Mass Wasting
Rotational Slide
Surface of rupture is concave upward, descending material moves downward, with outward rotation
The Stable Slope Angle
The angle of repose, Different for various materials, when unstable mass wasting occurs
Stream Valleys
The combined effect of mass wasting and running water
Gravity
The control of mass wasting
Mass Wasting
The process that most often follows weathering
Earthflow
Unconfined flow of clay-rich soil on hillside after heavy precipitation
Earthflow
Unconfined flow of saturated clay-rich soil; Occurs on hillside in humid area following heavy precipitation or snowmelt; Water saturates soil; Material breaks away leaves scar that forms tongue or lobe that flows downhill; Highly viscous - Slower than debris flow
Lahar
Volcanic mudflow, triggered by volcanic activity - eruption
Water-Saturated Surface Material
Behave as fluid-like masses that flow
Rockslide
Blocks of bedrock break loos, slide down slope; Generally very fast and destructive; Occurs where rock strata are inclined or joints and fractures in the rock are parallel to the slope; Triggered by rain or melting snow - Common in spring
Rockslide
Blocks of bedrock break loose and sliding downslope
Mountains
Eroded by rivers and glaciers to form steep, unstable slopes which enables mass wasting and erosional processes to slowly lore the land surface
Type of Motion in Mass Wasting Process
Fall, slide or flow
Slopes
Form as a result of mountain building and volcanic processes
Fall
Free-falling pieces
Creep
Gradual downhill movement of soil and regolith
Creep
Gradual downhill movement of soil and regolith; Aided by alternate expansion and contraction of surface material - freezing and thawing; Imperceptibly slow - can't be seen
Solifluction
Gradual flow of saturated surface layer underlain by impermeable layer
Importance of Mass Wasting
Landslides occur as a result of earthquakes and rain
Regolith
Layer of rock and mineral fragments produced by weathering
Weaken over time
Long-term weathering and infiltration of water cause slope materials to
Translational Slide
Material moves along a flat surface - joint, fault, bedding plane
Slide
Material moves along a surface as a coherent mass
Flow
Material moves as a viscous fluid
Classification of Mass-Wasting Processes
Material, movement, velocity of movement
Inertia
Other factors overcome this to enable mass wasting to occur
Permafrost
Permanently frozen ground(below 0 degrees C for two or more years); Ice underground affects behavior at surface; Thawing procedures unstable ground - slide, slump, subside
Removal of Vegetation
Plant roots bind soil
Solifluction
Promoted by the dense clay hardpan or impermeable bedrock layer; Common in regions underlain by permafrost; Can occur on gentle slopes
Debris Flow
Rapid flow of soil and regolith containing large amount of water
Rate of Movement of Mass Wasting Process
Rapid or slow
Bedrock
Rock
Mass Wasting
Slopes must be resent for this to occur
Rapid Mass Wasting
Slump, Rockslide, Debris Flow, and Earthflow
Slump
Downward sliding of mass of rock or unconsolidated material as unit along curved surface
Processes of Mass Wasting
1) Type of Material 2)Type of Motion 3) Rate of Movement
Soil
Combination of regolith, organic matter, water, and air
Debris Flow
Consists of soil and regolith with a large amount of water; Mudflows; Often confined to canyons and channels; Common in semiarid regions - Limited vegetation; Rate of flow depends on - slope and water content
Slow Mass Wasting
Creep and Solifluction
Unconsolidated Material
Debris, Earth, and Mud
Type of Material in Mass Wasting Process
Debris, mud, earth or rock;
Water
Diminishes particle cohesion(friction) and adds weight
Earthquakes
Dislodge rocks and unconsolidated materials, triggers mass wasting which can be even more damaging, can also cause liquefaction
Mass Wasting
Distinct from erosion in that it does not require a transporting medium
Mass Wasting
Downslope movement of rock, regolith and soil via gravity
Mass Wasting
Downward movement of rock, regolith and soil under the influence of gravity
Slump
Downward sliding of a mass of rock or unconsolidated material as a unit along a curved surface; often consists of multiple blocks; occurs along oversteepened slopes; Material above held in place by material below; Anchor at base is removed; Unstable material above reacts to gravity