Chapter 07: Mass Wasting Flashcards Preview

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Flashcards in Chapter 07: Mass Wasting Deck (13)
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1
Q

Mass wasting

A

General process of Earth materials moving downslope due only to gravity

2
Q

Trigger mechanisms (5)

A

Processes or events that reduce friction and/or increase effect of gravity

  1. Nature of material (some are more cohesive/stables, others not)
  2. Oversteepened slopes
  3. Water content (unsatured v. saturated)
  4. Loss of vegetation (e.g. wildfires)
  5. Earthquakes/volcanic activity (vibrations)
3
Q

Angle of repose

A

Steepest stable slope allowed by a loose material

35° is generally the steepest stable slope for loose material

4
Q

Planar surfaces and stability

A

Planar surfaces: bedding planes, faults, fractures, foliation

Such surfaces represent weaknesses within rocks that can greatly reduce slope stability (dangerous when inclined in same direction as slope)

5
Q

Fragment shapes and stability

A

Angular fragments have more frictional resistance than round fragments

6
Q

Oversteepened slopes

A

Naturally:
Formed by meandering/migrating streams that form the cutback/overhang combination; overhang eventually mass wastes

Manmade:
Leveling terrain for human activity (e.g. roads)

7
Q

Poor pressure

A

Pressure of groundwater held within a soil or rock; pressure increases as pores retain more water (from increased rainfall or snow melt)

8
Q

Adhesive force

A

Force keeping material together; in underground material, small amounts of water (water film) keep material together, but being saturated with water causes a loss of friction

9
Q

Frost wedging

A

Liquid water freezes, expands gaps in rock’s planar weakness (e.g. fractures, foliation, bedding), causing material to fall

10
Q

Risk management of mass wasting (6)

A
  1. Build retaining walls
  2. Drain excess moisture
  3. Terracing (building terrace steps/benches for gradual fall of material
  4. Covering steep slopes
  5. Re-grade slopes
  6. Plant anchor vegetation
11
Q

Land subsidence

A

Process of land either gradually lowering in elevation or suddenly falling after gradual removal of subsurface material

Subsurface ground failure

Natural: e.g. dissolution

Man-made:

  1. Withdrawal of fluids (water, petroleum)
  2. Withdrawal (mining) of solids (salts, minerals, rocks)
12
Q

Karst topography

A

Land with pock marks (sink holes, sinking streams) with caves underneath and collapsed sinks

13
Q

Sinkholes

A

Collapse of land due to subsurface failure with unusually large void spaces

Subsurface cavitites (caves) formed by groundwater dissolving rock; caves were filled with water, helped support weight of surface land. Once cavities are empty, sudden collapse occurs, forming sinkholes.