LA L1 Flashcards
Possible side effects of landslides?
contamination of water supplies, siltation of rivers and fisheries, and damage to transportation routes, dams, sewage lines, and forests
Economic consequences of a landslide?
costs to repair damaged structures and to replace damaged infrastructure as well as the cost to stabilize and prevent or mitigate the effects of future landslides, medical costs
_______ can have far greater economic consequences than the actual landslide itself
Indirect losses
Indirect losses caused by landslides?
a loss in property value, business lost as a result of the disruption of transportation routes, lost timber and fish stocks, and a decline in tourism
How long can economic damage of landslide extend to?
years after the event
what can save lives and reduce economic damage?
Employing proper mitigation techniques to stabilize dangerous slopes
How many people were killed by landslides and debris flows in Venezuela in December 1999?
Over 30 000
What increases vulnerability to landslides?
increasing population density, use of marginal land, rapid land-use change, global warming
Why are landslide fatalities typically underestimated?
Many fatalities are associated with the landslide trigger (earthquakes, floods, etc.) and not the landslide.
What do the world’s most devastating landslide disasters typically involve?
numerous fatalities due to both direct and indirect consequence
What increases logarithmically with population?
human cost of landslides (i.e. deaths)
Which country experienced the greatest economic damage from landslides overall from 1900 to 2016?
China
Which country experienced the greatest economic damage from landslides in one year?
Peru, in 1983
How many deaths in 1963 Vaiont Reservoir, Italy event?
~1900
Why was the 1881 Elm Event famous in landslide studies?
because the events leading up to and accompanying failure were well documented (one eyewitness used a stopwatch to time the initial failure)
How many people died in 1881 Elm Event?
115 people
Speed of 1881 Elm landslide?
80+ m/s (= 288+ km/h)
How much rock was released in 1881 Elm Event?
10 million m^3 of rock
The three stages of Elm landslide?
the fall, the jump, and the surgers
What caused the 1881 Elm landslide?
the extraction of slate from a quarry located at the foot of the slope. Quarry was developed by local farmer with no mining or geological experience.
What years did landslides occur in La Conchita California?
1995 and 2005
What is La Conchita?
a small Pacific coastal community located between Santa Barbara and Ventura, California
How big was the 1995 La Conchita landslide?
covered 4 hectares
How big was the 2005 La Conchita landslide?
1/6 of the size, 1/2 the mass of the 1995 event.
Where did the 2005 La Conchita landslide occur?
occurred in the southeastern portion of the 1995 landslide deposit and is a reactivation of the earlier event
How were the La Conchita landslides caused?
Both of these landslides were caused by heavy rainfall during the rainy season in the area.
Why is the La Conchita area particularly vulnerable to landslides?
because of a complex combination of faulting, tectonic uplift, very weak foundation, steep slopes, and presence of springs
Describe the landslide complex that the 1995 and 2005 landslides are part of.
The slope that failed in 1995 and 2005 are part of an ancient landslide that has produced prehistoric and historic slides, slumps, debris and mud flows.
How could the human and economic losses from both the 1995 and 2005 La Conchita disasters be prevented?
could have been prevent had the necessary and proper geologic engineering work were done prior to the development of the area
How many deaths did the 1920 Haiyuan earthquake and landslides cause (both indirectly and directly)? How?
responsible for 200 000 deaths. direct damage: destruction of homes. indirect damage: exposure to the harsh winter climate
What caused the 1920 Haiyuan landslide?
earthquake
Altitude of Haiyuan in Ningxia (Gansu)?
1200 - 1800m above sea level
Highest peak in Peru?
Nevado Huascaran
How much ice and rock in avalanche was displaced from summit of highest peak in Peru?
60 million m^3
What caused the 1970 avalanche on Nevado Huascaran?
M7.5 earthquake that occurred 30km off the coast of Peru.
How far did the slide debris of the 1970 Nevado Huascaran event travel? How fast did it go? Describe the damage it dealt.
Traveled ~20 km, speeds over 100 m/s (360 km/hr). Jumped a 200m ridge and wiped out town of Yungay and killed all but ~100 of its 20 000 inhabitants. Highways and railroad routes were buried, a diversion dam and access bridge to a major hydroelectric plant were destroyed.
How many survivors in the town of Yungay? What was the population of Yungay before the avalanche?
about 100 survivors. Originally 200 000 inhabitants.
What triggered a 2002 Lutzenberg landslide?
A strong rain event
How big was the 2002 Lutzenberg landslide?
small shallow landslide of about 4000 m^3
What is Lutzenberg?
a village in Switzerland
How many deaths due to 2002 Lutzenberg landslide?
3 deaths
Which areas have high potential for repeated occurrence of landslides?
Commonly found in Switzerland are deforested slopes, cultivated for pastureland.
Describe the 1911 Usoi rock avalanche.
In 1911 a rock avalanche near the village of Usoi in present-day Tajikistan caused 2.2 km^3 of fallen rock to block the flow of a river. The village was completely buried but no fatalities were reported. A natural landslide dam, the Usoi Dam, now stands where the village was and rises to a height of 500 to 700 m from the original valley floor.
What are rockfalls?
Event involving a smaller rockmass that disintegrates into numerous blocks that fall, bounce, and roll on steep slopes after detachment
What are rockfalls a hazard for?
highways and railways through rocky terrain in Canada and, though small, have resulted in numerous deaths in this century
What may add to hazardous conditions to contribute to landslides (besides steep slopes in mountainous regions)?
heavy rain and snowfall
Which area is most frequent with landslides?
mountainous region with steep slopes
What is mass wasting/ mass movement?
refers to the downslope motion of soil and/or rock materials under the influence of gravity
What is a landslide? Describe.
a general term for mass movements. These events occur when the gravitational force pulling the slope material down exceeds the slope material’s internal resistance to shear or failure. Materials move downslope by sliding or shearing along a weak failure plane or a number of failure planes.
Main force responsible for landslides?
gravity
Describe the relation between the angle of slope and gravity.
When the slope is steeper, the shear stress or tangential component of gravity INCREASES, while the perpendicular component of gravity DECREASES.
The component of gravity that acts perpendicular to the slope or parallel to and down the slope pulls an object or slope materials in the down-slope direction, causing a ___ ___.
shear stress.
Define shear strength
the internal resistance of a body to shear stress or a material’s internal shearing resistance.
As shear stress pulls slope material downslope, forces resisting this movement will be induced. These forces include _____ ______ and _____ among the particles of the slope material and are grouped under the term ____ ____.
frictional resistance; cohesion; shear strength
Relationship between friction, cohesion, and shear strength?
By increasing friction and cohesion, shear strength increases.
What factors affect friction and cohesion?
- type of soil of rock
- the condition of the geologic materials (how eroded are they)
- The presence of weak surfaces (joints and faults)
- Pore water pressure within the slope
When does slope failure occur?
when the force of gravity parallel to the slope, i.e. the shear stress, becomes greater than the strength of the materials that make-up the slope, which is acting to hold itself in place (shear strength). In other words, landslides occur when shear stress at the time of failure is greater than the shear strength of the geologic material.
What is the Factor of Safety?
equal to the ratio of shear strength at failure S_f to the average shear stress τ. The Factor of Safety can also be defined as the ratio of the forces that resist movement to the forces that drive movement.
What does the Factor of Safety indicate?
slope stability
When is slope stable? When is slope failure expected?
Stable when shear strength is greater than or equal to shear stress (i.e. F_s > 1.0).
Slope failure expected when shear stress is greater than shear strength. (i.e. F_s < 1.0
What is down-slope movement favored by?
(1) steeper slope angles which increase the shear stress,
and/or
(2) anything that reduces the shear strength of materials, such as lowering the cohesion among the particles or lowering the frictional resistance.
The converse is true for increasing slope stability
The effective stress of a slope is …. ?
the sum of the contact forces divided by the total area.
Which factors determine the resistance to slope failure?
- the weight of the material itself acting perpendicular to the slope, which helps to hold the slope materials in place. Another term for this is normal stress, σn.
- factors that adds to the spaces between grains (primarily water pressure), which decrease the strength of the material. We will represent this factor simply as pore water pressure, μ.
