Classifying Mass Movements

• Type
• Material
• Rate of movement
  

Type

Type of movement: Fall, Slide, Flow
Type of material: Rock or Regolith (debris or earth)
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Put together to describe! Examples: Rock Fall, Earth Slide, etc.

Slides and debris flows are the most common in Southern California.

Creep: gradual movement of slope materials
Slump: complex movement of materials on a slope
Topple: the end-over-end motion of rock down a slope.
Fall: material free falls
Flow: viscous to fluid-like motion of debris.
Torrent: a sporadic and sudden channelized discharge of water and debris
Slide: movement parallel to planes of weakness and slope.

Rotational landslides - These slides mostly occur in homogeneous material and have a curved slide plane

Translational landslide - these slides typically occur along a planar surface, such as between bedding planes. Translational slides are the most common in S. California in Miocene-aged Formation rocks.

Development of a rotational landslide in homogeneous material. The material fails, creating a curved slideplane. The gap at the top of the slide is called the scarp, and the excess material at the base of the slide is called the toe.

translational landslides begin in bedrock, such as siltstone, which is dipping in the same direction as the slope topography. Erosion occurs at the base of the hillside, either by a stream or even by a road cut. The bed no longer has anything to support it at its base, and begins to slide downslope.

Table 1 below (modified from Varnes, 1978) summarizes one way of naming slope-failure deposits and their associated slope failure type >


TYPE OF MATERIAL			TYPE OF MOVEMENT
BEDROCK	ENGINEERING SOILS
	Predominantly coarse	Predominantly fine
Rock fall	Debris fall	Earth fall	Falls
Rock topple	Debris topple	Earth topple	Topples
Rock slump	Debris slump	Earth slump	Slides	rotational	few units
Rock block slide Rock slide	Debris block slide Debris slide	Earth block slide Earth slide		translational	many units
Rock spread	Debris spread	Earth spread	Lateral Spreads
Rock flow (deep creep)	Debris flow (soil creep)	Earth flow	Flows
Combination of two or more principal types of movement			Complex

Rate of Movement

• Fast
  • Slumps
  • Rock slides
  • Debris flows
  • Earthflows
• Slow
  • Creep
  • Solifluction (the gradual flow of a saturated layer that is underlain by an impermeable zone)