Landslides and mass wasting
Mass Movements
Areas of mass movement problems. Note areas in NY.
From “Geohazards” by N. Coch.
The helderberg escarpment is
an example of a mass wasting
prone area in New York.
The shawangunk mountains
are another example of an area
prone to mass wasting in New
York.
Types of Mass movement:
•Creep
•Solifluction
•Rock glaciers
•Slumping
•Mud- and debris flows
•Landslides
•Avalanches
•Rock and debris falls
“Portrait of a Planet” by S. Marshak
Rock fall
Debris
avalanche
Rockslide
Mudflow &
Debris flow
Slump
Solifluction
& Creep
Very
slow
Very
fast
ment
e
v
o
m
s
f mas
o
y
t
i
c
o
l
e
Typical v
Slide
Slide
Mass movements can be broadly divided into falls, slides, and flows
From “Environmental Geology” by Pipkin
A landslide will move if the driving force (d, due to
gravity) exceeds the resistance force (f x n).
f is a material property (coefficient of friction) -- values
for various soils and rocks are available based on lab
measurements.
n is the component of gravity oriented normal to the
slide surface.
**Water in pores is under pressure (pore
pressure) from the weight of overlying
groundwater -- it thus acts to “buoy up” the slide,
essentially reducing n and thus allowing sliding
(or other mass movements) to occur under lower
driving force.
Increasing slope
increases driving force
d, thus making sliding
more likely.
Angle of repose: The angle of
the steepest slope that a pile of
uncemented material can attain
without collapsing from the pull
of gravity. As this angle is
exceeded, the slope will fail,
causing mass wasting.
Creep: gradual movement of soil
and rock downslope under the
influence of gravity and annual
freeze-thaw cycles.
Tell tail signs of soil creep are
tilted fences, poles,
gravestones, bent or curving
trees, foundation cracks in
buildings, and soil
encroachment onto
pavement.
“Portrait of a Planet” by S. Marshak
Solifluction: earth flow found in
periglacial environments underlain by
permafrost. During the summer the surface
layer of permafrost melts creating a watersaturated layer that becomes mobile. The
underlying frozen ground acts as a sliding
plane along which the mass of soil can
slowly move down slope over.
Permafrost: Permanently frozen ground.
Rock glaciers: lobate mixture of rock fragments and ice with rock
fragments out numbering ice. They move downslope slowly as the ice
slowly recrystallizes.
Slumping: soil slips downward
along a sliding surface that is
concave up, giving the
impression that the mass has
been scooped out.
Scarp
Former
slope
“Portrait of a Planet” by S. Marshak
Toe of
slump
Physical features of a slump
Slump in southern CA. Note
the broken and displaced road.
Landslides are common along coasts due to steepening of slopes by waves.
Slump-earthflow, east of San Francisco Bay
This is a very common type of landslide,
with slumping at the top, and the lower part
flowing. This landslide was almost certainly
triggered by deep roadcuts made during
construction of the freeway.
To stabilize this area, the entire landslide
was removed -- removing just part on the
highway would result in additional future
sliding.
Small
landslide
covering a
road
Mudslide in CA, induced by heavy rains.
Mudflow: A downslope movement of a mud water mixture. Usually occurs after
heavy rainfall, and in areas of little vegetation.
Debris flow: downslope movement of mud mixed with larger rock fragments.
Lahars: A mud or debris flow formed when volcanic ash and debris mix with
water, either in rivers or from rain or melting snow and ice on the flank of a
volcano.
MUDFLOWS
Mudflow in Rio de Janeiro, Brazil
“Portrait of a Planet” by S. Marshak
Volcanic mudflow (lahar) in
Columbia buried this town in
15 meters of mud, killing
20,000 people!
Volcanic mudflow (lahar) below Mt. St.
Helens, Washington
Mudflow in Nevada mountains. This flow may be sufficiently
rocky to be classified as a debris flow (>20% rock fragments)
Landslide: A sudden downslope movement of rock and debris down a
slope.
Rock slide: a landslide that only consists of rock.
Debris slide: a landslide that consists of both soil and rock.
Landslide scar: barren surface that forms after a landslide occurs.
Debris pile: pile at the base of the slope that consists of the material
produced by the landslide.
“Portrait of a Planet” by S. Marshak
Landslide in California on U.S. 101 in 1995 that
destroyed 9 houses, but no deaths or injuries. The
road cut on the highway may have been important
in causing this landslide. Other factors include
weakness of material and water content.
Landslide in Hong Kong that destroyed
buildings. As in slide to left, note road
built at level of uppermost tall buildings
(arrow)
Top of landslide triggered by
earthquake in southern California
Landslide triggered by heavy rains in
southern California. It is likely the
slope was over steepened during
construction of the highway.
slump
Landslide in ~10,000 year-old
lake clays near Glens Falls, NY.
Slump-mudflow(earthflow).
These lake clays occur up and
down the Hudson Valley.
mudflow
Roadcut showing glacial till on sandstone
bedrock, west of Albany. Tills in upstate NY
are typically clay rich and prone to
landsliding.
This is a “transported soil”.
Slide scar
Vaiont
dam
Landslide
deposit
1963 Vaiont landslide: 1900 lives lost,
water built up by the dam caused the
slope failure, 400 million cubic yards
of debris slid off slope, after smaller
slides had already occurred.
Displaced 67 million cubic yards of
water, the wave was 650 foot high
wave.
Extent of landslide damage caused
by the Vaiont Dam landslide.
Cross section of A to A’ line from
diagram from the left.
Slide scars
Bedding surface
Wave
produced
was
>200 m
high!
Slide scars
Landslide
deposit
Dam is
behind here
More photos of Vaiont
Dam landslide