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					         Mass Movements




GLY 2010 – Summer 2011 - Lecture 17   1
   Mass Movement - Definition
• Transporting of
  earth materials
  downslope due to
  gravity, without
  the aid of a
  transporting
  medium such as
  water or ice
                                2
     Mass Movement Triggers
• Gravity
• Vibration
• Water




                              3
                   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
                                                4
                  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 slide 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
                                                5
     Earthquake Triggered Slide




• Madison Canyon Earthquake of August 1959
• An estimated 19 people are still beneath the   6
  quake rubble
                               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
           Water’s Roles




• Water acts as “glue”
• Water acts as a “lubricant”   8
   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



                                            9
           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

                                              10
            Angle of Repose




• The maximum angle at which loose
  sediment can form a stable slope
• Different materials will have different
  angles of repose
                                            11
Angle of Repose - Examples
             • Typical angles:
                Fine sediment -
                30-35°
                Coarse sediment -
                to >40° (talus
                slopes)



                                 12
       Angle of Repose, Snow
      Snow Type       Temperature      Angle of
                                       Repose
      Fresh, Dry      -35ºC            63º

      Fresh, wet      -4ºC             Close to 90º

      Wet, 24%        >0ºC             2º
      water
Avalanches form when the angle of repose is exceeded
                                                       13
Avalanche Video




                  14
         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

                                                     15
Natural Oversteepening




                         16
 Types of Slow Mass Movements
• Creep
• Solifluction




                                17
                    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

                                               18
           Creep Mechanism




• Expansion and contraction leads to creep
• May be due to freeze/thaw or
  rain/evaporation cycles
                                             19
              Effect of Creep




• The tilted headstone is the result of creep
                                                20
        Bent Curbs Due To Creep




• Hollister, California – Left, 1966; Right, 1992   21
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
Photo by D.P. Schwert, North Dakota State     the trunk
University


                                                                           22
         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
Photo by D.P. Schwert, North Dakota     "rock" materials.
State University

                                                              23
                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



                                             24
           Solifluction Terraces




• Solifluction near Fairbanks, Alaska
                                        25
        Effects of Permafrost




• Thawing of Permafrost leads to slow
  subsidence of structures built on it
• Becoming a very common problem at high
                                           26
  northern latitudes
Effects of Permafrost
           • When a rail line was
             built across this
             permafrost landscape
             in Alaska, the ground
             subsided.




                                27
        Rapid Mass Movements
•   Slides
•   Falls
•   Flows
•   Debris avalanche



                               28
   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


                                         29
                                  Slides




• A single intact mass (rock, soil, or
  unconsolidated material) moves
  downslope along a slip plane
• Slip planes are planes of weakness
                                           30
                                 Slip Plane
                                 Geometry
                       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.


• 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
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


                               32
      Failure Along Metamorphic
           Foliation Surface




• Slaty cleavage seen here is at a high angle
• Failure has occurred along the foliation surface33
Slump Failure, McClure Pass,
         Colorado




• Note half buried automobile   34
Falls
   • Fastest type of mass
     movement
   • Occurs when
     material on a near
     vertical cliff breaks
     free and falls freely
     to the surface below


                             35
                 Picture of Fall




• A fall has left an obvious scar, and a talus pile
• Failure was caused by artificial oversteepening
                                                    36
  of the surface to make a road
              Recent Rock Fall




• Recent rock fall, Zion National Park, Utah
                                               37
Fall Video




             38
      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
                  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


                                               40
Mass Movement Animation




                          41
           Types of Flows
• Flows are broken into categories:
   Earthflow
   Mudflow
   Debris flow




                                      42
                                  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
                                                      43
                                        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
                                    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
                                                       45
                 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


                                         46
                                  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
                                                 47
Debris Flow
Animation
• Computer simulation
  depicting the Sourgrass
  debris flow (Sierra
  Nevada, North Fork of
  the Stanislaus River), of
  January 1, 1997




                         48
Debris Avalanche
• Very steep,
  unvegetated slopes
  may produce an
  avalanche




                       49
      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

                                                      50
        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
Photo: Jim Scheidt, U.S.     Springs area were seriously
Bureau of Land               impeded
Management

                                                         51
      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
                                              52
              Colluvium
• Any material deposited as the result
  of mass movement




                                         53
      Indications of Potential Mass
               Movement
•   Stream undercutting
•   Springs on a cliff face
•   Cracks near cliff top
•   Hillside creep
•   Talus

                                      54
   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
                                                  55
    Hazard
    Maps
• Example of an
  experimental
  map released to
  emergency
  planning and
  response teams in
  the San Francisco
  Bay Area
                 56
    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
                                             57
       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


                                            58
   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


                                        59
  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


                                       60
           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

                                              61

				
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