Chapter 15

Solifluction

(= soil flow) Promoted by a dense clay hardpan or impermeable bedrock layer; Common in regions underlain by permafrost; Can occur on gentle slopes

Mudflows

- Often confined to canyons and channels; Common in semiarid regions - Limited vegetation

Rockslide

- blocks of bedrock break loose, 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

Debris Flow

- consists of soil and regolith with a large amount of water;

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 over steepened slopes; Material above held in place by material below; Anchor at base is removed; Unstable material above reacts to gravity

Creep

- gradual downhill movement of soil and regolith; Aided by alternate expansion and contraction of surface material - freezing and thawing; Imperceptibly slow - cannot be seen

Over steepened Slopes

- slope angle, The stable slope angle (= the angle of repose) is different for various materials, When the slope becomes unstable, mass wasting occurs

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 Slow Movements

liquefaction

- water- saturated surface materials behave as fluid-like masses that flow

Translational slide

material moves along a flat surface - joint, fault, bedding plane;

Slide

material moves along a surface as a coherent mass;

Slow

Rate of Movement: Creep, Solifluction

Fast

Rate of Movement: Slump, Rockslide, Debris flow, Earthflow;

slope and water content

Rate of flow depends on (2)

Flow

: material moves as a viscous fluid

Rotational slide

: surface of rupture is concave upward, descending material moves downward, with outward rotation;

material

= Debris, Mud, Earth;

Bedrock

= Rock Type of Motion Fall: free-falling pieces

Soil

= combination of regolith, organic matter, water and air

Regolith

= layer of rock and mineral fragments produced by weathering

Mass wasting

= the downslope movement of rock, regolith and soil under the influence of gravity; It is distinct from erosion in that it does not require a transporting medium