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Geohazard > Lesson 5: Mass Wasting > Flashcards

Lesson 5: Mass Wasting Flashcards

1
Q

It is the downslope movement of rock and regolith near the Earth’s surface

A

mass wasting

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2
Q

what force is mainly responsible for mass wasting

A

gravity

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3
Q

why is mass wasting an integral part of erosional process?

A

because it moves material from higher elevations to lower elevations

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4
Q

T of F: Mass wasting processes are occurring sporadically on all slopes; some act very slowly, others occur very suddenly, often with disastrous results.

A

FALSE: Mass wasting processes are occurring CONTINUOUSLY on all slopes; some act very slowly, others occur very suddenly, often with disastrous results.

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5
Q

Any perceptible downslope movement of rock or regolith is often referred to in general terms as a ________

A

landslide

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6
Q

during the Cherry Hills Landslide,
-how many people died?
-when did it happen?
-what type of landslide?

A

50 people died
on August 1-3, 1999
complex slide: started as slump, developed into debris flow near base

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7
Q

how many percent of the philippines is classified as highly susceptible to landslides?

A

80%

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8
Q

during the Guinsaugon Landslide in Leyte (St. Bernard)
-how many people died?
-when did it happen?
-what type of landslide?

A

1126 people died
on February 17, 2006
Complex side: rockslide-debris avalanche

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9
Q

what was thought to be the cause of the guisaugon landslide?

A

it rained continuously for 2 weeks and also the slope was known to be a splay of the philippine fault

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10
Q

during the Brgy Tinaan, Naga City, Cebu landslide
-what was the cause?
-when did it happen?
-what type of landslide?

A
  • recent earthquakes caused groundwater to divert here & there was a fault 500m away
    -Sept 18, 2018
  • sinkhole collapse+ planar block slide = debris flow
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11
Q

Knowledge about the relationships between _________ and __________ can lead to better planning that can reduce vulnerability to such hazards

A

Knowledge about the relationships between LOCAL GEOLOGY and MASS WASTING PROCESSES can lead to better planning that can reduce vulnerability to such hazards

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12
Q

The material that is (practically) still in place and
adjacent to the highest parts of the main scarp

A

crown

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13
Q

A steep surface on the undisturbed ground at the
upper edge of the landslide

A

main scarp

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14
Q

It is the visible part of the surface of rupture.

A

main scarp

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15
Q

what causes the formation of the main scarp?

A

caused by movement of the displaced material away from the undisturbed ground

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16
Q

The highest point of contact between the displaced material and the main scarp

A

top

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17
Q

The upper parts of the landslide along the contact between the displaced material and the main scarp

A

head

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18
Q

A steep surface on the displaced material of the landslide produced by differential movements within the displaced material

A

minor scarp

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19
Q

The part of the displaced material of the landslide that overlies the surface of rupture between the main scarp and the toe of the surface of rupture

A

main body

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20
Q

The portion of the landslide that has moved beyond the toe of the surface of rupture and overlies the original ground surface.

A

foot

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21
Q

The point of the toe farthest from the top of the landslide

A

tip

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22
Q

The lower, usually curved margin of the displaced material of a landslide, it is the most distant from the main scarp.

A

toe

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23
Q

The surface that forms (or has formed) the lower boundary of the displaced material below the original ground surface

A

surface of rupture

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24
Q

The intersection (usually buried) between the lower part of the surface of rupture of a landslide and the original ground surface

A

toe of surface of rupture

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25
Q

The part of the original ground surface overlain by the foot of the landslide.

A

surface of separation

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26
Q

Material displaced from its original position on the slope by movement in the landslide

A

displaced material

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27
Q

what does the displaced material form?

A

both the depleted mass and the accumulation.

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28
Q

The area of the landslide within which the displaced material lies below the original ground surface.

A

zone of depletion

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29
Q

The area of the landslide within which the displaced material lies above the original ground surface.

A

zone of accumulation

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30
Q

The volume bounded by the main scarp, the depleted mass and the original ground surface.

A

depletion

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31
Q

The volume of the displaced material that overlies the rupture surface but underlies the original ground surface.

A

depleted mass

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32
Q

The volume of displaced material that lies above the original ground surface.

A

accumulation

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33
Q

The undisplaced material adjacent to the sides of the rupture surface.

A

flank

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34
Q

what is preferable in describing the flanks?

A

Compass directions, but if left and right are used, they refer to the flanks as viewed from the crown.

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35
Q

The surface of the slope that existed before the landslide took place.

A

original ground surface

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36
Q

8 types of states and distributions of mass movement activity

A
  1. active
  2. suspended
  3. reactivated
  4. inactive
  5. dormant
  6. abandoned
  7. stabilized
  8. relict
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37
Q

usually present if active

A

scarps and tension cracks

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38
Q

6 ways mass movements can be classified according to

A
  1. Type of movement
  2. Type of material involved
  3. Relative proportions of material and water
  4. Velocity of movement
  5. Thickness
  6. Type of triggering factor
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39
Q

reactivation is common for what types of mass movement

A

rockslides and slumping

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40
Q

how to tell if relict activity

A

if there are evidence of old landslides: significant weathering, look into morphology

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41
Q

the 5 different kinds of movement for mass movement

A

flow, slide, slump, creep, hello fall??

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42
Q

the 4 different kinds of material for mass movement

A

rock, debris, earth, mud

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43
Q

the 2 different kinds of thickness for mass movement

A

shallow or deep-seated

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44
Q

the 4 different kinds of triggers for mass movement

A

rain-induced, earthquake-induced, human-induced, volcanic-induced

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45
Q

mixture of rock, earth, plants and mud

A

debris

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46
Q

loose sediment, weathered rock fragments

A

earth

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47
Q

mixture of water and finer sized sediments

A

mud

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48
Q

for deep-seated landslides, do mitigation efforts work?

A

usually doesnt, and the only solution is relocation

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49
Q

comprise a detachment of soil or rock from a steep slope and the more or less free and extremely rapid descent of the material.

A

fall

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50
Q

Following the definition of fall, the movement is largely through _____, alternated with the _______ or ______ on the slope

A

Following this definition, the movement is largely through THE AIR, alternated with the BOUNCING OR ROLLING on the slope

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51
Q

what triggers falls?

A

triggered spontaneously by:
- lateral pressures: roots, crystallization pressures, ice wedging
- loss of underlying support: erosion on cliffs

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52
Q

what is preceded by falling?

A

falling will be preceded by SMALL SLIDING or TOPPLING MOVEMENTS that separate the material subject to fall from the undisturbed rock

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53
Q

scree vs talus

A

scree: coarse
talus: fine

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54
Q

constitutes a failure in the support conditions of bedrock

A

topple

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55
Q

is a forward rotation out of the slope of a mass of soil or rock about a point below the center of gravity of the displaced mass.

A

topple

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56
Q

identically to fall, associated with very steep slopes

A

topple

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57
Q

what can topples lead to?

A

Topples may lead to the sliding of the displaced mass

58
Q

T or F: toppling is mostly occurring in combination with slides.

A

FALSE: toppling is mostly occurring in combination with FALL.

59
Q

defined as a moving slab of soil or bedrock that moves downslope as a whole, Remaining in contact with the underlying material

A

slide

60
Q

Slides can be sub-differentiated in two essentially different groups, what are they?

A
  1. rotational slides
  2. translational slides
61
Q

slides that have a more or less circular failure surface

A

rotational slides

62
Q

show in general a steep, almost vertical headscarp (crown), with the slided mass in front of it. The movement makes that the slide mass (body) is backtilting towards the headscarp.

A

rotational slides

63
Q

what can occur in combination with tensional cracks for rotational slides?

A

small steps on the body

64
Q

slides where the sliding mass moves along a preexisting failure plane

A

translational slides

65
Q

4 examples of pre-existing failure planes fit for translational slides

A

bedding, schistosity, joint, discontinuity between slope debris and the underlying rock

66
Q

2 differences between translational and rotational slides?

A
  1. the total displacement along the failure plane of translational slides is generally longer
    = smaller depth/length ratio for translational slides (1/10) vs rotational (1/3)
  2. Translational slides are also frequently showing a considerable larger width than a rotational slide
67
Q

3 types of translational slides

A
  1. soil slips
  2. rocks slides
  3. debris slides
68
Q

shallow translational movement in soil material

A

soil slips

69
Q

usual thickness of soil slips

A

1-2 m

70
Q

small scale translational slides

A

soil slips

71
Q

2 kinds of soil slips

A

sheet slide and slab slide

72
Q

soil slips in cohesionless and dry soils

A

sheet slide

73
Q

soil slips in soil material saturated with water

A

slab slide

74
Q

3 types of rock slides

A

planar slides, stepped slides, wedge failures

75
Q

rock slide when the movement takes place along one and the same failure plane

A

planar slide

76
Q

rock slide when the movement occurs along a number of parallel failure planes

A

stepped slides

77
Q

rock slides when failure is controlled by two planes which define a wedge shaped block, which is loosened from the rock slope.

A

wedge failure

78
Q

translational slides with movements occurring on steeper slopes, where the slope debris slides off along the discontinuity with the underlying weathered rock.

A

debris slides

79
Q

the range of steep slopes of debris slides

A

25-35 degrees

80
Q

involve great internal deformation

A

flow movements

81
Q

what forces dominate over what for flow movements?

A

inter-granular movements dominate over shear surface movements

82
Q

for flows: _______________ is not uniform, but the material near the surface runs at ______ velocity rate than the _________. The most common subdivision of flows is based on ________.

A

THE INTERNAL VERTICAL VELOCITY DISTRIBUTION is not uniform, but the material near the surface runs at A HIGHER velocity rate than the UNDERLYING MATERIAL. The most common subdivision of flows is based on THE TYPE OF MATERIAL

83
Q

is a type of slow movement, in which the rate of internal deformation is limited.

A

earth flow

84
Q

type of flow that includes solifluction

A

earth flow

85
Q

The general form of faster earthflows is that _________, leaving a ________ bounded by a ________. The saturated material flows _______ to form a ________

A

The general form of faster earthflows is that MATERIAL SLUMPS AWAY FROM THE TOP, leaving a STEPLIKE TERRACE bounded by a CURVED, WALL-LIKE SCARP. The saturated material flows SLUGGISHLY to form a BULDGING TOE

86
Q

is a type of a fast moving flow. The material is (over)saturated with water

A

mudflow

87
Q

A mudflow mostly originates from ___________ in ________, dragging soil particles with it. The _______ can build up so high that and even stones can be taken along.

A

A mudflow mostly originates from OVERLAND FLOW in HEAVY RAINFALL, dragging soil particles with it. The KINETIC ENERGY can build up so high that and even stones can be taken along.

88
Q

where do mudflows commonly occur?

A

along rivers: if riverbanks (consolidated/semiconsolidated sediment) + lots of precipitation = mudflow

89
Q

T or F: lahar is technically mudflow

A

true

90
Q

when can debris from falls and high-energy slides also behave as a flow (debris flow)

A

this happens especially if:
- air or water is entrained in the initial movement.
- the trapped fluid may develop high pore pressures
= which buoy up the individual debris particles. Alternatively:
- the numerous interparticle impacts may produce an
effect analogous to intermolecular motion in a real fluid
=thus enabling even dry, non-cohesive, debris to flow

91
Q

the movement of debris from falls behaving like debris flows taking place in larger material is called?

A

block flow

92
Q

an extension of a cohesive soil or rock mass combined with a general subsidence of the broken mass of cohesive material into softer underlying material.

A

lateral spread

93
Q

T or F: for lateral spread, the surface of rupture is a surface of intense shear

A

FALSE: The surface of rupture is NOT a surface of intense shear

94
Q

Spreads may result from ________ or _______ of the softer material

A

Spreads may result from LIQUEFACTION or FLOW (AND EXTRUSION) of the softer material

95
Q

for lateral spreads, the horizontal movement is _________ over ________ and often also partly induced by ________ deformation of the underlying material

A

for lateral spreads, the horizontal movement is A SLIDING OF THE DETACHED BLOCKS OF COHESIVE MATERIAL over THE SOFTER and often also partly induced by A PLASTIC deformation of the underlying material

96
Q

is the slow movement of soil or bedrock down slope.

A

creep

97
Q

where does creep typically happen

A

It occurs where the stresses on the slope material are
too small to create a rapid failure, or as a result of thawing/freezing effects

98
Q

can be classified those slope movements whereby at least two different types of landslides together are responsible for the occurrence or continuation of the slope movement in the area

A

complex

99
Q

Some slopes are inherently _______ than others and are therefore more prone to mass wasting

A

LESS STABLE

100
Q

As the slope increases, so too does the _______ component acting _______ to the slope, which, in turn, allows more of the rock’s weight to be directed in the ________ direction. When gravitational force becomes _______ than the _________, ___________ can occur.

A

As the slope increases, so too does the GRAVITATIONAL component acting PARALLEL to the slope, which, in turn, allows more of the rock’s weight to be directed in the DOWNSLOPE direction. When gravitational force becomes GREATER than the FRICTIONAL FORCES, DOWNSLOPE MOVEMENT can occur.

101
Q

6 factors that may trigger mass wasting

A
  1. slope (steepness)
  2. nature of slope material: angle of repose, oversteepened slopes
  3. climate
  4. vegetation
  5. earthquakes
  6. volcanic activity
102
Q

example of rocks that are inherently so strong and homogeneous that they are able to form stable cliffs

A

granitic rocks of Yosemite Valley, California.

103
Q

explain how loose sediments are more prone to mass wasting than hard lithologies

A

frictional forces within loose or unconsolidated sediments are usually lower than solid rock, making sediment more prone to mass wasting and less able to form vertical slopes.

104
Q

is the steepest angle at which a sloping surface of unconsolidated sediments is stable

A

angle of repose

105
Q

typical range of angle of repose

A

typically less than 35 degrees

106
Q

Large angular fragments generate greater _________, and therefore are capable of ________ compared to _________.

A

Large angular fragments generate greater FRICTIONAL FORCES, and therefore are capable of MAINTAINING STEEPER SLOPES compared to SMALL, WELL-ROUNDED SEDIMENTS.

107
Q

Slippage can occur along ________, ______, ______ and _______ that are inclined in ________ direction as the slope

A

bedding planes, foliation planes, fractures and fault surfaces inclined in the SAME DIRECTION as the slope

108
Q

structures facing the slope

A

daylight structures

109
Q

On _______ hillsides the component of ______ operating the direction of slope is _______, which, in turn, _______ the potential for _________.

A

On STEEPER hillsides the component of GRAVITY operating the direction of slope is GREATER, which, in turn, INCREASES the potential for MASS WASTING.

110
Q

example of how natural oversteepened slopes can cause mass wasting

A

An common example:
- the undercutting of stream banks
- due to the natural migration of stream channels
= results to destabilizing/overhanging of riverbanks.
= River valleys become wider over time

111
Q

undercut stream banks

A

cutbanks

112
Q

example of how human induced oversteepened slopes can cause mass wasting

A

flat surfaces are required for the construction of roads, buildings, and parking lots
- means that material must be excavated from hillsides
- in order to create a leveled surface
= weakens the slope significantly
= greatly increases the potential for mass wasting

113
Q

The long-term average weather for a region is defined as

A

Climate

114
Q

2 reasons why climate is an important factor in slope stability

A
  1. because it ultimately determines how and when precipitation falls.
  2. determines the types of vegetation we see blanketing the various slopes
    = influences the fraction of rain or snow that infiltrates into the subsurface
115
Q

describe how vegetation can affect slopes

A
  1. fairly dense vegetation tends to stabilize slopes plant roots
    - help bind together loose particles of rock and sediment.
  2. during unusually large rainstorms or rapid snowmelts, dense vegetation will increase infiltration ( since it reduces the ability of surface water to move downslope)
    - excessive infiltration adds significant weight to a slope
    - reduces friction through higher pore pressures
116
Q

which factor is heavier? geology vs climate

A

geology

117
Q

2 ways seismic waves affect slopes

A
  1. as the seismic waves pass along the surface,
    = the least stable slopes will tend to fail
    BECAUSE the ground vibrations suddenly reduce the frictional forces within the slope materials
  2. seismic waves may also cause surface materials to liquefy
    = immediately destabilize a slope
    =trigger a mass wasting event
118
Q

how does rain/snow affect cause mass wasting

A
  1. Rain or melting snow will infiltrate
    = cause subsurface void spaces to become saturated
    = weight of the water in the saturated zone causes the fluid/pore pressure within the voids to increase
    = reduces the friction between the solids
    = Downslope movement occurs when the frictional forces
    become less than the gravitational force in the slope direction
119
Q

what are the 4 types of causes of mass wasting?

A
  1. geological
  2. morphological
  3. physical
  4. human
120
Q

geological causes of mass wasting

A

Weak material
* Sensitive material
* Weathered material
* Sheared material
* Jointed or fissured material
* Adversely oriented mass discontinuity (bedding, schistosity,
etc.)
* Adversely oriented structural discontinuity (fault, unconformity etc.)
* Contrast in permeability
* Contrast in stiffness (stiff, dense material over plastic material)

121
Q

morphological causes of mass wasting

A

*Tectonic or volcanic uplift
* Glacial rebound
* Erosion of slope toe
* Erosion of lateral margins
* Subterranean erosion (solution, piping)
* Deposition of load on the slope or its crest
* Vegetation removal

122
Q

physical causes of mass wasting

A

*Intense rainfall/ Prolonged exceptional precipitation
* Rapid snow melt/ Thawing/ Freeze-and-thaw weathering
* Earthquake/ Volcanic eruption

123
Q

human causes of mass wasting

A

*Excavation of the slope or its toe
* Deposition of load on the slope or its crest
* Drawdown (of reservoirs)
* Deforestation
* Irrigation
* Mining
* Artificial vibration
* Water leakage from utilities

124
Q

how to identify landslides: 6 indications

A
  1. Vegetation cover: intact/disrupted
  2. Presence of cracks or scars
  3. Disturbance of the drainage pattern
  4. Excessive soil moisture or abrupt soils moisture changes.
  5. Terrain form: hummocky, niche-lobe sequence
  6. if there is growing or tilting of trees, and electrical posts
125
Q

what are the 9 morphological diagnostics of mass wasting

A
  1. concave-convex
    2.semicircular niches
    3.back tilting of slope faces
    4.hummocky relief
  2. formation of cracks
    6.steepening of slopes
    7.vegetational clearances on steep scarps
  3. irregular linear clearances along the slope
126
Q

is associated with landslide niches and associated deposits.

A

The sequence of a concave and a convex part of the slope

127
Q

is related to retrogressive sliding

A

A step-like morphology

128
Q

are associated with the head part of a slide with the outcrop of the failure plane

A

semicircular niches

129
Q

how are semicircular niches recognized on photographs?

A

as a light toned scarp, with small light curved lineament

130
Q

indicates rotational movement of slide blocks and appears as oval or elongated depressions with imperfect drainage conditions

A

Back tilting of slope faces

131
Q

Irregular slope morphology. Micro-relief associated with shallow movements or small retrogressive slide blocks

A

hummocky relief

132
Q

what lithology is hummocky relief common?

A

areas underlain with limestone

133
Q

how is hummocky relief recognized in aerial photos?

A

coarse surface texture of hummocky terrains stand contrast with smooth surroundings

134
Q

an indication for recent mass wasting activity

A

The formation of new cracks

135
Q

occurs with sliding and toppling movement

A

crack formations

136
Q

how do crack formations appear?

A

They appear as lineaments more or less parallel to the existing scar

137
Q

can indicate the presence of a landslide scar. This type of slope anomaly is clearly visible on aerial photographs

A

steepening of slopes

138
Q

coincides with morphological steps. Headscarps and steps in a slide body often show this

A

Vegetational clearances on steep scarps

139
Q

how do vegetational clearances on steep scarps show on photos?

A

On photographs this shows as light-toned elongated areas at the crown or on the body of the mass movement.

140
Q

what causes the irregular linear clearances along the slopes?

A
  1. Flows and avalanches strip parts of the slope from vegetation; leaving the flowpath uncovered.
  2. Slip surface of translational slides as well are usually uncovered.
141
Q

what do irregular linear clearances along the slopes look like?

A

The denudated areas are showing light tones, often with linear pattern in direction of movement

Geohazard (7 decks)

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