GEOL 103 Mass Wasting
What makes a slope fail?
(1) Cause --make slope susceptible to movement without actually initiating failure = strain building up (2) trigger: initiate failure --CRITICAL POINT (3) effect: resulting failure --slide, topple, fall, flow?
The danger of Debris flows
(1) Debris flows are DENSE and FAST MOVING (high energy) =exert very high impact stresses Debris flow fans (2) Provide a great place to live (often easiest sites to build on in steep mountain areas) =large, flat, low-relief = ideal until another debris flow comes down same channel
Earthquake triggered landslides: Regional effects
(1) Density decay --number of landslides is highest close to the epicenter and along the fault rupture (2) Hanging wall vs Foot wall --more landslides on the side of the fault that is thrust upward = more on the hanging wall than the footwall
How to avoid: Modeling landslide occurrence
(1) Empirical models =example: rainfall intensity-duration thresholds can be used to determine likelihood of landslide False positives (and false negatives) = Only as good as the relationships established from the empirical data Use physical models to develop risk maps
increase the driving forces: increase the slope angle
(1) Human modification (engineering) --roads = increase slope angle and increase driving forces (2) tectonic tilting (seismic) (3) erosion of the toe --undercutting --steepen part of the slope
What can be done?
(1) Identify: map the hazard, exposure, vulnerability --> quantify risk =where the hazard is = potential exposure and vulnerability (2) Avoid: monitoring and modeling to try predict hazard occurrence under certain conditions = set up warning systems & evacuation plans (3) Prevent: manage hill slopes to reduce mass movements and or preventing them from reaching elements (assets)
Earthquake Triggered landslides: Local site effects
(1) Local elevation --different kind of signature in the land depending on how these are triggered --> rainfall triggered = landslides more commonly occur at hill slope toe near rivers (not always the case tho) --> Coseismic triggered = shaking of topography is maximized near ridges (more EQ triggered landslides imitate near to ridge lines) (2) Aspects --More landslides on slopes that dip in the direction that seismic waves travel --"back slopes"
Modes of failure: Flows
(1) Mode of failure --flows occur when large volume of WATER is present in a soil/debris mixture --sig rainfall or encounter river/stream and mixes (2) Transport --flows as a chaotic mixture rather than a coherent mass --debris flows (3) Material Type --soil, debris, loose rock (&water!) --chaotic mixture
Modes of failure: Toppling
(1) Mode of failure --toppling involves FORWARD ROTATION of rock blocks out of the slope about a point/axis (below center of gravity) (2) Transport --toppling, falling, bouncing, rolling (3) Material type --rock
Modes of failure: Sliding
(1) Mode of failure --slides involved LARGE VOLUMES of rock/soil moving as an (initially) coherent mass on a defined SHEAR (sliding) SURFACE --can be rotational (slump) = curved surface -- can be translational = plane (flatter surface) (2) Transport --rotational or translational sliding (3) Material Type --mixture rock, debris or soil
Runout: Source to sink
(1) Source area --initiation of failure, often as a slide. --visible often as steep-walled scarps (2) Transport zone --flow can "grow" as they scour material from the slope --some dispositional features visible here (as momentum is lost) --lot of energy (3) Deposition zone --deposit when the slope angle is low enough that their residual strength can resist deformation --Loss of potential energy --deposit morphology varies with type of flow --destroys homes/settlements = at ALL stages of runout, landslide will/can damage
Mapping vulnerability
(1) Topography =landslide susceptibilty map (2) Building heights =with more stories = more people? (3) land use =where important transport networks are? =critical facilities located? (4) Mapping of land use, population density =more people = more vulnerable (5) location and types of assets, their value (6) superimpose hazard maps
How to prevent: Education
(1) WHERE to build and where not to build (2) HOW to build (3) HOW to (not) de-stabilize slopes =drainage =vegetation (4) Detecting signs of instability =sings a slope is moving without sophisticated monitoring equipment (i.e. bending trees, cracks in foundations) (5) WHERE to go/WHAT to do = evacuation prodcedures
increase the driving forces: increase the weight on the slope
(1) building (human activity) on steep slopes (2) weathering, generating more material (climate or tectonic) --If material is deposited lower down on the slope, increases the weight on a different part of the slope
Decrease resisting forces: reduce the cohesion
(1) increase water content (2) deforestation (loss of root strength) --most susceptible to failure few years after deforestation --root strength immediately starts deteriorating but it takes time --if you take out tree completely by the root = immediately most susceptible (3) weathering (changing grain size)
Primary Impacts of Mass Movements
(1) loss of life --mostly with flows and falls Rock fall = due to sheer size and impact Flows = due to speed (lack of warning time) Death toll can vary from one event to another due to: --failure size? --transport speed --location (who is nearby?) (2) building and infrastructure damage
Define the hazard: Classification of mass movement
(1) mode of failure -- how something starts moving --how failure initially occurs (2) transport --how does the material move? --flow? slide? fall? (3) material type --bedrock? purely soil?
3 Characteristics of a landslide
(1) stochastic --difficult to predict --random element to behavior (2) catastrophic --important to know timing, location and magnitude --pose sig hazard to human life and infrastructure (3) threshold behavior --how can this be determined?
How socio-economic impact depends on type and characteristics of landslide hazard?
(1) water content --impacts ease of movement and speed of movement --faster = less warning time (2) runout --longer = more potential to hit people or buildings (3) time of year --seasonal impact on characteristics of landslide --rainy = higher water content = higher chance of mobilizing into a flow --freeze thaw = contribute to creep landslides (4) How big (size) (5) What type of material? --governs the style of failure --how far the material will run out (6) how the slope fails (type of landslide) --does it flow, slide or fall? (7) exposure --what and who is nearby?
Modes of failure: Falls
(1)Mode of failure --falls occur on steep slopes with loose rock that periodically detach from a surface on which little or no sliding takes place --No sliding (2) Transport --falling, bouncing, rolling (3) material type --rock (rather than loose soil) -- <50 % fine material = fair amount of larger rock and debris in mixture --near saturated
Landslide maps based on
--ground surveys (photos of evidence) --aerial/satellite imagery --media sources (landslide blog, summary of those that occur across globe) --historical records
Landslides triggered AFTER the earthquake
--higher probability (potential) of landslides in the months and years following --partially due to aftershocks --Shaking reduces the Factor Strength as particles have loosened but not yet surpassed the critical point of failure = distinction between CAUSE and TRIGGER --the loose deposits on the slopes can later be mobilized into a landslide
Landslide Risk: Size (human cost)
17% of fatalities due to natural hazards are due to landslides =Largest individual events contribute significantly to fatalities =Huge spike associated with single events 300 million (5%) of population exposed to landslides =66million in HIGH RISK areas
Landslide Risk: WHEN
2004-2016 =largely driven by climate (nonEQ) =4,862 landslides & 55,997 fatalities Increasing due to human activity (HUMANS CAN INFLUENCE THE HAZARD) =poor are disproportionately affected Seasonal trends --> peak landslide occurrence during N hemisphere summer and fall --> coincident with monsoons + typhoons --> asymmetry in curve reflecting continental-scale weather patterns (more landslides in 2 half of year)
Earthquake triggered landslides: Liquefaction landslides
3 Factors Needed: (1) Loose (unconsolidated), granular sediment --often located near water or where ground-water is already quite high (2)Saturation by ground-water --often loose sediments already contain water (because has space for it) (3) Strong shaking Example --> 1964 Price William Sound USA --9.2 Mw earthquake -Turnagain Heights experienced liquefaction landslides --> 75 homes destroyed
Runout: Connectivity with channel network
A slide can become a flow --entering a channel adds a significant amount of water to that material A slide/flow can travel further when it connects with a channel Determines the downstream sedimentation
Secondary impacts: River water levels
As sediment enters river in particular locations, it can change water levels Example --> Oso Landslide --initial spike in water depth immediately after landslide (18million tonnes entering river) --Slide blocked the river (valley) causing a rapid decline in water depth = dams the river, forming a lake behind it and causing widespread flooding upstream
Friction & Water
By adding water, slope can fail BELOW the friction angle Water reduces the friction, so the angle of internal friction decreases Example: La Conchita --at end of 15 days of rainfall --rotational slump-slide --followed by earth-flow (due to extreme amount of water)
What makes a slope fail? Cause trigger effect
Cause --> make slope SUSCEPTIBLE to movement --> increase driving forces --> decrease resisting forces --> human impacts --> failures without a trigger Trigger --> INITIATE failure Effect --> the resulting FAILURE, slide, topple, fall, flow impacts --> runout --> primary --> secondary
How to prevent: Hillslope stabilization
Decrease driving forces OR increase resisting forces Decrease driving: (1) weight on slope (try reduce) = remove material from head of slope (2) Slope angle (reduce) Increase resisting (1) cohesion = plant vegetation (2) water pressure = improve hill slope drainage to reduce forces from water (3) slope strength =cemented rock armor =Gabions = large cage filled with rocks =retaining walls =rock anchors (attaching loose sediment to bedrock) = ground to bedrock, steel pipe from surface to bedrock (4) weight on slope =load applied on toe increases resisting forces
Influence of geology
Direction that bedding planes are dipping are important (1) Anti-dip slope: toppling or rockfall could occur =far less likely landslide =dipping away from slope (2) Dip-slope: sliding is probable =dipping toward the slope
Earthquake triggered landslides: Mechanism
Earthquake shaking can change the packing arrangement of grains --earthquake waves can cause the grains to loose contact = loosing strength from inter-particle friction --material becomes a loose slurry, behaving like a liquid
Earthflow
Elongate, occurs in fine grained material (1) hourglass shape = from narrow flow channels =form a fan at bottom when deposit (2) moderate slopes =move more slowly =not as much power (not as much material) (3) saturated conditions
Landslide Risk: SIZE (economic cost)
Exceed $1bn per year Underestimated =average DIRECT costs (difficult to desperate from indirect costs) =data records incomplete =hard to obtain reliable values bc often merged with other associated natural disasters
Factor of Safety (FS)
Failure occurs when driving forces > resisting forces FS: balance of forces in a hill slope FS = Shear strength/shear stress FS =1 --> JUST stable (about at point of failure) FS >1 --> slope is stable (strength is winning), look for 1.1 to consider actually stable FS <1 --> slope is unstable (stress is winning), has probably failed
What type of movement would a lahar be classified as?
Flow! because it needs water to trigger it
Decrease resisting forces: reduce the friction
Frictional strength = function of particle interlocking and surface roughness (1) increase water content --lubricate contact between grains, reduces the friction between grains --adding water makes the slope susceptible to failure at an angle LESS than the angle of internal friction (2) seismic activity (3) weathering (changing roughness) --weather overtime = becomes smooth = reduces friction
Shear Strength: Friction
Frictional strength: a function of (1) particle interlocking and (2) surface roughness =helps material stay on slope =varies with different materials Little particle interlocking --> lower frictional strength =particles above and below shear surface not very interlocked High particle interlocking --> higher frictional strength =harder for particles to start to move apart =more friction = more strength in slope FRICTIONAL STRENGTH = angle of internal friction: the angle between normal and resisting force at the point of failure =a high angle of internal friction = stronger slope (requires more shear stress) =low angle = doesn't require as much for slope to fail If angle of IF > angle of slope = slope will be ok if angle of IF < angle of slope = slope will fail
Landslides: Causes
Geological Mechanical Hydrological Geomorphological Biological Human --> construction and mining are some of main ways humans can trigger landslides
Landslide Risk
Hazard = WHEN driving forces > resisting forces =WHERE there are conditions for slope failure (steep, loose material, trigger) =SIZE depends on material, slope length, type of failure Consequence = TYPE OF FAILURE: consequences look diff for diff types = CHARACTERISTICS of failure (speed, material) = WHERE people and infrastructure is located (exposure on or at the bottom or very top of slope)
Runout: Quantified by H/L ratio
Height length ratio governs how far the slide is able to run out Correlation with landslide volume --large landslides (volume) have a small H/L value = longer runout -- length of slope is larger than height giving it more space for it to go
Runout
How far something slides, falls or flows Impacted by: (1) Presence of WATER important in how far something will move (2) material (rocks vs mudflow) (3) viscosity of material --high water content = less viscous = flow more easily --low water content = more viscous = more resistant to flow (4) Slope angle and length
Identifying landslides: (3) Determine temporal probability (WHEN)
How often it is likely to occur Two options to do this: (1) Mag-frequency curve --plot --area and frequency --determine how often we expect (2) relate to trigger data (i.e. rainfall threshold) --generally when EQ >Mw5 they start to trigger small landslides --peaks in landslide coincide with peaks in rainfall =110mm>= rainfall = high probability of ~20 landslides
Shear Strength: Cohesion
How well grains (the particles) are held together Influenced by: (1) electrostatic bonding (2) inter-particle cementing (3) presence of water =material is least stable when saturated =dry = most stable =small amount of water = helps with cohesion (4)root binding =destabilize slopes when we chop down trees =roots hold things together = increase cohesion
Creep
Imperceptibly slow earthflow Often won't know its happening unless you stay in same place for a long time =curving of tree trunks (in some direction) =houses with cracks in foundation Steady downward movement of soil/rock Enough shear stress to produce deformation but not to produce failure Seasonal, continuous and progressive = associated with freeze thaw
Increase the driving forces
Increase the weight (w) on the slope Increase the slope angle
Secondary impacts: When landslides meet ice
Landslides that runout onto a glacier can increase the velocity and runout of the landslide and glacier: (1) due to sig REDUCED FRICTION of ice-rock interface (2) Entrainment of ice --> adds WATER --picks up some of the ice, which may start to melt and therefore add a certain amount of water = allowing it to flow further and faster Additional weight on glacier can also cause glacial surges --material can cause a surge of its movement
Societal impacts of landslides
Location and speed are important factors in governing socio-economic impact But, more complex than slow = less damage (damage in a diff way) --> the type of landslide and the characteristics of that movement (fast, slow, water content, size, slope, location) will all govern potential impact (NOT JUST SIZE)
Landslide Risk: WHERE
Lower risk in light blue colours Clusters of landslides around the world (some relationship between this and the other hazards) Non-seismically triggered, fatal landslides: Patterns? (1)availability of "RELIEF" upon which landslides can occur =steep slopes =difference in typography that generates steep slopes =cluster of landslides in mountainous (2)availability of PRECIPITATION =need a certain amount of water to initiate movement =often coincide with areas with high mountain environments (3) presence of victims (HUMANS) =in order to be fatal need humans
Landslide risk: Type = Fall
Material: Rock Speed: Very fast Runout distance: short
Landslide risk: Type = Flow
Material: debris, water Speed: very fast Runout distance: highly variable (usually very far)
Landslide risk: Type = Slide
Material: rock/soil Speed: slow --> very fast Runout distance: highly variable
Shear Strength: Weight
Normal Force: On = W*cosa =the force (perpendicular) to the slope contributes to RESISTING the downslope movement =with steeper slopes cos will be lower = harder to keep material on the slope
Debris flow (video example)
Power of the flow = large boulders at the front of the mix Large material chaotically tumbling around at the front of the flow = front is rich in debris and what comes behind is smaller slurry As it starts to loose its power = deposits leveys on the side -- channel becomes narrower and deposits on the banks of what was previously a stream Reach flat ground = loose momentum and stop flowing -- deposits spread out in a fan deposit
Decrease the resisting forces
Reduce the cohesion Reduce the friction
Angle of internal friction
Represents the maximum angle that the slope can be before it fails Slope > AIF = failed Slope < AIF = stable unless we add water, reduce cohesion etc
Slope stability
Resisting forces --> what holds the sediment in place? (shear strength, S) Driving forces --> what pulls it down slope? (shear stress, t) Typography --> unconsolidated sediment/rock -->"shear surface" --> bedrock (intact)
Impacts of mass movements
Runout: how FAR something slides, falls or flows PRIMARY impacts (loss of life, building damage) SECONDARY impacts -sedimentation -when landslides meet rivers --when landslides meet ice
Landslide risk: Where people are
Scenario 1: shallow slope experiencing creep, town on slope =probably not human harm (enough warning time as long as you see signs, recognize, and do something) =damage to foundations and house, power lines or trees bending = BUILDING and INFRA linked damage Scenario 2: Small access road that passes through old debris flow fan =evidence of past failure = high likelihood of future failure =cut off community accessed by road =not busy is unlikely that death occurs Scenario 3: Popular hiking trail below steep cliffs subject to rockfall =loss of life (popular trail = high exposure) =rockfall = dense and solid = damage and death example: Rocky Mountains
Identifying landslides: (4) Site investigations to determine SIZE
Scientists can investigate a site, and use monitoring techniques to ID most unstable parts of the slope = need detailed site investigations
Secondary impacts : Sedimentation
Sediment mobilization --> happens if landslides are able to connect with channel and get into a stream Landslides are a major contributor to sediment mobilization BOTH DURING and AFTER the initial trigger event Photos from Sichuan: -May 2008 = 1 month following Mw 7.9 earthquake = not much sediment has gotten down to the bottom of the valley -September 2008 = heavy monsoonal rains = by November sediment that was initially mobilized in the EQ that had been sitting on the hillside eventually got into the channel network = inundated many buildings in the town
Landslide Risk: SIZE
Smaller landslides are most common, large landslides are much rarer Power-law scaling for medium to large Roll-over for smaller landslides = peak is NOT the smallest =critical mass required to initiate slide =evidence of small landslides quickly erased "landscape healing" (or a larger coming on top of it)
Earthquake triggered landslides: Characteristics
Some of the largest landslides are often EQ triggered Correlation between total landslide area and earthquake Magnitude =higher mag = stronger shaking = larger area affected by landslides Example: Wenchuan Earthquake = landslide was one of the biggest killers in this EQ Landslides are triggered during the earthquake AND after the earthquake
Failure without a (clear) trigger
Sometimes occur on "nice hot sunny days" w no rainfall ACCUMULATION --graph suggests that damage accumulates in a slope = over time as environmental forces / smaller failures nearby = contribute to damage and strain build up THRESHOLD BEHAVIOR --not much happens, then we surpass critical level Example: North Coast of Cornwall 23rd Sept 2011 = followed period of warm sunny weather
Societal impacts: Location
Sometimes size and speed are not the defining features of the impact of a landslide. Example: Usoi Rock Avalanche was LARGE with no fatalities vs Lutzenburg landslide was SIG SMALLER but a home was hit so there were 3 fatalities Example: Frank Slide was a large rock avalanche over a mining town = 70 fatalities associated purely with location, vs Mt Meager rock avalanche (similar size) had no fatalities because it just missed the campsite due to impact with a river
what is the difference between flow and spread?
Speed! movements we classify as spreads move much more slowly than flows (that often have a slightly higher water content) move more quickly
Shear Stress
The DRIVING force t=Wsina --> the force parallel to slope pulls the mass downslope --> weight is concentrated at the center of the block (mass) and a downward force A product of: (1) weight of material (W) =mass (=density&depth) *acceleration (gravity) (2) slope of the angle (a) =the lower the slope angle, the more stable the slope
Mass Wasting Process
The downslope movement of material as slope fails =adopt a range of different speeds and reologies (composition of flow related to presence or absence of water) Under influence of gravity Variable speeds from creep (extremely slow) to debris flow or rockslide (very rapid) Presence of water plays an important role in type of transportation process (slide vs flow) Landslides -> move relatively fast (bottom right)
The slope "model": understanding slope stability
This is applicable to SHALLOW, TRANSLATIONAL landslides =illustrates key controls on hill slope stability =FS widely applied to ID potential unstable slopes =for rotational (and other) failures, the physics is more complex
Secondary impacts: Displacement waves
Under or above water landslides can cause displacement of water, which then triggers the 4 stage tsunami process: (1) in the ocean --underwater landslide --displaces water vertically (2) on land --large rock avalanche fall into ocean --displace water vertically example: Norwegian Tafjord 1934 --~3million m3 of rock --60m high local tsunami wave travelled 4.5km up the for = 40 people died = local narrow topography may amplify wave height example: Aknes rockslide, Norway --under close monitoring --scientists have figured out the 30-40million m3 of the slope that is unstable and slowly starting to creep --potential to generate 40m high displacement wave if enters the fjord --alarm threshold levels for nearby villages based on the movement of the slope SURFACE and SHEAR SURFACE (below what we can see)
How to avoid: Early Warning Systems
Use monitoring and/or modeling data to set up (1) early warning systems --i.e. when certain rainfall threshold is reached (2) evacuation plans -- when to go when warnings are issued Example --> Sea to Sky, Canada (subject to large rockfalls) =trigger wires that detect rockfall =send signal for barriers on the road to close =avoids vehicles colliding with debris on road Example --> Hong Kong slope safety: landslip warning system = example of a good warning system
Identifying landslides: (1) find past landslides
Using landslide maps Analyze locations where landslides occurred: (1) what was the SLOPE ANGLE (2) GEOLOGY (3) ELEVATION =lower down near channel network? =higher up near ridges? (4)ASPECT =NSEW? =if EQ triggered = slope facing direction that seismic waves are traveling =if RAINFALL triggered = certain facing slopes will get more rain (5)PROXIMITY TO CHANNEL NETWORK =if able to get into channel = runout increases =any relationship with landslide occurrence of characteristics? --> use info to ID when future landslides may occur
Factor of Safety: Soil Saturation
We need to know: (1) amount of soil saturated = m *m =zw/z* =m =1 = 100% saturated =m=0 = completely dry zw = water table (height from shear surface to water table) z = overall depth (2) force water is applying = on=w*cosa W= density*depth*acceleration = density (pw) =depth (z*m) force = pw*z*m*g*cosa
Identify vulnerability
What assets are at risk & what value do we place on these assets? (1) monetary value $ (2) intrinsic value: important or irreplaceable (3) Utilitarian value: usefulness of an asset (and $ value of its use) What value do we place on human life? (1) economic value: lost earnings, medical expenses, legal costs = estimated at $873k to $7million per life (2006) Elements to consider: --Buildings --transportation network --lifelines --essential facilities --population data --economic data --ecological data --agriculture data
Secondary impacts: Landslide dammed lakes
When landslides block rivers = cause the build up of water behind it --> lakes! common during EQ = "quake lakes" water builds up behind the temporary dam and eventually breaks through = large flood wave flows downstream (which Is often catastrophic) Attempts often made to drain the lake in a controlled way before it bursts
What is a landslide?
a general term used to describe the downslope movement of soil, rock, and organic materials under the effects of gravity and also the landform that results from such movement (1) the movement of material = scar it leaves on the landscape (2)deposit of that material =once the landslide stops moving
Landslide triggers: Non-seismic, non-rainfall triggered
account for 16% of all landslides Increasing numbers over time...improved records?
Mudflow
an earth flow where material is wet enough to flow rapidly = minimum 50% sand, silt, clay-sized particles = mostly FINE partciles =distinguished by an earthflow from amount of water = speed
Identifying landslides: (2) Determine landslide susceptibility (WHERE)
e.g. slopes above 20 degrees have a higher susceptibility Areas on steep slopes, near a river and.... will have highest susceptibility rating = gives spatial probability Alternative to landslide susceptibility analysis = FACTOR OF SAFTEY! =physically-based approach to ID most landslide-prone hill-slopes
Decrease resisting forces: seismic activity
earthquake waves generate both vertical and horizontal accelerations in the slope =vertical and horizontal shaking occurs in cycles VERTICAL force --> increases and decreases, as does friction --> waves come through the area, shaking the ground up and down --> friction is reduced when the ground is descending, increasing failure probability HORIZONTAL force --> increases shear force due to shaking =increased failure probability =reduces the friction in the slope
Societal impacts: speed
important when thinking about the TYPES of impacts associated with a landslide Slow moving landslides --Often very deep seated landslides --despite moving slowly, power to damage trees and bring material along the slope and this can sometimes keep going on for months --people probably don't die as a result but damage is being done to the landscape and infrastructure
Shear Strength
is VARIABLE through SPACE and TIME, and is a function of many factors including: (1) weight of material (2) friction (3) cohesion (4) amount of water present (saturation) S = cohesion * weight (normal force) * water pressure * cosa * friction
Why is number of landslides, fatalities and economic cost increasing?
population growth --> increased exposure land use changes (deforestation) --> changes in soil susceptibility Urbanisation --> changes in soil, increases vulnerability Infrastructure --> increase vulnerability, destabilization Climate change --> change weather patterns and migration Better data --> fewer undocumented events
Debris avalanche
regarded as a very rapid debris flow
How to avoid: Monitoring unstable slopes
remote monitoring via laser scanning systems can monitor remotely or can install instruments on the slope (geophones) --> 8 geophones (record seismic events) installed on the Aknes rockslide
Understand the process
to try and predict some of these fatal events, we need to understand what drives a slope to fail A balance of forces: DRIVING and RESISTING Key controls: --relief (slope angle) --soil water content --material strength --land use (vegetation, infrastructure) --seismicity
How to prevent: block landslide runout
we can try and prevent material from hitting people and infrastructure at the bottom of the slope by blocking the run out (1)damn (2) barrier fence (3) rock shed =protecting areas of road where known landslides/avalanches are most common =relies on where these are likely to occur, when they are likely to occur, and how BIG (so can withstand certain weight of material)
Identifying landslides: probability
what is the probability of a landslide occurring for any given location? (1)spatial probability (where) =how susceptible (2)temporal prob (when) =reccurence interval (3) prob of landslide (size) = how large is it likely to be and how far?