The Tsergo Ri landslide was a prehistoric landslide in the Nepalese Himalaya, which took place around 51,000±13,000 years ago, during the Last Glacial Period. During the collapse, a mass of rock of about 10–15 cubic kilometres (2.4–3.6 cu mi) detached from a previous mountain or ridge and descended with a speed of about 450 kilometres per hour (120 m/s); later, glaciers eroded almost the entire landslide mass. Previously weakened rocks may have contributed to the collapse, which was probably started by an earthquake.
Geomorphology and geology
The collapse of Tsergo Ri took place in Nepal's Langtang valley, perpendicular to the Himalaya and about 60 kilometres (37 mi) north of the Nepalese capital Kathmandu. The small settlement of Kyangjin Kharka lies at the foot of the landslide deposit. With a volume of 10–15 cubic kilometres (2.4–3.6 cu mi), it is one of the largest known mass movements on Earth and perhaps the largest known landslide in crystalline bedrock.
Causes and trigger
The collapse affected Himalayan gneiss rocks, which also contain migmatites and granites; they also include older pseudotachylite and ultramylonite rocks (both of which can be formed by collapses) and which acted as a sliding plane for the Tsergo Ri collapse. Rocks formed by deformation, intrusions of granite, and layers of pyrrhotite ore, which are unstable under mechanical load and neotectonic faults, may have been weak structures that facilitated the collapse.
The Tsergo Ri region is one of the fastest uplifting parts of the Himalaya. The Tsergo Ri landslide was probably triggered by seismic activity, perhaps on the Himalayan Main Central Thrust; a water level drop in the Paleo Kathmandu Lake took place at the same time and may have been caused by the same earthquake. The collapse occurred during a time of increased monsoon strength, which may have played a role in the collapse.
Pre-landslide topography and landslide
Based on reconstructions of the pre-landslide topography, there may have been a 7,500–8,500 metres (24,600–27,900 ft) high trilateral mountain in the area, or a set of ridges. The landslide detached in a southwest-west-southwest direction, with the sliding mass breaking apart into blocks. Owing to its fast speed of 450 kilometres per hour (120 m/s), rocks at the base of the slide melted. The landslide impacted other mountains and ridges, sometimes destroying them or triggering secondary collapses, and may have mixed with glacier ice.
It was eventually halted by topography such as the flanks of Pangshungtramo mountain before it could become a debris avalanche. The landslide debris consists of individual compact blocks on top of a basal breccia and originally may have reached a thickness of 600–800 metres (2,000–2,600 ft). Deformed structures inside the collapse debris indicate that small-scale movements occurred within the landslide. The slide obstructed several glacial valleys.
Timing and aftermath
The collapse took place about 51,000±13,000 years ago, between two phases of the Würm glaciation.
After the collapse, landslide debris was subject to glacial erosion and was largely removed in the process. About 3 cubic kilometres (0.72 cu mi) of debris is still present; it is found around Tsergo Ri mountain, which is formed by landslide debris and its location is in the central sector of the former landslide. Yala Peak and Dragpoche are in the area of the detachment, east of the seven-thousander Langtang Lirung. The glaciers that had had their valleys cut by the landslide readvanced during the youngest phase of the Würm glaciation and partially restored the valleys. Landslides take place to this day in the area, including during the 2015 Nepal earthquake when a landslide detached from Langtang Lirung peak and killed over 350 people in the Langtang valley. Slow mass movements into valleys and weather/monsoon-controlled mudflows also occur, and there is evidence that the debris from the Tsergo Ri landslide is especially unstable.
Research history
Molten rocks formed during the collapse were initially referred to by native people as "yak bones", while early researchers interpreted the rocks as a product of the Himalayan Main Central Thrust fault. In 1984 Heuberger et al. identified their actual origin in a giant landslide. The structure of the landslide body has been mapped using radon emissions and groundwater flows, and the most recent date estimates were obtained with fission track dating on pseudotachylites formed by the collapse.
References
- ^ Weidinger & Schramm 1995, p. 231.
- ^ Weidinger & Schramm 1995, p. 232.
- Weidinger 2001, p. 36.
- Ibetsberger 1996, p. 86.
- Marston, Miller & Devkota 1998, p. 146.
- Weidinger & Schramm 1995, pp. 232, 234.
- Weidinger & Schramm 1995, pp. 235–239.
- Weidinger 2003, p. 311.
- Weidinger & Schramm 1995b, p. 281.
- Weidinger & Schramm 1995, p. 239.
- Weidinger 2001, p. 38.
- Sakai et al. 2016, p. 8.
- Dortch et al. 2009, p. 1050.
- Weidinger 2003, p. 312.
- ^ Stumm et al. 2021, p. 3793.
- Weidinger 2001, p. 39.
- Weidinger & Schramm 1995b, p. 285.
- ^ Weidinger & Schramm 1995, p. 235.
- ^ Weidinger & Schramm 1995b, p. 287.
- Weidinger 2001, p. 40.
- Weidinger & Schramm 1995, p. 241.
- Weidinger & Schramm 1995, p. 242.
- Weidinger 2001, p. 46.
- Hewitt, Clague & Orwin 2008, p. 11.
- Weidinger & Schramm 1995, p. 234.
- Takagi et al. 2007, p. 467.
- ^ Weidinger & Schramm 1995, p. 240.
- ^ Stumm et al. 2021, p. 3794.
- Takagi et al. 2007, p. 471.
- Weidinger 2004, p. 145.
- Weidinger & Schramm 1995, p. 240,242.
- Dhakal et al. 2020, p. 1844.
- Weidinger 2001, p. 53.
- Ibetsberger 1996, p. 92.
- Tagami 2012, p. 79.
Sources
- Dhakal, Susmita; Cui, Peng; Rijal, Chandra Prasad; Su, Li-jun; Zou, Qiang; Mavrouli, Olga; Wu, Chun-hao (August 2020). "Landslide characteristics and its impact on tourism for two roadside towns along the Kathmandu Kyirong Highway". Journal of Mountain Science. 17 (8): 1840–1859. doi:10.1007/s11629-019-5871-3. S2CID 220656915.
- Dortch, Jason M.; Owen, Lewis A.; Haneberg, William C.; Caffee, Marc W.; Dietsch, Craig; Kamp, Ulrich (1 June 2009). "Nature and timing of large landslides in the Himalaya and Transhimalaya of northern India". Quaternary Science Reviews. 28 (11): 1037–1054. Bibcode:2009QSRv...28.1037D. doi:10.1016/j.quascirev.2008.05.002. ISSN 0277-3791.
- Hewitt, Kenneth; Clague, John J.; Orwin, John F. (1 February 2008). "Legacies of catastrophic rock slope failures in mountain landscapes". Earth-Science Reviews. 87 (1): 1–38. Bibcode:2008ESRv...87....1H. doi:10.1016/j.earscirev.2007.10.002. ISSN 0012-8252.
- Ibetsberger, Horst J. (30 July 1996). "The Tsergo Ri landslide: an uncommon area of high morphological activity in the Langthang valley, Nepal". Tectonophysics. 260 (1): 85–93. Bibcode:1996Tectp.260...85I. doi:10.1016/0040-1951(96)00077-7. ISSN 0040-1951.
- Marston, R. A.; Miller, M. M.; Devkota, L. P. (1 December 1998). "Geoecology and mass movement in the Manaslu-Ganesh and Langtang-Jugal Himals, Nepal". Geomorphology. 26 (1): 139–150. Bibcode:1998Geomo..26..139M. doi:10.1016/S0169-555X(98)00055-5. ISSN 0169-555X.
- Sakai, Harutaka; Fujii, Rie; Sugimoto, Misa; Setoguchi, Ryoko; Paudel, Mukunda Raj (27 February 2016). "Two times lowering of lake water at around 48 and 38 ka, caused by possible earthquakes, recorded in the Paleo-Kathmandu lake, central Nepal Himalaya". Earth, Planets and Space. 68 (1): 31. Bibcode:2016EP&S...68...31S. doi:10.1186/s40623-016-0413-5. ISSN 1880-5981. S2CID 34169506.
- Stumm, Dorothea; Joshi, Sharad Prasad; Gurung, Tika Ram; Silwal, Gunjan (6 August 2021). "Mass balances of Yala and Rikha Samba glaciers, Nepal, from 2000 to 2017". Earth System Science Data. 13 (8): 3791–3818. Bibcode:2021ESSD...13.3791S. doi:10.5194/essd-13-3791-2021. ISSN 1866-3508. S2CID 238808683.
- Tagami, Takahiro (4 May 2012). "Thermochronological investigation of fault zones". Tectonophysics. 538–540: 67–85. Bibcode:2012Tectp.538...67T. doi:10.1016/j.tecto.2012.01.032. hdl:2433/155980. ISSN 0040-1951.
- Takagi, Hideo; Arita, Kazunori; Danhara, Tohru; Iwano, Hideki (1 February 2007). "Timing of the Tsergo Ri landslide, Langtang Himal, determined by fission-track dating of pseudotachylyte". Journal of Asian Earth Sciences. 29 (2): 466–472. Bibcode:2007JAESc..29..466T. doi:10.1016/j.jseaes.2005.12.002. ISSN 1367-9120.
- Weidinger, Johannes T.; Schramm, Josef-Michael (1995). "Tsergo Ri (Langthang Himal, Nepal)–Rekonstruktion der "Paläogeographie" eines gigantischen Bergsturzes" (PDF). Geol. Paläont. Mitt. Innsbruck (in German). 20: 231–243.
- Weidinger, J. T.; Schramm, J. M. (1995b). "A Short Note on the Tsergo Ri Landslide, Langtang Himal, Nepal". Journal of Nepal Geological Society. 11: 281–287–281–287. doi:10.3126/jngs.v11i0.32803. ISSN 2676-1378.
- Weidinger, J.T. (2001). Der Tsergo Ri Bergsturz im Nepal Himalaja - Erforschung der größten Kristallinmassenbewegung der Erde als Grundlage für rezente Gefahrenzonenkartierungen (PDF). Geoforum Umhausen (in German). Vol. 2.
- Weidinger, J.T. (2003). "Die Verwitterung einer Erzstruktur als Ursache für den Einsturz des ehemals 15. Achttausenders im Hohen Himalaya Nepals" (PDF). Mitt. Österr.Miner.Ges. (in German) (148).
- Weidinger, JOHANNES T. (May 2004). "Das ERKUDOK © Institut im Stadtmuseum Gmunden – Eine geowissenschaftliche Forschungsstätte im Salzkammergut" (PDF). Jahrbuch der Geologischen Bundesanstalt (in German). 144 (1). Vienna: 141–153. ISSN 0016-7800.