Oct 14 Lecture: Mass Wasting Flashcards
mass wasting=
movement of earth material down slope via gravity
mass wasting can occur in ____ materials or ___
unconsolidated (sediment/ soil/ debris)
consolidated (rocks)
why do more landslides occur in wet season?
water acts as a lubricant, decreases friction, and adds weight
describe the air cushion model
- compressed air trapped beneath the debris reduces friction b/w debris and the slip plane
- this air cushion allows even large boulders to travel great distances
types of mass movements are characterized by: (3)
- material
- nature of movement
- speed of the movement
what are the 11 types of mass movements
- rock falls
- rockslide
- rock avalanche
- soil creep
- earth flow
- debris flow
- mudflow
- debris avalanche
- slump
- debris slide
- solifluction
rockfalls
- steep slopes
- newly detached blocks plummet in free-fall from a steep cliffside
- evidence= talus/ colluvium
talus/ colluvium =
rocky accumulations at the bottom of a cliff
- evidence of a rockfall
rockslide
gently sloping weak planes
- rocks don’t fall freely, but slide down the slope
anatomy of a landslide:
- zone of depletion (scarp): at top
- zone of accumulation: middle/ bottom
- toe: very bottom (looks like toes)
rock avalanche
- large quantities of material flow (not slide or fall)
- typically triggered by EQ, can travel at 100s of km/hr
in a rock avalanche, the ___ __ b/w rocks allows them to move very fast
compressed air (keeps the rocks apart= less friction)
soil creep=
slowest, unconsolidated mass movement
- regolith occurs
- slower moving= can contain more volume
2 mechanisms of soil creep
- freeze (expand)- thaw cycle
2. dry-wet cycle
regolith =
very slow deformation of surface debris- the upper layers move down the slope faster than those underneath
- soil creep
3 hallmarks of soil creep
- bent tree trunks
- bent rock layers
- fence zigzagging
T/F
soil creep is never a hazard because it is so slow
false
can still be a hazard to water/ gas lines, telephone poles, etc
earth flow
fluid movements of fine grained materials (soils, weathered shale, clay)
debris flow
- fluid movements of rock fragments supported by a muddy matrix
mudflow
- flowing masses of material finer than sand + some rock debris w/ lots of water
- water= less resistance= moves very fast
debris avalanche
- fast, downhill movement of soil, rocks, and trees
- typical in humid, mountainous regions
- fast (high water content, steep slopes)
slump=
- slow slides of unconsolidated material that travels as a unit
- scarp usually forms at top
- creates “steps”
debris slide=
- fast version of a slump
- debris move largely as a unit along planes of weakness (eg waterlogged clay zone)
solifluction=
- occurs in cold climates: water in surface layer freezes/ thaws
- when the surface thaws, soil becomes waterlogged, but water cannot seep downwards
- so, saturated soil oozes downhill, carrying rocks/ debris with it
what happened in the vajont dam disaster
massive amount of rock broke off the top of Monte Toc & fell into the Vajont dam, producing a tsunami-like wave. The wave overtopped the dam and rushed downstream, destroying villages
Explain the events of the Frank Slide
in Frank, Alberta
- rockslide buried the coal mine (people in the mine survived, people above ground died)
- caused by collapse of the unstable turtle mtn face
fold hinge fractures=
fractures commonly develop in rock @ fold hinges
- fractures oriented roughly perpendicular to the rock layering
- can allow ground water etc in, makes more unstable
