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Mass Wasting Flashcards

1
Q

what is mass wasting

A

the downslope movement of rock, regolith and soil under the influence of gravity

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2
Q

what are two roles of mass wasting

A
  1. geologic processes that often follows weathering
  2. combined effects of mass wasting and running water produce stream valleys
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3
Q

how do weathering and mass wasting compliment each other

A

weathering weakens the material and allows gravity to easier act of the material

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4
Q

what process does mass wasting often follow

A

weathering

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5
Q

describe the evolution of mass wasting on slopes over time

A

in areas of rugged, geologically YOUNG mountains there are the MOST RAPID events

over time mountain sides lower through mass wasting and erosion

the older landscapes are LESS dramatic downslopes than young ones so they have LESS dramatic movements downslope

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6
Q

what is the controlling force of mass wasting

A

gravity

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7
Q

what are triggers of mass wasting

A
  • water
  • over steepened slopes
  • loss of vegetation
  • earthquakes
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8
Q

how does water act as a trigger for mass movements

A

saturation of the material with water molecules reduces the particle cohesion which decreases the materials resistance to gravity

AND

saturated soils have more weight which makes the soils also more susceptible to gravity because it changes the balance on the slope

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9
Q

how do steepening slopes act as a trigger for mass movements

A

slopes have a set slope angle that maintains the balance of the slope (not too steep but not too shallow), over steepened slopes lose that balance,
(they have a steeper slope angle which makes it unstable and more susceptible to failure)

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10
Q

what is a natural process for steeper slopes

A
  • undercutting by streams or wave action (erodes the slope and increases steepness)

-

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11
Q

how does removal of vegetation act as a trigger for mass movements

A

removing vegetation from a slope removes the root systems that bind soil and regolith which were acting as protection for the slope from rainfall (increases saturation)

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11
Q

how does undercutting by streams/rivers cause steeper slopes

A

the process removes the slope’s base which both causes an increase in slope angle AND increases the gravitational force acting parallel to the slope

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11
Q

what are some human processes that cause steeper slopes

A
  • cutting into its side too deeply
  • excavation for road cuts and hillside building sites
  • dumping or filling areas to build houses on top of hills
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12
Q

how do earthquakes trigger mass movements

A

the shaking can dislodge large volumes of rock and unconsolidated material = the sediments lose their strong cohesion and induce failure

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13
Q

how to classify mass movements

A
  • type of material involved (debris, mud, earth or rock)
  • type of motion
    (fall, slide, flow)
  • rate of movement (fast or slow)
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14
Q

what type of movement is this

materials fall through the air from talus slopes

A

fall

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15
Q

what type of movement is this

material moves along a surface as a coherent mass

A

slide

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16
Q

what type of movement is this

materials viscously deforms - becomes a jumble of material

A

flow

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17
Q

what is a talus

A

a slope that is built of angular rock fragments that fall to the base of the cliff

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18
Q

are talus rock falls fast or slow

A

SLOW

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19
Q

what is a slump

A

the downward sliding mass of rock OR unconsolidated material as a unit along a CURVED surface

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20
Q

what are distinguishing features of slumps

A
  • crescent shaped scarp at the head
  • raised toe at the end
  • curved slump plane/surface with step-like blocks for each section of the slump detaches
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21
Q

where are slumps common

A

along river valleys and eroding shorelines

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22
Q

what kinds of slopes do slumps occur

A

those that are oversteepened and overloaded

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23
slump
24
what is indicative of a slump
the step-like pattern of the different slump slides
25
what is a rockslide
blocks of bedrock that slide down a slope very quickly
26
are slumps rotational or translational
rotational
27
where are rockslides common
where rocks and joints parallel the slope which gets undercut
28
what is a common example of rock slide
frank slide
29
what is a major cause of slides
frost wedging
30
rock slide
31
Soil slide
32
rock slide
33
rock fall
34
debris flow
very wet mixture of soil and regolith confined to channels that flow down the slope
35
where are debris flows found
in high relief areas (mountainous like BC) that have high saturation of soils
36
what is an example of debris flow
lahars
37
what are Lahars
debris flows composed mostly of wet VOLCANIC materials that rush down the flanks of volcanoes
38
debris vs earthflow
earth flows happen in lower reliefs than debris flows AND are made up of soil and regolith NOT debris
39
where are earthflows found
on hillsides in humid regions
40
how do earthflows form
when water saturates the soil and regolith, the weight eventually has the material break away from the hillside (leaving scar behind)
41
what makes up earthflows
commonly involves materials rich in clay and silt
42
earth flow
43
earthflow
44
what are two examples of slow moving mass movements
creeps and lateral spread
45
what is a creep
the gradual downhill movement of soil and regolith
46
what triggers a creep
the alternative freeze/thaw and expansion/contraction of the surface material
47
what is a dead giveaway for a creep
tilted trees, fences, utility poles and soil ripples
48
what is the fastest mass movement
debris flow
49
What is this mass movement?
Creep
50
Creep
51
what promotes a lateral spread
a dense clay impermeable bedrock layer
52
what forms lateral spreads
the impermeable bedrock layer does not allow water to penetrate it, so it collects on the layers above = saturates that layer and eventually that leads to failure
53
where are lateral spreads common
in areas with PERMAFROST where the active layer gets statured in summer and frozen in winter
54
what is a dead giveaway of lateral spreads
vegetation on the earth that move as a series of lobes
55
lateral spread
56
what is subsidence
a form of subsurface ground failure where the surface collapses on itself
57
where is subsidence most common
in KARST topography
58
what causes subsidence
the withdrawal of fluids (water, oil, gas, steam) OR removal of soil materials (dissolution, mining) below the surface
59
are the causes of subsidence only human activities
NO can be natural as well
60
subsidence
61
how does California show subsidence
they have a very high level of irrigation to support the activities there so they pull a load of water from the water table = lowering the table and forcing the soil to compact in the absence of water
62
what is an example of subsidence
sinkholes
63
sinkholes form because of
the dissolution of carbonate rocks, limestones and dolomite AS WELL AS fluctuations in water tables
64
what is a problem caused by sinkholes
the giant holes trigger people to use them as giant waste dumping sites HOWEVER these holes are often right over the water table and any leakage of the garbage will go right into the water table
65
what are two rotational mass movements
rock and soil SLUMPS
66
what are two translational mass movements
rock slide (c) and soil slide (d)
67
what are the slowest flows
rock creep and soil creep (f)
68
what are examples of fast flows
earth flows and debris flows
69
what is the fastest flow
debris avalanche
70
what is a snow avalanche
the rapid downslope movement of snow and ice
71
how can snow avalanches become MORE deadly
behave like a rock slide where large layers of ice slide down the slope and break up as they go
72
what are some prevention methods against snow avalanches
- well designed explosions (or triggering controlled avalanches) - engineering structures to retain or divert avalanches
73
snow avalanche
74
submarine landslides
these are underwater slumps and debris flows
75
submarine landslides
76
what is an integral part of the growth of passive continental margins
submarine landslides
77
what triggers submarine landslides
the rapid buildup of unstable sediments OR by storms and earthquakes
78
where are submarine landslides especially active
near deltas (massive sediment deposits at the mouths of rivers)
79
what was the Grand Banks case study about
a magnitude 7.4 earthquake hit the south of Newfoundland along the Grand Banks it ultimately triggered a tsunami which was recorded along the east coast of US and as far south as the Caribbean and Portugal caused 1 million dollars in damages and cost 27 deaths
80
why was this the most severe damage regarding the Grand Banks case study
because that stretch along the island was most exposed to the sea and thus the tsunami BUT ALSO had the best topography to enhance and strength the tsunami
81
what was ridiculous about the La Conchita landslide
the small costal community right on the coast of the ocean was built ON PAST landslide deposits SO THE AREA HAS HAD THEM BEFORE In the 2005 landside, a debris flow was triggered by heavy rainfall
82
what was a giveaway that the slope in La Conchita was NOT stable
the daylighting beds - bedding planes that were almost parallel to the slope that have become mostly VISIBLE to the outside of the slope
83
what was the Vaiont Dam case study about
In Italy a landslide above the dam was triggered by weak carbonate rocks and clay layer and the steep slope surface already showing signs of creep the fast moving earth filled the dam and displaced tons of water the displaced water flowed down the dam to the settlement below in up to 300 foot waves
84
what is NOT a good prevention of mass movements
cut and fill - cutting into a slope to fill the indent with earth to build on
85
what is beneficial to have on slopes to prevent mass wasting
surface drainage to PREVENT water from being absorbed into the soil and waterlogging it
86
what is the benches approach to mass wasting prevention
changing the slope by pushing the top BACK and NOT filling it (like in cut and fill)
87
what is the ABSOLUTE BEST method for mass wasting prevention
1. have a good retaining wall WITH DRAINAGE to prevent failures 2. have a cut and fill for the house pad or base 3. have piles dug BELOW the fill so they reach stable rock below

Geomorphology (12 decks)

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