~60 km long reach of the Ravi River in the western Higher Himalaya and a ~20 km reach of its main tributary, the Suil River, extending into the Sub-Himalaya. Using 12 new luminescence ages, 36 cosmogenic nuclide (10Be and 26Al) samples, remote sensing analysis, and detailed field observation, we reconstruct the formation of fluvial terraces and constrain the timing of subsequent erosion processes. We identify 10 recurring terrace levels, reaching elevations of up to ~225 m above the present rivers, with most terrace surfaces capped by a colluvial layer. The luminescence chronology documents repeated phases of fluvial aggradation, followed by major incision periods during the Late Pleistocene (~30–13 ky). In contrast, the cosmogenic surface exposure ages do not reveal terrace abandonment ages, but indicate distinct, Late-to-Mid Holocene reworking (~7–2 ky) on all but two terrace surfaces. Our topographic analysis suggests that up to ~50% of the Ravi and Suil catchment areas may have been influenced by glacial coverage during the Late Pleistocene, likely contributing significantly to sediment aggradation during this time. The Holocene surface exposure ages, in contrast, are interpreted to reflect post-depositional modification by mass wasting processes (e.g., landslides or debris flow) and, in some cases, by potentially vigorous glacial lake outburst floods.
The manuscript focuses on understanding the phases of aggradation and incision that occurred in the late Pleistocene and mid- to late Holocene. The authors explained the aggradation history using previously published OSL ages and added 12 new luminescence ages and 36 new cosmogenic nuclide exposure ages, of which 22 were rejected due to no or low signals, low current, or high uncertainties. But the figures show different numbers of ages used (7 OSL and 19 exposure ages). The major concerns in this study are (1) sedimentological constraint sections, (2) the incision in the valley during the mid-late Holocene is explained because of glacial/landslide-dammed lake outburst floods (GLOF/LLOF); however, no evidence of damming is preserved in the valley, and (3) the sampling strategy. The authors sampled both valleys, without regard for what they were sampling. The sedimentological characterization of litho-units is missing throughout the manuscript. None of the sections is explained sedimentologically, and it is not explained why the depositional or erosional ages are needed to characterize the particular event. The event should be characterized in the field itself (sedimentologically and geomorphologically).
Specific comments:
Line 43-45; the strong monsoon in general enhances the melting of the glaciers. The monsoon's penetration into the hinterland is driven by the formation of low-pressure zones in the Himalayan/Tibetan region, which attract monsoon winds intensified by strong warming. During such warming conditions, glacier growth in the southern Himalaya is speculative. This may occur in the Greater Himalaya or Trans-Himalaya.
Line 51-69; It is true that short-term events such as floods, landslides and debris flows alter the local base level of the river and modify the aggradation and incision processes locally. It is also true that to better understand such processes, we need more data, but the extreme northwestern Himalaya, where annual precipitation is limited to ~1400-800 mm/yr, is restricted by the Dhauladhar ranges from further penetration to the north. This section needs more clarification. Further, the tectonic framework and its role should be mentioned.
Line 118; The authors mentioned that in a previous study in the region, 8 cut-fill terraces were identified; however, this study has identified 10.
Line 166-167; The statement is confusing. How can an older surface give a higher erosional rate? Rather, a younger surface should.
Line 167-171; Again, the paragraph creates confusion between samples and rates, which is lower than what. Need corrections.
Line 197; How was the preheat temperature decided? How many aliquots yielded palaeodose under the aforementioned boundary conditions? There should be a figure showing the decay curve of the IRSL and OSL signals. Overdispersion should be mentioned in Table 2.
Line 262-268; In general, lithofacies analysis is the most suitable method to characterize the sedimentation processes. The explanation needs more information to characterize the terrace sediment (facies codes).
Discussion:
5.1 Caveats of cosmogenic nuclide exposure ages
All 26Al/10Be exposure ages are younger than the depositional OSL ages, hinting at possible flaws in the sampling. The authors ignored the sediment packages that need to be targeted for dating. To justify the younger ages, authors state the possibility of debris flows and landslides, but no sedimentological evidence is provided.
5.3 Sediment Transport and climate variability
There is recent work available from NW Himalaya on sediment transport and the role of climate variability, which the authors should incorporate.
Authors argued that sediment aggradation and incision during MIS-3 and gLGM were controlled by glacial activities in both studied valleys, which seems speculative. None of the sections is constrained by sedimentological characterization or photographs to evidence the glaciogenic processes. However, the older aggradation phase mentioned in this study is synchronous with the aggradation phase present throughout the Himalaya (northwestern as well as in northeastern Himalaya).
5.4 Widespread Holocene overprinting of fluvial terrace surface across the catchment
Lines 469-475: It is true that aggradation ages reflect the timing of sedimentation; however, 10Be ages represent younger surface processes, so they are genetically different. This is probably not underestimated; rather, the selection of the horizon for dating is doubtful. It would be nice if authors select a well-constrained section (lithofacies) for exposure ages and then correlate these ages with geomorphological processes. That would have provided a logical interpretation of all younger ages.
Line 513 onward, suddenly the discussion shifted to the role of GLOF/LLOF, which enabled the modulation of the T-8, -9 and -10 surfaces situated at ~200 m above the river. In northwestern Himalaya, there is no evidence of palaeoflood records that have reached more than ~ 30 m from the present-day river. Only the Indus River attains such heights because of the availability of a large sediment flux (see Srivastava et al., 2017). So, building a flooding scenario (GLOF/LLOF) for modulating the T-9 or T-10 surfaces is more hypothetical.
Line 538, None of the terraces is explained as a strath terrace. No details on the bedrock bench is provided.
Figures
Figure 1; The inset Indian map has the wrong international boundaries. Authors are requested to change the map as per SOI.
Figures 3 and 4; Figure 3 shows an unpaired terrace configuration along both rivers, specifically at the higher levels T-9 and T-10; in contrast, Figure 4 shows continuous terraces along both banks.
Figure 6; (A) shows cross-beds in the colluvium; (B) In the silty-clay units of colluvium, faint ripples marks can be seen. These sedimentary features indicate channelized processes and underscore the importance of sediment characterization prior to establishing the chronologies of any horizons.
Figure 11: How can the Chinese cave located near the South China Sea sense the climatic perturbation that occurred on the NW Himalaya? Himalayan data are also available for the same time.