This document summarizes research on understanding long-term slope deformation and stability assessment of rock slopes, using the case study of the Oppstadhornet rockslide in Norway. It describes Norway's systematic mapping program to identify unstable rock slopes, characterizes fjord lands prone to rockslides, and details the geology and slip history of the Oppstadhornet rockslide which began moving 14,000 years ago as the glacier receded. Long-term low slip rates are important for detecting acceleration that could lead to failure, and many unstable slopes in Norway may be moving slowly since deglaciation.

1. Understanding long-term slope deformation for
stability assessment of rock slopes: The case of
the Oppstadhornet rockslide, Norway
Reginald L. Hermanns
Thierry Oppikofer, Halgeir Dahle, Trond Eiken,
Susan Ivy-Ochs, Lars Harald Blikra
Vajont conference, Padova, October 8th -10th, 2013

2. Content
• Characterisation of fjord lands
• Systematic mapping program for unstable rock slopes in Norway
• Oppstadhornet rockslide in western Norway
• Unstable rock slopes and deglaciation in Norway

3. Characterisation of fjord lands

4. The challenge:

6. 1947
today
Tjelle, 1756

8. Characterisation of fjord lands
Tafjord 1934

9. Characterisation of fjord lands

10. Certain fjellskred events
Name
Tjelle
Tafjordulykka
Skafjellet
Lausneset
Loenulykke 1
Loenulykke 3
Pollfjellet
County
Møre og Romsdal
Møre og Romsdal
Møre og Romsdal
Møre og Romsdal
Sogn og Fjordane
Sogn og Fjordane
Troms
Municipality
Nesset
Norddal
Stranda
Stranda
Stryn
Stryn
Lyngen
Year
1756
1934
1731
1300
1905
1936
1810
Municipality
Sande
Stranda
Stranda
Norddal
Gaular
Årdal
Year
1700
1749
1938
1811
1786
1983
Volume
Displaceme
[Mm3]
Lives
nt wave
15.0
32
Yes
3.0
40
Yes
6.0
17
Yes
0
Yes
0.4
61
Yes
1.0
74
Yes
14
Yes
Uncertain fjellskred events
Name
Storefonna
Geirangerfjorden
Skafjellet
Arnafjord
Hestadfjorden
Årdalsfjorden
County
Møre og Romsdal
Møre og Romsdal
Møre og Romsdal
Sogn og Fjordane
Sogn og Fjordane
Sogn og Fjordane
Volume
[Mm3]
0.1
0.4
0.2
Lives
0
0
0
45
0
0
Displaceme
nt wave
Yes
Yes
Yes
Yes
Yes
Yes

11. Systematic mapping program for unstable rock slopes in Norway
Tafjord 1934
Assumption:
• Slow deformation indicating slope instability
• Acceleration phase prior to collapse

12. Systematic mapping program for unstable rock slopes in Norway
Task:
•
•
•
•
Tafjord 1934
Find all unstable rock slopes which may collapse catastrophically
Understand geologic condition of each unstable slope
Rank all slopes based upon their hazard and risk
24/7 monitoring and early warning
Mapping approach:
• Risk based

13. Mapping of unstable rock slopes in Norway

14. Systematic mapping program for unstable rock slopes in Norway

15. Systematic mapping program for unstable rock slopes in Norway

16. Oppstadhornet rockslide in western Norway

17. Oppstadhornet rockslide in western Norway
After Braathen et al., 2004

18. Oppstadhornet rockslide in western Norway
After Braathen et al., 2004

19. Oppstadhornet rockslide in western Norway
Bhasin and
Kaynia, 2004

20. Oppstadhornet rockslide in western Norway

21. Oppstadhornet rockslide in western Norway
10Be
exposure age
4.50 m
4
5
6600
4.00 m
3200 a
0.1 mm/a
2.05 m
10300
2.20 m
1.1
3
0.4 mm/a
2.10 m
1.6
2
1700 a
2.2 mm/a
12500
2.85 m
3.2
1
700 a

22. Oppstadhornet rockslide in western Norway
10Be
exposure age Slip rate
2.10 m
3
2.05 m
10300
2.20 m
4
5
6600
4.00 m
2.2 mm/a
2
1700 a
3.2
1
12500
2.85 m
3200 a
700 a
Start of sliding: 14.2 ka ago (16.6 ka)
4.50 m

23. Why did the Oppstadhornet slope did not failed
during a seismic event in the geological history?

24. Understand geologic condition of each unstable slope /
Rank all slopes based on their hazard and risk

25. Understand geologic condition of each unstable slope /
Rank all slopes based on their hazard and risk

26. Unstable rock slopes and deglaciation in Norway
12.8
13.7

27. Oppstadhornet rockslide in western Norway
12.8
13.7
Start of sliding: 10 ka ago
Hermanns et al. 2012

28. Conclusion
• In fjord lands is the area of impact of rock slides often larger than in normal
mountain settings
• Norwegian fjord land is densely settled and systematic mapping is
necessary in order to be able to prepare for future events
• Oppstadhornet rockslide is a typical rockslide in western Norway that has
large consequences
• Oppstadhornet has moved constantly with low rate and is still moving
• Movement started 14 ka ago when the top came out of the ice
• Other landslides have been moving since the location melted out of the ice
sheet with low rate
• Long term slip rates are important information to detect acceleration

29. Thank you for your attention
Reginald.Hermanns@NGU.NO