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Processes of Mass Wasting

Janet KochEDU 290

PowerPoint Presentation

Definition•Mass wasting is the down-slope movement of material under direct influence of gravity

•Water influences the effects of mass wasting but gravity is the most important factor

Determining Factors of Mass Wasting

•Slope Stability

Gravity

Friction

Angle of Repose

•Type of Material (Rock, soil, sediment)

•Water saturation (increases slope failure)

How Does it Happen?

Rock

Slide component

Stick component

Shear stress vs. shear strength

When Gravity Wins

•When the force of gravity exceeds the friction of the slope, material begins to move

•Shear strength resists movement, if gravity is too strong the object loses friction

Angle of Repose

The steepness of a slope is an important factor

Steeper the slope increase in the amount of gravity pulling on the object

The angle of repose is the steepest angle a slope can maintain without collapse

Around 25-40 degrees

Weathering and Climate•Weathering: wind and water erosion weakens surfaces

•Weathering decomposes material and reduces the strength of the slope

•Loose materials are most susceptible as they are not stable

Triggering Events

Events that encourage mass wasting:› Earthquakes› Snowmelt› Heavy rainstorms

› Why?

Vegetation

Increases slope stability!

Absorb water from rainfall and roots stabilize within soil

Criteria for Mass Wasting

Type of material…

Type of movement…

Rate of movement…

Rock, debris, soil, mud

Fall, slide, slump, flow, creep

Fast, slow, not visible

Falls

Very rapid movement, talus formation, often triggered by earthquakes.

Slump

Movement along a curved surface, caused by steepening of the slope

Flow

Slow to rapid movement but often appears to have a plastic movement (Debris-flow vs. Mudflow)

Solifluction

Common in areas of permafrost, very slow movement when frozen surface melts in summer

Creep

Slowest flow, visible through features such at tilted trees or telephone poles

How do we control masswasting?

1. Improve drainage› Ditches, gutters, vegetation, drainpipes

2. Decrease slope› Cut and fill, benching

3. Build retaining walls› Provide support at the bottom of a slope

References

Text and FiguresSchaetzl, Randy, 2011, Masswasting, Environmental Geomorphology 306

Steinbis, Martin, 20ll, Masswaste pdf, Geology 100

PicturesClip art images