Plate Tectonics

Question 1

Continental drift

Answer 1

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

Question 2

Evidence for continental drift

Answer 2

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

Question 3

Paleomagnetism

Answer 3

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.

Question 4

Constructive margin landforms

Answer 4

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.

Question 5

Destructive plate margins

Answer 5

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.

Question 6

Intrusive volcanic activity

Answer 6

Beneath the surface

Forms large magma chambers and magma forced into crust

Question 7

Extrusive volcanic activity

Answer 7

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

Question 8

Intrusive volcanic activity landforms

Answer 8

Dykes
Sills
Batholiths

Question 9

Dykes

Answer 9

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

Question 10

Sills

Answer 10

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

Question 11

Batholiths

Answer 11

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.

Question 12

Joints

Answer 12

Cracks in the magma formed from when the magma cools.

Question 13

Basaltic/basic lava

Answer 13

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

Question 14

Andesitic/intermediate lava

Answer 14

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.

Question 15

Rhyolitic/acidic lava

Answer 15

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

Question 16

Types of volcanoes- shape

Answer 16

Dome
Composite
Caldera
Shield
Fissure

Question 17

Dome volcano

Answer 17

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

Destructive margins
Rhyolitic/andesitic lava

Question 18

Composite volcano

Answer 18

Same to dome except:

Alternating layers of lava and ash/cinder.

Question 19

Caldera volcano

Answer 19

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

Question 20

Shield volcano

Answer 20

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

Constructive margins
Basaltic lava

Question 21

Fissure volcano

Answer 21

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

Question 22

Hot springs

Answer 22

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

Question 23

Geysers

Answer 23

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.

Question 24

Boiling mud pools

Answer 24

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

Question 25

Hotspots

Answer 25

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.

Question 26

Earthquake causes

Answer 26

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

Question 27

Tree main types of seismic waves

Answer 27

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

Question 28

Seismometers

Answer 28

Measure amount of energy released (magnitude). | Measure duration and direction of vibrations.

Question 29

Richter scale

Answer 29

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

Question 30

Merchalli scale

Answer 30

``` Measure impacts. Using observations. 1-12 scale. 1 felt only by instruments. 12 complete destruction. ```

Question 31

Tsunamis

Answer 31

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.

Question 32

What determines the impact of an earthquake

Answer 32

- 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

Question 33

What determines the impact of an earthquake | Landscape ad rock type

Answer 33

soil: liquefied during earthquake (Japan 1995) rock: granite - won't liquefy topography: low lying = more damage from tsunamis mountainous = landslides block roads

Question 34

What determines the impact of an earthquake | Time of day and day of week

Answer 34

``` 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 ```

Question 35

What determines the impact of an earthquake | Weather and season

Answer 35

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

Question 36

What determines the impact of an earthquake | Urban or rural area

Answer 36

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

Question 37

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

Answer 37

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

Question 38

What determines the impact of an earthquake | Economic Development of Location

Answer 38

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