mass wasting integrated earth science€¦ · • the downslope movement of material under the...
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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/