Hillslopes - moving mass: creep,slides and flows 1. Force balance - driving vs resisting forces 2. Soil creep - slope dependent, diffusive processes 3.

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Presentation transcript:

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

rning/module11swf.swf

Processes that move mass on slopes first consider infiltration rate  Rainsplash (bare soil only)  Channels (ephemeral, permanent)  Creep (grab-bag, many processes)  Mass movement (landsliding = translational, rotational and rockfall)  Flowage (debris and mud)

Slope types – connect to process

Rain splash Rainsplash - 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 = channelization 2

Soil Creep - evidence 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 processes Storms Disturbance Landslides Debris Flows

The Ritterbush Record 50 cm Calendar Years BP

AMS 14 C Analysis

Storm Frequency 4 maxima; currently increasing—observed? Calendar kyr BP

North Atlantic Climate GISP2 nssK GISP2 ssNa Coolings Stor m Freq. Storms Floods Calendar kyr BP

Hillslope- channel transition, colluvial hollows

Bank erosion?