Colluvium
Mixture of weathered rock, soil, and other, usually angular, material on a slope; produced by creep, landsliding, and other surface processes.
Creep
Slow downslope movement of soil and other weakly consolidated earth materials; characterized by slow flowing, sliding, or slipping.
Debris Flow
Rapid downslope movement of unconsolidated, water-saturated earth material that became unstable because of torrential rain, rapid melting of snow and ice, or sudden drainage of a pond or lake; sometimes restricted to flows of this type that contain mainly
Driving Forces
An influence that tends to make earth material move downslope.
Falling
Earth materials such as rocks dropping through the air from steep slopes.
Flow
Downslope movement of earth materials that deform as a fluid, such as the fluid movement of grains of sand, rock, snow or ice, debris, and mud.
Landslide
Rapid downslope movement of rock or soil; also a general term for all types of downslope movement.
Mass Wasting
The downslope movement of earth materials under the direct influence of gravity.
Resisting Forces
An influence that tends to oppose downslope movement.
Safety Factor
The ratio of resisting to driving forces; a safety factor >1 suggests a slope is stable.
Shear Strength
The internal resistance in earth material to shear stress; on slopes this strength resists failure by sliding or flowing.
Sliding
The deformation or downslope movement of a nearly intact block of earth material along a slip surface.
Slumping
The downslope movement of a mass of earth material, generally along a curved slip surface.
Snow Avalanche
Rapid downslope movement of snow, ice, and rock.
Talus
Pieces of rock that have accumulated at the base of a cliff or steep slope; may form individual piles or a continuous slope composed of blocks or rock that have fallen from above.
What is a landslide?
A landslide is any type of downslope movement of earth materials including earthflows, debris flows, rock falls, and avalanches.
What are slope segments?
Slope segments are the different parts of a slope that may be straight or curved, and have different dips and characteristics from adjacent segments.
What are the common types of slope segments and how do they differ?
A free face is a nearly vertical segment. The talus slope forms at the base of the cliff and is composed of fallen rock fragments. An upper convex slope makes up what would be the top of a hill as it begins to slope down. The lower concave slope makes up
What are the three main ways that materials on a slope may fail?
Materials may fall (freefall), slide, or slump (flow) off the face of a slope.
What is the safety factor and how is it defined?
The safety factor (SF) is the ratio of the resisting forces to the driving forces.
How do slumps (rotational slides) differ from soil slips and rock slides (translational slides)?
Slumps have curved slip surfaces, while translational slides have planar slip surfaces.
How does the slope angle affect the incidence of landslides?
In general, the steeper the slope the greater the driving force, and therefore as the slope angle increases, the incidence of landslides will increase as well.
How and where do debris flows occur?
Debris flows are thick mixtures of mud, debris, and water that form on slopes after rainfall. They occur on mountains in North America, more specifically the Great Plains, the Arctic, the Great Lakes, and the southwestern United States.
What are the three ways that vegetation is important in slope stability?
Vegetation is important because it provides a protective cover that cushions the impact of falling rain, plant roots add strength and cohesion to slope materials, and the vegetation also adds weight to the slope.
Why does time play an important role in landslides?
Time plays an important role because forces often change with time. What may be affecting a slope one year may have no effect in subsequent years.
What is the relationship between the downslope force and normal force?
The downslope force or driving force (D) is parallel to the slope of the potential slip plane, whereas the normal force (N) is perpendicular.
What variables interact to cause snow avalanches?
Snow avalanches are affected by steepness of the slope, stability of the snowpack, and the weather.
What is the angle of repose?
The angle of repose is the steepest angle at which any snow or loose material is stable.
What are the two types of snow avalanches and how do they differ?
The two types of snow avalanche include loose snow avalanches�which start at a point and widen as they move downhill�and slab avalanches, which start as cohesive blocks of snow and ice that move downslope.
How might processes involved in urbanization increase or decrease the stability of slopes?
Urbanization, the expansion of urban areas, transportation networks, and natural resource use, has increased the number and frequency of landslides. Many slopes are over steepened to make way for roads, buildings, and other features. Natural vegetation is
What types of surface features are associated with landslides?
Surface features associated with landslides are crescent-shaped cracks on a hillside, a tongue-shaped area of bare soil on a hillside, large boulders at the base of a cliff, exposed bedrock laying parallel to the cliff, tongue-shaped masses of sediment, a
What are the main steps that can be taken to prevent landslides?
Some of the main steps taken to avoid landslides are drainage control, grading, and slope supports.
Your consulting company is hired by the national park department in your region to estimate the future risk from landsliding. Develop a plan of attack that outlines what must be done to achieve this objective.
We will determine the safety factor (SF; the ratio of the resisting forces to the driving forces) for different slopes in the area, and determine how this might change with seasons (wet, ice, dry, etc.), and also factor in such variables as likelihood of
Why do you think that few people are easily swayed by technical information concerning hazards such as landslides? Assume you have been hired by a municipality to make its citizens more aware of landslide hazards on the steep slopes in the community. Outl
Few people are swayed because few people actually see landslides as a plausible threat. It always appears to be something that happens to someone else. However, if citizens see maps that include the risk factors for their homes, and are educated (through
The Wasatch Front in central Utah frequently experiences wildfires followed by debris flows that exit mountain canyons and flood parts of communities built next to the mountain front. You have been hired by the state emergency management office to establi
First the region would need to be mapped for hazard potential, and dangerous low-lying areas or alluvial fans identified. Maps and escape routes should be posted on signs in these areas. The warning system would notify people via siren, TV, and radio, inf
Slip plane
Plane of weakness in landslide. Slide moved across it in single mass. Usually flat or planar. (p. 211)
Daylighting beds
Where the planes of weakness are rock bedding planes (p. 214)
Two basic patterns of slide movement
1. rotational slides,or slumps, have curved slip surfaces.
2. translational slides have planar (flat) slip surfaces. (p. 214)
Soil slip
A type of translational slide. A shallow slide of unconsolidated material over bedrock. (p. 216)
Foliation planes
Weak clay layers, and surfaces, between layers in metamorphic rocks. (p. 216)
Permeability
The ability of earth material to transmit water. (p. 216)
Slope
The slant or incline of the land surface. In general, the steeper the slope, the greater the driving force. Steep slopes are associated with rock falls, avalanches, and soil slips. (p. 217)
The Role of Water
Water is almost always directly or indirectly involved with landslides. Water affects slope stability in 3 basic ways:
(1) many landslide such as shallow soil slips and debris flows, develop during rainstorms when slopes become saturated;
(2) other landsl
Driving and resisting forces on slopes are determined by
The interrelationships of the following variables:
� Type of earth materials
� slope angle and topography
� climate
� vegetation
� water
� time (p. 213)
Angle of repose
The steepest angle at which snow, or any loose material, is stable. (p. 222)
Two common types of snow avalanches
1) Loose-snow avalanche - start at a point and widen as they move downslope.
2) Slab avalanches - start as cohesive blocks of snow and ice that move downslope. (most dangerous and damaging). (p. 222)
Mechanism - Fall
Rock fall - individual rocks fall through the air and may accumulate as talus.
Slump - Cohesive blocks of soft earth material slide on a curved surface; also called a rotational landslide. (p. 212)
Mechanism - Slide
Soil Slip - soil and other weathered earth material slide on a tilted surface of bedrock or cohesive sediment; also called a debris slide or earth slide.
Rock slide - Large blocks of bedrock slide on a planar surface, such as layering in sedimentary or me
Mechanism - Flow
Creep - very slow, downslope movement of rocks and soil.
Earthflow - Wet, partially cohesive and internally deformed mass of soil and weathered rock.
Debris flow - Fluid mixture of rocks, sand, mud, and water that is intermediate between a landslide and a
Complex
A combination of two or more types of sliding, flowage, and occasionally falls; forms where one type of landslide changes into another as it moves downslope. (p. 212)
The most rapid form of mass wasting
Rock fall.
The most important driving force in landslides
Weight.
Contributes to a potential soil slip
Planting of native grasses on a previously bare hillside.
Human activities can decrease the incidence of mass wasting?
Improving drainage from the slope.
How do drains help to prevent landslides?
Drains divert water away from the slope.
Downslope movements are classified according to all but one of the following variables:
The amount of development present.
What method is applied to assess the stability of a slope:
Determining relationship between driving forces and resisting forces.
What are the two basic patterns of movement for slides?
Rotational and translational.
The ability of the earth material to transmit water is known as?
Permeability
Why do people chose to live in landslide areas?
Slide risk is not known.