Glacial lake outburst floods as drivers of fluvial erosion in the Himalaya

Abstract

Himalayan rivers are frequently hit by catastrophic floods that are caused by the failure of glacial lake and landslide dams; however, the dynamics and long-term impacts of such floods remain poorly understood. We present a comprehensive set of observations that capture the July 2016 glacial lake outburst flood (GLOF) in the Bhotekoshi/Sunkoshi River of Nepal. Seismic records of the flood provide new insights into GLOF mechanics and their ability to mobilize large boulders that otherwise prevent channel erosion. Because of this boulder mobilization, GLOF impacts far exceed those of the annual summer monsoon, and GLOFs may dominate fluvial erosion and channel-hillslope coupling many tens of kilometers downstream of glaciated areas. Long-term valley evolution in these regions may therefore be driven by GLOF frequency and magnitude, rather than by precipitation.

The Geomorphic Impact of Outburst Floods: Integrating Observations and Numerical Simulations of the 2000 Yigong Flood, Eastern Himalaya

“…Yet links between spatial patterns of flood hydraulics and geomorphic observations are lacking for some of the largest, most devastating historical outburst floods (e.g., Hewitt, ; O'Connor et al, ), and for many of the largest ancient outburst megafloods (>10 6 m 3 /s) that have occurred on Earth (e.g., Baker, ; Baynes et al, ; Bretz, ; Carling, , ; Lamb, Dietrich, Aciego, et al, ; Malde, ; Montgomery et al, ; O'Connor, ) and on Mars (Baker, ; Baker & Milton, ; Chapman et al, ; Goudge & Fassett, ). Opportunities are rare to study outburst floods and their geomorphic consequences (Cook et al, ; Lamb & Fonstad, ). As a result, questions remain regarding the net impact of outburst floods on landscapes, particularly in mountainous settings where the interaction of flood hydraulics with valley topography is complex.…”

Particle transport mechanics and induced seismic noise in steep flume experiments with accelerometer‐embedded tracers

“…; Cook et al. ). Seismic instrumentation offers the advantage of being relatively straightforward and low cost, potentially allowing more and larger rivers to be safely instrumented with minimal environmental perturbation.…”

“…Recent studies have demonstrated that high-frequency (1-50 Hz) river-induced ground vibrations can be used to monitor key physical processes in rivers such as bedload sediment transport (Govi et al, 1993;Burtin et al, 2008;Tsai et al, 2012;Cook et al, 2018) and turbulent fluid flow (Schmandt et al, 2013;Gimbert et al, 2014). Of central interest is the sensitivity of near-river seismic observations to bedload transport, in particular bedload transport rates that control river morphology and erosion rates but remain challenging to measure directly (Garcia et al, 2000;Rickenmann et al, 2012;Lamb et al, 2015;Whipple et al, 2000;Cook et al, 2013).…”

“…Seismic waves generated by single-grain impacts are often not distinguishable in seismic records, but the integrated contribution of impacts from all transported grains generates sufficient ground motion energy to be detectable (Burtin et al, 2008;Burtin et al, 2011;Hsu et al, 2011;Schmandt et al, 2013;Roth et al, 2014;Díaz et al, 2014;Gimbert et al, 2016). Although turbulent fluid flow also generates seismic noise (Schmandt et al, 2013;Gimbert et al, 2014;Gimbert et al, 2016;Roth et al, 2017), previous theory and its application at a natural scale suggest that the bedload and turbulent flow sources may be distinguished by analyzing ground motion at various frequencies and river-to-station distances (Gimbert et al, 2014;Cook et al, 2018). Seismic instrumentation offers the advantage of being relatively straightforward and low cost, potentially allowing more and larger rivers to be safely instrumented with minimal environmental perturbation.…”

Quantifying bed‐related suspended load in gravel bed rivers through an analysis of the bedload‐suspended load relationship

“…A similar correlation was observed by Métivier et al (2004) in a mountainous river in China. More recently, Cook et al (2018) used seismometers to study the bedload dynamics during a glacial lake outburst flood in a Himalayan river. Following these field evidences, Park and Hunt (2017) proposed a conceptual model for GBRs by considering an accumulation of fine sediments within the riverbed when the armor layer was stable and a release of fine sediments when this protective layer was broken.…”