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geog 198 > Gravity-driven Natural Exogenous Processes > Flashcards

Gravity-driven Natural Exogenous Processes Flashcards

1
Q
  • All downhill rock and soil movement due to gravity
  • can range from small roadside slides to a full mountain being set in movement
  • In gravity events, the size of debris can range from few mm to several km
  • In mixtures of water and debris, even the smallest material fraction plays an important role in the events
A

Mass Wasting/Gravity-driven Natural Exogenous Processes

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2
Q

a set of processes that smooths the Earth surface (against the endogenous forces) mostly driven by water (on, in the ground), atmospheric processes, and gravity

A

Erosion

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3
Q

FACTORS AFFECTING MAGNITUDE

A

FREQUENCY
VELOCITY AND ENERGY
SLOPE ANGLE/MATERIAL/WATER CONTENT
FAHRBOSCHUNG ANGLE

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4
Q
  • Energy > mass
  • Emphasis on the speed
  • Causes casualties, quickly modifies natural and built environment
A

Rapid-onset hazards

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5
Q
  • Mass > energy
  • Emphasis on the deformation
  • More of a concern on infrastructure
A

Slow-onset hazards

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6
Q

___causes mass movements in earthquake-induced acceleration and on sliding blocks with faults or cracks in between

A

Water

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7
Q

Source of water:

A

intense rainfall, snowmelts, groundwater level modification

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8
Q

Water has a role in increasing mass of sliding unit by replacing ____by water in the soil

A

weightless air

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9
Q

Reduced slope stability due to decrease in ____ (between soil particles)
More water in soil pores makes the soil more susceptible to sliding

A

shear resistance

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10
Q

the heavier mass movement is, the lower the ______

A

Fahrboschung angle

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11
Q

2 criteria that classify mass movement

A
  • type of movement
  • material involved
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12
Q

Occurrence ranges from frequent small-scale (small rock falls, scree) and infrequent large-scale (debris avalanche, large bedrock deformation)

A

Mass Movement in Rocks and Bedrocks

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13
Q

Properties of Mass Movement

A

Intact Rock - Uniaxial Compressive Strength (UCS)

Discontinuity - A mechanical break that occurs from natural or anthropogenic processes.

Slope Control - For Strong Rocks (>25 MPa): Mainly controlled by discontinuities.

SID

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14
Q

Characteristics of Mass Movement

A

Volume and Velocity
Activity
Progressive Failure
Runout

(VAPR)

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15
Q

Types of Mass Movement in Rocks and Bedrocks

A

Rockfalls
Rockslides
Rock Spreads
Rock Avalanches
Rock Topple
Sackungen

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16
Q
  • Weathering > Detachment > Freefall
  • Individual rocks don’t interact
  • Common during rainy and ice thawing
A

Rockfalls

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17
Q
  • Extremely rapid velocities
  • Wide range of volume
  • Can escalate into Rock Avalanches
  • Result of slope failures
    Planar: strata/bedding
    Circular: MPa
    Compound: deformation zone
A

Rockslides

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18
Q
  • Can be dynamic or static
  • Associated with slope deformation
A

Rock Spreads

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19
Q
  • Rapid fragmentation of intact rock during transport
  • At least >1 cubic megameter for overburden
  • Called a Debris Avalanche, if a volcanic cone collapses
A

Rock Avalanches

20
Q

Toppling: falls over if the center of gravity is not at its base

A

Rock Topple

21
Q

Also known as DSGSD, Deep-seated gravitational slope deformation

Slow to very slow slope deformation

Intact Rock Failures: Weak Rocks (weather and discontinuity) and Hard Rocks (rupture of intact rocks)

A

Sackungen

22
Q

Movement along one discontinuity

A

Planar Sliding

23
Q

Movement along two discontinuities

A

Wedge Sliding:

24
Q

Bulk movement of soil and rock debris down slope in response to the pull of gravity; predominantly vertical in direction

  • can be shallow or deep seated events.
  • Short term modification of landforms
A

Mass Movement in Soil

25
Q

Weathering Agents Key Concepts

A

Capacity
Competence
Water

26
Q

how much mass it can carry

A

Capacity

27
Q

how big is the largest grain size it can carry

A

Competence

28
Q

principal weathering agent

A

Water

29
Q

Types of events in mass movement of soils

A

Shallow
Large

30
Q

Concerned with the first few meters of the subsurface. Dominated by soil flows, solifluction, earth creep, earth flows, spreads

A

Shallow

31
Q
  • Sector collapses, deep-seated landslides

Deep-seated landslides: can destroy a valley and human settlements in seconds

A

Large

32
Q

Types of landslides

A

Translational landslide
Rotational landslide

33
Q
  • A landslide translating on a planar rupture surface, which moves downward in a relatively homogeneous way.
  • Occurs in a distinctive planar surface (BGS).
  • Common along rivers (erosion of slope’s toe can destabilize)
  • Can be slow (velocity - less than a meter per year) or rapid (seconds to minutes)
  • Possible triggers: Seismic activity, intense rainfall water accumulation between sliding mass and substratum (more impermeable)
A

Translational landslide

34
Q
  • A landslide for which the surface of rupture is curved upward along a spoon-shaped surface on which the landslide rotates whilst sliding.
  • Upper surface of the displaced material may tilt backwards toward the scarp (BGS)
  • Slopes: 20-40 degrees Velocity: can be very slow (0.3 m/year) to several meters per months, can be different speeds during its lifetime with phases of acceleration and speed decrease
  • Occurs in soils through deformation of media (wet saturating of soil after intense/sustained rainfalls, rapid snowmelt, earthquakes)
A

Rotational landslide

35
Q

Kinds of soil mass wasting

A

Earthflow
Creep
Debris Flow
Earthflow

36
Q

Flows often leave behind a distinctive, upside-down funnel shaped deposit where the landslide material has stopped moving.

Movements in fine-grained soil

A

Earthflow

37
Q

Slowest form of mass wasting

Allows soil to conserve elements in the original structure.

Plastic flow.

Generates micro-landforms, steps, ridges perpendicular to slope direction

A

Creep

38
Q
  • Complex lateral movement of relatively coherent earth materials resting on a weaker substrate that is subject to liquefaction or plastic flow
  • Occur as the result of liquefaction caused by water saturation or earthquake shock in such substrates as loess, a weakly cemented wind-lain silt. Ridges perpendicular to slope direction

Extension of material - causes cracks to appear
- Material spreads apart
Blocks slide and subside due to the movement
- Occurs during earthquakes along rivers (riverbanks slide inward into the river and generates spread)

A

Spread

39
Q

Closer to the boundary with waterborne hazards and flood phenomenon (very complex categorization) but within landslide family.

Highly unpredictable hazard: can carry large debris (creates important damages away from its source)

Most mobile hazards

Ex.
Lahar - Climate change raises frequency and magnitude, increases issue for mountain food and plain settlements (located near sediment-rich slopes)

A

Debris flow

40
Q

TRIGGER MECHANISMS

A

Triggering of mass movement in soil is mostly attributed to physical characteristics of soils and rocks + temporally limited trigger

Seismic triggers

Phase relationships of soils: combinations of solid particles

Fluvial factors: Water is the principal weathering agent
Rainfall liquefaction

41
Q

Spatial movement

A

Initiation zone
Transport zone
Deposition zone

42
Q

Hazard Analysis

A

main triggers of mass movement:
soil and rock characteristics
temporally limited trigger

methods, instruments vary based on the scale hazard

43
Q

Not possible to instrument every site
Similar datasets (groundwater, geology, geomorphology, rainfall patterns) are used
Inference + data combination as extrapolation for local site research

A

regional scale

44
Q

scope of analysis: local scale

A

presence of features that indicate landslide movement

zones of extension: cracking

Zones of compression: bulking

45
Q

Preparation/Methods

A

Hazard Mapping
Landslide Warning Signs
Benching, Retaining Wall, Riprap, Gabion Walls, Shotcrete, Drainage, Erosion-Control (Coconet and Vetiver Grass) and Early Warning Systems

46
Q

give 1 case study

A

Bedrock Movement: Debris Avalanche in Naga City

Soil Movement: Debris Flowing New Bataan, Compostela Valley

geog 198 (4 decks)

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