MASS WASTINGIntegrated Earth Science

• Dr. Gregg Wilkerson and Larry Drennen

• Lecture #14

1

2

Mass Wasting

https://www.planetmountain.com/en/news/environment/el-capitan-video-footage-of-the-enormous-second-rockfall-in-yosemite.html

Yosemite Rockfall II 0:49Yosemite Rockfall I 2:09 FW

Rockfall II

3

Mass Wasting, Landslides and

Slope Failure

https://www.kget.com/news/traffic-alert-chp-reports-another-boulder-has-fallen-onto-the-178-near-white-oaks-campground/262367036

Rockfall: Highway 178, Kern River Canyon

• Does mass wasting occur in our area?

• Are there places in our communities that are characterized by steep slopes where landslides have occurred?

https://abc30.com/weather/highway-190-past-springville-closed-all-weekend-due-to-a-mudslide/3253405/

Rockfall: Highway 190, past Springville

March 2018

Near area burned by the Pier Fire

4

Mass Wasting

https://www.theguardian.com/

global/video/2018/sep/06/land

slide-buries-homes-in-japans-

hokkaido-after-66-quake-

video

Hokkaido, Japan,

September, 2018

Hokkaido -

aftermath of

6.6 EQ 0:44

Discussion Topics:

• What is mass wasting?

• Hazards

• Factors contributing to

slope failure

• Types of mass wasting

• Human influence

• Mitigation

Mass wasting: the movement of rock and soil down a slope under the force of gravity.

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Slope Failure Processes

Mass Wasting

6

Montecito, California, January 2018

The U.S. Geological

Survey estimates that

landslides kill 25 to 50

people a year in the

United States – more

than earthquakes or

volcanoes.

Mass Wasting

7

Montecito, California, January 2018

“In a general sense, the threat to Montecito was clear.” • Scientists and planners know that the landscape of Southern California is shaped by a

cycle of fire, rain and debris flows • Following the Thomas wildfire in December 2017, U.S. Geological Survey warned of high

potential for disastrous landslides if intense rain fell on mountainsides around Santa Barbara.

• In 2018, when a big storm hit, it landed on bare, baked soil that could not readily absorb water.

• The rain ran off, picking up soil, boulders and debris as it surged down canyons and streams.

8

Mass Wasting

Burn Area

9

Mass Wasting

Montecito, California, January, 2018

12/2017 1/2018 12/2017 1/2018

10

Mass Wasting

11

Mass Wasting

Mass Wasting• The downslope movement of material under the

influence of gravity.

• Landslide – a term used to describe many rapid forms of mass wasting

Areas of highest

risk for slope failure

Orange and brown = high

to moderate incidence

Gold = high susceptibility

but moderate incidence

Factors Influencing Slope Failure

• Gravity moves materials down a slope

– However, friction acts to prevent or slow the movement of material down a slope

• Steeper slopes are more likely to fail

Analogy – a slide on a playground• The steeper and smoother the slide, the faster you go

Water: A small amount of water holds grains together (cohesion)

Factors Influencing Slope Failure

Dry sand slopes will fail above angles of about 35 degrees

Too much water forces grains apart leading to instability

Regolith: the layer of unconsolidated superficial deposits covering bedrock (dust, soil, broken rock)

Kelso Dunes, CA

7-15© McGraw-Hill Education.

Factors Influencing Slope FailureToo much water promotes instability

• Very wet sediment flows like a liquid

• Excess water reduces cohesion between grains (allows them to move more freely)

• Adds weight to a slope

• Water supports some of the weight of overlying materialreducing the friction that counterbalances gravity

https://blogs.agu.org/landslide

blog/2018/07/12/japan-1/

Japan Landslide 0:54

Fukuoka Prefecture, Japan, July, 2018

• Record rainfall following Typhoon Prapiroon

• Landslides and floods resulted in more than

200 deaths

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Mass wasting processes vary in speed, moisture content, and type of material (rock, soil, mud, etc.)

Decreasing speed →

Inc

rea

sin

g m

ois

ture

co

nte

nt →

Slope Failure Processes

Slow✓ Creep✓ Solifluction

Intermediate✓ Rockslide✓ Slump✓ Debris slide

Fast✓ Debris & Rockfall✓ Debris flow✓ Mudflow

Various materials

10-17© McGraw-Hill Education.

Slope Failure Processes

Creep – the very slow movement of material downhill under the influence of gravity

• Slow speed,

Medium to low

moisture content

http://web.pdx.edu/~jjackson/Exercises.html

Solifluction: A type of soil creep that occurs in water-saturated

regolith in cold climates.

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Slope Failure Processes

Wet & Slow

Tien Shan Mountains, Kyrgyzstan

Rockslides

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

• Medium Fast, Dry(ish)

Slope Failure ProcessesRockslides – Large-scale movements of rock traveling rapidly down a slope along a surface

https://kmph.com/news/local/gallery/hwy-178-closed-through-the-canyon-after-rockslides#photo-7

Hwy 178, Kern Canyon

March 6, 2019

Slope Failure Processes

Slump – The movement of material down a slope on a curved slip surface

a: USGS

Medium fast, medium moisture

https://digitalatlas.cose.isu.edu/geo/basics/massmvnt.htm

La Conchita, California

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Debris Slide – Material slidingdownhill as a chaotic mixture of soil, rock, and water

Slope Failure Processes

https://norberthaupt.com/tag/debris-slide/

• Medium Fast, Wet

Camarillo Springs, CA - December 2014

Debris slide following heavy rains

https://www.thoughtco.com/p

ictures-of-landslides-

4122955

Slope Failure ProcessesEl Capitan,

Yosemite - 2017Debris/Rockfall – The dislodging of rocks from a steep slope.

Yosemite Rockfall II 0:49

• Fast, Dry

https://www.nps.gov/yose/learn/nature/rockfall.htm

Pressure release cracks, exfoliation &

gravity

Slope Failure Processes

b: © Kevork Djansezian/AP Images

Debris Flow – Material flowing downhill as a chaotic mixture of soil, rock, and water

Fast, medium moisture

http://geofaculty.uwyo.edu/neil/teac

hing/Geomorph/lect_notes.htm

La Conchita, California

Fast-moving mass wasting events tend to be the most dangerous.

Mud flow - a mass of water and fine-grained earth materials that flows very rapidly down a stream, ravine, canyon, arroyo or gulch.

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Slope Failure Processes

• Fast & Wet

https://watchoutnaturaldis

asters.weebly.com/mudflo

ws.html

25

Mud FlowsMontecito, California, January, 2018

Avalanches, lahars, and submarine landslides are special types of mass-wasting processes.

Avalanche: fast-flowing, fluidized (by air, not water) mass of snow, ice, air, and occasionally some regolith, that cascades down a mountainside following the collapse of a snowfield.Lahar: a mud flow composed of pyroclastic material and water that flows down the slopes of a volcano.

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Mass Wasting Processes

27

Mass WastingCase Study

• 2005 La Conchita disaster

28

Mass WastingLa Conchita Timeline

• In 1995 a large slump destroyed 9 homes

• Blamed on over-watering of crops above the bluff

• January 2005

• A series of storms soaked the area

• Adding mass to the unstable slopes

• Lubricating the sediment grains – reducing friction

• A sudden rupture occurred, releasing a slump block which instantly crumbled into a

fast-moving, fluid-rich debris flow which roared into the eastern part of La Conchita

• Estimated that 400,000 tons of earth moved

• Buried 4 blocks of town 30’ deep

Killed 10 people

and destroyed

13 homes

2005 La Conchita Landslide 0:18

29

Mass Wasting1995 slump event

https://web.csulb.edu/depts/geology/facultypages/bperry/Mass%20Wasting/LaConchita.htm

Mass Wasting

https://www.flickr.com/photos/vision_aerie/4833281

https://www.usgs.gov/media/images/2005-landslide-

conchita-ca

Landslide: 2005 disaster

Factors Influencing Slope FailureHuman influence• Venezuela disaster – very little

urban planning

• La Conchita – earlier slump blamed on overwatering of crops above the bluff

• Italy 1998 landslide – poor land management (deforestation)

• Montecito, 2018 - Forest fires (also logging) removes protective vegetation

Caraballeda, Venezuela

USGS

32

Next Time

Mass Wasting - Continued

Streams and Floods

• Reading: Connect Chapter 11

Discussion Topics:

• What is mass wasting?

• Hazards

• Factors contributing to

slope failure

• Types of mass wasting

• Human influence

• Mitigation

Landslides and Slope Failure

Improve slope drainage

© 2018 LDrennan

Torrey Pines State Park,San Diego, California

Can we mitigate slope failure risk?

34

Mitigating Slope Failure Risk

https://www.geobrugg.com/file-68815/downloadcenter/level1-media-review/02-US-Highway-395-

in-Erosion-Control_.pdf

Slope stabilization - Lee Vining Rockfall

Project, Highway 395 at Mono Lake

Mitigating Slope Failure RiskAttach the slope

material to

bedrock with

physical restraints

Rockbolts

https://www.google.com/search?ei=5Iq6W_aBGoKgtQWF0KOwAQ&

q=rockfall+mitigation+georgetown&oq=rockfall+mitigation+georgetow

n&gs_l=psy-

ab.3..33i160l3.5732.7848..9677...0.0..0.233.1337.0j9j1......0....1..gws

-wiz.......0i71j33i299.wAuTJyuTD9Y#

Mitigating Slope Failure Risk

© David McConnell

Install physical barriers

Wire fence

Impact walls

protecting

condos in

Vail, CO

http://2fdpn7hy0ht206jws2e

9og41.wpengine.netdna-

cdn.com/wp-

content/uploads/2013/08/P

ost-fire-Rockfall-flyer.pdf

Mitigating Slope Failure RiskCaltrans: “Clogged culverts were cleared; flow lines were established, and dikes were

constructed to help collect and divert water off highways in the future. Mountains have

also been scaled to remove loose rocks to lessen the chance of debris.”

Tehachapi News 10/2016

38

California Geological Survey –

Landslide Hazard Assessment Map

Avoidance!

Landslide Hazard Mapping

DOC – CGS Maps

Mudflow Highway 58 near Tehachapi,

October 15, 2015

MudflowHighway 58 near

Tehachapi,

October 15, 2015

41

Mudflow Highway 58 near Tehachapi,

October 15, 2015

Copyright © 2014 John Wiley & Sons,

Inc. All rights reserved.

Mass wasting processes vary in speed, moisture content, and type of material (rock, soil, mud, etc.)

Decreasing speed →

Inc

rea

sin

g m

ois

ture

co

nte

nt →

Slope Failure Processes

Various materials

A rapidly flowing mass of water

and earth materials

• More than ½ of the material is

sand-sized or smaller

Tehachapi mudflow:

Trigger = a lot of

rain in a short time

period causing flash

flooding

Can we mitigate slope failure risk?Can we minimize slope failuresand human risk? How?

© 2018 LDrennan

• Vegetation cover• Improve slope drainage• Attach the slope material to

bedrock with physical restraints• Install physical barriers• Avoid high risk areas?

Torrey Pines State Park,San Diego, California

44

Mitigating Slope Failure RiskVegetation for erosion control

Reseed an area with grasses to control erosion & slope instability

Erosion and slope instability are especially serious after wildfires or human activity such as road construction or development

https://ucanr.edu/sites/fire/Recovery/Revegetation/Erosion/