1 mass movements gly 2010 – summer 2012 - lecture 17
TRANSCRIPT
![Page 1: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/1.jpg)
1
Mass Movements
GLY 2010 – Summer 2012 - Lecture 17
![Page 2: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/2.jpg)
2
Mass Movement - Definition
• Transporting of earth materials downslope due to gravity, without the aid of a transporting medium such as water or ice
![Page 3: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/3.jpg)
3
Mass Movement Triggers
• Gravity
• Vibration
• Water
![Page 4: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/4.jpg)
4
Gravity
• Gravity constantly pulls materials downslope, opposed by friction
• If gravity overcomes friction, the material moves
• The steeper the slope, the greater the proportion of full gravity works on the material
![Page 5: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/5.jpg)
5
Vibration• Earthquakes, explosions, or other seismic
energy sources energize particles on the slope, and they begin to move around - some of them may slide downhill
• If enough slides at once, an “avalanching effect” is generated, pushing the material downhill ahead and triggering mass movement
• A blast of air, approaching hurricane force, may precede the front of a large mass movement
![Page 6: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/6.jpg)
6
Earthquake Triggered Slide
• Madison Canyon Earthquake of August 1959• An estimated 19 people are still beneath the quake rubble
![Page 7: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/7.jpg)
Water
• The weight of water soaking into soil, increases the force from gravity
• This may be enough to overcome friction and start mass movement
7
![Page 8: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/8.jpg)
Water’s Roles
• Water acts as “glue”• Water acts as a “lubricant”
8
![Page 9: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/9.jpg)
9
Water As Glue - Surface Tension
• Water has a very high surface tension
• Small amounts of water in sediment, which is essentially all surface, act to hold the sediment together
![Page 10: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/10.jpg)
10
Water As Lubricant
• As more water is added, it forms layers with greater thickness between particles
• Surface tension is no longer important, because the water layer is thicker
• Water acts as a lubricant, cutting frictional forces, and making mass movement easier
![Page 11: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/11.jpg)
Angle of Repose
• The maximum angle at which loose sediment can form a stable slope
• Different materials will have different angles of repose
11
![Page 12: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/12.jpg)
Angle of Repose - Examples
• Typical angles: Fine sediment -
30-35° Coarse
sediment - to >40° (talus slopes)
12
![Page 13: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/13.jpg)
13
Angle of Repose, Snow
Snow Type Temperature Angle of Repose
Fresh, Dry -35ºC 63º
Fresh, wet -4ºC Close to 90º
Wet, 24% water
>0ºC 2º
Avalanches form when the angle of repose is exceeded
![Page 14: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/14.jpg)
Avalanche Video
14
![Page 15: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/15.jpg)
15
Artificial Oversteepening
• Man activities may create unstable slopes
• Examples: Road building Mining
Blasting narrow roads through mountains often leads to slope failure
In mountainous states, particularly those that get a lot of rain, road failure is a fact of life
![Page 16: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/16.jpg)
Natural Oversteepening
16
![Page 17: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/17.jpg)
17
Types of Slow Mass Movements
• Creep
• Solifluction
![Page 18: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/18.jpg)
18
Creep• Creep is the imperceptibly slow down-slope
movement of soil and near-surface rock materials• Process is generally not directly observed -
instead, creep is best discerned through the movement or response of objects affected by the process
• Typical movement = mm’s to cm’s per year• Extremely common on sloping terrain
![Page 19: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/19.jpg)
Creep Mechanism
• Expansion and contraction leads to creep
• May be due to freeze/thaw or rain/evaporation cycles
19
![Page 20: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/20.jpg)
20
Effect of Creep
• The tilted headstone is the result of creep
![Page 21: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/21.jpg)
21
Bent Curbs Due To Creep
• Hollister, California – Left, 1966; Right, 1992
![Page 22: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/22.jpg)
22
Leaning Fence Posts – Barnes County, N.D.
• Fenceposts, being shallowly-seated objects, are particularly prone to creep, and have tilted down-slope under creep almost to a horizontal position
• Small trees on this slope likewise show the influence of creep: as their trunks are progressively tilted over by creep, their new growth responds phototropically back upwards towards the sun, leading to a curved appearance of the trunkPhoto by D.P. Schwert, North Dakota State
University
![Page 23: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/23.jpg)
23
CREEP Cass County, N.D.
• Photo under an I-94 overpass at Fargo
• Concrete pads have shifted down-slope on soils affected by creep
• Upward squeezing of the pads is induced by differential down-slope flow velocities of soil and "rock" materials.Photo by D.P. Schwert, North Dakota
State University
![Page 24: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/24.jpg)
24
Solifluction
• A type of “fast” creep
• Occurs in cold regions where the soil remains frozen most of the year (permafrost)
• May occur in other boggy soils, especially after vegetation removal
![Page 25: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/25.jpg)
25
Solifluction Terraces
• Solifluction near Fairbanks, Alaska
![Page 26: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/26.jpg)
Effects of Permafrost
• Thawing of Permafrost leads to slow subsidence of structures built on it
• Becoming a very common problem at high northern latitudes
26
![Page 27: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/27.jpg)
Effects of Permafrost
• When a rail line was built across this permafrost landscape in Alaska, the ground subsided.
27
![Page 28: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/28.jpg)
28
Rapid Mass Movements
• Slides
• Falls
• Flows
• Debris avalanche
![Page 29: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/29.jpg)
29
Rapid Mass Movement Rates
• Rapid mass movements are much faster than creep or solifluction
• They may move within seconds to a minute or so, at rates of meters per second, or more slowly, or days and weeks, at rates of meters per day
![Page 30: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/30.jpg)
Slides
• A single intact mass (rock, soil, or unconsolidated material) moves downslope along a slip plane
• Slip planes are planes of weakness 30
![Page 31: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/31.jpg)
Slip Plane Geometry
• Slip planes are usually flat
• If they are curved, the slide moving along a concave slip plane is known as a slump
• Some rotation of the material is involved in slumping
31
As the photo illustrates, even though the Gros Ventre rockslide occurred in 1925, the scar left on the side of Sheep Mountain is still a prominent feature.
![Page 32: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/32.jpg)
32
Slump Animation
• Computer simulation of a deep-seated "slump“ type landslide in San Mateo County, California
• Over 250,000 tons of rock and soil moved in this landslide
![Page 33: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/33.jpg)
33
Failure Along Metamorphic Foliation Surface
• Slaty cleavage seen here is at a high angle• Failure has occurred along the foliation surface
![Page 34: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/34.jpg)
34
Slump Failure, McClure Pass, Colorado
• Note half buried automobile
![Page 35: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/35.jpg)
35
Falls
• Fastest type of mass movement
• Occurs when material on a near vertical cliff breaks free and falls freely to the surface below
![Page 36: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/36.jpg)
36
Picture of Fall
• A fall has left an obvious scar, and a talus pile• Failure was caused by artificial oversteepening of the surface to make a road
![Page 37: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/37.jpg)
37
Recent Rock Fall
• Recent rock fall, Zion National Park, Utah
![Page 38: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/38.jpg)
Fall Video
38
![Page 39: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/39.jpg)
Ocoee River Valley – US 64
• On November 10, 2009, a series of rockfalls preceded a landslide, which would have killed people had geologist Vanessa Bateman not cleared the area prior to the slide
39
![Page 40: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/40.jpg)
40
Flows
• Mass of mostly unconsolidated material moving downslope as a viscous liquid May be dry or wet Move rapidly, especially when wet Considerable mixing may occur during the
movement
![Page 41: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/41.jpg)
Mass Movement Animation
41
![Page 42: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/42.jpg)
42
Types of Flows
• Flows are broken into categories: Earthflow Mudflow Debris flow
![Page 43: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/43.jpg)
43
Earthflow
• Dry masses of clay or silt regolith• They have high viscosity, and typically move
relatively slowly (meters/hour to meters/minute)• The slow movement usually precludes loss of life,
but they do cause substantial property damage
![Page 44: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/44.jpg)
Earthflow Effect
• This small, tongue-shaped earthflow occurred on a newly formed slope along a recently constructed highway
• It formed in clay-rich material following a period of heavy rain
• Notice the small slump at the head of the earthflow
44
![Page 45: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/45.jpg)
45
Mudflow
• Composed of wet mixtures of mud and water, they move swiftly
• Mudflows often develop after heavy rains (cloudbursts) in semi-arid regions, where sparsely vegetated slopes have masses of loose regolith
• Canyons in semi-arid deserts are prone to mudflows
![Page 46: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/46.jpg)
46
Lahars
• Lahars are a special type of mudflow produced on the slopes of a volcano
• Volcanic ash and hot gases melt accumulated snow and glacial ice, producing large quantities of mud
![Page 47: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/47.jpg)
47
Debris Flow
• Similar to mudflows, but consisting of particles larger then sand-sized, often with some boulders of a meter or more
• Because of the larger particles size, they require steep slopes
![Page 48: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/48.jpg)
48
Debris Flow Animation
• Computer simulation depicting the Sourgrass debris flow (Sierra Nevada, North Fork of the Stanislaus River), of January 1, 1997
![Page 49: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/49.jpg)
49
Debris Avalanche• Very steep,
unvegetated slopes may produce an avalanche
![Page 50: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/50.jpg)
50
Wildfires and Debris Flows
• Wildfires can lead to destructive debris-flow activity• In July 1994, a severe wildfire swept Storm King
Mountain west of Glenwood Springs, Colorado, denuding the slopes of vegetation
• Heavy rains on the mountain in September resulted in numerous debris flows, one of which blocked Interstate 70 and threatened to dam the Colorado River
• A 3-mile length of the highway was inundated with tons of rock, mud, and burned trees
![Page 51: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/51.jpg)
51
Glenwood Springs, Colorado
• Personal injuries and damage to 30 vehicles engulfed by these flows
• Transportation along the Interstate 70 corridor was brought to a standstill for a day
• Business and emergency operations in the Glenwood Springs area were seriously impeded
Photo: Jim Scheidt, U.S. Bureau of Land Management
![Page 52: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/52.jpg)
52
Soils and Mass Movements
• Quick clays - Waterlogged clay sediments, when energized by seismic waves from earthquakes or explosions, can lose adhesion, and become a viscous liquid
• Resulting flows can be very large Ex. One in Quebec in 1971, in which almost
seven million cubic meters of quick clay moved and killed 31 people, doing hundreds of millions of dollars in damage
![Page 53: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/53.jpg)
53
Colluvium
• Any material deposited as the result of mass movement
![Page 54: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/54.jpg)
54
Indications of Potential Mass Movement
• Stream undercutting
• Springs on a cliff face
• Cracks near cliff top
• Hillside creep
• Talus
![Page 55: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/55.jpg)
55
Avoidance of Mass Movements• Certain activities, such as farming or
ranching, may take place if the potential for rapid, unpredictable failure is low
• Avoidance is facilitated by the development of risk maps, which inform people of where dangerous areas are
• However, many people already work or live in danger zones, and are understandably reluctant to abandon property or homes
![Page 56: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/56.jpg)
56
Hazard Maps
• Example of an experimental map released to emergency planning and response teams in the San Francisco Bay Area
![Page 57: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/57.jpg)
57
Prevention of Mass Movement• Control of nature is a very difficult, and
usually a very risky, business• If control is attempted, we must understand
the subsurface geology, revealing for example, whether their are dangerous boundary layers along which slippage might occur
• Then strategies can be planned to reduce the danger, which may be either structural or non-structural
![Page 58: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/58.jpg)
58
Non-structural Solutions
• Non-structural methods often involve planting vegetation, including grasses, shrubs, and fast-growing trees
• Cement is sometimes injected into a moving slide to try and strengthen unconsolidated material
![Page 59: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/59.jpg)
59
Non-structural Solutions Cont.• Dewatering solutions are often the
most useful
• Water can be prevented from entering a slide by the construction of barriers or diversions to keep water away from the potential mass movement site
![Page 60: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/60.jpg)
60
Non-structural Solutions Cont.
• Active site can also be dewatered by drilling into the toe of the slide and inserting perforated pipes which help water to flow out quickly, or by drilling wells and pumping water out
![Page 61: 1 Mass Movements GLY 2010 – Summer 2012 - Lecture 17](https://reader036.vdocuments.us/reader036/viewer/2022062407/56649d8b5503460f94a71b50/html5/thumbnails/61.jpg)
61
Structural Solutions
• Retaining walls, which attempt to contain the slide may be built
• Site may be regraded, to reduce slope angles
• Wooden or steel pilings can be driven through the slide, to try and strengthen it
• Terraces can be built to catch material which starts to slide