1
Mass Wasting
Presentation Modified from Instructor Resource Center on CD-ROM,
Foundations of Earth Science, 4th Edition, Lutgens & Tarbuck
Mass Wasting
2
DownDown-slope movement of rock, loose material & soil
under direct influence of gravity.
3
Earth’s External Processes
Weathering, mass wasting, and erosion are all
called external processes because they occur at
or near Earth’
Earth’s surface
Internal processes, such as mountain building
and volcanic activity, derive their energy from
Earth’
Earth’s interior
1
4
Mass Wasting: The
Work of Gravity
Mass wasting is the downslope movement of
rock and soil due to gravity
Controls and triggers of mass wasting
Water—
Water—Reduces the internal resistance of materials
and adds weight to a slope
Oversteepening of slopes
List factors that will affect how easily 5
mass wasting occurs.
Steepness of slope
Water
Adds weight
“lubricates”
lubricates” failure surfaces
Vegetation
Roots hold soil
Absorb water
Triggers
Earthquakes
Thunder
6
Mass Wasting: The
Work of Gravity
Controls and triggers of mass wasting
Removal of vegetation
• Root systems bind soil and regolith together
Earthquakes
• Earthquakes and aftershocks can dislodge large volumes of
rock and unconsolidated material
Thunder
2
Mass Wasting
DownDown-slope movement of rock, loose material &
soil under direct influence of gravity.
List factors that will affect how easily
mass wasting occurs.
7
8
Steepness of slope
Water
Adds weight
“lubricates”
lubricates” failure surfaces
Vegetation
Roots hold soil
Absorb water
Triggers
Earthquakes
Thunder
Types of Mass Wasting
9
Figure 3.3
3
Mass Wasting
10
Classified as…
as…
Creep
(Slow down-slope
movement of soil or
regolith)
Falls
Slumps
Slides
Flows
(Rock falls)
(Rock slides) (Debris Flows,
Mud flows)
Amount of Water
Steepness of Slope – The Angle of Repose
11
Angle of Repose: The steepest angle at which
loose material remains stationary without
sliding downslope.
downslope.
Angle of Repose
Mass Wasting
12
Classified as…
as…
Creep
(Slow down-slope
movement of soil or
regolith)
Falls
Slumps
Slides
Flows
(Rock falls)
(Rock slides) (Debris Flows,
Mud flows)
Amount of Water
4
13
Creep
Slow, downdown-slope
movement of soil or
sediment.
Responsible for building
and road damage.
http://www.structures.ucsd.edu/Taiwaneq/geotechnical.html
Mass Wasting
14
Classified as…
as…
Creep
(Slow down-slope
movement of soil or
regolith)
Falls
Slumps
Slides
Flows
(Rock falls)
(Rock slides) (Debris Flows,
Mud flows)
Amount of Water
1999 Yosemite
Rockfall
15
Exfoliation Cracks
Talus Cone
Curry Village
5
Mass Wasting
16
Classified as…
as…
Creep
(Slow down-slope
movement of soil or
regolith)
Falls
Slumps
Slides
Flows
(Rock falls)
(Rock slides) (Debris Flows,
Mud flows)
Amount of Water
Slumps
17
Sliding of
Unconsolidated material
As an intact unit
Curved failure surface(s)
Often after
rainfall
Figure 3.3
Slumping at Devil’
Devil’s Slide
18
Highway 1 south of SF
6
19
Devil’
Devil’s Slide
What are some of the factors that cause
Devil’
Devil’s Slide to slide?
Cross Section
Spring
(water seep)
20
Jeep
Trail
Shale,
Siltstone &
Sandstone
Hard Sandstone
Mass Wasting
21
Classified as…
as…
Creep
(Slow down-slope
movement of soil or
regolith)
Falls
Slumps
Slides
Flows
(Rock falls)
(Rock slides) (Debris Flows,
Mud flows)
Amount of Water
7
Slides
22
Rapid downdown-slope movement
Sediment, soil & regolith break loose
Mountainous areas
Rapid and destructive
Often after
rainfall
Figure 3.3
1997 Highway 50 Landslide
23
“Mill Creek Slide”
Slide”
January 24, 1997
Closed Hwy 50
Destroyed 3 cabins
Dammed South
Fork of American
River for 5 hours
Many cabins
destroyed in
flooding after Am.
River breeched dam
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
Mill Creek Landslide
24
Hwy 50 closed
4 weeks
35,000 truck
loads of earth
material
$4.5 million
+ >$1M/day
related
costs
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
8
CrossCross-Sectional View
25
Burned
vegitation
Gabbro
(actually pyroxenite)
pyroxenite)
Granite
(actually granodiorite)
granodiorite)
Joints
From R.H. Syndor, Calif. Geology, May/June 1997
Observations
26
Parent rock has composition
similar to gabbro
Pyroxenite
A forest fire burned this area
in 1992.
There are distinct sets of
joints in the rock.
Early snow fell in Dec. 1996.
Unusual tropical rains fell
after the snow.
Jan. 1997 received a record 19 inches of rain.
Explain how each of these observations contributed to the Mill
Creek landslide.
Open cracks
observed in 1996
27
Upper section “Slide”
Slide”
Lower section “Flow”
Flow”
Slide
Flow
Moved 50 feet
upup-slope
9
Hwy 50 Now Completely Mapped for
Landslide Hazards
28
Cleveland Corral
Landslide
Mill Creek
Landslide
From T.E. Spitter and D.L. Wagner, Calif. Geol., May/June 1998
Cleveland Corral Slide
29
Near Mill Creek Slide
Actively Monitored by USGS
Potential for
blocking
Hwy 50
Potential for
damming
American
River
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
Monitoring System
30
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
10
Monitoring Movement
31
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
Slide History
32
http://vulcan.wr.usgs.gov/Projects/CalifLandslide/framework.html
11