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U.S. Department of the InteriorUNITED STATE Geological Survey

Fact Sheet 2004-3072

July 2004

Landslides in the USA happen in all 50 States. The major areas of landslide incident and potential are the seaside and mountainous locations of The golden state, Oregon, and Washington, the States making up the intermountain west, and also the mountainous and hilly areas of the Eastern USA. Alaska and also Hawaii likewise endure all types of landslides.

Landslides in the United States cause roughly $3.5 billion (year 2001 dollars) in damages, and kill in between 25 and 50 civilization yearly. Casualties in the United States are mainly brought about by rockfalls, rock slides, and debris flows. Worldwide, landslides occur and also cause countless casualties and billions in financial losses yearly.

The indevelopment in this publication gives an introductory primer on expertise standard scientific facts around landslides—the different forms of landslides, how they are initiated, and some fundamental information about just how they have the right to start to be controlled as a hazard.

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You are watching: Which of the following are classifications describing how rock and other material move downslope?

La Conchita, seaside area of southerly California. This landslide and also earthflow arisen in the spring of 1995. People were evacuated and also the residences nearest the slide were totally destroyed. This is a typical form of landslide. Picture by R.L. Schuster, U.S. Geological Survey.

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Figure 1. An idealized slump-earth flow mirroring frequently used nomenclature for labeling the components of a landslide.

TYPES OF LANDSLIDES

The term "landslide" defines a wide selection of processes that result in the downward and outward activity of slope-creating materials including rock, soil, artificial fill, or a mix of these. The materials might relocate by falling, toppling, sliding, spanalysis, or flowing. Figure 1 mirrors a graphic illustration of a landslide, with the commonly welcomed terminology describing its functions.

The assorted forms of landslides have the right to be distinguished by the kinds of product affiliated and the mode of movement. A classification system based on these parameters is presented in number 2. Other classification units incorporate additional variables, such as the price of movement and also the water, air, or ice content of the landslide product.

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Figure 2. Types of landslides. Abbreviated variation of Varnes" classificationofslope motions (Varnes, 1978).

Although landslides are generally connected with mountainous areas, they deserve to additionally occur in areas of mainly low relief. In low-relief areas, landslides happen as cut-and-fill failures (roadway and building excavations), river bluff failures, lateral spanalysis landslides, collapse of mine-waste piles (specifically coal), and a wide variety of slope failures linked through quarries and open-pit mines. The most common kinds of landslides are described as follows and are depicted in figure 3.

SLIDES: Although many kind of types of mass motions are included in the general term "landslide," the more restrictive use of the term refers just to mass movements, where tbelow is a distinct zamong weakness that sepaprices the slide material from more stable underlying product. The two significant types of slides are rotational slides and translational slides.Rotational slide: This is a slide in which the surface of rupture is curved concavely upward and the slide activity is around rotational around an axis that is parallel to the ground surface and transverse across the slide (fig. 3A). Translational slide: In this form of slide, the landslide mass moves alengthy a approximately planar surconfront through little bit rotation or backward tilting (fig. 3B). A block slide is a translational slide in which the relocating mass is composed of a single unit or a couple of very closely associated units that relocate downslope as a relatively coherent mass (fig. 3C).

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Figure 3. These schematics illustrate the major kinds of landslide motion that are explained in the previous pages. For extra indevelopment on these procedures and where to discover photos, please view "Where to Go For More Information" at the finish of this reality sheet.

FALLS: Falls are abrupt activities of masses of geologic products, such as rocks and also boulders, that end up being detached from steep slopes or cliffs (fig. 3D). Separation occurs along discontinuities such as fractures, joints, and also bedding planes, and movement occurs by free-loss, bouncing, and rolling. Falls are strongly influenced by gravity, mechanical weathering, and the visibility of interstitial water.

TOPPLES: Toppling failures are distinguished by the forward rotation of a unit or devices around some pivotal suggest, listed below or low in the unit, under the actions of gravity and also forces exerted by adjacent systems or by fluids in cracks (fig. 3E).

FLOWS: Tbelow are five fundamental categories of flows that differ from one one more in standard methods. a. Debris flow: A debris circulation is a kind of quick mass activity in which a mix of loose soil, rock, organic issue, air, and water mobilize as a slurry that flows downslope (fig. 3F). Debris flows encompass b. Debris avalanche: This is a selection of extremely fast to very fast debris circulation (fig. 3G). c. Earthflow: Earthflows have a characteristic "hourglass" form (fig. 3H). The slope material liquefies and runs out, forming a bowl or depression at the head. The circulation itself is elongate and generally occurs in fine-grained materials or clay-bearing rocks on moderate slopes and also under saturated conditions. However before, dry flows of granular material are also possible. d. Mudflow: A mudflow is an earthcirculation consisting of material that is wet sufficient to circulation swiftly and that consists of at least 50 percent sand-, silt-, and also clay-sized pwrite-ups. In some instances, for example in many type of newspaper reports, mudflows and also debris flows are commonly described as "mudslides." e. Creep: Creep is the imperceptibly sluggish, steady, downward activity of slope-forming soil or rock. Movement is brought about by shear tension enough to produce irreversible dedevelopment, however too tiny to produce shear faientice. Tright here are primarily 3 kinds of creep: (1) seasonal, wbelow movement is within the depth of soil influenced by seasonal transforms in soil moisture and soil temperature; (2) constant, where shear stress and anxiety continuously exceeds the stamina of the material; and also (3) progressive, wbelow slopes are getting to the suggest of failure as other types of mass movements. Creep is indicated by curved tree trunks, bent fences or retaining walls, tilted poles or fences, and small soil ripples or ridges (fig. 3I).

LATERAL SPREADS: Lateral spreads are distinctive bereason they generally occur on exceptionally gentle slopes or level terrain (fig. 3J). The leading mode of activity is lateral extension accompanied by shear or tensile fractures. The faitempt is led to by liquefaction, the procedure through which saturated, loose, cohesionless sediments (typically sands and silts) are transformed from a solid right into a liquefied state. Faiattract is typically motivated by rapid ground activity, such as that knowledgeable throughout an earthquake, however can likewise be artificially induced. When coherent product, either bedrock or soil, rests on products that liquefy, the upper units may undergo fracturing and also expansion and might then subside, interpret, rotate, discombine, or liquefy and circulation. Lateral spreading in fine-grained materials on shpermit slopes is commonly gradual. The faitempt starts suddenly in a tiny area and spreads swiftly. Often the initial failure is a slump, however in some products motion occurs for no obvious reason. Combicountry of 2 or even more of the over kinds is known as a facility landslide.

LANDSLIDE CAUSES

1. Geological causesa.Weak or sensitive materialsb.Weathered materialsc.Sheared, jointed, or fissured materialsd.Adversely oriented discontinuity (bedding, schistosity, fault, unconformity, call, and also so forth)e.Contrast in permecapacity and/or stiffness of materials

2. Morphological causesa.Tectonic or volcanic upliftb.Glacial reboundc.Fluvial, wave, or glacial erosion of slope toe or lateral marginsd.Subterranean erosion (solution, piping)e.Deplace loading slope or its crestf.Vegetation removal (by fire, drought)g.Thawingh.Freeze-and-thaw weatheringi.Shrink-and-swell weathering

3. Person causesa.Excavation of slope or its toeb.Loading of slope or its crestc.Drawdvery own (of reservoirs)d.Deforestatione.Irrigationf.Miningg.Artificial vibrationh.Water leakage from utilities

Although tbelow are multiple types of causes of landslides, the three that reason the majority of of the damaging landslides roughly the human being are these:

Landslides and Water

Slope saturation by water is a major reason of landslides. This impact deserve to happen in the create of intense rainautumn, snowmelt, transforms in ground-water levels, and water-level alters along coasts, earth dams, and the banks of lakes, reservoirs, canals, and also rivers.

Landsliding and flooding are very closely allied because both are concerned precipitation, runoff, and also the saturation of ground by water. In enhancement, debris flows and also mudflows typically happen in small, steep stream networks and frequently are mistaken for floods; in reality, these two occasions regularly happen all at once in the exact same location.

Landslides deserve to cause flooding by forming landslide dams that block valleys and also stream channels, permitting large amounts of water to back up. This causes backwater flooding and also, if the dam fails, subsequent downstream flooding. Also, solid landslide debris have the right to "bulk" or include volume and also thickness to otherwise normal streamflow or cause channel blockperiods and also diversions creating flood problems or localized erosion. Landslides can also reason overtopping of reservoirs and/or lessened capacity of reservoirs to keep water.

Landslides and also Seismic Activity

Many mountainous locations that are breakable to landslides have actually likewise skilled at least modeprice rates of earthquake incident in recorded times. The event of earthquakes in steep landslide-prone areas substantially increases the likelihood that landslides will certainly take place, because of ground shaking alone or shaking-led to dilation of soil products, which permits quick infiltration of water. The 1964 Great Alaska Earthquake resulted in widespread landsliding and various other ground faiattract, which brought about many of the financial loss due to the earthquake. Other areas of the United States, such as The golden state and also the Pugain Sound area in Washington, have knowledgeable slides, lateral spreading, and other types of ground faiattract due to moderate to huge earthquakes. Widespcheck out rockfalls likewise are brought about by loosening of rocks as a result of ground shaking. Worldwide, landslides led to by earthquakes kill world and damages frameworks at better rates than in the USA.

Landslides and also Volcanic Activity

Landslides as a result of volcanic activity are some of the most damaging kinds. Volcanic lava may melt snow at a rapid rate, resulting in a deluge of rock, soil, ash, and also water that increases quickly on the steep slopes of volcanoes, destructive anypoint in its course. These volcanic debris flows (also well-known as lahars) reach excellent distances, when they leave the flanks of the volcano, and also deserve to damages structures in flat locations bordering the volcanoes. The 1980 eruption of Mount St. Helens, in Washington prompted a huge landslide on the north flank of the volcano, the biggest landslide in recorded times.

Landslide Mitigation—How to Reduce the Effects of Landslides

Vulnercapability to landslide hazards is a function of place, form of huguy task, usage, and frequency of landslide events. The results of landslides on civilization and also frameworks deserve to be decreased by total avoidance of landslide peril locations or by restricting, prohibiting, or imposing problems on hazard-zone task. Local governments deserve to mitigate landslide results via land-use plans and also regulations. Individuals can mitigate their exposure to dangers by educating themselves on the previous danger background of a website and by making inquiries to planning and design departments of local governments. They can likewise obtain the expert services of an engineering geologist, a geotechnological engineer, or a civil engineer, who can effectively evaluate the risk potential of a website, constructed or unbuilt.

The hazard from landslides have the right to be reduced by preventing building and construction on steep slopes and also existing landslides, or by stabilizing the slopes. Stcapability boosts as soon as ground water is prevented from increasing in the landslide mass by (1) spanning the landslide with an impermeable membrane, (2) directing surconfront water ameans from the landslide, (3) draining ground water amethod from the landslide, and also (4) minimizing surchallenge watering. Slope stcapability is likewise enhanced as soon as a retaining framework and/or the weight of a soil/rock berm are inserted at the toe of the landslide or when mass is removed from the optimal of the slope.

Where to go for even more information

1. The UNITED STATE Geological Survey Landslide Program has actually indevelopment, publications, and also educational information on its Net site. Please see: http://landslides.nlinux.org.govor phone toll-free:1-800-654-4966

2. For general information about slides, debris flows, rock drops, or various other forms of landslides in your area, call your city or county geology or planning office. In enhancement, all 50 States have actually State Geological Surveys that have the right to be accessed with a link at the nlinux.org Net site, http://landslides.nlinux.org.gov

3. For an assessment of the landslide danger to an individual home or homewebsite, attain the solutions of a State-licensed geotechnical engineer or engineering geologist. These specialists deserve to be discovered through the membership listings of two skilled cultures, the American Society of Civil Engineers (ASCE), http://www.asce.org and the Association of Engineering Geologists http://www.aeginternet.org. Often, personnel in State or county planning or engineering departments can refer proficient geotechnological engineers or engineering geologists.

4. For more indevelopment about the architecture and building and construction of debris-circulation mitigation actions which may include debris containers, debris fences, deflection walls, or other protective functions, consult your city or county engineer, neighborhood flood-control firm, or the UNITED STATE Department of Agriculture, Natural Resources Conservation Service: http://www.ncgc.nrcs.usda.gov/

5. For photos of landslide forms please see: nlinux.org Circular 1325: The Landslide Handbook—A Guide to Understanding Landslides

6. For more detailed information: 2 great publications that very plainly define the procedures of landslides were consulted for this fact sheet:Varnes, D.J., 1978, Slope movement kinds and also processes, in Schuster, R.L., and Krizek, R.J., eds., Landslides—Analysis and also control: National Research Council, Washington, D.C., Transportation Research Board, Special Report 176, p. 11–33.Turner, Keith A., and also Schuster, Robert L., 1996, Landslides—Investigation and also mitigation: Transportation Research Board, National Research Council, National Academy Press.

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