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Hazards > Theory of Plate Tectonics > Flashcards

Theory of Plate Tectonics Flashcards

1
Q

What are the characteristics of the core?

A
  • dense rock : iron, nickel ores (outer is molten, inner is solid)
  • temp 5000 degrees bc primordial + radiogenic heat
    (formation + radioactive decay)
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2
Q

What are the characteristics of the mantle?

A

molten + semi molten rock (silicon + o2)

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3
Q

What are the characteristics of the crust?

A
  • light elements
  • ocean 6-10km
    continents 30-40km
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4
Q

What is the lithosphere?

A

contains the crusts and upper section of the mantle.

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5
Q

What is the asthenosphere?

A

lies beneath lithosphere + semi-molten rock plates move on

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6
Q

Is continental crust or oceanic crust older?

A

continental is older (1500 million years and ocean 200 million)

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7
Q

What is continental drift and who made this theory?

A 
Alfred Wegner (1912)
gradual movement of the continents across the earth's surface
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8
Q

What geological evidence of the continental drift?

A
  • fit of S. america + W. africa

- rock sequences in scotland + E.canada suggests they were put under the same conditions at one point

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9
Q

What biological evidence of the continental drift?

A

Fossil from mesosaurus found in both s.america + s.africa.

indian limestone geology similiar to australias fossils

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10
Q

Where can Sea-floor spreading be found?

A

mid- atlantic ridge

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11
Q

What is the evidence for sea-floor spreading?

A
  • alternating polarity of rocks - lava solidifies leaving record of Earths polarity at time of eruption (palaeomagnetism)
  • striped pattern = earths crust is spreading away from he boundary.
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12
Q

How do convection currents work?

A

mantle heated from core = positive buoyancy (less dense + expands)
mantle closer to surface = cools (more dense) :. sinks back down.
currents pressure + heat can move the plate boundaries

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13
Q

What are ocean ridges and how are the formed?

A

plates move apart = space in between filled with basaltic lava. submarine volcanoes occur here e.g. Surtsey to the south of Iceland

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14
Q

What are rift valleys and how are they formed?

A

plate moves = crust drops between parallel faults to form the valley. area between this is the upstanding block (horst) e.g. Great Rift Valley , Kenya

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15
Q

How are deep sea trenches formed?

A

oceanic + conti meet (or sometimes both oceanic) = subduction forming trench e.g. Peru-Chile trench (coast of s.america) or Marianas trench (Pacific ocean)

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16
Q

How are island arcs formed?

A

As a lithospheric slab is being subducted, the slab melts when the edges reach a depth which is sufficiently hot. Hot, remelted material from the subducting slab rises and leaks into the crust (plutons of magma), forming a series of volcanoes. These volcanoes can make a chain of islands called an “island arc”.

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17
Q

How are young fold mountains forms?

A

2 continental plates meet = little subduction :. sediments forced up into mountains. (no volcanic activity) also some material forced downwards to form deep roots. (indo-australian plating moving towards Eurasian plate)

18
Q

What is ridge push?

A

(gravitational sliding) oceanic plates move away from the ridge =gravity acts down the slope from the ridge. Occurs at constructive plate boundaries where upwelling hot material generates - buoyancy effects that stand 2-3km above ocean floor. there is also frictional resistance to ridge push as shallow earthquakes occur.

19
Q

What is slab pull?

A

where older, denser tectonic plates sink into the mantle at subduction zones due to the - buoyancy effect. force between plates = frictional resistance = earthquakes

20
Q

where are volcanoes usually distributed?

A

ocean ridges, subduction zones, rift valleys, hot spots

21
Q

what are the primary effects of volcanic activity?

A

Tephra’s, pyroclastic flows, lava flows, volcanic gases ( co2, co, in 1986 emissions from lake Nyos Cameroon killed 1700 people.

22
Q

what are the secondary effects of volcanic activity?

A

lahars, flooding, landslides, tsunamis, acid rain, climate change

23
Q

what can be used to predict volcanoes?

A

monitoring land swelling, changes in groundwater levels, chemical composition of groundwater and gas emissions , shock waves by magma moving towards the surface breaking through other rocks

24
Q

what can be used to protect from volcanoes?

A

prepare for even e.g. evacuation systems, governments (e.g. new Zealand) making risk assessments and series of alert levels in order to warn public.

25
Q

what type of focuses are there?

A
  • shallow focus (0-70km)
  • intermediate focus (70-300km)
  • deep focus (300-700km)
26
Q

what is the Richter scale?

A

logarithmic scale 1-10. 1-3 = not felt but detected by seismographs. 9-10 = extreme earthquake causing major damage in a large region.

27
Q

what is the Mercalli scale?

A

scale of impacts, subjective, scale 1-13, I: not felt , XIII: damage total, waves seen on the ground surfaces, objects up in the air

28
Q

what is the moment magnitude scale?

A

record from seismographs , logarithmic scale (inspired by richter scale)

29
Q

primary effects of earthquakes?

A

ground shaking, ground rupture (visible breaking of ground surface)

30
Q

secondary effects of earthquakes?

A

soil liquefaction, landslides/avalanches, tsunamis, fires, effects on people + environment

31
Q

causes of tsunamis

A

volcanic eruptions, underwater debris slides, landslides, shallow underwater earthquakes

32
Q

characteristics of tsunamis in open ocean

A

long wavelength (sometimes over 100km) and low wave height (under 1m) + travel over 700km/h. when tsunami reach shallower water, height increases rapidly

33
Q

what is the first warning that a tsunami is about to occur?

A

wave trough in front of tsunami = reduction in sea levels (drawdown) = then tsunami comes (excess 25m high)

34
Q

when tsunami reaches land, the effects depend on…

A

height of waves + distance they travelled, length of event at source, the extent at which warnings are given, coastal geography, coastal land use and pop density

35
Q

facts about recent 2004 26th Dec tsunami Indian ocean

A

9.0 magnitude, 25km below Indian ocean floor off northwest Sumatra, killed 300,000 people, warning systems are now made in the Indian ocean, disaster damage costs $5 billion

36
Q

facts about recent July 2006 south java coast

A

7.7 magnitude 112miles offshore, damaged Panjandrum = 600 deaths

37
Q

facts about April Solomon islands

A

8.0 magnitude killed 15 people

38
Q

facts about march 2011 Tohoku region japan

A

occurred 70 km offshore 9.0 magnitude, 40m in height of wave+ 10km inland, 16000 deaths 6000 injured 2500 missing,. 300000 displaced from their homes, 127000 buildings destroyed, Fukushima nuclear power plant = people 20km radius had to evacuate. cost of damage = $30 billion + economic cost to japan = $235 billion

39
Q

predicting seismic hazards

A

regions that are at higher risk can be identified (destructive plate boundaries), study of pattern of events along the san Andrea fault between 1969 and 1988 indicated existence of the ‘seismic gap’ in an area of Loma Prieto (no seismic activity within the past 20 years)

40
Q

protecting seismic hazards in USA

A

In the USA, the Federal Emergency programme has objectives: promote understanding of earthquakes + effects, work to better identify earthquake risk, improve earthquake resistant design and construction techniques, use earthquake planning practices

41
Q

protecting seismic : hazard resistant structures

A

putting large concrete weight on top of building which will move in opposite direction of earthquake to counteract stress. putting rubber shock absorbers in the foundations which allow some movement in building. adding cross-bracing to structure to hold it together when it shakes

42
Q

protecting seismic : education

A

Japan sep 1st is disaster prevention day where they are educated about the supplies to have during an earthquake and also what to do

Hazards (2 decks)

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