GEO TECTONICS > PHYSICIAL TECTONIC PROCESSES > Flashcards

PHYSICIAL TECTONIC PROCESSES Flashcards

(43 cards)

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1
Q

What is an intra plate earthquake

A

Middle of plates e.g. Rhine Rift Valley

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2
Q

What is a hotspot

A

Upwelling of hot molten material from the core e.g. Hawaii
OR from the top of a large mantle plume e.g. Cape Verde

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3
Q

What is mantle convection?

A

Heat radiating outwards from the inner core.
Peridotite Mantle under pressure and behaves like liquid
Frictional Drag

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4
Q

Evidence for mantle convection

A

Rayleigh Benard theory

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5
Q

What is slab pull?

A

The gravitational force exerted by a sinking, subducting oceanic plate that drags the rest of the plate down into the mantle.

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6
Q

What is ridge push?

A

The force created by the height of mid-ocean ridges, where newly formed, hot crust slides away under gravity, pushing plates outward.

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7
Q

What is subduction?

A

The process where a denser oceanic plate sinks beneath a lighter continental or oceanic plate into the mantle at a destructive plate boundary.

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8
Q

Example of mantle plumes

A

Under West Africa may have caused the Atlantic Ocean and Iceland to form with the creation of the Mid-Atlantic Ridge

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9
Q

CRUST: oceanic 7km thick, continental 70km
1. Temperature
2. Density
3. Composition
4. State
5. Seismic Waves

A
  1. 400 degrees
  2. Less dense
  3. Continental = Granite,
    Oceanic = basalt
  4. Solid
  5. Surface & body waves able to pass through
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10
Q

MANTLE 700 - 2890km deep:
1. Temperature
2. Density
3. Composition
4. State
5. Seismic Waves

A
  1. 870 degrees
  2. Medium density
  3. Peridotite
  4. phases of liquid & solid in layers
  5. Body waves pass through at variable rates due to density changes
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11
Q

OUTER CORE 2890 - 5159km deep:
1. Temperature
2. Density
3. Composition
4. State
5. Seismic Waves

A
  1. 4400 - 6100 degrees
  2. Dense
  3. 12% sulphur, 88% iron
  4. Liquid & generates magnetic field
  5. Only P waves able to pass through
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12
Q

INNER CORE: 5150km deep
1. Temperature
2. Density
3. Composition
4. State
5. Seismic Waves

A
  1. 7000 degrees
  2. Very dense
  3. 20% nickel, 80% iron
  4. Solid & generates heat
  5. Only P waves
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13
Q

What is a Wadati-Benioff Zone?

A

A zone of earthquake foci that occurs along a subducting oceanic plate as it descends into the mantle beneath another plate at a destructive plate boundary.

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14
Q

Early evidence for plate tectonic theory

A

Continental fit (South America + Africa).

Fossils (Cynognathus, Glossopteris).

Glacial + coal evidence in opposite climates.

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15
Q

Later discoveries for plate tectonic theory

A

Wadati-Benioff zones show subduction (up to 700 km deep).

Palaeomagnetism – symmetrical magnetic stripes at mid-ocean ridges → sea-floor spreading.

Polar wandering – continents drifted from Pangaea.

Hot spots (e.g. Hawaii) show plate movement (7 cm/year).

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16
Q

What is sea floor spreading?

A

new oceanic crust is created at mid-ocean ridges as magma rises, cools, and solidifies, causing the ocean floor to gradually move away from the ridge and widening the ocean basin.
e.g. The mid atlantic ridge, eurasian & north american plate moving apart

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17
Q

What is paleomagnetism

A
  • liquid iron outer core convects
  • creates magnetic field for earth
  • direction changes every 100 000 yr
  • when new igneous rocks cool to form solids, they trap magnetic field direction of the time
  • geological records are symmetrical either side of constructive plate boundaries, proving the oceanic crust has been diverging in places for a very long time
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18
Q

FEATURES & PROCESSES OF DESTRUCTIVE PLATE BOUNDARY

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A
  • trench
  • accretion wedge
  • fold mountains
  • continental volcanoes
  • earthquakes along Benioff zone
  • batholiths
  • subduction w slab pull
  • friction along benioff zone
  • melting of crustal material
  • unstable mantle material melting & forcing way to surface
19
Q

FEATURES & PROCESSES OF CONSTRUCTIVE PLATE BOUNDARY

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A
  • Rifting, fissures, faults, undersea ridges, sub marine volcanic activity, volcanic islands
  • Decompression w magma rising, ridge push
20
Q

FEATURES & PROCESSES OF COLLISION PLATE BOUNDARY

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A
  • Fold mountains, faulting, shallow earthquakes
  • Uplift & subduction w slab pull
21
Q

FEATURES & PROCESSES OF TRANSFORM PLATE BOUNDARY

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A
  • major & minor fault lines & frequent earthquakes
  • friction between two plates
22
Q

(P) Primary waves

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A
  • arrives first
  • fast
  • moves through solid rock and fluids
  • compresses in direction of travel
23
Q

(S) Secondary waves

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A
  • slower than P waves
  • only moves through solid rock
  • up and down movement
  • most damaging of body waves due to high amplitude & slow speed
24
Q

(L) Love waves

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A
  • Only travels through the surface of the crust
  • fastest of the surface waves
  • moves from side to side ( horizontal)
  • Arrives after s & p Waves
25
PRIMARY HAZARD: Crustal fracturing
Shockwaves travel fast through solid rock and can increase stress in it esp if rock types are different - as waves travel at different speeds through them - Stress can cause strain until rock fracture CAUSES FAULTS can rupture surface -> uplift -> damage
26
PRIMARY HAZARD: Ground Shaking
Pushing & Pulling - P waves Up & down - S waves Side to side - L waves buildings that arent aseismic may only survive some types of shaking and will be damaged If buildings have same resonance as seismic energy, impact is intensified
27
SECONDARY HAZARD: Liquefaction
Occurs when shock waves travel through loose unconsolidated material, shaking it so it acts like a fluid e.g. Christchurch 2011 Causes buildings to tilt over or collapse & ground to crack. Underground infrastructure may be ruptured
28
SECONDARY HAZARD: Landslides
Occurs when there are steep slopes and shockwaves loosen rock and cause it to move downslope under gravity e.g. Kashmir 2005 Landslides may hit settlements or block transport & comms
29
ASH FALLS
- forced to a high altitude, so light that they can be carried round planet in atmosphere - lot of ash can fall locally causing roofs to collapse - gets into machinary & eletronics causing them to fail - ash clouds disrupt flight paths of aeroplanes as it damages engines
30
PYROCLASTIC FLOWS
- Dense mixture of superheated solid particles (tephra) & poisonous gases moving at a great speed - buildings / people destroyed thru impact, burying, incineration or poisoning - Deposition of material may also block river chanels -> floods
31
GAS ERUPTIONS
E.g. WATER VAPOUR: - may condense locally & mix w other erupted material E.g. SULPHUR DIOXIDE: - poisonous, acid rain -> damage - may cool earth, blockss suns heat - crop failure and famine
32
LAVA FLOWS
Molten magma erupted from volcanoes flows down sides til it cools. - basaltic lava flows fastest - constructions cannot be moved in time
33
LAHARS
- Mix of water & volcanic material - Major hazard along valleys (usually where settlements and people located. - moves quick over long distances (difficult to escape)
34
JOKULHLAUPS
Volcano erupts under an ice cap, heat melts some of ice Meltwater builds up around top of volcano, lifts ice off ground and flows to lower ground rapidly Anything in path is washed away or covered by volcanic & glacial deposits
35
FEATURES OF TSUNAMIS
- sequence of waves of varying heights - 1960 chile tsunami at hawaii 3rd wave did most damage - long wavelength in open ocean but short in shallow water - very fast speed in deep water but slower in shallow - low heigh in ocean ocean but significant height in shallow water (20x)
36
CAUSES OF TSUNAMIS
Undersea earthquake at a subduction zone may cause a rapid movement of the seabed. Column of water above epicentre is displaced creating wave OR - violent explosive eruptions of volcanic islands - major landslides or volcanic cone collapse into sea - underwater landslides at the edge of continental shelves
37
TSUNAMI CASE STUDY: - Location - movement - deaths - damage x2 - Tsunami intensity scale - reached where 8.5 hours later?
GREAT EAST JAPAN EARTHQUAKE & TSUNAMI: Tohoku 2011 - Undersea earthquake at junction of plates. Ruptures along Benioff zone. Magnitude 9 - 35m vertical uplift, 50m horizontal movement displaced water column - 18500 people killed - $220 billion & damage of nuclear plants (Fukushima) - Category VI (highest) - Hawaiii
38
What is a natural hazard?
natural event that causes a disruption to daily lives or death and destruction
39
What is a disaster?
scale of impact of a natural hazard are great. UN suggests 500+ deaths or millions of $ damage
40
What is a mega disaster?
over 2000 deaths, GDP reduction of 5% or more
41
The San andreas fault: good or bad?
GOOD: - trapped oil allowing for 700 000 barrels a day -> worth $100 billion annually - agriculturally highly productive - tourist destination BAD: Every 100 - 150 yrs a major quake hits Cali, creating up to $250 billion in damages
42
Rayleigh waves (R)
Surface waves rolling motion vertical & horizontal movement moderate damage
43
GEO TECTONICS
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