Tsergo Ri landslide

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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

Himalaya[2] and about 60 kilometres (37 mi) north of the Nepalese capital Kathmandu.[3] The small settlement of Kyangjin Kharka lies at the foot of the landslide deposit.[4] With a volume of 10–15 cubic kilometres (2.4–3.6 cu mi),[2] it is one of the largest known mass movements on Earth[1] and perhaps the largest known landslide in crystalline bedrock.[5]

Causes and trigger

The collapse affected Himalayan

neotectonic faults, may have been weak structures that facilitated the collapse.[7][8]

The Tsergo Ri region is one of the fastest uplifting parts of the Himalaya.

seismic activity,[10] perhaps on the Himalayan Main Central Thrust;[11] a water level drop in the Paleo Kathmandu Lake took place at the same time and may have been caused by the same earthquake.[12] The collapse occurred during a time of increased monsoon strength, which may have played a role in the collapse.[13]

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[14][15] trilateral mountain in the area,[16] or a set of ridges.[17] The landslide detached in a southwest-west-southwest direction,[18] with the sliding mass breaking apart into blocks.[19] Owing to its fast speed of 450 kilometres per hour (120 m/s), rocks at the base of the slide melted.[20] The landslide impacted other mountains and ridges, sometimes destroying them[21] or triggering secondary collapses,[19] and may have mixed with glacier ice.[22]

It was eventually halted by topography such as the flanks of Pangshungtramo mountain

glacial valleys.[27]

Timing and aftermath

The collapse took place about 51,000±13,000 years ago,[28] between two phases of the Würm glaciation.[29]

After the collapse, landslide debris was subject to

2015 Nepal earthquake[15] when a landslide detached from Langtang Lirung peak and killed over 350 people in the Langtang valley.[32] Slow mass movements into valleys[19] and weather/monsoon-controlled mudflows also occur,[33] and there is evidence that the debris from the Tsergo Ri landslide is especially unstable.[34]

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.[1] The structure of the landslide body has been mapped using radon emissions and groundwater flows,[18] and the most recent date estimates were obtained with fission track dating on pseudotachylites formed by the collapse.[35]

References

  1. ^ a b c d Weidinger & Schramm 1995, p. 231.
  2. ^ a b c Weidinger & Schramm 1995, p. 232.
  3. ^ Weidinger 2001, p. 36.
  4. ^ Ibetsberger 1996, p. 86.
  5. ^ Marston, Miller & Devkota 1998, p. 146.
  6. ^ Weidinger & Schramm 1995, pp. 232, 234.
  7. ^ Weidinger & Schramm 1995, pp. 235–239.
  8. ^ Weidinger 2003, p. 311.
  9. ^ Weidinger & Schramm 1995b, p. 281.
  10. ^ Weidinger & Schramm 1995, p. 239.
  11. ^ Weidinger 2001, p. 38.
  12. ^ Sakai et al. 2016, p. 8.
  13. ^ Dortch et al. 2009, p. 1050.
  14. ^ Weidinger 2003, p. 312.
  15. ^ a b Stumm et al. 2021, p. 3793.
  16. ^ Weidinger 2001, p. 39.
  17. ^ Weidinger & Schramm 1995b, p. 285.
  18. ^ a b c Weidinger & Schramm 1995, p. 235.
  19. ^ a b c Weidinger & Schramm 1995b, p. 287.
  20. ^ Weidinger 2001, p. 40.
  21. ^ Weidinger & Schramm 1995, p. 241.
  22. ^ Weidinger & Schramm 1995, p. 242.
  23. ^ Weidinger 2001, p. 46.
  24. ^ Hewitt, Clague & Orwin 2008, p. 11.
  25. ^ Weidinger & Schramm 1995, p. 234.
  26. ^ Takagi et al. 2007, p. 467.
  27. ^ a b Weidinger & Schramm 1995, p. 240.
  28. ^ a b Stumm et al. 2021, p. 3794.
  29. ^ Takagi et al. 2007, p. 471.
  30. ^ Weidinger 2004, p. 145.
  31. ^ Weidinger & Schramm 1995, p. 240,242.
  32. ^ Dhakal et al. 2020, p. 1844.
  33. ^ Weidinger 2001, p. 53.
  34. ^ Ibetsberger 1996, p. 92.
  35. ^ Tagami 2012, p. 79.

Sources

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