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A2 Geography > Plate Tectonics > Flashcards

Plate Tectonics Flashcards

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1
Q

Continental drift

A

Alfred Wegener, 1912, meteorologist.
All continents joined to form supercontinent Pangaea.
Had geological evidence but no evidence to support mechanism of moving continents.

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2
Q

Evidence for continental drift

A

Geology - S. America and S. Africa
Fossil records - Glossopteris, Meseosaurus (fresh water animal)
Climatology - past climates were similar but now 1000 miles apart
Paleomagnetism - earths magnetic field, reverse polarity = sea floor spreading

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3
Q

Paleomagnetism

A

Polarity changes every 200,000 years or so.
Magma erupts - magnetic minerals align - cool and fix.
So alternating magnetic strips along sea floor - crust is older further away from mid ocean ridge - plates moving apart.

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4
Q

Constructive margin landforms

A

Mid-ocean ridge e.g. Mid-Atlantic Ridge. Underwater volcanoes erupt along these ridges and can build up to surface e.g. Iceland.

Rift Valley e.g. African Rift Valley.

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5
Q

Destructive plate margins

A

O-C: oceanic subducts = deep sea trench e.g. Chile trench. Fold mountains.

O-O: denser one subducts =deep sea trench, earthquakes and eruptions. Underwater eruptions = island arcs e.g. Mariana islands.

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6
Q

Intrusive volcanic activity

A

Beneath the surface

Forms large magma chambers and magma forced into crust

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7
Q

Extrusive volcanic activity

A

On surface
Major form is eruptions
Minor forms: hot springs, geysers, boiling mud

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8
Q

Intrusive volcanic activity landforms

A

Dykes
Sills
Batholiths

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9
Q

Dykes

A

Where the magma has flowed into cracks in the crust and cools vertically.
Discordant to strata.

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10
Q

Sills

A

When magma flows into gaps in crust and cools between layers of rock (horizontal).
Concordant to strata.

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11
Q

Batholiths

A

When large chambers of magma cool underground they form domes of igneous rock.

E.g. Dartmoor batholith spreading across south west England. 309 million years old.

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12
Q

Joints

A

Cracks in the magma formed from when the magma cools.

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13
Q

Basaltic/basic lava

A

At constructive margins.
Low silica content.
Low viscosity/runny - gases escape easily.
Over 950C temp.
Effusive eruption, frequent, long duration.

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14
Q

Andesitic/intermediate lava

A 
Destructive margins.
Medium silica content.
Medium viscosity.
750-950C temp.
More explosive, more gases (don't escape easily).
Pressure can build from trapped lava.
Intermittent and short-lived.
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15
Q

Rhyolitic/acidic lava

A 
Destructive margins.
High silica content.
Very viscous.
Less than 750C temp.
Lots of pressure - gas and trapped lava. 
Very violent.
Intermittent and short-lived.
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16
Q

Types of volcanoes- shape

A 
Dome
Composite
Caldera
Shield
Fissure
17
Q

Dome volcano

A

Central vent.
Layers of lava.
Steep sides from v viscous lava that flows short distances.

Destructive margins
Rhyolitic/andesitic lava

18
Q

Composite volcano

A

Same to dome except:

Alternating layers of lava and ash/cinder.

19
Q

Caldera volcano

A

Layers of lava or lava/ash/cinders.
Central part of volcano collapsed as magma chamber below emptied.
Wide, circular crater, can be several km across.

Destructive margins
Andesitic/rhyolitic lava

20
Q

Shield volcano

A

Layers of lava
Central vent
Gently sloping sides cause by runny lava flowing long distances

Constructive margins
Basaltic lava

21
Q

Fissure volcano

A

Layers of lava
Long, linear vent, few metres wide but several km long
Fairly flat surface due to runny lava that flows long distances

Constructive margins
Basaltic lava

22
Q

Hot springs

A

Where groundwater emerges at surface.
Close to intrusive volcanic activity.
Temps from 20-90C.
High mineral content as hot water can hold more dissolved solids.

E.g. Blue Lagoon

23
Q

Geysers

A

Type of hot spring - hot water and steam ejected from surface. Near intense intrusive volcanic activity.
Groundwater heated above boiling point by magma deep in crust.
Hot water becomes pressurised, forces its way to surface along cracks in the rocks.
Sprays out of a vent - periodically.

E.g. Stokkur, Iceland.

24
Q

Boiling mud pools

A

Type of hot spring.
Form in areas with fine-grain soil - mixes with water = boiling mud pool.
Can be brightly colourd due to minerals (iron and sulfur rich - purple, orange, yellow).

E.g. Iceland and Yellowstone National Park

25
Q

Hotspots

A

Caused by a magma plume that rises up from the mantle.
Volcano forms.
Magma plume does not move but plate does, new volcanoes form = chain of islands e.g. Hawaii.

26
Q

Earthquake causes

A

Tension

Jerking movement sends out seismic waves from focus through to epicentre.

27
Q

Tree main types of seismic waves

A

Body:
Primary waves- compressional, through solids and liquids, fastest

Secondary waves- move 90degree to wave direction, through solids not liquids

Surface: slower
Love- through solids, move side to side, damaging due to shearing effect

Rayleigh- through solids and liquids, move in rolling motion

28
Q

Seismometers

A

Measure amount of energy released (magnitude).

Measure duration and direction of vibrations.

29
Q

Richter scale

A

Measures magnitude.
Logarithmic (each level of magnitude increases by x10).
No upper limit.
Each value increases by x30 for strength.

30
Q

Merchalli scale

A 
Measure impacts.
Using observations.
1-12 scale.
1 felt only by instruments.
12 complete destruction.
31
Q

Tsunamis

A

Convection currents cause plates to move (reverse or thrust fault)
Which displaces the water upwards causing a large wave
In deep water the tsunami moves very fast (800km/hr)
As the wave gets to shallow land, it slows but increases in height.
This is because there is friction at the bottom of the wave against the sand, but no friction at the top so it grows.

32
Q

What determines the impact of an earthquake

A
  • distance from epicentre (power dec further away)
  • landscape and rock type
  • time of day and day of week
  • weather and season
  • urban or rural area
  • emergency services and response plans
  • economic development of location
33
Q

What determines the impact of an earthquake

Landscape ad rock type

A

soil: liquefied during earthquake (Japan 1995)
rock: granite - won’t liquefy

topography:
low lying = more damage from tsunamis
mountainous = landslides block roads

34
Q

What determines the impact of an earthquake

Time of day and day of week

A 
Time: 
night: in bed = safer
day: in town so more vulnerable
Day:
working: more vulnerable in urban area
weekend: home = safer
San Fran 1989: 5pm = few died
Japan 1995: 7000 buildings destroyed, 300 fires
35
Q

What determines the impact of an earthquake

Weather and season

A

bad: hampers rescue efforts
cold: vulnerable - frost bite. hypothermia
warm: spread disease faster, speeds up decomposition, hygiene problems

36
Q

What determines the impact of an earthquake

Urban or rural area

A

Rural: small pop density, less affected, fewer issues
Urban: high pop density, more impacts/vulnerable

San Fran 1989: millions dollars damage
Middle of Alaska: almost 0 affected

37
Q

What determines the impact of an earthquake Emergency Services and Response Plans

A

More developed: plans and drills, swift, organised, prompt
e.g. Japan/CA: millions dollars spent

Less developed: can’t afford plans
e.g. Gujarat, India 2001: no plans, education but no money for it

38
Q

What determines the impact of an earthquake

Economic Development of Location

A

MEDCs: money to building design to withstand earthquakes (rubber pads - shock absorbers, deep foundations, built on hard rock and spread out), plans and drills, stores of medicine, saved money, food, shelter, self reliant
e.g. Kobe, Japan 1995: 7.2 quake killed 5000 / Turkey 1999, smaller quake and killed 17,000

LEDCs: can’t afford structured buildings, plans and supplies (rely on international aid), LEDCs not close to help/resources

A2 Geography (4 decks)

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