BYU GEO 110 Ch 7

What is mass wasting?
downslope movement of earth’s materials
the term landslides sometimes includes
debris flow, rock falls, and avalanches
The most common landform on the erath
Where are free face slopes more common?
On strong rocks or in arid environments.
Describe a free face slope.
A high cliff of hard rock that forms a straight, nearly vertical slope segment.
What is talus?
Rock fall that accumulates at the base of a cliff or slope
Types of landslides
Falling landslide
free fall of material
Sliding landslide
downslope movement of a coherent block of earthmaterial along a planar slip plane
Slumping landslide
Sliding along a curved slip plane producing slump blocks.
Flowage or flow landslide
Downslope movement of unconsolidated material in which particles move about and mix within the mass
Creep landslides
Very slow flowage. Progressively tilts telephone poles, fences and tree trunks. Trees grow faster than creep moves, so tress are crooked.
Four variables in downslope movement
1- The mechanism of the movement (slide, fall, flow or complex movement) 2- Type of earth material (solid rock, soft consolidated sediment or loose material) 3- Amount of water present 4- Rate of movement
Forces that influence slope stability
Driving forces
Resisting forces
Shear strength
Driving forces on slopes
Move earth materials down a slope
Resisting forces on slopes
Oppose the downward driving forces
Shear strength on slopes
The most common resisting force. Resists by sliding or flowing along potential slip lines
Slope stability is evaluated by…
calculating the Safety Factor.
How to calculate safety factor
The ratio of the resisting forces to the driving forces. Greater than 1 is stable, the resisting forces exceed the driving forces. Less than 1 – slope failure can be expected b/c driving forces exceed the resisting forces.
The shape of the slip surface in slides is strongly conrolled by the type of __________________.
earth material
Slides have two basic patterns of movement.
Rotational, with curved slip surfaces
Translational, planar slip surfaces
Slumps are most common in
unconsolidated earth material and in mudstone, shale and other weak rocks.
Movement in translational slides
moves along inclined slip planes within and parallel to a slope.
Debris flow
thick mixtures of mud, debris, and water.
Angle of repose
The angle at which snow, or any loose material, is stable. Generally, stable at less than 25 degrees.
Two types of snow avalanches
Loose-snow avalanches – starts at a point and widens as it moves downslope Slab avalanches – start has cohesive blocks of snow and ice that move downslope.
Tracks produced by previous avalanches that future avalanches will usually follow
Three factors that will increase world-wide landslide activity.
Development in landslide prone areas
Treecutting in landslide prone areas
Changing global climate patterns will produce regional increases in precipitation
Direct effects of landslides
-Injury from falling debris
-damaged homes
-blocked roads and railroads
Indirect effects of landslides
-upstream flooding
-transmission of disease

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