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OCR A LEVEL GEOLOGY > Geohazards and Risk > Flashcards

Geohazards and Risk Flashcards

1
Q

What is a crown hole?

A

-Due to mining such as gypsum mining in Yorkshire
-Heavy rainfall falls into these voids and enlarges them
-Increase in size, holds more water, more solution until roof collapses

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2
Q

What are sink holes?

A

-Result from the natural dissolution of bed rock
-Usually happens in chalk/limestone where the rain acidity dissolves the rock
-Creates a funnel shaped depression

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3
Q

What are limestone sink holes?

A

(aka dolines) ore swallow holes
-if a river enters into the ground where carboniferous limestone is present (in the peak district)

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4
Q

How can salts such as halite and gypsum create subsidence?

A

Are prone to in situ solution, so when they are dissolved it will cause movement

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5
Q

What responses can be done to reduce subsidence?

A

-Avoiding Karst terrain
-Attention to drainage
-Reinforced raft foundations
-Refill with granite chippings
-Traditional ground surveys
-Satellite radar imaging
-Old maps/records
-Avoid

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6
Q

What are 10 types of mass movements?

A
  1. Rotational landslide
  2. Translational landslide
  3. Block slide
  4. Rockfall
  5. Topple
  6. Debris flow
  7. Debris avalanche
  8. Earthflow
  9. Creep
  10. Lateral spread
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7
Q

What are the slowest types of mass movement?

A

Fastest at the top, slowest at the bottom

  1. Rockfall
  2. Mud and debris flow
  3. Landslides and slumps
  4. soil creep
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8
Q

What is the difference between a landslide and rotational landslide?

A

Have a curved bottom instead of a straight bedding plane

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9
Q

What are 2 properties of rotational landslides?

A
  1. Talus - debris accumulated at the foot of a slope
  2. Translational slide - material begins to move as an entity, usually breaks up as it gathers speed and energy increases.
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10
Q

What is tsunamite?

A

a sedimentary unit deposited as the result of a tsunami.

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11
Q

What are ways to stabilise slopes?

A
  1. Slope modification - Angle is reduced
  2. Retaining wall - to support the sides of road cuttings
  3. Gabions - Wire mesh with rocks at the bottom of a slope to prevent slumping
  4. Rock bolts - steel rods are drilled and cemented
  5. Rock drains - Used to drain water to stop failure
  6. Shotcrete - Concrete is sprayed onto a rock surface to increase strength
  7. Vegetation - Plants fix soil in place and reduce infiltration of water
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12
Q

What were the Storegga Slides?

A

-Landslide off the Norwegian coast possibly due to methane hydrates
-81,000 years ago
-Sea level was 10-15m lower than the body
-The tsunamite deposit are 9m above the current sea level
-Meaning it was 20m
-Deposits contained rip-up clasts, sand layers, redeposited sediments and diatoms

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13
Q

What is liquefaction?

A

-When saturated, unconsolidated sediment loses strength and rigidity when under stress, acts as a liquid, but will only happen when water is present.

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14
Q

What are flow failures?

A

-Displace large masses of soil for many meters

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15
Q

What is lateral spread?

A

-Displace large blocks of soil down gentle slopes due to liquefaction underneath

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16
Q

What is ground oscillation?

A

-Happens when liquefaction at depth causes overlying soil to separate taking from of ground waves, accompanied by opening and closing of fissures

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17
Q

What is Mercalli’s scale?

A

-Scale from 1-12
-Based on damage
-Intensity
-Plot isoseismic lines but will not be circular
-But problems consist of mis-reporting and variations in building quality

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18
Q

How are buildings designed to withstand earthquakes?

A

PDBASS
Planning - Avoid wet areas and slopes
Design - Wood/steel frames, flex better than bricks; use strong foundations
Base location - Rollers, rubber pads, springs
Absorb sway - Rubber, silicone, hydraulic rams
Shear forces - Connect walls to floors; use diagonal bracing, no soft layers in building
Services - Flexible piping

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19
Q

What is the focus of an earthquake?

A

The point where the earthquake occurs and the energy is emitted from

20
Q

What is the epicentre of an earthquake?

A

The point on the surface above the ground of the focus

21
Q

What is amplitude?

A

The maximum extent of an oscillation, measured from the position of rest

22
Q

What is magnitude?

A

The amplitude/energy of an earthquake

23
Q

What is attenuation?

A

loss of energy of a wave as it passes through a material (the rate)

24
Q

What is the difference between rigid and unconsolidated rock?

A

rigid rocks have a low attenuation, unconsolidated rocks have a high attenuation as wave hits more particles causing friction

25
Q

What are 9 ways to predict earthquakes?

A
  1. Seismic gap theory -A computer model showed that stress is transferred to another place, where the next earthquake should happen.
  2. Detailed measurement of gases - Increases in fluctuation in radon gas when earthquakes are about to happen
    3.Stress in rocks - measured using strain gauges
  3. Water levels - will change before earthquakes
  4. Ground level - will tilt or rise, use tiltmeters and GPS
  5. Changes in P-Wave velocity
  6. Changes in electrical
  7. Patterns of foreshocks and aftershocks
  8. Strange animal behaviour
26
Q

What is the moment?

A

-Turning effect of a force around a pivot
-Real earthquakes are complex to measure because of fault geometry, measuring displacement gives a better idea of relative earthquake size
-The sum of rotational movements at a fault is the “seismic moment”

27
Q

What are seismic warnings?

A

A warning that alerts people to an event which has started. Once an earthquake occurs, it creates movement in the crust, which sets off seismographs that identifies the focus and strength of the earthquake that will then be used to evacuate people.

28
Q

What elements are clays rich in?

A

Hydrous aluminium phyllosilicates

29
Q

What are the four clay groups?

A
  1. Kaolin - Serpentine group
  2. Smectite group
  3. Vermiculite group
  4. Mica group
30
Q

Give facts about the kaolin-serpentine group

A

-An example is kaolinite
-Non-expanding, low shrink-swell capacity
-Ceramic, porcelain
-Used as filler eg paint, rubber and plastics

31
Q

What layering order does the kaolin-serpentine group have?

A

1:1 layering (TOTOTOT)

32
Q

Give facts about the smectite group?

A

An example is Montmorillonite
Expanding, high-shrink swell capacity
Used in drilling “mud”, protective liners, catalyst, fillers

33
Q

What layering does the smectite group have?

A

2:1 layering (TOTTOTTOT)

34
Q

Give facts about the Vermiculite group

A

An example is vermiculite
Limited expansion, medium shrink-swell capacity
When heated, expands to low-density
Used for insulation, packing material, gardening, cat litter

35
Q

What layering does the Vermiculite group have?

A

2:1 layering (TOTTOTTOT)

36
Q

Give facts about the Mica group

A

An example is illite
Muscovite, biotite
Non-expanding, low-shrink-swell capacity
Used in ceramics, store ware and fillers

37
Q

What layering does the Mica group have?

A

2:1 layering (TOTTOTTOT)

38
Q

What clay group has the highest shrink swell capacity?

A
  1. Smectite
  2. Vermiculite
  3. Mica and Kaolin-serpentine group
39
Q

What is the formula for tetrahedra sheets (T)

A

Si2O3(OH)2

40
Q

What is the formula for octahedral sheet (O)

A

Al2(OH)6

41
Q

In the Kaolin group, why has it got a low shrink-swell capacity?

A

-Strong bonding between the sheets
-No water can get between them
-So low plasticity, swelling and shrinking
-Doesn’t expand in contact with water

42
Q

In the smectite group, why has it got a high shrink-swell capacity?

A

-Weakly bonded between sheets
-Water molecules can enter the spaces between the sheets
-High cohesion
-High plasticity

43
Q

How can clays cause a geohazard?

A

Buildings in the UK on clay deposits (usually glacial) will swell and shrink when it rains, which causes stress on structures, subsidence of roads, tilting of buildings, and affects on water transportation

44
Q

How is the geohazard of clays mitigated?

A

-Desk study (BGS (Superficial geology map” that can be used when planning where to build)
-Site investigation
-Deeper foundations
-“raft construction” for buildings (for marshy/unstable ground)
-Avoid variations of geology (ei half on clay half off)
-Keeping clays under a building dry or saturated (change in these is what causes movement)
-Avoid “edge effect
-“French drains” are gravel filled trenches round the outside the edge of a house to transport water away
-Under-pinning, adding foundations across the corners of a building

45
Q

How does the chemical mitigation of the clays reduce the change of a geohazard?

A

-Treatment with lime, expansion of Na-Smectite is 1500%, calcium-smectite is 100%
-Bacteria to reduce Fe3+ to Fe2+ which decreases smectites tendency to swell

OCR A LEVEL GEOLOGY (12 decks)

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