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Geology > Test 3 (Lectures 9-12) Pt. 2 > Flashcards

Test 3 (Lectures 9-12) Pt. 2 Flashcards

1
Q

What is a mass movement (or mass wasting)?

A
  • Downslope motion of rock, soil, sediment, snow, and ice
  • Driven by gravity operating on any sloping surface
  • Characterized by a wide range of rates (fast to slow)
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2
Q

What does mass-wasting depend on?

A

It depends on slope stability

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3
Q

Slope stability is a balance between…

A

Stabilizing/resisting forces and driving forces

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4
Q

Slope stability is a balance between stabilizing/resisting forces and driving forces . What is the driving force in this scenario?

A

Gravity

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5
Q

Slope stability is a balance between stabilizing/resisting forces and driving forces. What is the stabilizing force in this scenario?

A

Friction; cohesion

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6
Q

What is the safety factor calculation?

A

Resisting forces/ driving forces

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7
Q

If the safety factor calculation comes upto a number HIGHER than 1 then the place is….?

A

Safe/ stable

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8
Q

If the safety factor calculation comes upto a number LESS than 1 then the place is…?

A

Unsafe

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9
Q

What is the angel of repose?

A

The angle where loose materials will lie without cascading down

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10
Q

What is the effect of water on stability?

A
  • Small amounts of water can increase the surface tension between grains
  • Large amounts of water can lubricate the gains, allowing them to flow much more easily
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11
Q

Infiltration of fluids can _____ the stability of the slope

A

Decrease

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12
Q

What are some ways that water can reduce slope strength?

A
  • Adds a great deal of weight
  • Water in pores pushes grains apart, easing disintegration
  • Water lubricates grain contacts
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13
Q

How do mass movements occur?

A
  • Changes in slope strength (such as weathering, forest fires)
  • Changes in characteristics that can destabilize a slope (such as undercutting a slope)
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14
Q

What are two different ways of undercutting?

A
  • Natural (i.e. a river eroding
    the base of a slope)
  • Human-induced (i.e.
    excavating the base of a
    slope)
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15
Q

Classification of mass movement are based upon four primary factors, what are they?

A
  1. Type of material (rock, regolith, snow, ice)
  2. The velocity of movement (fast, intermediate or slow)
  3. Amount of water present
  4. The type of movement.
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16
Q

What type of rock movement is generally considered the fastest?

A

Falls

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17
Q

What is a talus?

A

The pile of angular rock fragments that accumulates at the base of the slope

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18
Q

What is the difference between falls and flows?

A
  • Falls/Slides: moves more
    or less as a coherent unit
  • Flows: moves as if it were a
    fluid
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19
Q

What is a slide?

A

Shearing displacement between two masses of material (sliding) along a plane and with little deformation within the
sliding mass (stays as one cohesive piece)

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20
Q

What are the two different types of slides?

A
  • Curved - slump (slow)
  • Planar - rock/ debris slides (faster)
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21
Q

What is a flow?

A

Downslope movement of continuously internally deforming (mixing) material

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22
Q

What does a flow depend on?

A
  • Type of material
  • Water content
  • Velocity
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23
Q

What is the slowest type of mass movement?

A

Creep

24
Q

What are some ways to prevent mass movements?

A
  • Retaining Walls - prevent sediment transport and erosion
  • Rock bolts - holds things together
  • Controlling water - redirects water away. Installing pipes can also drain water
  • Terracing - creates a set of benches so the hills won’t be extremely parallel
  • Covering steep slopes - adding in vegetation, rocks, synthetic covering to increase frictional forces within the slope
  • Reducing slope materials
  • Adding in protective structures - retaining walls -diverts material away, debris trap - prevents large materials of debris from moving downslope, shelters - tunnels where the debris can flow above the road surface
25
Q

What is subsidence?

A

Sinking of the land surface,
resulting from the removal of subsurface support

26
Q

What can cause subsidence?

A
  • Withdrawal of fluids
  • Sinkholes from karst limestone
  • Underground mining
  • Clays (shrinking/swelling)
27
Q

What is an overland flow?

A

Precipitation moving downslope over the land surface

28
Q

What is a stream discharge?

A

Volume of water moving through the channel in a given time [ex. cubic feet per second (ft3/s)]

29
Q

What is a groundwater baseflow?

A

Groundwater that discharges to the surface

30
Q

What are the two different types of streams?

A
  • Permanent stream (Gaining) - water that is always there for year-around. Always at or below the water table
  • Losing (ephemeral) - dry up part of the year. Above the water table
31
Q

Discharge is….?

A

Amount of water flowing in a channel

32
Q

Is velocity uniform in a channel?

A

No

33
Q

What is a hydrograph?

A

A plot of discharge versus time

34
Q

What is a watershed?

A

The area of land that drains into a stream

35
Q

What do drainage divides do?

A

They separate drainage basins

36
Q

What do the sides look like in a younger stream?

A

They tend to have steeper sides

37
Q

What do the sides look like in a middle-aged stream?

A

They tend to have somewhat curved sides

38
Q

What do the sides look like in a old-aged stream?

A

They tend to have almost flat sides

39
Q

What does the area look like near the headwater?

A

Steep and straight

40
Q

What does the area look like near the mouth of the stream?

A

Flat and curved

41
Q

How do streams erode?

A
  • Scouring – water picks up and moves sediment
  • Breaking and lifting – rapidly moving water can:
    Break chunks of rock off the channel
    Lift rocks and sediment off the channel bottom
  • Abrasion – the “sandblasting” of rock by particles in fastmoving water
  • Dissolution – running water can dissolve soluble minerals
42
Q

What is a sediment load?

A

Material moved by running water

43
Q

What are three types of sediment load?

A
  • Dissolved
  • Suspended
  • Bed load
44
Q

How does decrease in water velocity affect sediment transport?

A
  • Competence reduced, sediment drops out
  • Boulders, then gravels, then sands fill channel bottoms
  • Sands form inside banks (point bars)
  • Silts and clays drape floodplains
45
Q

If you start to slow things down then the process from erosion changes to ……?

A

Deposition

46
Q

Looping streams are referred to as …..?

A

Meandering streams

47
Q

Where do meandering streams form?

A
  • They form where the stream gradient is low
  • The substrate is soft and easily eroded
  • The stream exists within a broad floodplain
48
Q

Oxbow lakes are formed from …?

A

Cutoff meanders

49
Q

What is the base level?

A

Lowest level to which a
stream can cut downward

50
Q

As streams approach their base level what happens to the stream gradient, meanders, and the floodplain?

A
  • Stream gradient decreases
  • Meanders get wider
  • Stream carves out a wider
    floodplain
51
Q

When does a delta form?

A

When a stream enters standing water

52
Q

Floods are triggered by different conditions such as :

A

Heavy rainfall
Snowmelt
Failure of dam or levy

53
Q

What are some different types of floods?

A
  • Flash floods
  • Downstream floods
  • Dam failure
54
Q

What is a recurrence interval?

A

The average number of years
between floods of a particular size

55
Q

What type of human activities can trigger flooding?

A
  • Removal of natural vegetation
  • Destruction of wetlands
  • Construction activity
  • Urbanization (Creation of large areas of impermeable surfaces to prevent infiltration (slow) and promote overland flow (fast))
56
Q

What structures can stop floods?

A
  • Flood walls
  • Dams
  • Artificial Levees
  • Channelization
  • Retention Basins
  • Erosion Controls
  • Wetlands Restoration
  • Floodplain Management
  • Education

Geology (19 decks)

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