Plate tectonics

Plate boundary – where plates meet

Tectonic plate – section of earth’s crust

Earth structure

• Crust – thin, rocky
• Mantle – molten rock

– upper: lithosphere, lower: asthenosphere

• Outer core – liquid nickel & iron
• Inner core – solid nickel & iron

Crust – 7 large plates & 12 smaller plates

• Oceanic crust – thin, dense, young
• Continental crust – thick light, old

Plate tectonics (movement of plates)

Suggest where new oceanic plate is formed – at mid-ocean ridge

Suggest how new oceanic plate is formed – magma rises to surface, cools down & solidifies

Suggest why oceanic plate moves – Convection currents cause circular movement of magma within mantle, which causes plates to move

Destructive	Oceanic plate subducted under continental plate Eg Indo-Australian & Eurasian plate
Conservative	2 plates slide past each other Eg North American & Caribbean plate
Constructive	2 plates move away from each other Eg North American & Eurasian plate
Collision	2 continental plates move towards each other Eg Indo-Australian and Eurasian Plate Continental plates same dense, crumple upwards Form folded mountains (eg Himalayas)

Earthquake

Focus – point underground where earthquake starts

Epicentre – point on surface directly above focus

Seismic waves – wave which travels within earth

Magnitude – amount of energy released

Describe relationship between earthquakes & plate boundaries

• On plate boundaries
• Some away from boundaries

Hazards

Buildings collapse, fire

Cause

1. Plates collide / a plate subducts under another plate
2. Plates get stuck
3. Fault line formed
4. Pressure builds up due to fraction
5. Pressure too big, plates jerk apart
6. Pressure released
7. Seismic waves within earth in all directions, cause ground shaking
8. Plates move to new positions
9. Aftershock occurs

Measurement (Richter scale)

• measures magnitude of earthquakes
• Scale 0-12

Opportunities

• Employment in tourist industry eg tourist guides

• Fertile soils → high crop yield
• Extract raw materials eg gold
• Family & friends live in the areas
• Can’t afford to move
• Confident in protection methods

Preparation

• Build earthquake-proof buildings
• Train emergency services
• Set up warning system
• Create evacuation routes
• Practice earthquake drills

Earthquake proof buildings

• Rubber shock-absorbers between foundations
• Deeper foundations
• Shatterproof glass
• Pyramid shape
• Open areas for evacuation

Extinct volcano – will not erupt again

Variation in deaths – some area more densely populated, better prepared, time of day

Case study – Haitian earthquake

 

Where?	West of capital Port-au-Prince (1million ppl)
When?	Jan 2010
Magnitude	7 (high)
Focus	10km deep (shallow)
Cause	North American & Caribbean plate (conservation) Plate stuck for 200 years
Hazards	Ground shaking 50s Aftershock magnitude 6
Impacts	230000ppl killed, 300000ppl injured 50% of buildings in Port-au-Prince damaged Eg gov buildings (Presidential Palace) 5 million ppl displaced Loss of electricity / communications Roads damaged Disrupt businesses (cost $14 billion) Loss of jobs

Volcano

Types

Stratovolcano	Shield volcano
Steep sides Narrow base Alternative layers of ash & lava Small crater More explosive	Gentle sides Wide base Made of lava Large crater Less explosive

Causes

Destructive	Constructive
Plates move towards each other & converge due to convection current Oceanic plate is denser & subducts under continental plate Plate sinks into hot mantle & melt → form magma Build up of manga increases pressure Magma forced upward through cracks in crust Lava cools down & form new crust	Plate move apart due to convection current Gap created Magma rises to reach surface

Opportunities – geothermal power, hot springs, (same as earthquakes)

Hazards

• Lava flows – flow down volcano sides
• Lahars – mudflows – destroy roads and settlements, people evaluate
• Ash cloud – ash around volcano – suffocation / gases – poisoned
• Pyroclastic flow – ash + lava + poisonous gas flow down volcano sides rapidly – killed by force / burning
• Volcanic bombs – killed by force
• Lateral blast – killed by force
• Post-eruption famine

Why it’s important to give warnings when volcano erupt (3)

• Ppl live nearby
• Danger to life
• Need to evacuate
• Road blocked
• Explosive eruption towards town

Why volcano change shape before erupt?

Pressure builds-up /magma/gas movement

Why volcano extinct? No magma supply coz far away from rising magma

Case study – Mount Sinabung, Indonesia

Where?	Northern Sumatra
When?	Main eruption in Feb 2014 Still show signs of being active
Cause	Indo-Australian subducted under Eurasian plate (destructive)
Impacts	16ppl died 14000ppl evacuated to temporary camps Crop damaged → loss £50000+ Ash caused air pollution Houses collapsed coz of heavy ash Ash & pyroclastic material poisoned Sumatra’s wildlife
Opportunities	Fertile soil & higher altitude → coffee (main source of income)