Mass Wasting

Classifying Mass Wasting Events

Classified by

• Type
• Material
• Rate of movement
  

Type

There are several types of mass movement. Here is a Shockwave animation from Pearson Education showing the five main types of mass movements.

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 (aka rotational): 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 (aka translational): movement parallel to planes of weakness and slope.

The table 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)