SETTING OFF A MASS MOVEMENT

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SETTING OFF A MASS MOVEMENT
TRIGGERING MECHANISMS
NATURAL TRIGGERS
Earthquakes cause liquefaction
Peru, 1970
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SETTING OFF A MASS MOVEMENT
TRIGGERING MECHANISMS
NATURAL TRIGGERS
Volcanic events induce lahars.
Mt. St. Helens, WA 1980
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SETTING OFF A MASS MOVEMENT
TRIGGERING MECHANISMS
ANTRHOPOGENIC TRIGGERS
Clear-cutting and Forest Fires
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SETTING OFF A MASS MOVEMENT
TRIGGERING MECHANISMS
ANTRHOPOGENIC TRIGGERS
Building on Steep Slopes
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SETTING OFF A MASS MOVEMENT
TRIGGERING MECHANISMS
ANTRHOPOGENIC TRIGGERS
Mining
In April 29th, 1903 a disastrous landslide took
place at Frank, Alberta. A huge slab of
limestone slid from the face of Turtle Mountain
and wiped out part of the town.
Before
Turtle Mountain or Mountain That Walks
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100 seconds later, it was all over. Survivors
described a cracking sound like cannon fire
echoing throughout the mountains. A 640 metre
high, 915 metre wide, 152 metre thick (2,100 feet
by 3,000 feet by 500 feet) wedge of the eastern
slope of Turtle Mountain gave way and slid 700
metres (2,300 feet) down the mountain side. An
estimated 182,000,000,000,000 kg (one hundred
million tons) of limestone slid into the valley
and onto the town of Frank.
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All mass movements are influenced by
weathering and erosion, water, tectonics and
biology. Results of mass movement stem from
interaction between lithosphere, biosphere,
atmosphere and hydrosphere.
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TYPES OF MASS MOVEMENT
SLOW MASS MOVEMENT
SURFACE CREEP
Slowest form of mass movement. Gradual downslope
movement of unconsolidated material. Invokes
only upper few meters of sediment. Moves faster
at the surface than at depth.
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TYPES OF MASS MOVEMENT
SLOW MASS MOVEMENT
SURFACE CREEP
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TYPES OF MASS MOVEMENT
SLOW MASS MOVEMENT
SOLIFLUCTION (SOIL FLOW)
Result of movement attributed to freeze-thaw
action. Thawed material becomes saturated and can
flow.
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TYPES OF MASS MOVEMENT
SLOW MASS MOVEMENT
SOLIFLUCTION (SOIL FLOW)
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
Particles move at rates of km/hr or m/sec.
ROCK FALL
Fastest type of rapid mass movement. Particles
fall from steep slope.
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TYPES OF MASS MOVEMENT
Arizona
RAPID MASS MOVEMENT
ROCK FALL
British Columbia
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
ROCK SLIDE or LANDSLIDE
Occurs when rock, sediment, or unconsolidated
material breaks loose and moves in contact
with underlying slope along a pre-existing plane
of weakness such as a fault, fracture or
bedding plane. Plane of weakness is called a
SLIP-PLANE. SLIP-PLANE is usually flat or
planar. Slide moves in a single, intact mass.
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
ROCK SLIDE or LANDSLIDE
Gros Ventre Slide Wyoming 1925
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
ROCK SLIDE or LANDSLIDE
Gros Ventre Slide Wyoming 1925
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
SLUMPS
A slide that occurs on a curved or concave
slip-plane moving in a downward and outward
motion. Slumps create their own
slip-plane. Usually have a crescent-shape scar at
top of slope. Steep slope at the top of the scar
is called a scarp. End of the slump is called the
toe. Slumps dont usually travel far.
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
SLUMPS
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TYPES OF MASS MOVEMENT
CO Rt. 93, Golden, CO
RAPID MASS MOVEMENT
SLUMPS
Rt. 36, Boulder, CO
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Occurs when a mixture of rock fragments, soil
and/or sediment moves downslope as a highly
viscous fluid. Flows move rapidly. Dangerous
when they have a high water content. Can be
related to rainfall.
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Earthflow - relatively dry during movement.
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Earthflow
Slumgullion Slide, western CO 700 yBP
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Mudflow - fine-grained particles mixed with water.
Mudflow Guatemala, 1989
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Quick Clay - ground vibrations liquefy sediments.
Quick Clay slide, Rockland, Maine, April 24, 1996
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Debris Flow - contains coarser than
sand-sized particles. Occurs with a sudden
introduction of water.
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TYPES OF MASS MOVEMENT
RAPID MASS MOVEMENT
FLOWS
Debris Flow
Revelstoke, BC, Canada
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PREDICTION OF MASS MOVEMENT
Study local geology. Consider local historical
record. Determine if patterns of mass movement
exist. Use 14C, cosmogenic dating,
lichenometry, and dendrochronology of older
mass movements. Consider animal behavior.
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AVOIDANCE OF MASS MOVEMENT
Avoid slide prone areas. Look for signs of
historical mass movement. Bent trees Cracks in
slope Cuts at base of slope Tilted utility
poles Unusually low house prices Check out the
neighborhood Read the local newspaper before
buying
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WATER DISTRIBUTION ON EARTH
The amount of water in, on, and above Earth
is approximately 1.36 billion cubic
kilometers. This amount has been fairly constant
over past 1 by.
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HYDROLOGIC CYCLE
Consider only the surface water component in this
chapter.
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STREAMS
A stream is any surface water whose flow is
confined to a channel. Stream and river should
be used interchangeably.
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FLOODPLAIN
A floodplain is any flat land immediately
surrounding a stream channel. Floodplains would
be submerged if stream overspilled its banks.
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DRAINAGE BASIN
The drainage basin of a stream is the
water-collecting area of a stream.
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TRIBUTARIES
Tributaries are any smaller streams that feed
larger streams within a drainage basin.
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DRAINAGE DIVIDE
A drainage divide is an area of high topography
that separates drainage basins (Rocky
Mountains).
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STREAM FLOW AND DISCHARGE
Flow of any stream is driven by its
gradient. GRADIENT is the vertical drop over the
course of a stream. Gradient depends upon
topography.
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STREAM FLOW AND DISCHARGE
DISCHARGE is the volume of water passing a
given point in a given amount of time.
Q D x W x V
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STREAM FLOW AND DISCHARGE
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STREAM FLOW AND DISCHARGE
Mississippi River discharge 18,000 cms (600,000
cfs) Amazon River Drains area 75 smaller than
U.S. Discharge 200,000 cms (7,000,000 cfs)
1/5 of the Earths freshwater flow 1 days
discharge from the Amazon would supply NYC
with fresh water for 5 YEARS.
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GEOLOGIC WORK OF STREAMS
Streams are responsible for erosion and
deposition of sediment. Streams cut through
uplifted land toward base level. BASE LEVEL is
the lowest level to which a stream can erode its
channel. Ultimate base level is sea level. Local
base levels can occur.
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GEOLOGIC WORK OF STREAMS
Ultimate Base Level Mississippi Delta, LA
Local Base Level Yosemite Falls, CA
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GEOLOGIC WORK OF STREAMS
Streams can respond to changes in sea
level. Erode rapidly downward when sea level
falls. Deposit rapidly when sea level rises.
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GEOLOGIC WORK OF STREAMS
GRADED STREAMS
AGGRADATION occurs when deposition is
greater than erosion.
Aggradation of the Rivière des Ha! Ha! in Quebec
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GEOLOGIC WORK OF STREAMS
GRADED STREAMS
DEGRADATION occurs when erosion is greater than
deposition.
Broadstreet Hollow Stream, NY
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CHANNEL PATTERNS
STRAIGHT CHANNELS
Channels are dominated by fractures, faults and
joints.
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CHANNEL PATTERNS
BRAIDED CHANNELS
Converging and diverging stream channels
separated by sand and gravel bars. Usually occur
in aggrading streams. Deposit most of their
sediment in channel beds.
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CHANNEL PATTERNS
BRAIDED CHANNELS
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CHANNEL PATTERNS
MEANDERING CHANNELS
Streams wind across relatively flat
landscape. Loops or MEANDERS form as stream
erodes its banks. Erosion takes place on the
CUT BANK, which is the outside loop of the
meander. Deposition takes place on the POINT BAR,
which is on the inside loop of the meander.
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CHANNEL PATTERNS
MEANDERING CHANNELS
Cut Banks
Point Bars
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WATERFALLS
Occur where barriers to down-cutting
exist. Usually only last as long as the barrier
exists.
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WATERFALLS
May develop a PLUNGE POOL at the base.
Lower Yellowstone Falls, WY Courtesy of Lindsay
Masters
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Very dynamic settings. Affected by tides, waves
and nearshore currents. Change can be rapid and
dramatic.
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The COAST is the entire region bordering a body
of water. A SHORELINE is the precise border
where a body of water meets adjacent dry land.
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WAVES, CURRENTS AND TIDES
WAVES AND CURRENTS
Waves are produced as air flows from high
pressure areas to low pressure areas. Air moves
across water surface and with friction reshapes
water surface into waves. Velocity of 3 km/hr (2
mph) is all that is needed to generate waves.
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WAVES, CURRENTS AND TIDES
WAVES AND CURRENTS
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WAVES, CURRENTS AND TIDES
WAVES AND CURRENTS
Wave Nomenclature
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WAVES, CURRENTS AND TIDES
WAVES AND CURRENTS
The distance that the wind travels over water is
called its FETCH. Greater the fetch, the larger
the waves.
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WAVES, CURRENTS AND TIDES
WAVES AND CURRENTS
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
Wave form moves horizontally, water particles do
not. Water particles move in a circular
orbit. Called OSCILLATORY MOTION. This motion
disappears below WAVE BASE. Wave base 1/2 the
wavelength. Water below wave base is generally
undisturbed.
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
BREAKING WAVES
As waves touch bottom, velocity
decreases. Wavelength decreases, wave height
increases. Waves bunch up and steepen Wave crests
move faster than troughs. Crest overruns the wave
and BREAKS. Motion changes from oscillatory to
translatory. Water moving forward on the beach
becomes SURF.
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
BREAKING WAVES
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
SWASH
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WAVES, CURRENTS AND TIDES
WAVES MOVEMENT
BACKWASH
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WAVES, CURRENTS AND TIDES
WAVE REFRACTION COASTAL CURRENTS
Produces LONGSHORE CURRENT.
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WAVES, CURRENTS AND TIDES
TIDES
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WAVES, CURRENTS AND TIDES
TIDES
Rising tide is called FLOOD TIDE. Under right
geologic and geographic conditions can produce
TIDAL BORE. Lowering or falling tide is called
EBB TIDE.
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WAVES, CURRENTS AND TIDES
TIDAL BORE
Bay of Fundy, NS and NB, Canada
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WAVES, CURRENTS AND TIDES
TIDES
Hopewell Rocks, New Brunswick, Canada
Low tide
High tide
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COASTAL EROSION
Due to the concentration of wave energy on
shorelines and coasts. 14,000 waves hit exposed
rock or beaches every day. Erosion is caused by
the forcing of water and air under high
pressure into small crevices. Once rock is broken
up, pieces are abraded against the coast.
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COASTAL EROSION
Coastal erosion is driven by Wave size and
energy Erodibility of local rocks Slope of the
sea floor Gentle slope, waves break
offshore Steep slope, wave break close to
shore Common in headland areas.
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EROSIONAL LANDFORMS
WAVE CUT NOTCH
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EROSIONAL LANDFORMS
WAVE CUT BENCH
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EROSIONAL LANDFORMS
SEA CAVES
Australia
Wisconsin
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EROSIONAL LANDFORMS
Elephant Rock, PEI, Canada
SEA ARCH
London Bridge, Australia Courtesy of Lorraine
Beane
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EROSIONAL LANDFORMS
SEA STACK
Acadia
Percé Rock, Quebec
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PROTECTION FROM EROSION
RIP RAP
Heaps of large angular to subangular
boulders. These boulders are piled along the
shoreline to slow or reduce erosion.
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PROTECTION FROM EROSION
SEAWALLS
Structures built parallel to shore to prohibit
erosion.
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COASTAL TRANSPORT AND DEPOSITION
Most commonly produces a feature known as a
BEACH. A BEACH is a dynamic, relatively narrow
segment of coast washed by waves and tides and
covered with sediments of various sizes and
composition. DUNES can develop at the back of a
beach. DUNES are long ridges of sand formed by
wind blowing sand from the front of the beach to
the back of the beach.