Environmental Geology lecture outline - Mass wasting and associated concerns.

Definition of mass wasting = down slope movement of earth material (solid masses, dry aggregates and slurries) under the influence of gravity.

Extent of concern - low grade chronic problem:

" In geology, it would be known as a debris flow. Debris flows amass in stream valleys and more or less resemble fresh concrete. They consist of water mixed with a good deal of solid material, most of which is above sand size. Some of it is Chevrolet size. Boulders bigger than cars ride long distances in debris flows. Boulders grouped like fish eggs pour downhill in debris flows. The dark material coming toward the Genofiles was not only full of boulders: it ws so full of automobiles it was like bread dough mixed with raisins. On its way down Pine Cone Road, it plucked up cars from driveways and the street. When it crashed into the Genofile's house, the shattering of glass made terrific explosive sounds. A door burst open. Mud and boulders poured into the hall. We're going to go, Jackie thought. Oh, my God, what a hell of a way for the four of us to die together." From John McPhee, 1989, Los Angeles Against the Mountains, in The Control of Nature, Publisher -Farrar, Straus, Giroux.

Questions to play with:


What are the various types of mass wasting events (classification)?

Important variables used to classify:

Examples of some types:


What is the largest mass wasting event possible on earth?


What factors promote slope stability versus slope instability?


Can future sites of slope failure be predicted?

The best predictor of future behavior is past behavior.

Recognition of past occurrences:

Human activity can induce mass wasting in an area that has been historically stable.

Slope stability analysis - what is strength and what are forces acting on slope material.

Cretaceous Pierre shale: low strength and very prone to mass wasting, widespread in upper midwest.


Can mass wasting be prevented and/or mitigated?


A few more spectacular case histories:


Some interesting links:

USGS mass wasting site.

Mini-field trips:


Some references:

Hungr, O., Evans, S. G., Bovis, M. J. & Hutchinson, J. N., 2001, A review of the Classification of Landslide of the Flow Type; Environmental and Engineering Geoscience, v. VII, p. 221-238.

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