Debris flow: A debris flow is a form of rapid mass Or units about some pivotal point, below or low in the unit, under theĪctions of gravity and forces exerted by adjacent units or by fluids in cracksįLOWS: There are five basic categories of flows that differ from one another TOPPLES: Toppling failures are distinguished by the forward rotation of a unit FallsĪre strongly influenced by gravity, mechanical weathering, and the presence Separation occurs along discontinuities such as fractures, joints, andīedding planes, and movement occurs by free-fall, bouncing, and rolling. Rocks and boulders, that become detached from steep slopes or cliffs (fig.ģD). For additional information on these processes and where to find photos, please see "Where to Go For More Information" at the end of this fact sheet.įALLS: Falls are abrupt movements of masses of geologic materials, such as These schematics illustrate the major types of landslide movement that are described in the previous pages. A block slide is a translational slide in which the moving mass consists of a single unit or a few closely related units that move downslope as a relatively coherent mass (fig. Translational slide: In this type of slide, the landslide mass moves along a roughly planar surface with little rotation or backward tilting (fig. Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide movement is roughly rotational about an axis that is parallel to the ground surface and transverse across the slide (fig. The two major types of slides are rotational slides and translational slides. SLIDES: Although many types of mass movements are included in the general term "landslide," the more restrictive use of the term refers only to mass movements, where there is a distinct zone of weakness that separates the slide material from more stable underlying material. The most common types of landslides are described as follows and are illustrated in figure 3. In low-relief areas, landslides occur as cut-and-fill failures (roadway and building excavations), river bluff failures, lateral spreading landslides, collapse of mine-waste piles (especially coal), and a wide variety of slope failures associated with quarries and open-pit mines. Abbreviated version of Varnes' classificationĪlthough landslides are primarily associated with mountainous regions, they can also occur in areas of generally low relief. Other classification systems incorporate additional variables, such as the rate of movement and the water, air, or ice content of the landslide material.įigure 2. A classification system based on these parameters is shown in figure 2.
The various types of landslides can be differentiated by the kinds of material involved and the mode of movement. Figure 1 shows a graphic illustration of a landslide, with the commonly accepted terminology describing its features. The materials may move by falling, toppling, sliding, spreading, or flowing. The term "landslide" describes a wide variety of processes that result in the downward and outward movement of slope-forming materials including rock, soil, artificial fill, or a combination of these. An idealized slump-earth flow showing commonly used nomenclature for labeling the parts of a landslide. People were evacuated and the houses nearest the slide were completely destroyed.
This landslide and earthflow occurred in the spring of 1995. La Conchita, coastal area of southern California. The information in this publication provides an introductory primer on understandingīasic scientific facts about landslides-the different types of landslides, how they are initiated, and some basic informationĪbout how they can begin to be managed as a hazard. Worldwide, landslides occur and cause thousands of casualties and billions in monetary losses annually. Casualties in the United States are primarily caused by rockfalls, rock slides, and debris flows. Landslides in the United States cause approximately $3.5 billion (year 2001 dollars) in damage, and kill between 25 and 50 people annually.
Alaska and Hawaii also experience all types of landslides. The primary regions of landslide occurrence and potential are the coastal and mountainous areas of California, Oregon, and Washington, the States comprising the intermountain west, and the mountainous and hilly regions of the Eastern United States. July 2004 Landslides in the United States occur in all 50 States.
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Landslide Types and Processes The PDF for the report is 1 MB
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