Physical Geology Chapter 9: Mass Wasting

Vocabulary flashcards covering key definitions, mechanics, controlling factors, movement classifications, and stabilization techniques of mass wasting from Physical Geology (17th Edition), Chapter 9.

Mass Wasting

The downslope movement of bedrock, rock debris, or soil in bulk or as a mass under the direct influence of gravity.

Normal Force

The component of gravitational force acting perpendicular to a slope that acts to hold material in place against the slope.

Shear Force

The component of gravitational force acting parallel to a slope that promotes downslope movement of rock and debris.

Shear Strength

The internal resistance of slope material to movement and deformation, controlled by material cohesiveness and related to the normal force.

Relief

The vertical elevation difference between the valley floor and the adjacent mountain summit.

Debris

Unconsolidated surface material consisting of soil, rock fragments, earth, or mud.

Flow

A type of mass movement in which descending material moves downslope by internal shearing, behaving as a viscous fluid.

Fall

A mass movement process where rock or debris drops through the air, free-falling or bouncing down a steep cliff or slope.

Slide

A type of mass movement where a coherent, relatively intact descending mass moves downslope along one or more discrete surfaces of failure.

Translational Slide

A landslide in which a relatively intact mass moves downslope along a planar surface or weakness plane parallel to the slope face with little rotation.

Rotational Slide (Slump)

A landslide occurring along a concave-upward, curved failure surface where the upper part rotates downward while the lower part moves outward.

Block Slide

A translational landslide consisting primarily of a single coherent unit or block of surface material sliding downslope.

Creep

The extremely slow, imperceptible downward movement of soil or unconsolidated regolith at rates typically less than $1\,\text{cm/year}$, often facilitated by freeze-thaw cycles.

Debris Flow

A relatively rapid downslope movement involving turbulent flow of soil and regolith containing large amounts of water and coarse material such as gravel and boulders.

Earthflow

A slow to rapid downslope movement of thick debris as a viscous fluid, typically developing on hillsides after heavy rainfall saturates the soil beneath a blanket of vegetation.

Solifluction

A cold-climate form of earthflow in which water-saturated surface soil and debris slowly creep over an underlying impermeable substrate, such as permafrost or solid bedrock.

Permafrost

Ground, soil, or sediment that remains completely frozen continuously for several years, forming an impermeable barrier to water drainage.

Mudflow

A rapidly flowing, channelized slurry composed of predominantly fine-grained debris (clay and silt) mixed with water, commonly triggered by heavy rain in sparsely vegetated regions.

Debris Avalanche

The fastest variety of debris flow, consisting of a turbulent, chaotic mass of debris, trapped air, and water rushing down steep slopes at high velocities.

Lahar

A dangerous, rapidly flowing mudflow or debris flow composed of volcanic ash, pyroclastic debris, and water on the flanks of a volcano.

Rockfall

A mass wasting event where individual blocks or fragments of bedrock detach from a steep cliff face and plummet or bounce freely downslope.

Talus

An apron or sloping pile of angular rock fragments and rubble that accumulates at the base of steep cliffs and slopes through rockfall.

Rockslide

The rapid downslope movement of a coherent mass of bedrock along an inclined plane of weakness, such as a bedding plane, joint, or foliation plane.

Rock Avalanche

An extremely high-velocity, turbulent mass of broken-up and shattered bedrock moving down a slope, often supported by a cushion of trapped air.

Stitching

An engineering slope-stabilization method where holes are drilled through unstable rock layers into solid bedrock, secured with cemented steel cables, and tightened with surface steel plates to prevent sliding.