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🌄 > Topic 1b - Tectonics > Flashcards

Topic 1b - Tectonics Flashcards

1
Q

Describe the crust

A
  • thinnest layer
  • made of silicon-based rocks
  • it has 2 types of crust: Oceanic and Continental
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2
Q

What is Oceanic crust like?

A
  • thin - 5 to 8km
  • made of basaltic rock
  • denser than continental crust
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3
Q

What is continental crust like?

A
  • thick - 30 to 40 km
  • can reach 70km under mountain ranges
  • lighter than oceanic crust
  • made of granatic rock mostly
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4
Q

Describe the core

A
  • hot and very dense
  • inner core is a ball of solid
  • outer core is a liquid made of iron and nickel
  • temp bw 4400-6000*
  • under high Pa so can’t melt
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5
Q

Describe the mantle

A
  • thickest layer of Earth - 2900km
  • temp bw 1000 to 3700
  • upper mantle = mostly solid but some melting at plate boundaries and flows very slowly
  • mantle becomes more depth with depth and high pa
  • the very top bit of mantle is rigid and nearest to the core is rigid
    made of silicon-based rocks
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6
Q

What is the upper mantle divided into?

A
  • Lithosphere

- Asthenosphere

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7
Q

Describe the lithosphere:

A
  • includes the crust and top layer of the upper mantle
  • made of peridotite
  • about 800-1000km
  • broken into tectonic plates
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8
Q

Describe the asthenosphere:

A
  • denser mobile layer of the upper part of the mantle
  • 100-300km deep
  • high temp = 1300*
  • Pa is low enough so that the rocks can flow very slowly
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9
Q

What do tectonic plates float on?

A

on the mantle

- asthenosphere

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10
Q

How is heat generated in the mantle?

A

Through the radioactive decay of some elements in the mantle such as uranium

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11
Q

How do convection currents form?

A
  • lower part of asthenosphere heat up, they become less dense and rise
  • move towards the top, cool down and become more dense = sink
  • circular movements of semi-molten rock create convection currents
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12
Q

Why do the tectonic plates move due to convection currents?

A
  • convection currents create drag at the base of the tectonic plate as they are solid and rigid
  • this causes them to move and creates earthquakes and volcano formation
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13
Q

What are the 3 types of plate boundaries?

A
  • convergent
  • divergent
  • conservative
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14
Q

Describe convergent plate boundaries:

A
  • plates move towards each other
  • oceanic + continental plate = subduction and creates trenches and forms composite volcanoes
  • cont + cont plate = collide and form mountains/ major earthquakes as high Pa = rocks snap along faults
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15
Q

What is subduction?

A
  • when denser oceanic plate sinks under continental plate into the asthenosphere
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16
Q

How do composite volcanoes form?

A
  • oceanic plate subduction = more temp and Pa released water and impurities into asthenosphere = which melts into the molten rock
  • magma rises and breaks through the Earth’s surface as a composite volcano
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17
Q

Describe divergent plate boundaries:

A
  • move apart from each other
  • mostly under oceans
  • plates break part = more heat and less Pa = sheild volcanoes
  • very small earthquakes = if any
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18
Q

How do shield volcanoes form?

A
  • plates breaking apart = high heat and low Pa = causes asthenosphere to melt - magma rises to fil in the gap/rift valley between the plates
  • this cools to form new oceanic lithosphere but this may break through Earth’s surface = shield volcanoes
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19
Q

Give an example of where convergent plates are found?

A
  • West Coast and South Africa
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20
Q

Give an example of where divergent plates are found?

A
  • North American and African Plate
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21
Q

Describe conservative plate boundaries:

A
  • slide past each other
  • plates may move in same/ opp directions at diff speed and angles
  • crust not created or destroyed
  • Pa along the boundary builds up until one jerks = earthquakes
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22
Q

Give an example of where conservative plates are found?

A
  • North American and Caribbean plate moving opp
  • North American and Pacific Plate moving in the same direction
  • West coast of USA
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23
Q

What are the volcanic hazards associated with convergent plates?

A
  • subduction = melts and destroys mantle
  • pool of magma forms and rises through the cracks in the vents
  • magma erupts on the surface forming a volcano-
24
Q

What are the volcanic hazards associated with divergent plates?

A
  • magma rises up into the gap and forms a volcano
25
Q

What comes out in a volcanic eruption?

A
  • lava
  • gases
  • ash formed (can cover the land, block out the sun and form pyroclastic flows)
26
Q

What are hotspots?

A
  • where volcanoes form at not between plate boundaries
27
Q

How are hotspots formed?

A
  • formed by a plume of superheated rock/magma rising very slowly through the mantle
  • causes asthenosphere and base of lithosphere to melt
  • magma produced rises through crust’s weakness and erupts at earth’s surface
28
Q

How do hotspots form chains of volcanic islands?

A
  • hotspots are stationary but the crust above them moves to create chains of volcanic islands
  • e.g. Hawaii - in the middle of the Pacific Ocean
29
Q

What type of eruption happens in oceanic hotspots?

A
  • erupts basaltic lava

- creates shield volcanoes

30
Q

What type of eruption happens in continental hotspots?

A
  • erupts viscous granitic lava

- this may erupt explosively

31
Q

Where are composite volcanoes formed?

A
  • formed alongside convergent plate boundaries
32
Q

What do composite volcanoes look like?

A
  • steep-sided cones rising up several thousand km
33
Q

Why are composite volcanoes so eruptive?

A
  • subducted oceanic crust has water which reacts with magma and creates gases causing the crust to erupt = explosive
  • start with ashy explosions that deposit layers of ash
  • then erupt andesitic lava with high silica content, making it viscous so it flows slowly and travels a short distance before cooling
34
Q

When do composite volcanoes erupt?

A
  • infrequent but violent
35
Q

What are the primary and secondary hazards after an eruption from a composite volcano?

A

primary
- vent is blocked with solidified lava = build-up of Pa in next eruption
- lava may shatter into pieces = lava bombs
- hot flows of gas and ash (pyroclastic flows) hazard
secondary
- more deaths may be caused by mudflows (lahars)

36
Q

Where are shield volcanoes formed?

A
  • over hotspots and divergent plate boundaries

- not very explosive and made up only of lava (erupt from fissures and the crater)

37
Q

What do shield volcanoes look like?

A
  • low gentle sloping domes with a wide base
38
Q

Why are shield volcanoes not eruptive?

A
  • erupt basaltic lava which has low silica content so are runny and flows a long distance before cooling
  • frequent but not explosive eruptions
39
Q

What are the primary hazards after an eruption from a shield volcano?

A
  • basaltic flows destroy property and crops but loves are rarely ost
40
Q

What are the earthquake hazards associated with convergent boundaries?

A
  • most occur here

- tension builds up when one plate gets stuck as its move past another into the mantle

41
Q

What are the earthquake hazards associated with divergent boundaries?

A
  • tension builds up along the cracks as they move past
42
Q

What are the earthquake hazards associated with conservative boundaries?

A
  • tension builds up when plates that are grinding past each other get stuck
  • plates eventually jerk past each other = shock waves are sent out (vibrations) = earthquake
43
Q

How are earthquakes measured?

A
  • moment magnitude scale (Mw)
  • it measures the amount of energy released
  • also a seismometer
44
Q

What is the focus?

A
  • where it started below the Earth’s surface

- can be up to 700km below

45
Q

What is the shallow focus?

A
  • caused by tectonic plates moving at or near the surface

- focus is around 0-70 km

46
Q

What is the deep focus?

A
  • caused by a crust that has been subducted into the mantle

- focus is around 70-700 km

47
Q

What is the epicentre?

A
  • the point on the ground surface directly above the focus
48
Q

Why do deeper earthquakes create less damage?

A
  • less damage at the surface

- this is as shock waves travel through more rocks so thus they have less power when they reach the surface

49
Q

How do earthquakes cause tsunamis?

A
  • underwater earthquakes cause the seabed to move
  • the water is displaced and waves spread out from the epicentre
    • waves travel very fast in deep water and cab hit the shore without much warning = high death toll
50
Q

Why do shallow focus earthquakes create bigger tsunamis?

A
  • they can displace more water
  • thus stronger and more powerful waves hitting the shore
  • even higher death toll than deep focus
51
Q

How can earthquakes be predicted?

A

not reliable but scientists can monitor signs:

  • lasers detect movement of tectonic plates
  • vibrations in Earth’s crust can be measured by seismometers (more vib = earthquake)
  • gases measured (radon) - escapes from cracks in the crust before the earthquake (Eq)
  • rocks crack and expand due to more Pa before eq
52
Q

How can volcanic eruptions be predicted?

A

can be told if they’re well monitored:

  • tiny earthquakes and changes in shape of a volcano (bulges in the land where magma built up under)
  • thermal imaging camera - detects change in temp
  • analyse gases escaping as they emit lots of sulfurous gases before an eruption
53
Q

What long term planning can we do to prepare for tectonic hazards?

A

more dev countries = plan for impacts

  • emergency services train and prepare for disasters
  • buildings designed to withstand earthquakes
  • educating people
  • gov can plan evacuation routes = fewer people killed by mudflows, fires and pyroclastic flows
  • emergency supplies
54
Q

How can buildings be designed to prepare for tectonic hazards?

A
  • reinforced concrete

- foundations that absorb earthquake’s energy

55
Q

What emergency supplies can be stockpiled to help prepare for tectonic hazards?

A
  • blankets
  • clean water and canned food
  • these stockpiles can be moved close to areas that are less likely to be affected
56
Q

What short term relief is needed right after a disaster?

A

deals with immediate impacts of tectonic hazards so more dev countries can:
- provide food, drink and shelter to help evacuated people
- treat injured people = fewer deaths
- recover dead bodies = prevents diseases spreading
= rescue trapped people or people cut off by damage to roads and buildings
- provide temp supplies of gas, electricity, and communication if regular supplies damaged

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