test 1 - mass movement and hillslopes Flashcards
What are the erosional forces
Driving and resistant forces
Why might a material have a higher erosional rate
low resistance; driving forces higher than resistant forces
In a rock, what does physical weathering lower
its strength
What influences the shear strength of a rock
frictional characteristics:
- plane friction
- interlocking friction between grains (greater than plane friction)
Effective NORMAL STRESS increases what in a rock
internal resistance to shear; compacts/holds the material together
What does cohesion of a rock increase
The shear strength; through cementation
What are the resistant forces
Frictional factors
Effective normal stress
Cohesion
How does a solid behave like a plastic and why
overburden stresses/strains the underlying rock or sediment, if the overburden is removed the underlying rock may rebound to its original shape/expand, this rebound can cause movement downslope
If the stress on the material is great enough, it may be permanently deformed
How does a sediment behave like a fluid
sediment can be filled with water or air and move without a high degree of internal friction
What are the factors that INCREASE shear stress (driving forces)
Removal of lateral support
- erosion (river action, freeze/thaw, wave action, wind)
- human activity (road cuts, quarries)
Addition of mass
- natural (rain, talus)
- human caused (fills, ore stockpile, urbanization)
Earthquakes -lost of cohesion (shaking adds air/space) Regional Tilting Removal of underlying support Weathering Pore water Structural changes
What are the three types of basic hillslope movement (failures)
Slides
-cohesive blocks of material move on a well defined
plane; no internal shearing
Flows
-moves by differential shearing and mixing; no clear
plane at base of movement
Heaves
-expansion of material; creep; swelling and
contraction propagated by gravity; forces act
perpendicular to ground surface
What are some resisting factors
vegetation, soil type, shear strength
What are some driving forces
gravity, force of flowing water, freeze/thaw etc.
What are the 4 major controls on slope form: TLCP
Time
Lithology
Climate
Process
What are the models of slope development
Process model
Evolutionary model
Explain the evolutionary model of slope development
slope depends on time and the slope decreased with time (erodes)
Explain the process model of slope development
slope is time dependent
slope is dependent on material and slope process
-slope angle decreases with increased erodability of
rock type
How does slope change according to evolutionary model vs process model
evolutionary model says time is the only factor for decrease in slope angle, process model takes into account slope material and its erodability over time.
What type of slope are you likely to have with coherent resistant rocks
steep slopes
If you have massive bedding will you have steep or shallow slopes
steep slopes
Alternating strong and weak strata generate what type of slopes
irregular slopes
If a strata has a high erodability, what angle is its slope likely to be
shallow slope/angle
What is slope replacement
when the steepest angle is progressively replaced by upward expansion of gentler slope developed near the base
