slope systems

Question 1

slopes and mass wasting

Answer 1

All slopes are inherently unstable
Therefore all slopes will experience slope failure
This is known as Mass Wasting

Question 2

mass wasting

Answer 2

The transfer of rock and regolith (soil, sediment, debris) downslope by GRAVITY
With minor help from water, sometimes
Main types
Creep
Slump
Debris flow
Landslide
Rockslide/Rockfall
Subsidence

Question 3

case studies: Huascaran Landslide (Peru)

Answer 3

May 31, 1970
Great Peruvian Earthquake (7.9M)
North side of Mt. Huascaran collapsed
80 million cubic feet of ice, mud, and rock
11 miles from start to finish
Average speed: Up to 200 mph
Killed up to 30,000 people at the base of the mountain
Town of Yungay (5 miles from Huascaran Peak) almost completely wiped out

Question 4

case studies: Bingham Canyon Copper Mine Landslide

Answer 4

April 10, 2013
“Largest non-volcanic landslide…in North America in modern times”
144 million tons of dirt and rock
Equivalent to more than 90 acres
Enough to bury NYC Central Park 66’ deep
Costliest landslide in Earth’s history
No fatalities or injuries
Successful forecasting

“successful failure”
February 2013
Movement on the NE wall first detected
TARP (Trigger Action Response Plan) initiated
March 2013
Relocation of employees, equipment, and facilities
Including the visitors’ center
Notification of local community
Access to lower pit limited
April 2013
April 9
Acceleration of movement on slope detected
Haul road closure
Access to pit restricted to special permission only
Sentries posted
April 10
9:30am
TARP hit highest threshold
Full pit closure
No access permitted
9:30pm
Slide occurs along weak layer at the bottom of the Manefay geological unit
11:00pm
Second slide in same place

Question 5

case study: vajont landslide, Italy

Answer 5

October 9, 1963
A dam was built in a deep canyon
270 million cubic meters slid into the lake
Within 45 seconds
68 mph
Displaced 50 million cubic meters of water
250 meter (820 ft!!) high wave
~2000 people killed

Question 6

Why do slopes fail

Answer 6

Gravity + …
Gravity is a constant force
So something else must change as well

Slope angle change

Overloading
Increasing the weight

Decreasing the resistance
Lowering friction

Question 7

Slope stability

Answer 7

Downslope force = gravity
Resisting force = friction, weight, retention measures
Failure = when downslope force is greater than resisting force Fd>Fr

Question 8

Mass Movement Triggers

Answer 8

cause resistance to decrease or downslope force to increase

Water
Oversaturation
Adds weight
Reduces friction
Vajont Landslide, Italy

Oversteepened Slopes
Angle of repose
Steepest angle at which the material is stable
Changes to the slope angle introduce instability
Bingham Canyon Mine landslide

Question 9

Mass movement triggers: oversteepened slopes

Answer 9

Slope is at angle of repose

Toe of the slope is cut away (freeway, railroad, stream erosion, etc). Part of the slope is much steeper than the angle of repose.

Slope regains equilibrium (of a sort)

see screenshot

Question 10

oversteepened slopes: undercutting

Answer 10

see screen shot:
weathering by water below, wedge piece above falls as rockfall

Question 11

other Mass movement triggers

Answer 11

Removal of Vegetation
Root systems bind soil and regolith together
Deforestation
Range fires
Insect infestation
plants disperse and use up water so it doesn’t all settle in soil

Earthquakes
Temporary lessening of friction
Huascaran Disaster

Planes of weakness
Saturated sand or clay layers
Joints parallel to the land surface
Weak sedimentary bedding
Shale, evaporites
Metamorphic foliation

Question 12

mass wasting

Answer 12

The transfer of rock and regolith (soil, sediment, debris) downslope by GRAVITY
With minor help from water, sometimes

Main types
Creep
Slump
Debris flow
Landslide
Rockslide/Rockfall
Subsidence

Question 13

types of mass movement

Answer 13

Creep
Very slow (slowest)
Alternating expansion and contraction of loose rocks
Temperature fluctuations
Solifluction
ground movement
j trees

Landslides/Slumps
Debris Flows
Rockslides/Rockfalls
Land subsidence

Question 14

Creep: solifluction

Answer 14

Polar regions
Top part of soil thaws
Deep soil is permanently frozen
Rainwater collects in top part of soil
Becomes heavy and slick

Question 15

Mass Movement: landslide/slump

Answer 15

Mass movement along well-defined failure surface
Sliding of regolith as coherent blocks
Variable speed
“Slump” when slow
“Landslide” when fast
see screen shot

wet year April 1983
Thistle, Utah
1000 ft in width
200 ft thick
1 mile length

Baldy below timpanogos

Question 16

mass movement: debris flow

Answer 16

Debris Flows
“Mudslides”
Rock fragments, soil, mud, water
Happen during intense rainfall or sudden thaw
(kind of just a muddy flood)

Speed
Fast when high volumes of water/steep slopes
Slower when less water/gentler slopes

Two main types
Mudflows/Debris flows
Common in tropical/subtropical settings
Deep regolith
Abundant water
Grain sizes range from pebbles to large boulders
Cars, trees, cabins, bulldozers

Lahars

Question 17

la conchita debris flow

Answer 17

Built on narrow flat land between steep slopes and beach
200 homes
1995
Heavy rain year
Slow moving slump
Buried nine houses
No loss of life
2005
Heavy rain year
Slumping turned into mudflow
Buried 13 houses
Killed 10 people

Question 18

debris flows: lahars

Answer 18

Special kind of debris flow
Common in loose pyroclastic material
Can be very fast flowing
Up to 150 km/hr
(~90 mph)
Warm or cold

Question 19

mass movement: rockslides/rockfalls (debris falls)

Answer 19

Rockslides/Rockfalls (Debris Falls)
Free-fall of rocks from steep cliffs; OR
Avalanche of rocks down a slope

Question 20

Frank, Alberta rock fall

Answer 20

1903
Giant wedge of limestone
400 m high
1200 m wide
160 m thick
Seven million tons of rock
Buried the town in 30 m of rock
(~90 feet!)
Over in 100 seconds
Nearly 100 people died

Question 21

submarine landslides

Answer 21

Deposits
Slurry of mud with larger clasts
=“Olistostrome”
Turbidity currents
“Graded beds”
Can be very large
Hawaiian Islands
***any one that ends in water
can be catastrophic causing water displacement tsunamis, you can’t usually feel landslides so they have to get the word of warning out

Question 22

mass movement: land subsidence

Answer 22

Land subsidence
Sinkholes are one example
More details in groundwater chapter

Question 23

Landslide potential mapping

Answer 23

Assesses multiple factors
Slope steepness, strength of bedrock, water saturation, bedding, vegetation cover, earthquake probability…
Uses computer modeling
Can be updated with drastic changes
Wildfire, past landslides, etc
help city planners, contractors, etc.

Question 24

mass movement prevention strategies

Answer 24

Revegetation
Regrading
Engineering Structures
Drainage
Riprap
Retaining walls
Joints and bolts

Question 25

test review picture order

Answer 25

g,z,p,a(because the tiny rocks within a rock are older than the rock they are in, and there is a baked mragin where t baked it so it had to exist before),t,d,y,m,e,c,x,b,l,s

q,o,n,l,m,p,h,i,j,k

Question 26

tr: half life q

Answer 26

17,190

Question 27

picture

Answer 27

synclines, anticlines, oxidation: chemical weathering, angular unconformity, convergence creates folds, erogenies,

Question 28

review question: rainbow arches which is older middle or outside

Answer 28

middle, lower numbers are older