Mass Wasting - TRIGERRING MECHANISM Flashcards
it is the most significant factor that could trigger mass wasting
degree of slope
t or f: as the slope increases, the gravitational component acting parallel to the slope, also increases
T
when ______ becomes greater than the ______, downslope movement can occur
gravitational force ; frictional forces
the following factors may trigger mass wasting:
Nature of slope material;
oversteepened slopes
vegetation and climate;
earthquake and volcanic activities
t or f: strong and homogenous rocks are able to form stable cliffs
T
what type of rock is the cliff on Yosemite Valley, California?
granite rock
how long was the rock in Yosemite Valley, California? how did it become so stable?
2,000 foot
interlocking mineral grains and resistance to weathering
t or f: frictional forces in loose sediments are higher than in solid rocks
F (lower)
is the steepest angle at which a sloping surface of unconsolidated sediment is stable
angle of repose
angle of repose is typically
<35 degrees
t or f: large angular fragments generate greater frictional forces compared to small, well-rounded fragments
T
can occur along bedding planes, foliation planes, fractures, and fault surfaces that are inclined in the same direction as the slope
slippage
where does slippage usually occur?
foliation plane, bedding plane, fracture and fault surfaces
t or f: slippage are inclined in the opposite direction as the slope
F (same direction)
in the Grand Canyon, steep cliffs develop in resistant ______ and ______, whereas broad, gentle slopes form in much weaker ______
limestones and sandstones;
shales
what is daylight structure?
areas of high susceptibility to mass wasting because it is facing plane of weaknesses inclined to the slope
undercutting of stream banks results in _____ and _____
cutbanks and overhang
what causes cutbanks?
natural migration of stream channel
t or f: river valleys become wider over time due to undercutting of stream banks
T
example of oversteepened slopes caused by human actvity
excavation of materials from hillsides in order to create a leveled surface for construction of roads, buildings, and parking lots
t or f: only natural processes can destabilize a slope by increasing its steepness
F (natural and unnatural)
long-term average weather
climate
vegetation that blankets slopes influences the fraction of _____ or ____ that ______ into the subsurface
rain or snow;
infiltrates
how does fairly dense vegetation stabilize slopes?
plant roots help in binding particles and loose sediments together
t or f: during unusually large rainstorms or rapid snowmelts, dense vegetation will increase infiltration since it reduces the ability of surface water to move downslope, therefore destabilizing the slope bc of excessive infiltration
T
________ adds significant weight to a slope and reduces friction through higher pore pressures
excessive infiltration
excessive infiltration reduces friction in slope because of ______
increased pore pressure
vegetation vs geology:
which is more influential factor of mass wasting?
geology
how does seismic waves destabilize slopes?
ground vibrations reduces the frictional forces within the slope material, as well as causing them to liquefy
seismic waves also cause materials to ____, which can immediately destabilize a slope and trigger a mass wasting event
liquefy
infiltrated water within slope material increases _______, which then reduces _______ between the solids
pore pressure ; frictional forces
general potential causes of mass movements
geological
morphological
physical
anthropogenic
give at least 3 geological causes of mass movements
weak material
sensitive material
weathered material
sheared material
jointed or fissured material
give at least 3 morphological causes of mass movements
tectonic or volcanic uplift
glacial rebound
erosion of slope toe
erosion of lateral margins
vegetation removal
give at least 3 physical causes of mass movements
intense rainfall
rapid snow melt
earthquake
volcanic eruption
give at least 3 human causes of mass movements
deforestation
irrigation
mining
drawdown of reservoirs
excavation of the slope
give at least 3 human causes of mass movements
deforestation
irrigation
mining
drawdown of reservoirs
excavation of the slope
manifestations to look at when identifying landslides
vegetation cover;
presence of cracks or scars;
disrupted drainage pattern;
excessive soil moisture/abrupt soil moisture changes;
terrain form;
tilting of trees/posts
morphological diagnostics
concave-convex;
step-like morphology;
semicircular niche;
back tilting of slope faces;
hummocky relief;
formation of cracks;
steepening of slopes;
vegetation clearances on steep scarps;
irregular linear clearances along the slope
the sequence of a concave and convex part of the slope is associated with :
landslide niches and associated deposit
a step-like morphology is related to
retrogressive sliding
t or f: step-like morphology includes presence of tension scarps
T
are associated with the head part of a slide with the outcrop of a failure plane
semicircular niche
semicircular niche are recognizable on photographs as a ________
light-toned scarp with small light curved lineaments
back tilting of slope faces indicates
rotational movement of slide blocks
back tilting of slope faces appear as
oval or elongated depressions with imperfect drainage conditions
irregular slope morphology. micro relief associated with shallow movements or small retrogressive slide blocks
hummocky relief
hummocky relief are associated with
shallow movements with retrogressive slide blocks
t or f: the coarse surface texture of hummocky terrains stand in contrast with smooth surroundings
T
morphological indication of recent activity
formation of cracks
crack formation occurs with _______ movements
sliding and toppling
t or f: cracks appear as lineaments more or less perpendicular to the existing scar
F (parallel)
morphological indication of a presence of a landslide scar
steepening of slopes
it is the top of a scar and would indicate the original slope if it is connected to the tip of the landslide
break point
t or f: vegetational clearances coincide with morphological steps
T
______ and _____ in a slide body often lack vegetation
headscarps and steps
vegetational clearances on photographs shows as
light-toned elongated areas at the crown or on the body of mass movement
_____ and ____ strip parts of the slope from vegetation; leaving the flowpath _____
flows and avalanches;
uncovered
t or f: slip surfaces of translational slides are uncovered with vegetation
T
the denudated areas of irregular linear clearances are shown as
light tones, with linear pattern in direction of movement
