Mass Wasting
What is Mass Wasting? The downslope movement of slope material. Gravity is the key to mass wasting. Landslides are mass wasting.
Colluvium The term “colluvium” describes the angular pieces of rock that are moved by mass wasting [contrasting with “alluvium” or water moved rock.]
Weathering, then Detachment Solid rock must first weather. Then, the weathered rock must detach.
Lots of ways to organize processes that influence people 1.Creep 2.Rock Fall 3. Topple 4. Rotational Slump 5. Translational Slide (Block Glide) 6. Rock slide 7. Flows
Key is gravity
Order Present 1. Creep 2. Rock Fall 3. Topple 4. Rotational Slump 5. Translational Slide ( & Block Glide) 6. Rock slide 7. Flows
Soil Creep
In the wetting or freezing soil zone
Very Slow, mm/yr to cm/yr
rock fall
rock fall produces talus, often Talus Cones at Angle of Repose
Detachment and Gravity Fall not limited to rocks
How do you discuss this?
topple
Top falls, but bottom stays
Rotational Slump
Laguna Beach
Translational Slide
Translational Slide at Torrey Pines
Snow Avalanches Often Start As Translational Slides, that then flow
Often Occur in Same Places: Avalanche Chutes
3 Strategies: Avoid, Engineer, Ignore
Engineer
Mostly Ignore
Rock Slide
Gros Ventre Rock Slide
Madison Canyon Slide
crushed dolomite stayed on top
Army Corp Prevent Disaster
Attabad Pakistan (Hunza River)
Steep Jointing - Set Stage
Spillway Creation & Widening: Race to Avoid Bursting the Dam
More added, keep widening
Marcus Rockslide in Scottsdale
Virtual Field Trip to Marcus Slide
Can occur elsewhere there is steep jointing, and weathered granite on slick, fresh joint faces
Flows, mudflow (few rocks)
Flows, debris flow (more rocks mixed with mud)
KOA Campground
Slide Mountain, Nevada
La Canada, California
Debris flows can occur in Phoenix
Earth flow, slower & thicker
Why? What Causes Mass Wasting? GRAVITY!! Steeper slopes = more likely
Steep Slopes One Reason why California experiences problem Az Can Too
Undercutting steepens the slope, wave action in this case
Undercutting steepens the slope, stream action in this case
Undercutting can be from earlier mass wasting
Human activities dangerous around steep slopes: Telegraph Hill 2007
Or from construction
Oversteepening from from new fault scarp
Hard caprock creates situation where weaker material erodes away until slope is so steep that caprock erodes
Whole idea of a Mesa relies on undercutting by erosion of weaker rock
Another Reason: Weak Material
Palos Verdes: Weak & Undercut
Best solution: land use that can be disturbed, like a golf course
Another Reason: Weak Material
Weakness can be a joint (fracture) in a strong rock
Weakness can be a joint (fracture): but orientation is important
Lots of water
Lots of water (rain, snowmelt)
Exert pore pressure
Reaches thixotropic behavior (solid, then liquify into plastic)
Get some corn starch …
Result: Liquifaction
Liquifaction leads to flows (debris flows, mudflows, earthflows)
Entire valley filled with mud
Russian Roulette
Alaska Landslide from 1980 Quake
Earth Shaking (earthquakes, or even bouncing large trucks)
1970 Earthquake
disaster
Earthquake & Moisture: Las Colinas, El Salvador Disaster (2001)
Earthquake in Wet Winter: Future California Disaster
Blackhawk Landslide Example
Shaking can be from volcanic eruption, case of Mt Shasta
Big Az Concern: Fire & Hydrophobic soils
Cave Creek Complex Fire
Forest Wildfires: Idaho
Los Alamos Fire
Online Video/Animations Mass Wasting and Landslide Animations ctions/mass_wasting.html
Net Effect: Slow, Steady Inevitable