Glacial Lake Inventory and Lake Outburst Flood/Debris Flow Hazard Assessment after the Gorkha Earthquake in the Bhote Koshi Basin

Abstract

Glacial lake outburst floods (GLOF) evolve into debris flows by erosion and sediment entrainment while propagating down a valley, which highly increases peak discharge and volume and causes destructive damage downstream. This study focuses on GLOF hazard assessment in the Bhote Koshi Basin (BKB), where was highly developed glacial lakes and was intensely affected by the Gorkha earthquake. A new 2016 glacial lake inventory was established, and six unreported GLOF events were identified with geomorphic outburst evidence from GaoFen-1 satellite images and Google Earth. A new method was proposed to assess GLOF hazard, in which large numbers of landslides triggered by earthquake were considered to enter into outburst floods enlarge the discharge and volume of debris flow in the downstream. Four GLOF hazard classes were derived according to glacial lake outburst potential and a flow magnitude assessment matrix, in which 11 glacial lakes were identified to have very high hazard and 24 to have high hazard. The GLOF hazard in BKB increased after the earthquake due to landslide deposits, which increased by 216.03 × 106 m3, and provides abundant deposits for outburst floods to evolve into debris flows. We suggest that in regional GLOF hazard assessment, small glacial lakes should not be overlooked for landslide deposit entrainment along a flood route that would increase the peak discharge, especially in earthquake-affected areas where large numbers of landslides were triggered.

Evaluation of Glacial Lake Outburst Flood Susceptibility Using Multi-Criteria Assessment Framework in Mahalangur Himalaya

“…This does not imply that small lakes (<0.045 km 2 ) are not susceptible to burst. For example, 2016 GLOF from Gongbatongsha Tsho (0.017 km 2 ) was transboundary and destructive as it destroyed infrastructures and settlements along the SINO-Nepal highway (Liu et al, 2020). We used lake area rather than lake volume as a factor in determining the possible magnitude of a GLOF because most existing empirical formulas for volume calculation are areadependent (Fujita et al, 2013;Sakai, 2012).…”

Timing of exotic, far-traveled boulder emplacement and paleo-outburst flooding in the central Himalayas

“…Larger events, such as the possibility for earthquakes greater than M w 9.0 with a suggested recurrence interval of more than 800 yr along the entire Himalayan arc (Stevens and Avouac, 2016), could also trigger rare and large LLOFs. However, large hillslope failures and valley fills have been shown to occur for lower earthquake magnitudes as well (e.g., Schwanghart et al, 2016a), and other controls on landslide initiation are likely important factors as well, e.g., hillslope saturation (Lu and Godt, 2013). We, therefore, consider it unlikely that LLOFs are restricted to large (≥ M w 9.0) events.…”

Development of smart boulders to monitor mass movements via the Internet of Things: a pilot study in Nepal

“…For example, early warning systems have been based on traditional techniques such as topographic benchmarks or extensometers, often in combination with more advanced techniques such as ground-based radar interferometry (GB-InSAR) (e.g. Intrieri et al, 2012;Loew et al, 2017). Geodetic techniques based on GPS or total stations are also widely used and documented to remotely monitor surface displacements of active landslides (e.g.…”