Mass Wastings Flashcards
Landslides are linked to many other _______
natural hazards
Landslide benefits:
- disturbances increase ______
- provide ________ in steep terrain
- ecological diversity
- habitable terraces
Slopes are dynamic evolving systems and are the products of _____ and ____
- evolving
- substrate
- climate
Fatalities due to landalides 1900-2015
almost 70,000
slopes fail when ________ exceed the strength of the ____ or ____ that comprise the slope
- gravitational forces
- rock
- soil
Slopes fail when they are _______ or _____
- oversteepened
- debuttressed
slope zones of weakness develop due to certain combinations of _______ and _______ accumulation over impermeable _________ layers
- soils/bedrock
- groundwater
- silt and clay
Landslides are classified by:
- type of material
- type of motion
- rate of movement
- water content
unconsolidated material is ______ and consolidated material is ______ and ______
- loose
- cohesive
- adhesive
Role of water in landslides:
- adds ____ to slope
- decreases _______
- clay minerals become hydrated and _____ with high pore pressure
- minerals holding ________ together may ______
- mass
- material strength
- expand
- individual grains
- dissolve
Rockfall (consolidated)
- free fall or bouncing of rock
- 10km/hr
Rock slide/avalanche (consolidated)
- flow of fragmented rock from large rock slide or fall
- 10km/hr
Causes of rock slide/avalanche
- vibration
- undercutting
- differential weathering
creep (consolidated)
- cm/yr
- rock movement along deep failure plains
toppling (consolidated)
- movement of rock around pivot point away from slope
- common in steeply dipping joints/bedding planes
- km/hr
slump (unconsolidated)
- slow slide of material as coherent unit
- concave failure surface
Causes of slumps
- liquefaction
- quick clay
- km/hr
flow (unconsolidated) + triggers
- significant internal deformation
- dense fluid can transport large blocks of material
- can be triggered by rainfall/ snow melt
creep (unconsolidated)
- slow flow, slide or deformation
- soil expansion due to water in clay or freeze/thaw
earth flows
fluid movement of fine grained soils
debris/mud flows
fluid movement of coarser material & rock in mud matrix
debris avalanche
rapid movement of slope materials (70km/hr)
solifluction
soil freeze/thaw in cold regions. Upper “active layer” deforms over frozen layer
submarine mass movements can be triggered by:
- accumulated sediments
- earthquakes
- extreme tides
submarine mass movements are commen at ______ and may cause _______
- fronts of active defaults or volcanic islands
- tsunamis
complex mass movements involve some ______ of mass movement types
combination
driving forces
drive rock or sediment down slops
resistive forces
- oppose driving forces
- shear strength, slope of material
Material type affects event ____ and ____
- frequency
- type
Important characteristics of minerals in mass wastings
- mineral composition
- degree of consolidation
- planes of weakness
- inclanation of plain
clay
fine grained sediment created by chemical weathering of rocks
clay has low ____ and high _____
- strength
- pore pressure
steep slopes increase _______
driving force
high topography means high ______
gravitational potential energy
Vegetation influences mass wastings through:
- protective cover
- increases material strength
- increases load
_____ is almost always involved in mass movement
water
how water affects mass movement
- saturation increases probability of landslides
- deep infiltration may cause delayed triggering
- may erode base of slope
Factors contributing to increased risk of landslides
- regrading surfaces
- cut and fill
- vegetation removal
- surface loading
- undercutting slopes
- watering lawns
Minimizing landslide risk:
- _______ areas where landslides have occurred in the past or are likely to occur
- _____ these sites
- ______ exposure with engineered structures
- ______ landslides with engineered structures
- _____ active slides
- _______ of impending failure
- identify
- avoid
- reduce
- prevent
- control
- warn
indicators of potential landslides:
- _______ cracks on hillside
- _________ of valley wall
- lobate area of _______ on hillside
- _____ trees
- bedrock laying ______ to slope
- ______ terrain
- crescent shaped
- scalloped crest
- exposed material
- tilted
- parallel
- hummocky (bumpy)
drains cannot prevent ______, but can _________
- large landslides
- minimize hazards
objective of drains
keep water from infiltrating slope
cut and fill
- material moved from upper to lower slope
- reduces gradient, increases resistent forces
- not applicable to high/steep slopes
benches or steps:
- surface drains ______
- provide sites for ______
- divert runoff
- falling rock/small slides
_______ are one of the most common landslide mitigation measures
slope supports
slops supports anchor below ______, have backfill with ______ material, and allow for ______
- slope base
- permeable
- drainage
rock bolts are _____ that are inserted into _____ and anchored with _______
- steel rods
- drill holes
- facing plates
screens and fences are intended to intercept _______ and do not provide protection from _______
- small rocks
- larger slides
types of landslide identifiers
- human
- electrical
- tiltmeters
- geophones
- rain guages
- surveying
- sattelite
