Mass Wasting - PROCESSES AND CLASSIFICATION Flashcards
what is a landlside?
it is a downslope movement of rock or regolith near the earth’s surface due to gravity (nelson, 2006)
mass wasting is an integral part of ______ as it move material from _____ elevations to _____ elevations
erosional processes ; higher elevations ; lower elevations
what is a regolith?
loose unconsolidated materials sitting atop a bedrock layer
differentiate weathering and erosion
weathering is the breakdown of rocks in situ, while erosion involves mobilization and transportation of weathered materials
t or f: mass wasting are occurring continuously on all slopes, some are very slow while others occur very suddenly, often with disastrous results
T
any perceptible downslope movement of rock or regolith are referred to in general as ______
landslide
landslide is also known as:
Debris Slump
Cherry Hills Landslide: location and date
August 1-3, 1999
Antipolo, Philippines
about how many percent of the land area of the Philippines is susceptible to lanlsides?
up to 80%
what was the specific mass wasting events that occurred in cherry hills landslide?
slump to debris flow near the base
Village of Saint Bernard landslide location and date
Guinsaugon, Leyte
Feb 17, 2006
what triggered the saint bernad village landslide?
two-week continuous rainfall
at 10:26 am, an earthquake followed the saint bernard village landslide, what is the magnitude of the earthquake?
Mag 2.16
t or f: part of the slope in guinsaugon leyte lansdlide was transected by the PFZ
T
what mass wasting event occurred in Andap, New Bataan in 2012?
Debris Flow
when was the Andap, New Bataan Mass wasting?
December 4, 2012
what river was close during the Andap mass wasting
Mayo River
maximum runup height of Andap new bataan mass wasting
1.8m
what specific mass wasting events occurred in Guinsaugon, Leyte?
Rock slide to Debris avalache
Naga City Landlside, location and date?
Brgy. Tinaan, Naga City, Cebu
Sept. 20, 2018
the Naga city landslide was a combination of what processes?
sinkhole collapse + planar block slides + debris flow
during the Naga City landslide, a fault was traced ______ away from the area
500m
what possibly triggered Naga landslide?
during 2013 NBF earthquake, groundwater flow diverted through the area (with karst terrain), causing sinkhole collapse
knowledge about the relationships between ______ and _____ can lead to better planning that can reduce ______ to such hazards
local geology ; mass wasting processes ; vulnerability
states and distributions of activity of a landslide
active
suspended
reactivated
inactive
dormant
abandoned
stabilized
relict
t or f: relict landslides have undergone weathering
t
t or f: cracks present in dormant landslides are indicators of another episode of mass wasting
T
what are indicators that a past landslide have occurred in an area
concave topography
sparse vegetation
bulging toe / old landslide deposits at the bottom
mass movements can be classified according to:
- type of movement
- type of material
- relative proportion of water and mater
- velocity (slow or rapid)
- thickness (shallow or deep seated)
- triggering factors
types of material involved in mass wasting
rock, debris, earth, mud
types of triggering factors of mass movements
earthquake induced, rainfall induced, or human induced
t or f: for deep seated landslides, mitigation measures are of no work, evacuation should be done.
T
mixture of rock, earth, plants, and mud
Debris
composed of loose sediment and weathered rock fragments
Earth
mixture of water and finer-sized sediments
mud
regolith are composed of
rock fragment, sheared bedrock, weathered zone, organic soils
solifluction is a mixture of
creep and flow
two type of debris avalanches
hot and cold
comprises a detachment of soil or rock from a steep slope and the more or less free and extremely rapid descent of the material
Fall
_______ refers to fine-grained deposits at the bottom of a slope, while ______ refers to coarse grained deposits
Talus ; Scree
the movement of fall is largely through the ____, alternated with the ______ or ______ on the slope
air ; bouncing or rolling
falling will be preceded by
small sliding or toppling movements
t or f: falls can also be triggered by lateral pressures (roots, ice wedging, crystallization pressures) or by lost of underlying support (erosion on cliffs)
T
t or f: falls are more common in soft roxks
F (hard rocks)
constitutes a failure in the support conditions of a bedrock
fall
a topple is a _____ out of the slope of a mass of soil or rock about a point below the ________ of the _______
forward rotation ; center of gravity ; displaced mass
this process is identical to fall, associated with very steep slopes
topple
topples may lead to _____
sliding of the displaced mass
toppling is mostly occurring in combination with ____
fall
a moving slab of soil or bedrock that moves as a whole, remaining in contact with the underlying material
slide
two types of slides
rotational and translational
a slump is an example of a _____ type of slide
rotational
a type of slide that have more or less circular failure surface
rotational slide
a type of slide where sliding occurs along a pre-existing failure plane
translational slide
t or f: rotational slides are shallower than translational slides
F (deeper)
t or f: rotational slides are narrower than translational slides
T
three types of translational slides
soil slips
rock slides
debris slides
shallow translational movement in soil materials
soil slips
two types of soil slips
sheet slide
slab slide
scale of soil slips
1-2m in thickness
occurs in cohesionless, dry soils
sheet slides
occurs in saturated soil materia
slab slides
three types of rock slides
planar slides
stepped slides
wedge failure
what type of rocks slide occurred in Guinsaugon, Leyte?
Planar slide
a type of rock slide where movement takes place in a single failure plane
planar slides
a type of rock slide where movement occurs along a number of parallel failure plane
stepped slides
a type of rockslide where failure is controlled by two planes which define a wedge-shaped block loosened from the rock slope
wedge failure
debris slides occur on what slopes
steep (25-35 degrees)
what is a debris slide?
a slope debris slides off along a discontinuity with the underlying weathered rock
movements involving great internal deformation
flow
flow involves ________, where ______ dominates over _________
internal deformation ; inter-granular movements ; shear-surface movements
t or f: the internal vertical velocity distribution of a flow is uniform
false (not uniform)
in a flow the vertical velocity of the material near the surface is _______ than the velocity of the underlying material
higher
the most common subdivision of flow is based on the _____
type of material
t or f: materials in flow movement are cohesive
F (not cohesive)
a type of slow moving flow
earthflow
in an earth flow, the rate of internal deformation is _____
limited
t or f: earthflow includes solifluction
T
the saturated material in an earthflow moves ______ and forms a _____
sluggishly ; bulging toe
is a type of fast moving flow
mudflow
t or f: the material in mudflow is oversaturated with water
t
a mudflow mostly originates from ________, dragging soil particles with it
overland flow in heavy rainfall
t or f: kinetic energy in a mudflow can be so high, it could take along stones
T
in a debris flow, the trapped fluid may develop _______ buoying up individual debris particles
high pore pressures
t or f: dry, non-cohesive debris can move like a flow due to interparticle impacts (similar to intermolecular motion in fluid)
T
a flow taking place in larger materials
block flow
t or f: mudflows are common along rivers that are composed of consolidated materials plus rainfall
F (semi-unconsolidated)
an extension of a cohesive mass of rock or soil combined with the general subsidence of a broken cohesive mass into a softer underlying material
lateral spreads
t or f: the surface of rupture in a lateral spread is a surface of intense shear
F (not a surface)
spread may result from _____ or _____ and _______
liquefaction or flow;
extrusion of softer material
t or f: in lateral spreads, the vertical component is more important than the horizontal component
False (the horizontal is more important)
the horizontal movement of a spread is the ________
sliding of detached blocks over a softer material
spread is also partly induced by _____ of the underlying material
plastic deformation
what is the slowest type of mass wasting
creep
fastest type of mass wasting
rock fall
is the slow movement of soil or bedrock downslope owing to periodic expansion and contraction
creep
what causes expansion and contraction of the slope?
cyclic wetting and drying or thawing and freezing
t or f: the stresses on a slope material in a creep is to small to generate a rapid failure
T
at least two different types of landslides occur together
complex
what is regarded as the most dangerous geohazard?
landslide
what does EGGAR stand for?
Engineering Geological and Geohazard Assessment Report
