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Geomorphology > Mass Wasting > Flashcards

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
Q
A

slump

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24
Q

what is indicative of a slump

A

the step-like pattern of the different slump slides

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25
Q

what is a rockslide

A

blocks of bedrock that slide down a slope very quickly

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26
Q

are slumps rotational or translational

A

rotational

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27
Q

where are rockslides common

A

where rocks and joints parallel the slope which gets undercut

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28
Q

what is a common example of rock slide

A

frank slide

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29
Q

what is a major cause of slides

A

frost wedging

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30
Q
A

rock slide

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31
Q
A

Soil slide

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32
Q
A

rock slide

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33
Q
A

rock fall

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34
Q

debris flow

A

very wet mixture of soil and regolith confined to channels that flow down the slope

35
Q

where are debris flows found

A

in high relief areas (mountainous like BC) that have high saturation of soils

36
Q

what is an example of debris flow

A

lahars

37
Q

what are Lahars

A

debris flows composed mostly of wet VOLCANIC materials that rush down the flanks of volcanoes

38
Q

debris vs earthflow

A

earth flows happen in lower reliefs than debris flows AND are made up of soil and regolith NOT debris

39
Q

where are earthflows found

A

on hillsides in humid regions

40
Q

how do earthflows form

A

when water saturates the soil and regolith, the weight eventually has the material break away from the hillside (leaving scar behind)

41
Q

what makes up earthflows

A

commonly involves materials rich in clay and silt

42
Q
A

earth flow

43
Q
A

earthflow

44
Q

what are two examples of slow moving mass movements

A

creeps and lateral spread

45
Q

what is a creep

A

the gradual downhill movement of soil and regolith

46
Q

what triggers a creep

A

the alternative freeze/thaw and expansion/contraction of the surface material

47
Q

what is a dead giveaway for a creep

A

tilted trees, fences, utility poles and soil ripples

48
Q

what is the fastest mass movement

A

debris flow

49
Q

What is this mass movement?

A

Creep

50
Q
A

Creep

51
Q

what promotes a lateral spread

A

a dense clay impermeable bedrock layer

52
Q

what forms lateral spreads

A

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
Q

where are lateral spreads common

A

in areas with PERMAFROST where the active layer gets statured in summer and frozen in winter

54
Q

what is a dead giveaway of lateral spreads

A

vegetation on the earth that move as a series of lobes

55
Q
A

lateral spread

56
Q

what is subsidence

A

a form of subsurface ground failure where the surface collapses on itself

57
Q

where is subsidence most common

A

in KARST topography

58
Q

what causes subsidence

A

the withdrawal of fluids (water, oil, gas, steam) OR removal of soil materials (dissolution, mining) below the surface

59
Q

are the causes of subsidence only human activities

A

NO can be natural as well

60
Q
A

subsidence

61
Q

how does California show subsidence

A

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
Q

what is an example of subsidence

A

sinkholes

63
Q

sinkholes form because of

A

the dissolution of carbonate rocks, limestones and dolomite AS WELL AS fluctuations in water tables

64
Q

what is a problem caused by sinkholes

A

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
Q

what are two rotational mass movements

A

rock and soil SLUMPS

66
Q

what are two translational mass movements

A

rock slide (c) and soil slide (d)

67
Q

what are the slowest flows

A

rock creep and soil creep (f)

68
Q

what are examples of fast flows

A

earth flows and debris flows

69
Q

what is the fastest flow

A

debris avalanche

70
Q

what is a snow avalanche

A

the rapid downslope movement of snow and ice

71
Q

how can snow avalanches become MORE deadly

A

behave like a rock slide where large layers of ice slide down the slope and break up as they go

72
Q

what are some prevention methods against snow avalanches

A
  • well designed explosions (or triggering controlled avalanches)
  • engineering structures to retain or divert avalanches
73
Q
A

snow avalanche

74
Q

submarine landslides

A

these are underwater slumps and debris flows

75
Q
A

submarine landslides

76
Q

what is an integral part of the growth of passive continental margins

A

submarine landslides

77
Q

what triggers submarine landslides

A

the rapid buildup of unstable sediments OR by storms and earthquakes

78
Q

where are submarine landslides especially active

A

near deltas (massive sediment deposits at the mouths of rivers)

79
Q

what was the Grand Banks case study about

A

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
Q

why was this the most severe damage regarding the Grand Banks case study

A

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
Q

what was ridiculous about the La Conchita landslide

A

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
Q

what was a giveaway that the slope in La Conchita was NOT stable

A

the daylighting beds - bedding planes that were almost parallel to the slope that have become mostly VISIBLE to the outside of the slope

83
Q

what was the Vaiont Dam case study about

A

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
Q

what is NOT a good prevention of mass movements

A

cut and fill
- cutting into a slope to fill the indent with earth to build on

85
Q

what is beneficial to have on slopes to prevent mass wasting

A

surface drainage to PREVENT water from being absorbed into the soil and waterlogging it

86
Q

what is the benches approach to mass wasting prevention

A

changing the slope by pushing the top BACK and NOT filling it (like in cut and fill)

87
Q

what is the ABSOLUTE BEST method for mass wasting prevention

A
  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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