hillslopes - moving mass: creep,slides and flows force balance - driving vs resisting forces
DESCRIPTION
Hillslopes - moving mass: creep,slides and flows Force balance - driving vs resisting forces Soil creep - slope dependent, diffusive processes Mass movements - landslides and rock falls Flows - of debris and mud. FORCE BALANCE. DRIVING VERSUS RESISTING. GRAVITY. SHEAR STRENGTH (FRICTION - PowerPoint PPT PresentationTRANSCRIPT
Hillslopes - moving mass: creep,slides and flows
1. Force balance - driving vs resisting forces
2. Soil creep - slope dependent, diffusive processes
3. Mass movements - landslides and rock falls
4. Flows - of debris and mud
FORCE BALANCE
GRAVITY
SHEAR STRENGTH (FRICTION
AND COHESION or VISCOSITY)
DRIVING VERSUS RESISTING
http://ees.as.uky.edu/sites/default/files/elearning/module11swf.swf
Processes that move mass on slopes
first consider infiltration rate
Rainsplash (bare soil only)Rainsplash (bare soil only) Channels (ephemeral, permanent) Channels (ephemeral, permanent) Creep (grab-bag, many processes)Creep (grab-bag, many processes) Mass movement (landsliding = translational, Mass movement (landsliding = translational,
rotational and rockfall)rotational and rockfall) Flowage (debris and mud)Flowage (debris and mud)
Slope types – connect to process
Rain splashRainsplash - splatering, downslope component
2
Where flow is thin, rainsplash disturbance prevents channelization
Incision begins when shear stress exceeds
strength
2
Critical Distance from drainage divide = channelization2
Soil Creep - evidence
Marathon Basin, west Texas. J.S. Aber.Marathon Basin, west Texas. J.S. Aber.
3
Which way is soil moving?
Rate is a function of slope Q= ks
Other biotic effects - vary by climate and location
3
Mammals (gophers here)3
NET DOWNSLOPE TRANSPORT
Rotational failure - clay, silt, homogeneous material
Rotational Failures
Bishop method of slices
Importance of unique events/thresholds
Discrete vs. continuous processesStorms
DisturbanceLandslides
Debris Flows
2000
2600
5900680082009400
The Ritterbush Record 50 cm
Cal
end
ar Y
ears
BP
AMS 14C Analysis
Storm Frequency
• 4 maxima; currently increasing—observed?
0 2 4 6 8 10 12
Calendar kyr BP
NorthAtlanticClimate
GISP2 nssK
GISP2 ssNa
Coolings
Storm
Freq.
StormsFloods
0 2 4 6 8 10 12Calendar kyr BP
Hillslope- channel transition, colluvial hollows
Bank erosion?