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The high mountain cryosphere: processes and risks
GEO 415 / 856
Jérome Faillettaz & Christian Huggel
Slope stability & mass flows II: rock slides & landslides, debris flows
Andina
Landslides in Lurigancho / Chosica (Lima), Peru, March 2015
El Comercio
Dave Petley, landslide blog
INDECI
Existing hazard map…
C. Larsen
Mt. Steller region, Alaska, 2008
Huascarán, Peru
Flow transformations
J. Clague
Mt Meager (B.C.) Aug 2010
Flow transformations
Debris flow
depositionVal Varuna, Poschiavo (CH),
18.7. + 24.8.1987•Large event (200,000 m3) consisting of 3 – 4 surges (up to 50,000 m3) and many smaller surges
•Multiple lobes of deposits (stopped at railway tracks)
•Runout reached main river in the valley
•Similar “valley-blocking” cases may create a flooding hazard situation upstream and a dambreak flooding situation downstream
Debris flow processes and dynamics
Learning objectives
• Distinguish between trigger, flow/transport and deposition regimes of mass movements (in terms of processes, geomorphology, hazards implications)
• Recognize some basics of mass movement failure and flow classification
• Understand basic concepts of slope (in-)stability in terms of (dynamic) forces applied
• Understand how cascading processes related to mass movements can be produced and what effects can result thereof
Student presentation
Basic concept of mass movements
U.S. Geological Survey
Types of mass movements
After Coussot and Meunier, 1996, and Schatzmann, 2005
Classification of mass movements
Smithson et al., 2002
Classification of mass movements
Basic principles
Sliding block model
Coulomb friction (dry friction)
ϕ = angle of friction (also used: θ), max. angle before which block starts to slideμ = coefficient of friction
FN = normal force; FR = friction force; FG = gravitational force
Factor of Safety (FS) concept
resisting force (shear strength)
(downslope) driving force (shear stress)FS =
FS > 1 : slope considered ~ stable
FS < 1 : slope considered ~ unstable
(Infinite slope)
Shear strength
Infinite slope concept
Shear strength is the load / pressure per unit area a material can withstand before undergoing shearing failure
Shear strength is the normal stress plus cohesion of the material
Shear strength
Cohesion
Angle of friction
Normal stress on potential failure surface
Infinite slope concept
Shear strength
R
R
Shear stress
Angle of slope
Normal stress on potential failure surface
Infinite slope concept
Shear stress
D
D
Huggel et al., 2012
Slope instability and driving forces (incl. climatic change)
Huggel et al., 2010
Slope instability and time scales