1. Lecture Outlines Physical Geology, 10/e
Plummer, McGeary & Carlson

2. Mass Wasting Physical Geology 10/e, Chapter 9
Steve Kadel, Glendale Community College

3. Mass Wasting
Mass wasting is downhill movement of masses of bedrock, rock debris or soil, under the pull of gravity
Landslides are much more costly over time in the U.S., in terms of both lives and dollars, than all other geologic and weather hazards combined
Mass wasting is, with proper planning, perhaps the most easily avoidable of the major geologic hazards

4. Yungay Peru Avalanche: 1970

5. Classification of Mass Wasting
Types of mass wasting are classified based on:
Rate of movement
Wide range from < 1cm/year to >100 km/hour
Type of material
Did moving mass start out as solid bedrock or as debris (unconsolidated material at Earth’s surface)
Type of movement
Flow, slide, or fall

6. Classification of Mass Wasting
Types of movement
Flow
Descending mass moves downhill as a viscous fluid
Slide
Descending mass remains relatively intact, and descends along well-defined surfaces
Translational slide - movement along plane parallel to motion
Rotational slide (slump) - movement along a curved surface
Fall
Material free-falls or bounces down a cliff

8. Factors Controlling Mass Wasting
Factors making mass wasting likely:
Steep slopes
Shear forces maximized by gravity
Large relief
(large elevation change from top of
mountains/hills to valley floor)
Thick layer(s) of loose rock,
debris, soil
Presence of water
Lubricates moving rocks/debris/soil
Lack of vegetation
No roots to hold rock/soil in place
Seismic (earthquake) activity

10. Think Pair Share What are the three classifications of Mass wasting?
What would an avalanche of snow be classified?
The Yungay avalanche?
What are the controlling factors of mass wasting?

11. Types of Mass Wasting Creep
Very slow downslope movement of soil or unconsolidated debris
Major contributing factors include water in soil and daily freeze-thaw cycles
Can be costly to maintain homes, etc., on creeping ground as foundations, walls, pipes and driveways crack and shift downslope over time

12. Types of Mass Wasting
Debris flow - mass wasting in which motion takes place throughout the moving mass (flow)
Earthflow - debris moves downslope, slowly or rapidly, as a viscous fluid
Commonly occurs on steep hills, with thick debris cover, after heavy rains
Solifluction of saturated debris is an example
Mudflow - flowing mixture of debris and water, usually down a channel
Most likely to occur on steep unvegetated slopes with thick debris cover
Heavy rains on the slopes of stratocone volcanoes with fresh ash layers are triggers
Debris avalanches are very rapid and turbulent
Can reach speeds of several hundred km/hr

13. Types of Mass Wasting
Rockfall - when a block of bedrock breaks free and falls or bounces down a cliff
Commonly an apron of fallen rock fragments (talus) accumulates at cliff base
Rockslide - the 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
Debris slide - a coherent mass of debris moving along a well-defined surface
Debris fall - a free-falling mass of debris

14. Preventing Landslides
Preventing mass wasting of debris
Construct retaining wall with drains
Don’t oversteepen slopes during construction
Preventing rockfalls and rockslides on highways
Remove all rock that is prone to sliding
“Stitch” together outcrop
Important to know the susceptibility of land to mass wasting before building any road or structure

15. Think Pair Share List three types of mass wasting and describe them
What are the three major ways to prevent landslides?
Does this match with what you wrote in the warm up?