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Geography-Tectonics > Tectonic-EQ1 > Flashcards

Tectonic-EQ1 Flashcards

1
Q

What 4 processes is plate movement driven by?

A

-Mantle Convection
-Seafloor Spreading
-Subduction
-Seafloor Spreading

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2
Q

What is Mantle Convection?

A

Heat produced by radioactive decay in the core heats the lower mantle, creating convection currents within the atmosphere, causing plate movements.

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3
Q

What is Seafloor Spreading?

A

A process that occurs at mid-ocean ridges, where new oceanic crust is formed through volcanic activity and then gradually moves away from the ridge.

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4
Q

What is Subduction?

A

As two plates move towards each other, one slides into the ,mantle in a subduction zone.

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5
Q

What is Slab Pull?

A

Newly formed oceanic material at mid ocean ridges becomes denser and thicker as it cools, causing it to sink into the mantle, pulling the plate down.

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6
Q

What is the historical evidence for the plate tectonic theory?

A

Wegener’s Continental Drift Theory (1915)

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7
Q

Why was Wegner’s Theory not accepted by the scientific community?

A

As it could not explain what caused plates to move and the plates don’t move through oceans.

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8
Q

What are some examples of historical evidence that we can see and study today?

A

Fossils, Glaciers and Mountain Ranges.

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9
Q

Historical Evidence-WW1

A

It is found that there are geologic features on the ocean floor. It is not flat and featureless as originally thought-discovered by ships using sonar.

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10
Q

Historical Evidence-1919

A

Arthur Holmes develops a theory that may explain how the plates actually move via convection currents in the mantle.

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11
Q

Historical Evidence-1946

A

The ocean floor is mapped to reveal ridges, mountains, volcanoes and trenches. This is done again through the use of military equipment.

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12
Q

Historical Evidence-1954

A

A world map of volcanic eruptions and earthquake epicentres reveals a world-wide pattern.

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13
Q

Historical Evidence-1960

A

Hess and Dietz develop the theory of sea-floor spreading. Molten rock oozes up from the Earth’s interior along mid-ocean ridges, creating new seafloor. Also in 1960’ the discovery of the atmosphere, a weak, deformable layer beneath the rigid lithosphere on which the lithosphere moves.

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14
Q

Historical Evidence-1963

A

Magnetic rock reveals a pattern of spreading away from the centre, away from the Atlantic Ocean. This is called palaeomagnetism.

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15
Q

Historical Evidence-1965

A

Wilson proposes the idea that Earth’s crust is made of giant chunks of rock, called plates as well as the recognition of transform faults.

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16
Q

Historical Evidence-1983

A

The first GPS is available for public use. Monitoring devices are placed around the world. Final conclusions that all of Earth’s surface is made of tectonic plates that move.

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17
Q

Historical Evidence-2000’s

A

Slab pull and Ridge Push. This was taken from Holmes’ theory.

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18
Q

What is Ridge Push?

A

Newly formed plates at oceanic ridges are warm, and so have a higher elevation at the oceanic ridge than the colder, more dense plate material further away ; gravity causes the higher -plate at the ridge to push away the lithosphere that lies further from the ridge.

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19
Q

What is Slab Pull?

A

Older, cooler plate sink at subduction zones because as they cool, they become more dense than the underlying mantle. The cooler sinking plate plus the rest of the warmer plate along behind it.

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20
Q

What does Degg’s Model Show?

A

Shows that a natural disaster only occurs if a vulnerable population is exposed to a hazard.

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21
Q

What is a Natural Hazard?

A

A naturally occurring processes or event that has the potential to affect people.

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22
Q

What is a Natural Disaster?

A

A major natural Hazard that causes significant socioeconomic and environmental damage.

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23
Q

What does vulnerability mean?

A

The ability to anticipate, cope with, and resist and recover from a natural hazard.

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24
Q

What is a Fracture Zone?

A

A belt of Activity.

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25
Q

What are the two types of fracture zones?

A

Oceanic and Continental.

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26
Q

Where is the Ring of fire and and how many earthquakes are found there?

A

In the Pacific Ocean, 70% of all earthquakes.

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27
Q

What are the most powerful earthquakes associated with?

A

Convergent and Conservative plate boundaries.

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28
Q

What is an Intra plate earthquake?

A

An earthquake that occurs within the interior of a tectonic plate, as opposed to it’s edges.

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29
Q

What is an Oceanic Fracture Zone? (OFZ)

A

A belt of activity through the oceans along the mid-ocean ridges, coming ashore in Africa, the Red Sea, the Dead Sea Rift and California.

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30
Q

What is an Continental Fracture Zone? (CFZ)

A

A belt of activity following the mountain range from Spain, via the alps, to the middle east, the Himalayas to the East Indies and then circumscribing the Pacific.

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31
Q

What is the first physical reason for a communities vulnerability?

A

Tectonic Setting of the location which affects the likely magnitude and frequency of the tectonic event.

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32
Q

What is the second physical reason for a communities vulnerability?

A

90% of all tsunami are recorded in the Pacific Ocean making communities in this religion more vulnerable than communities situated on the other seaboards.

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33
Q

What is the third physical reason for a communities vulnerability?

A

The frequency of tectonic events are however also important as the more frequent the event the higher the vulnerability.

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34
Q

In short, what are the decade volcanoes?

A

16 volcanoes were identified by IAVCEI as being worthy of particular study in light of the history of large, destructive eruptions and proximity to densely populated areas.

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35
Q

What are the 3 possibilities for a convergent (destructive) plate boundary?

A

-Oceanic meets continental
-Oceanic meets oceanic
-Continental meets continental

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36
Q

What happens when a oceanic meets a continental plate?

A

-Oceanic plate is denser than continental so when they collide, the oceanic subducts under the continental plate into the mantle and melts.
-Deep Ocean Trenches mark the place where the oceanic plate starts to sink beneath the continental plate.
-Formation of fold mountains and since the plates are constantly pushing towards each other the fold mountains will continue to grow.
-Benioff Zone is created due to the friction which is created between the colliding plates which causes intermediate and deep earthquakes in this area.

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37
Q

What happens when a oceanic meets a oceanic plate?

A

-One plate (denser or faster) is subducted beneath the other. Deep Ocean trenches also occur and the subducted plate melts- creating magma which rises from the Benioff Zone to form underwater volcanoes.
-Over years these rise above sea level to form separate island volcanoes which are usually found in curved lines called Island Arcs. Also produces shallow to deep focus earthquakes .

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38
Q

What happens when a continental meets a continental plate?

A

-A Collision Margin occurs . As both plates have around the same density and are less dense than the asthenosphere beneath them, neither plate subducts.
-They collide instead and sediments between them are crumpled and forced up to form high fold mountains.
-However, there can be some subduction which is caused when the compressed sediments result in plate subduction beneath them.
-No Volcanic Activity but any earthquakes are likely to have a shallow focus.

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39
Q

What happens at a constructive plate boundary?

A

-Plates are moving apart (diverging)-leads to formation of new crust.
-In Oceans it forms mid-ocean ridges and on continental it forms rift valleys.

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40
Q

What are the characteristics of Mid-Ocean Ridges?

A

-Extend for over 60,000 km
-Breaks called transform faults occur as the ridges spread at different rates.
-Shallow focus earthquakes (5-6 magnitude)
-No Volcanic Activity
-Plates sometimes stick causing pressure to build and when it is released it causes an earthquake.

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41
Q

What is a Rift Valley?

A

Formed on Continental and on parallel cracks (faults) land between collapses creating steep valleys.

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42
Q

What are Transform Faults?

A

-Can create submarine volcanoes
-Some grow to sea level and form new islands, Effusive Eruption (Low VEI scale 1-3)
-High heat flow
-Young Basaltic Rock
-Symmetrical Magnetic Anomalies (Stripes) in oceanic crustal rock.

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43
Q

What is a Conservative Plate Boundary?

A

-Two plates slide past each other
-Results in a major break (fault) in the crust between them as they move.
-When this major break (fault) occurs on a large scale it’s known as a transform fault.
-No crust is made or destroyed (no volcanic activity) but is very tectonically active and can be associated with powerful earthquakes.
-The two plates sometimes stick together as they move past, causing stress and pressure to build up. This is released as a strong shallow-focus earthquake.

44
Q

What is a Volcanic Hotspot?

A

They are situated amongst the centre of plates. This is a localised area of the lithosphere which has an unusually high temperature due to the upwelling of hot molten material from the core. RING OF FIRE

45
Q

What is the first step in the formation of earthquakes?

A

The movements are preceded by a gradual build-up of tectonic strain which stores elastic energy in crustal rocks.

46
Q

What is the second step in the formation of earthquakes?

A

When the pressure exceeds the strength of the fault, the rock fractures. (Rock Faults)

47
Q

What is the third step in the formation of earthquakes?

A

This produces the sudden release of energy, creating seismic waves that radiate away from the point of fracture.

48
Q

What is the forth step in the formation of earthquakes?

A

The brittle crust then rebounds either side of the fracture, which is the ground shaking, that is, the earthquake felt on the surface.

49
Q

What is the fifth step in the formation of earthquakes?

A

The point inside the crust from which the pressure is released is called the focus or hypocentre. The point on the surface directly above is called the epicentre.

50
Q

How are Seismic Waves measured?

A

Using a seismometer, which detects and measures ground movements.

51
Q

What are Seismic Waves?

A

The release of earths energy which radiate out from the focus.

52
Q

What are the 3 main type of Seismic waves?

A

Primary, Secondary and Love.

53
Q

What are Primary Waves?

A

-Body Waves
-Fastest and first to reach the surface.
-Travel through both solids and liquids.
-Shake in a back and forth motion
-Only damaging in the most powerful earthquakes.

54
Q

What are Secondary Waves?

A

-Body Waves
-Slower (60% the speed of S waves).
-Only travel through solids.
-Move with a sideways motion, shaking at right angles to the direction of travel).
-Do more damage than P waves.

55
Q

What are Love Waves?

A

-Surface Waves
-Slowest and last to arrive.
-Cause the most damage.
-Shake ground from side to side.
-Are larger and focus all their energy on the Earth’s surface.

56
Q

What two characteristics are used in measuring earthquakes?

A

Magnitude and Intensity

57
Q

What is the main scale used to measure magnitude?

A

Moment Magnitude Scale

58
Q

Why is the Moment Magnitude Scale preferred?

A

It’s accurate and better at measuring large earthquakes

59
Q

What does the Moment Magnitude Scale measure?

A

The total energy released at the moment it occurs using the:
-Size of seismic waves
-Amount of slippage or rock movement
-Area of the fault surface broken by the earthquake.
-Resistance of the affected rocks.

60
Q

How does the Moment Magnitude Scale work?

A

The scale goes from 1(smallest) to infinite but generally stops at 10. It is a logarithmic scale (each number is 10 times the magnitude than the number before). Mag 5 is x10 more powerful than mag 4.

61
Q

What s meant by an earthquakes intensity?

A

An earthquake’s effect on people, structures and the natural environment.

62
Q

What scale is used to measure and Earthquakes intensity?

A

Modified Mercalli Intensity Scale.

63
Q

How does the Modified Mercalli Intensity Scale work?

A

It takes observations from people who experienced the earthquake and rates them on a scale of I (hardly noticeable) to X (catastrophic).

64
Q

What does an earthquakes impact depend on?

A

A range of factors including Primary and Secondary, Human and Physical.

65
Q

What are the Human Factors associated with earthquakes?

A

-Country’s level of development
-Population (size, age, health)
-Level of preparedness
-Effectiveness of emergency responses
-Impact of indirect hazards on the population (fire)

66
Q

What are the Physical Factors associated with earthquakes?

A

-Magnitude and depth
-Distance from epicentre
-Physical landscape (near coast)

67
Q

What are Primary Hazards?

A

Those that happen as a direct result of an earthquake.

68
Q

What are Secondary Hazards?

A

Side effects on an earthquake.

69
Q

What are Primary Hazards associated with earthquakes?

A

-Crustal fracturing
-Ground Shaking

70
Q

What are Secondary Hazards associated with earthquakes?

A

-Tsunami
-Liquefaction-the violent shaking during an earthquake causes surface rocks to lose strength and become more liquid than solid. The subsoil loses its ability to support building foundations.
-Landslide/Avalanches

71
Q

How are volcanoes structured?

A

-Volcanoes are openings in the earth crust through which lava, gas and ash erupt.
-Like earthquakes they are associated with certain plate margins.
-As tectonic plates move, pressure builds up and hot magma and gases push up from the mantle to the earth’s crust and erupt.
-When magma reaches the earth’s surface it’s called lava. When lava cools, it forms rock so as volcanoes erupt over time they get bigger.

72
Q

What are the two types of Volcanoes?

A

Composite and Shield.

73
Q

Where are Composite Volcanoes found and how explosive are they?

A

Violently Explosive, Convergent (Destructive) plate boundaries

74
Q

Where are Shield Volcanoes found and how explosive are they?

A

Non Explosive, Divergent (Constructive) plate boundaries

75
Q

What are Composite Volcanoes made out of?

A

Felsic to intermediate rock.

76
Q

Why are Composite Volcanoes so explosive?

A

The viscosity of the lava.

77
Q

What creates the steep sides of the volcano?

A

The viscous lava cannot travel far down the sides of the volcano before it solidifies.

78
Q

What does viscosity change about some explosions?

A

Can cause some eruptions to explode as ash and small rocks.

79
Q

How are composite volcanoes constructed?

A

Layer by layer, as ash and lava solidify, one upon the other.

80
Q

What is the shape of a composite volcano?

A

Classic Cone shape, tall, symmetrical with steep sides.

81
Q

What are some examples of Composite volcanoes?

A

Mount Fuji, Mount Lassen.

82
Q

What is the shape of shield volcanoes?

A

Not steep but they may be very large.

83
Q

Where are shield volcanoes common at?

A

Spreading centres or intraplate hot spots

84
Q

What type of lava is produced by shield volcanoes?

A

Fluid and flows easily.

85
Q

What creates the shield shape of these volcanoes?

A

The spreading lava.

86
Q

How are shield volcanoes formed?

A

Built by many layers over time and the layers are usually of very similar composition.

87
Q

Why are shield volcanoes non-explosive?

A

As they have low viscosity.

88
Q

What are the two other types of volcanoes?

A

Cinder Cones and Super volcanoes

89
Q

What are cinder cones?

A

-Most common type of volcano. Cone shape but much smaller than a composite volcano. Steep sides but rarely reach 300m in height.
-Cinder cones grow rapidly, usually from a single eruption.
-Composed of small fragments of soft rock, such as pumice, piled on top of one another. The rock shoots up in the air and doesn’t fall far from the vent. The exact composition depends on the composition of the lava ejected from the volcano. Usually there is a crater at the summit.

90
Q

What are super volcanoes?

A

-Extremely rare in Earth history.
-Unimaginably large. Must erupt more than 1,000 cubic km of material compared with 1.2 km cubed from Mount St. Helens
-Most dangerous type

91
Q

What are the 3 types of magma?

A

Basalt, Andesite, Rhyolite

92
Q

What is Basalt magma and it’s characteristics?

A

-Black to dark grey
-80% of earth’s surface volume
-1000 -1200 degrees
-Low viscosity
-Peaceful eruption

93
Q

What is Andesite magma and it’s characteristics?

A

-Medium to dark grey
-10% of earths surface volume
-800 to 1000 degrees
-Intermediate viscosity
-Intermediate eruption

94
Q

What is Rhyolite magma and it’s characteristics?

A

-Light coloured
-10% of earths surface volume
-600 to 900 degrees
-High viscosity
-Explosive eruption

95
Q

What are the human impacts associated with volcanoes?

A

-Country’s level of development
-Population (size,age,health)
-Level of preparedness
-Effectiveness of emergency responses
-Warning Systems in place

96
Q

What are the physical factors associated with volcanoes?

A

-Area ash, lava and pyroclastic flow cover
-Distance from volcano
-Physical landscape (near coast) / on ice

97
Q

What are the primary hazards associated with volcanoes?

A

-Lava flows
-Pyroclastic flows
-Tephra(fragmental material) and Ash falls
-Gas eruptions

98
Q

What are the secondary hazards associated with volcanoes?

A

-Lahars-Volcanic mudflows which occur when rainfall mobilises volcanic ash. They travel at high speed down rivers and cause major destruction.
-Jökulhlaup-Devastating floods are caused when volcanoes erupt beneath glaciers and ice caps, creating a huge volume of meltwater. Common in Iceland.

99
Q

What are Benioff Zones?

A

They are dipping roughly planar zones of increased earthquake activity produced by the interaction of a down going oceanic crustal plate with an overriding continental or oceanic plate.

100
Q

Where do Benioff Zones occur?

A

At boundaries of crustal plates called subduction zones.

101
Q

How does an Earthquake generate a Tsunami?

A

Tsunami’s are a major secondary hazard because of the potential destructive ability and the spatial area they cover.

102
Q

How can the earthquakes be produced in the Benioff Zones?

A

By slip along the subduction thrust fall or by slip on faults within the down going plate, as a result of bending and extension as the plate is pulled into the mantle.

103
Q

What 3 things must happen for a tsunami to happen?

A

-Earthquake at least 7.0 on Richter Scale
-Sea bed must be lifted or lowered by the earthquake.
-The focus of the earthquake near the earth’s surface

104
Q

What are the tsunami characteristics?

A

-Move through the entire depth of the ocean.
-Can move through entire ocean floors.
-Move at great speeds with lots of energy.
-Speed depends on the depth of the water.
-When it enters shallow water, it slows down but it gets larger in height.
-The deeper water the higher the speed.

105
Q

What is the global distribution of tsunamis? And why is it fairly predictable?

A

Fairly predictable in terms of source areas; around 90% of all events occur in the Pacific Basin, associated with the activity of plate margins. Most are generated at subduction zones particularly off the Japan-Taiwan arc, South America and Aleutian Islands

Geography-Tectonics (4 decks)

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