Mass Wasting
Movement in which bedrock; debris, rock debris, or soil moves downslope in bulk, or as a mass, because of the pull of gravity.
Landslide
Slow to very rapid descent of rock or soil.
Soil
Any unconsolidated or weakly consolidated material at the Earth's surface, regardless of particle size or composition.
Debris
Unconsolidated material (soil) in which coarse-grained fragments predominate.
Earth
In mass wasting, soil in which fine-grained particles are predominant.
Mud
High content of silt and clay, usually wet.
Flow
A type of movement that implies that a descending mass is moving downslope as a viscous fluid.
Slide
In mass wasting, movement of a relatively coherent descending mass along one or more well defined surfaces.
Fall
The situation in mass wasting that occurs when material free falls- or bounces down a cliff.
Translational Slide
In mass wasting, movement of a descending mass along a plane approximately parallel to the slope of the surface.
Rotational Slide
In mass wasting, movement along a curved surface in which the upper part moves vertically downward while the lower part moves outward. Also called a slump.
Relief
The vertical distance between points on Earth's surface.
Trigger
The immediate cause of failure of already unstable ground.
Shear Force
In mass wasting, the component of gravitational force that is parallel to the forces being extended.
Shear Strength
In mass wasting, the resistance to movement or deformation of material.
Creep
Very slow, continuos downslope movement of soil or debris.
Earthflow
Slow-to-rapid mass wasting in which fine-grained soils moves downslope as a very viscous fluid.
Solifluction
Flow of water-saturtated soil over impermeable material.
Permafrost
Ground that remains permanently frozen for many years.
Debris Flow
Mass wasting involving the flow of soil (unconsolidated material) in which coarse material (gravel, boulders) is predominant.
Mudflow
A flowing mixture of debris and water, usually moving down a channel.
Debris Avalanche
Very rapid and turbulent mass wasting of debris, air, and water.
Rockfall
Rock falling freely or bouncing down a cliff.
Talus
An accumulation of broken rock at the base of a cliff.
Rockslide
Rapid sliding of a mass of bedrock along an inclined surface of weakness.
Rock Avalanche
A very rapidly moving, turbulent mass of broken-up bedrock.