Mass Wasting

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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 3 4 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 7 8 Types of Rock Mass Movement • Rock fall • Rock slide • Rock avalanche 9 10 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 13 14 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 15 16 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 19 20 Evidence of Creep 21 22 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 25 26 Debris Flow Debris Flow 27 28 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 31 32 Mt. Huascaran, Peru (before 1970) Mt. Huascaran, Peru (after 1970) 33 34 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 37 38 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. 39 40 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 41 42.

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Types of Landslides.Indd
Landslide Types and Processes andslides in the United States occur in all 50 States. The primary regions of landslide occurrence and potential are the coastal and mountainous areas of California, Oregon, Land Washington, the States comprising the intermountain west, and the mountainous and hilly regions of the Eastern United States. Alaska and Hawaii also experience all types of landslides. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in dam- age, and kill between 25 and 50 people annually. Casualties in the United States are primar- ily caused by rockfalls, rock slides, and debris flows. Worldwide, landslides occur and cause thousands of casualties and billions in monetary losses annually. The information in this publication provides an introductory primer on understanding basic scientific facts about landslides—the different types of landslides, how they are initiated, and some basic information about how they can begin to be managed as a hazard. TYPES OF LANDSLIDES porate additional variables, such as the rate of movement and the water, air, or ice content of The term “landslide” describes a wide variety the landslide material. of processes that result in the downward and outward movement of slope-forming materials Although landslides are primarily associ- including rock, soil, artificial fill, or a com- ated with mountainous regions, they can bination of these. The materials may move also occur in areas of generally low relief. In by falling, toppling, sliding, spreading, or low-relief areas, landslides occur as cut-and- La Conchita, coastal area of southern Califor- flowing. Figure 1 shows a graphic illustration fill failures (roadway and building excava- nia.
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Mass Wasting and Landslides
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