Frank Press, Raymond Siever, John Grotzinger, and Thomas H. Jordan Mass Wasting
Understanding Earth Process by which Fourth Edition material moves downslope under Chapter 12: Mass the force of gravity Wasting
Copyright © 2004 by W. H. Freeman & Company 1 2
Factors Influencing Mass Movement Mass Movement is Classified on the Basis of: • Nature of slope materials • Nature of material • Steepness of slope • Velocity of movement • Water content • Nature of movement • Slope stability
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Mass Movement Depends on Water Content
5 6 Water Content Lose of Steep slopes vegetations and in damp sand root systems maintained by increases moisture susceptibility of between soils to erosion grains and mass movement
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Types of Rock Mass Movement
• Rock fall • Rock slide • Rock avalanche
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Rock Fall Rockfall in Zion National Park
11 12 Rockslide Rockslide The rapid movement of large blocks of detached bedrock sliding more or less as a unit
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Rockslide Rock Avalanche
The rapid* mass movement of broken rock material, often riding on a cushion of trapped air. Usually triggered b y an earthquake.
*10’s to 100’s of km/hr
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Rock Avalanches Triggered by an Rock Avalanche Earthquake (Nov. 3, 2002) in Alaska
17 18 Types of Unconsolidated Mass Creep Movement
Unconsolidated Flows The downhill movement of soil and other debris, typically at rates of Creep about 1 to 10 mm/year
Earth Flow Increased velocity Debris Flow Earth Flow
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Evidence of Creep
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Earthflow Earthflow A fluid movement of relatively fine‐ grained material, e.g. soil, weathered shale, and clay.
23 24 Debris Flow A fluid mass Earthflow movement of rock fragments supported by a muddy matrix. May move at speeds of up to 100 km/hr
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Debris Flow Debris Flow
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Mudflow Mudflow
A flowing mass of material (mostly finer than sand, along with some rock debris) containing a large amount of water. It may travel large distances and high speeds, and carry particles as large as a house!
29 30 Debris Avalanche Debris Avalanche
Fast* downhill movements of soil and rock, usually occurring in humid mountainous regions.
* Up to 280 km/hr
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Mt. Huascaran, Peru (before 1970) Mt. Huascaran, Peru (after 1970)
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Types of Unconsolidated Slump Mass Movement
Unconsolidated Slides and Falls A slow slide of unconsolidated Slump material that travels as a unit. Increased velocity Debris slide
Debris avalanche
35 36 Slump Slump
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Debris Slide Debris Slide A type of mass of material in which rock material and soil move largely as one or more units along planes of weakness.
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Debris Slide Ways to Reduce Losses Due to Landslides Include: • Avoid construction in areas prone to mass movement • Build in a way that does not make naturally stable slope unstable • Engineer water drainage to prevent strata to become water saturated and prone to fail
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