Mass Wasting. What is Mass Wasting? The downslope movement of slope material. Gravity is the key to mass wasting. Landslides are mass wasting.

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 processesthat influence people

1. Creep2. Rock Fall 3. Topple

4. Rotational Slump5. Translational Slide (Block Glide)6. Rock slide7. 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

Very Slow, mm/yr to cm/yr

rock fall

rock fall

rock fall

rock fall produces talus, often

Talus Cones atAngle of Repose

Detachment and Gravity

Fallnot limited to

rocks

How do you

discuss this?

topple

Top falls, butbottom stays

Rotational Slump

Laguna Beach

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

MostlyIgnore

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, 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 CanToo

Undercutting steepens the slope,wave action in this case

Undercutting steepens the slope,stream action in this case

Undercutting steepens the slope,stream action in this case

Undercuttingcan 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 onundercutting 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)

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 Animationshttp://serc.carleton.edu/NAGTWorkshops/visualization/

collections/mass_wasting.html

Net Effect: Slow,

Steady Inevitable