M1 - Geomorphology
Philippe Steer* MCF Géosciences Rennes
*with the help of Rodolphe Catttin, Dimitri Lague, Stéphane Bonnet and many other colleagues
Landslides …
Pantai Remis landslide (Malaysia, 1993)
Plan
1. Introduction
–
Processes / Bestiary / Transport
2. Landslides and rockfalls
–
Shallow sliding / Slope stability analysis / Examples
3. Debris flow and surface runoff
–
Debris flow / Overland flow
4. Soil production and transport
–
Production / Transport / Diffusion
1) Introduction
Hillslope Processes
Hillslopes are an important part of the
terrestrial landscape.
The Earth's landscape can be thought of as
being composed of a mosaic of slope types,
ranging from steep mountains and cliffs to
almost flat plains.
On most hillslopes large quantities of soil
and sediment are moved over time via the
mediums of air, water, and ice often under
the direct influence of gravity.
Hillslope Processes
Fabriques of weak materials
Physical processes
- heating and cooling cycles
- freeze-thaw cycles
- Dry – wet cycles …
Chemical processes (weathering)
Bioturbation (fauna and flora)
Hillslope transport
Hillslope Transport
Surface runoff
Wet
Debris flow
Landslide
Solifluction
Rock falls
Soil creep
Dry
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Fast
Slow
Soil creep
Hillslope Transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Soil creep
Hillslope Transport
A rock fall consists of one or maybe a few
rocks that detach from the high part of a
steep slope, dropping and perhaps bouncing
a few times as they move very rapidly down
slope.
Rock falls are very dangerous because they
can occur without warning, and because the
rocks are traveling at high velocity.
You can usually tell where rock falls are
common by identifying talus at the base of
steep slopes.
Taiwan, Badouzi
Hillslope Transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Soil creep
Hillslope Transport
Rock slide occurs where there is a tilted,
pre-existing plane of weakness within a
slope which serves as a slide surface for
overlying
sediment/rock
to
move
downward. Such planes of weakness are
either flat sedimentary surfaces (usually
where one layer of sediment or sedimentary
rock is in contact with another layer), planes
of cleavage (determined by mineral foliation)
within metamorphic rocks, or a fracture (fault
or joint) within a body of rock. Rock slides
can be massive, occasionally involving an
entire mountainside, making them a real
hazard in areas where a surface of
weakness tilts in the same direction as the
surface of the slope. Rock slides can be
triggered by earthquakes or by the
saturation of a slope with water.
USA, Tenesse
Hillslope Transport: Bestiary
rock
debris
Material + Motion
Examples:
- Rock-slide
- Mud-flow
- Debris-flow
- Soil-creep
- ...
earth/soil
mud
candy
Hillslope Transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Soil creep
Hillslope Transport
before
after
As the name implies, this type of flow contains a
variety of particles or fragments, mainly small
to large rock fragments but also trees, animal
carcasses, cars and buildings.
Debris flows usually contain a high water
content which enables them to travel at fairly
high velocity for some distance from where they
originated. Debris flows tend to follow the paths
of pre-existing stream channels and valleys, but
debris flows are much denser than water, so
they can destroy anything in their paths such as
houses, bridges, or highways.
In volcanically active regions, ash on the slopes
of volcanoes can readily mix with water from
rainfall or snowmelt. When this occurs, a lowviscosity debris flow, called by the Indonesian
term lahar, can form and move very rapidly down
slope.
USA, Buckskin Walsh Gulch
Hillslope Transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Soil creep
Hillslope Transport
Hillslope Transport
This is the slowest type of mass wasting, requiring years of gradual
movement to have a pronounced effect on a slope. Slopes creep
due to the expansion and contraction of surface sediment, and the
pull of gravity.
The pull of gravity is a constant, but the forces
causing expansion and contraction of sediment are not.
The
presence of water is generally required, but in a desert lacking
vegetative ground cover even dry sediment will creep due to daily
heating and cooling of surface sediment grains.
Hillslope Transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
M. Summerfield, Global Geomophology,1991
Soil creep
Hillslope Transport
Solifluction: Mass movement of
soil and regolith affected by
alternate freezing and thawing.
Characteristic of saturated soils in
high latitudes, both within and
beyond the permafrost zone.
Hillslope Transport
A number of features contribute to
active solifluction:
• frequent freeze-thaw cycles
• saturated soils and regolith, after
snow melt and heavy rainfall
• frost-susceptible
materials,
with
significant contents of silt and clay,
at least at depth
• extensive regolith across a range of
slope angles
2) Landslides and rockfalls
Pamir landslide, Pakistan (Pamir Times)
Shallow/Deep Sliding
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
Soil creep
Swiss Alps (2012) 0.3 106 m3
Landslide
Hillslope Stability
What happened
here?
Hillslope Stability
Hillslope Stability
Hillslope Stability
Angle of repose
Hillslope Stability
Every body knows about friction !
Static friction
Sliding friction
Hillslope Stability
Pore pressure
Hillslope Stability
Slope Stability Analysis
volume fraction water
solids
density
wet bulk density
h
 b   s  s  m(1   s )  w  (1  m)(1   s )  a
solid
density
b

fraction of soil
depth saturated
air
density
Slope Stability Analysis
volume fraction solids
wet bulk density
h
water
density
 b   s  s  m(1   s )  w
solid
density
b

fraction of soil
depth saturated
Slope Stability Analysis
volume fraction solids
Driving stresses
wet bulk density
 b   s  s  m(1   s )  w
h
b
 b   b gh cos 
b
solid
density
fraction of soil
depth saturated
b

normal stress
water
density
shear stress
 b   b gh sin 
Slope Stability Analysis
volume fraction solids
wet bulk density
water
density
 b   s  s  m(1   s )  w
h
b
b
sb
solid
density
fraction of soil
depth saturated
b

Resisting stresses
cohesion
friction
sb  c  ( b  Pp )   c  ( b  Pp ) tan 
resisting stress
pore pressure
internal friction
angle
Slope Stability Analysis
volume fraction solids
wet bulk density
 b   s  s  m(1   s )  w
h
b
b
 b   b gh cos 
sb
normal stress
cohesion
shear stress
solid
density
fraction of soil
depth saturated
b

 b   b gh sin 
friction
sb  c  ( b  Pp )   c  ( b  Pp ) tan 
resisting stress
water
density
pore pressure
internal friction
angle
Slope Stability Analysis
b
F=1
F<1
sb

C
F>1
b
Slope Stability Analysis
h
soil surface
water table
impermeable horizon

F
c  ( b  Pp ) tan 
b
c  (  b   w m) gh cos tan 

 b gh sin 
(c / gh)  (  s   w m) s cos tan 

( s  s  m(1   s )  w ) sin 
mh
 b   s  s  m(1   s )  w
 b   b gh cos 
Pp   w gmh cos 
Slope Stability Analysis
Implication for dry cohesionless soil
(c / gh)  (  s   w m) s cos tan 
F
( s  s  m(1   s )  w ) sin 
m0 c0
 s s cos tan  tan 
F

 s  s sin 
tan 
F=1 at maximum stable slope
angle of repose = angle of internal friction!
Slope Stability Analysis
b
b
b
b
The saturation of soil
materials increases the
weight of slope materials
The presence of bedding planes in the
hillslope material can cause material
above a particular plane below ground
level to slide along a surface
lubricated by percolating moisture
Saturation of soil materials
can reduce the cohesive
bonds between individual
soil particles resulting in the
reduction of the internal
strength of the hillslope
b
b
Landslides
Holidays picture: Tsergo Ri (5000 m)
Why does he talk about
his holidays?
Largest continental mega-landslide
Korup et al.,
2010
Largest continental mega-landslide
Weidinger et al.,
2002
volume Tsergo Ri landslide ~109 m3
volume olympic swiming pool ~2.5 103 m3
Tsergo Ri=400.000 swiming pool
Worldwide landslike hazard
To create this landslide risk map scientists mapped all of the regions
that featured some combination of coarse soil, land cover that was
inadequate to stabilize the surface, and/or steep mountains.
Scaling laws
area-frequency
Malamud et al., 2004
Hovius et al., 1997
Scaling laws
Volume, Area, Depth
Larsen et al., 2010
Scaling laws
Material influence
Larsen et al., 2010
Wenchuan earthquake 2008
Scaling laws
Landslides and Earthquakes
Malamud et al.,
2004
Landslides triggered by earthquakes
Finisterre Mountains
Papua New Guinea
Meunier et al., 2008
earthquake
Landslide
position
and
triggering
earthquake
precipitation
Meunier et al., 2008
precipitation
earthquake
precipitation
Landslide position, site effect,
and peak ground acceleration PGA
Meunier et al., 2008
Landslides to determine seismic
rupture plane
Inversion from
landslides position
Meunier et al., 2012
Classical seismic
inversion
Landslides and rainfall (Seattle)
Coe et al., 2004
Landslides and rainfaill (world)
Hong et al., 2006
Landslides and rainfall (Nepal)
Gabet et al., 2004
The Geneva Lake Tsunami 563 AD
Tsunami wave
Kremer et al., 2012
Chain of
Events
Fort et al., 2009
The Geneva Lake Tsunami
Massive turbidites
in the lake sediments
Kremer et al., 2012
Kremer et al., 2012
The Geneva
Lake Tsunami
Resulting flood
in Geneva
Kremer et al., 2012
Mont Granier
Landslide 1248 AD
Mont Granier Landslide 1248 AD
Mont Granier Landslide 1248 AD
Fort et al., 2009
mudslide
rockslide
Heart Mountain landslide
Heart Mountain landslide
50 Ma old rocks
500-350 Ma old rocks
Huge landslide:
• Thickness: 4-5 km
• Distance: 40 km
• Speed: 150 km/h
• Slope: < 2°
Heart Mountain landslide
50 Ma old rocks
500-350 Ma old rocks
Huge landslide:
• Thickness: 4-5 km
• Distance: 40 km
• Speed: 150 km/h
• Slope: < 2°
Heart Mountain landslide
How is it possible?
Remember that the stability
angle of rocks is ~ 40º
50 Ma old rocks
500-350 Ma old rocks
Heart Mountain landslide
Huge landslide (48 Myr ago):
• Thickness: 4-5 km
• Distance: 40 km
• Speed: 150 km/h
• Slope: < 2°
How is it possible?
1) Fusion on the landslide
plane (800-1000º)
2) Formation of pseudotachylites and CO2
3) Supercritical CO2 played
the role of an air cushion
(friction reduced)
3) Debris flow and surface
runoff
Debris flow close to
Mount Ranier, USA
(2001)
Surface Runoff
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
Soil creep
Debris Flow
Debris flow and scars
near Los Angeles
Debris Flow
• Debris flow are defined by:
– fast moving, liquefied landslides of mixed and
unconsolidated water and debris that look like flowing
concrete
– Non-Newtonian viscous material
ε ∝ σ 𝑛 𝑤𝑖𝑡ℎ 𝑛 > 1
– Dense flow (ρ > > ρw)
– Sediment volume > 0.6 x total flow volume
Flow density:
Rockslide > Debris flow > Fluvial flow
ρ ~ 2800 ρ ~ 2300
ρ ~ 1000
kg/m3
Debris Flow
• Debris flow near
Flagstaff (USA)
sediment dense!
Debris Flow
Debris Flow
cohesion
Kessler & Bédard, 2000
Debris Flow: flow geometry
Potential energy lost by
motion:
Iverson, 1997
L = debris flow length
H = height difference
M = debris flow mass
R = dimensionless resisting
coefficient
Energy lost by friction
resistance:
Energy conservation:
Debris Flow: flow geometry
1/R
Iverson, 1997
Debris Flow: head geometry
𝝈
𝝉
Debris flow solid head mass
𝟏
𝒎 = 𝝆𝒉 𝒉𝒍𝒘
𝟐
Tangential force
𝛕 = 𝐦 𝐠 𝐬𝐢𝐧 𝛉
Normal force
𝝈 = 𝒎 𝒈 𝐜𝐨𝐬 𝜽
Debris Flow: head geometry
𝝈
𝝉
𝑷𝒖𝒔𝒉
Coulomb resisting force 𝑺 = σ 𝒕𝒂𝒏ϕ
(cohesionless)
Debris flow solid head mass
𝟏
𝒎 = 𝝆𝒉 𝒉𝒍𝒘
𝟐
Tangential force
𝛕 = 𝐦 𝐠 𝐬𝐢𝐧 𝛉
Normal force
𝝈 = 𝒎 𝒈 𝐜𝐨𝐬 𝜽
Debris Flow: head geometry
𝝈
𝝉
𝑷𝒖𝒔𝒉
Coulomb resisting force 𝑺 = σ 𝒕𝒂𝒏ϕ
(cohesionless)
Debris flow solid head mass
𝟏
𝒎 = 𝝆𝒉 𝒉𝒍𝒘
𝟐
Tangential force
𝛕 = 𝐦 𝐠 𝐬𝐢𝐧 𝛉
Normal force
𝝈 = 𝒎 𝒈 𝐜𝐨𝐬 𝜽
Liquid pushing force
𝟏
𝟐
𝑷𝒖𝒔𝒉 = 𝝆𝒃 𝒉𝟐 𝒘 𝒈 𝐜𝐨𝐬 𝜽
Debris Flow: head geometry
𝝈
𝝉
𝑷𝒖𝒔𝒉
Debris flow solid head mass
𝟏
𝒎 = 𝝆𝒉 𝒉𝒍𝒘
𝟐
Tangential force
𝛕 = 𝐦 𝐠 𝐬𝐢𝐧 𝛉
Normal force
𝝈 = 𝒎 𝒈 𝐜𝐨𝐬 𝜽
Liquid pushing force
𝟏
𝑷𝒖𝒔𝒉 = 𝝆𝒃 𝒉𝟐 𝒘 𝒈 𝐜𝐨𝐬 𝜽
Coulomb resisting force 𝑺 = σ 𝒕𝒂𝒏ϕ
𝟐
(cohesionless)
Force balance (neglecting pore pressure and inertia)
𝑻𝒂𝒏𝒈𝒆𝒏𝒕𝒊𝒂𝒍 − 𝑹𝒆𝒔𝒊𝒔𝒕𝒊𝒏𝒈 + 𝑷𝒖𝒔𝒉 = 𝟎
Debris Flow: head geometry
𝝈
𝝉
𝑷𝒖𝒔𝒉
Debris flow solid head mass
𝟏
𝒎 = 𝝆𝒉 𝒉𝒍𝒘
𝟐
Tangential force
𝛕 = 𝐦 𝐠 𝐬𝐢𝐧 𝛉
Normal force
𝝈 = 𝒎 𝒈 𝐜𝐨𝐬 𝜽
Liquid pushing force
𝟏
𝑷𝒖𝒔𝒉 = 𝝆𝒃 𝒉𝟐 𝒘 𝒈 𝐜𝐨𝐬 𝜽
Coulomb resisting force 𝑺 = σ 𝒕𝒂𝒏ϕ
𝟐
(cohesionless)
Force balance (neglecting pore pressure and inertia)
𝝉 − 𝝈 𝐭𝐚𝐧 𝝓 + 𝑷𝒖𝒔𝒉 = 𝟎
𝒉
𝝆𝒉
=
𝐭𝐚𝐧 𝝓 − 𝐭𝐚𝐧 𝜽 ≈ 𝐭𝐚𝐧 𝝓 − 𝐭𝐚𝐧 𝜽
𝒍
𝝆𝒃
Debris Flow
In the Southern Alps(France)
Debris Flow
Debris Flow
In the Southern
Alps (France)
Overland Flow
Overland Flow
length & width
1-10 m
10-100m
Rills
Gullies
Overland Flow
Overland Flow
L
Geometric parameters
• Length L
• Width D
• Slope S0
Physical parameters
• Mean water velocity V
• Water discharge q
• Sediment discharge qs
• kinematic viscosity 
• Water thickness h
• Basal shear stress c
• Rainfall intensity R
• Bedrock rugosity k
Overland Flow
Dimensionless number
Reynolds number
Re 
inertial forces V .D

viscous forces

Low Re laminar flow - sheet
High Re turbulent flow – rills & gullies
Froude number
inertial forces
V
Fr 

gravitational forces
gh
Fr < 1 subcritical flow – fluvial
Fr > 1 supercritical flow - torrential
Nearing et al., 1997
Overland Flow
Dimensionless number
Nearing et al., 1997
Reynolds number
Re 
inertial forces V .D

viscous forces

Low Re laminar flow - sheet
High Re turbulent flow – rills & gullies
Froude number
inertial forces
V
Fr 

gravitational forces
gh
Fr < 1 subcritical flow – fluvial
Fr > 1 supercritical flow - torrential
Rill formation is not easily expalined
By Re and Fr variations
Overland Flow
• Rills behave as a source of
sediments
• The rate of erosion is
related to stream power
• Empirical relationship
Nearing et al., 1997
Overland Flow
• The system is mostly transport-limited (TL)
• Except for very high contents of rock/sand, where is
detachment-limited (DL)
Pelletier, 2011
4) Soil production and
transport
Soil creep, Utah (from Tom McGuire)
Soil transport
Surface runoff
Debris flow
Landslide
Solifluction
Rock fall
Soil creep
Shallow/Deep
sliding
Soil creep
Soil Profile
Fletcher et al., 2006, Anderson etal., 2007
Soil Production and Transport
q
h
 production transport  P  s
t
x
Heimstat et al., 1997
qs
h
 production transport  P 
t
x
Soil Production and Transport
Soil
production
q
h
 production transport  P  s
t
x
Heimstat et al., 1997
qs
h
 production transport  P 
t
x
Soil Prodcution
Which one produces more soil?
Bare bedrock
Bedrock soil-mantled
Soil Prodcution
Grove Karl Gilbert (1843–1918)
Which one produces more soil?
Bare bedrock
Bedrock soil-mantled
Soil Production
Exponential
or humped?
Maximum of soil
production
Exposed bedrock
samples
P~e
Heimstat et al., 2001
 ah
Soil Production and Transport
Soil
transport
q
h
 production transport  P  s
t
x
Heimstat et al., 1997
qs
h
 production transport  P 
t
x
Soil Transport
Roering, 2004
Soil Creep
Initial
After 1.25 s
tracers
acoustic
waves =
disturbance
Roering, 2004
Soil Creep
Initial
After 1.25 s
tracers
acoustic
waves =
disturbance
Roering, 2004
Soil Creep
Initial
After 1.25 s
tracers
acoustic
waves =
disturbance
Roering, 2004
Soil Creep
𝟒
extension
𝟏
𝟑
𝟓
compression
𝟐
𝟏
Pu > Pd
𝟑
Pu
Pu
Pd
Pd
𝟐
𝟒
Pu
Pu
Pd
Pd
𝟑
𝟓
Pu
Pu
Pd
Pd
Soil Creep
Instant and delayed compression
Total
volumetric
strain
ln c
ec
e
Deformation
during primary
consolidation Effective
creep time
t’ = t-c
ln t
*
compression
index
time scale
parameter
Madurapperuma & Puswewala, 2008
Rainsplash erosion
Rainsplash erosion
John Wainwright
Rainsplash erosion
John Wainwright
Rainsplash
erosion
Lup < Ldown
Rainsplash
erosion
Assuming no air friction, force balance
once integrated gives:
Vx(t) = cst = Vo cos(θ)
Vz(t) = Vo sin(θ) – g t
Integrating for position gives:
x(t) = Vo cos(θ) t
z(t) = Vo sin(θ) t – ½ g t2
The z(x) parabolic trajectory is then:
z(x)= x tan(θ) – g x2 / (2 Vo2 cos2(θ))
Vo
θ
Now you know that the soil slope has for equation:
α
Lup < Ldown
z(x)= x tan α + cte
What are the x-positions of the two landing zones?
xup= ?
xdown= ?
Rainsplash
erosion
The z(x) parabolic trajectory is then:
z(x)= x tan θ – g x2 / (2 Vo2 cos2 θ)
Now you know that the soil slope has for equation:
z(x)= x tan α + cte
What are the x-positions of the two landing zones?
xup= ?
xdown= ?
Vo
θ
α
Lup < Ldown
Resolution d’un polynome du 2nd degré
Δ = b2 – 4 a c
if Δ>0
xdown = (-b -Δ1/2 ) / 2 a
xup = (-b +Δ1/2 ) / 2 a
Hillslope Evolution
Transport
qs  
h
x
The flux of sediment is
proportional to the hillslope
gradient
h
qs  
x
Diffusivity in units of L2/T
Dietrich et al., 2003
Hillslope Evolution
Diffusion law
«Fick law»
The flux of sediment is proportional to the
hillslope gradient
h
qs  
x
Conservation of mass: an increase or a
decrease in the elevation is equal the change
in flux per unit length
qs
h

t
x
Diffusion law
h
 2h
 2
t
x
  2h  2h 
h
   2  2    2 h
t
y 
 x
qin
qout
Hillslope Evolution
Diffusion law
h
 2h
 2
t
x
h
L
x
Assuming a constant incision rate
1. Find the equation associated with the hillslope geometry.
2. What is the maximum variation in elevation ?
3. Where is the highest slope ?
4. Give its expression.
Hillslope Evolution
Diffusion law
Lachlan Valley, SE Australia
Diffusion model leads to a parabolic elevation profile
Hillslope Evolution
Diffusion law
Surface runoff
Debris flow
Landslide
Solifluction
Rock falls
Slope < 20°
Diffusion
Soil creep
Shallow/Deep
Soil creep
sliding
The applicability of the diffusion model to hillslope
evolution depends on both the local slope and the
processes acting to move sediment on the hillslope.
Hillslope Evolution
Non-linear erosion law
Anderson, 1994
Shoalhaven valley, SE Australia
Hillslope Evolution
Non-linear erosion law
Sc
qs  
Roering et al., 2001
h
x




h 
1

qs  
x   1 h  2 
1  


  S c x  
Hillslope Evolution
Non-linear erosion law
Roering et al., 2001
Hillslope Evolution
Non-linear erosion law
Montgomery & Brandon, 2002
Hillslope Evolution
Non-linear erosion law
Taiwan
SE Australia
Lesser Himalaya
Alps
SE Australia
Montgomery & Brandon, 2002
Hillslope Evolution
Non-linear erosion law
Montgomery & Brandon, 2002
Hillslope Evolution and Processes
Tectonic activity
Hillslope process
Sediment flux
low
diffusion
continuous
sliding
high
rock fall
stochastic
Hillslope Evolution and Processes
Dietrich et al., Nature, 2006