03 Aug 2021
03 Aug 2021
Status: a revised version of this preprint is currently under review for the journal ESurf.

Central Himalayan rivers record the topographic signature of erosion by glacial lake outburst floods

Maxwell P. Dahlquist1 and A. Joshua West2 Maxwell P. Dahlquist and A. Joshua West
  • 1Department of Earth and Environmental Systems, Sewanee: The University of the South, Sewanee, Tennessee, 37383, USA
  • 2Department of Earth Sciences, University of Southern California, Los Angeles, California 90089, USA

Abstract. In steep landscapes, river incision sets the pace of landscape evolution. Transport of coarse sediment controls incision by evacuating material delivered to river channels by landslides. However, large landslide-derived boulders that impede bedrock erosion are immobile even in major runoff-driven floods. Glacial lake outburst floods (GLOFs) mobilize these boulders and drive incision, yet their role in regional-scale erosion is poorly understood, largely because of their rarity. Here, we find a topographic signature consistent with widespread GLOF erosion in the Nepal Himalaya. In rivers with glaciated headwaters that generate GLOFs, valleys stay narrow and relatively free of sediment, with bedrock often exposed to erosion. In turn, tributaries to these valleys are steep, allowing less efficient erosional regimes to keep pace with GLOF-driven incision. Where GLOFs are less frequent, valleys are more alluviated and incision stalls. Our results suggest the extent of headwater glaciation may play an important role in erosion of Himalayan river valleys and deserves more attention in future work.

Maxwell P. Dahlquist and A. Joshua West

Status: final response (author comments only)

Comment types: AC – author | RC – referee | CC – community | EC – editor | CEC – chief editor | : Report abuse
  • RC1: 'Comment on esurf-2021-54', Anonymous Referee #1, 02 Sep 2021
    • AC1: 'Reply on RC1', Maxwell Dahlquist, 01 Nov 2021
  • RC2: 'Comment on esurf-2021-54', John Jansen, 24 Sep 2021
    • AC2: 'Reply on RC2', Maxwell Dahlquist, 01 Nov 2021

Maxwell P. Dahlquist and A. Joshua West

Maxwell P. Dahlquist and A. Joshua West


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Short summary
Himalayan rivers are full of giant boulders that almost never move except during glacial lake outburst floods (GLOFs). GLOFs therefore must be very important for driving erosion. GLOFs are rare, so little is known about how they control erosion long-term. We analyzed rivers in the Nepal Himalaya and found the slopes and widths of channels and valleys suggest GLOFs as the dominant means of erosion. This is often unaccounted for in erosion and landscape evolution studies and should be considered.