Things are going downhill fast - a public lecture on massive landslides

1. Things are going downhill fast: understanding
massive landslides
Dave Petley
Vice-President, Research and Innovation
Twitter: @davepetley Blog: https://blogs.agu.org/landslideblog/

2. What is a landslide?
• A landslide is the process that
occurs when a slope collapses
• The dominant material is rock,
debris or soil
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3. Landslides have a huge range
of scales
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4. Three massive landslides:
1. Aberfan, Wales 1966
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5. Three massive landslides:
2. Anak Krakatau, 2018

6. Three massive landslides:
3. Brumadinho, Brazil 2019

7. Five key slope processes:
1. the role of water
• Friction is a key control
• Water creates buoyancy,
reducing friction
• As slopes become saturated
they are more likely to slide

8. 2: As earth materials deform they
can go from solid to fluid

9. Alaska 2018
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New Zealand
2011

10. 3: Rocks with defects are much
weaker than those without

11. 4: Earthquakes in mountains
generate many slope failures

12. 5: We don’t understand why the
biggest landslides travel far and fast

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GNS Science interpretation of the
Mount Haast (Mount Dixon) rockslide

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Landslides are often a part of a highly
complex chain of events
Palu, Sulawesi earthquake, 2018

15. The 2008 Wenchuan earthquake
in China: a true landslide crisis
Final toll: 69,181 killed and 18,498 missing

16. 2008 Wenchuan (Sichuan) earthquake, China
14:28 12 May 2008; Mw = 7.9; Depth = 19 km

18. The Pengguan fault

19. The Beichuan fault

21. Landslides: before and after
Landsat 5
18/09/2007
SPOT5
13/10/2008

22. Shallow rockslides

23. Wenjiagou landslide

25. Case study – Beichuan Town
Beichuan town 2007

27. Beichuan Middle
School landslide
Location of school
700 people
killed

28. Old Town Landslide (10 mins after
main shock)

29. Hattian landslide, Pakistan
Kashmir earthquake 2005

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32. Post-seismic
debris flows

33. The 2010 Attabad crisis in Northern Pakistan

35. Slope identified as unstable in
2003

36. Collapse event: 4th January 2010

38. 1. Progressive failure over >7 years, scar height = 1175 m
2. Catastrophic failure event in Jan 2010 with no trigger
3. Emplacement of
rockslide onto lake
sediments triggered
secondary high
velocity mudflow
event
Cross valley runout =
1300 m
Deposit height = 120
to 200 m

41. 1858 landslide dam

42. Wenchuan Earthquake barrier lake
risk table
Yang et al 2010

43. Management of the hazard
• Initial management
response was the
construction of a
spillway.
• Original intention: 30
metres deep
• Actual depth at time of
overtopping: 15 metres
• Final spillway was very
narrow and unlined

44. ∂
Water level rise
-1
0
1
2
3
4
5
6
7
8
0
20
40
60
80
100
120
Rateoffilling(metresperday)
Waterdepth(metres)
Date
Water depth (m)
Height of lowest point of completed spillway
Filling rate

45. Evacuations
• After the landslide,
Focus installed sirens
in 15 villages
• People in most
hazardous areas
relocated into camps
• Boat service
established on lake,
but enormous hardship
upstream
• One month before
overtopping NDMA
evacuated 15,000
people downstream of
barrier

46. Seepage

47. Spillway evolution

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0
20000
40000
60000
80000
100000
120000
2002
2003
2004
2005
2006
2007
2008
2009
2010
2011
2012
2013
2014
2015
2016
2017
Cumulativenumberoffatalities
Date
111,000 fatalities since Sept 2002

52. 11/03/2019 © The University of Sheffield

53. Dave Petley
Vice-President, Research and Innovation
Twitter: @davepetley Blog: Search “landslide blog”
Email: d.n.petley@sheffield.ac.uk