Plate Tectonics Flashcards
Describe the structure of the earth
From centre:
Inner core - temp of around 5500°C
Outer core
Mantle - made up of molten rock (magma), heat from core sets up convection currents in the mantle, where these currents reach the surface they cause the plates above them to move
Crust- two types, oceanic and continental
Describe the different types of crust
Continental crust - is lighter, cannot sink and cannot be removed or destroyed (permanent)
Oceanic crust - is denser, can sink and is continually being removed and destroyed
Describe the distribution of earthquakes and volcanoes
Earthquakes and volcanoes occur in long lines and narrow bands. There is a band off the west coast of North and South America. There is also a long line across southern Europe and into Asia. There is another band of earthquakes and volcanoes surrounding the Pacific Ocean, which is known as the Pacific Ring of Fire
Describe what happens at a constructive (divergent) plate boundary
Convection currents move two plates apart and magma rises to fill the gap, causing volcanoes. The magma can easily escape at the surface, so the volcano doesn’t erupt with much force. There are also earthquakes. E.g. the Mid-Atlantic ridge.
Describe what happens at a destructive (convergent) plate boundary
Where a continental and oceanic plate meet. The oceanic plate subducts because it is denser. As the plate descends, it becomes magma, which rises through the gaps in the continental plate and if it reaches the surface, it becomes a volcano. E.g. where the Nazca and South American plates converge
Describe what happens at a collision plate boundary
Two plates of similar density collide causing the material (sediment) to buckle and rise up, forming fold mountains. E.g. the Himalayas rising approx 2 cm a year (African + Eurasian plates)
What happens at a conservative plate boundary (transform fault)
Two plates slide past each other but don’t directly collide. No volcanoes, but earthquakes do occur. Plates rub against each other and the friction causes earthquake. E.g. San Andreas fault in California, Pacific plate moving 6cm faster than North American plate
Describe the features of a shield volcano
- On constructive boundaries
- low silica content
- lava has low viscosity, runs easily for longer distances
- wide base, gentle sloping sides
- e.g. submarine volcanoes along Mid-Atlantic ridge
Describe the features of a composite cone volcano
On destructive plate boundaries (under great pressure)
- high silica content
- lava doesn’t run easily
- high viscosity
- steep sided symmetrical cone
- high with narrow base
- alternate layers of acid lava and ash
- very explosive eruption to remove plug from lava cooling
- e.g. Mt Etna
Describe the causes of the Chiaten volcanic eruption
- converging convection currents causes Nazca and South American plates to collide
- Nazca plate subducts under SA plate
- plate melts to magma
- magma rises under faults
- magma reaches surface, cools and forms a volcano
What was the background of the Chiaten eruption?
- 2nd May 2008
- dormant 9000 years
- Chiaten town, pop of 4,500, located 10km SW of volcano
- composite cone volcano, narrow base, steep sides
What were the short term impacts of the Chiaten eruption?
- people were evacuated by sea by the 8th May, one death
- ash contaminated grass land, livestock dead, farmer’s incomes decreased
- ground water contaminated by sulphur
- skin, eyes and lungs irritated by ash
- lahars destroyed buildings in the south and left a layer of ash 1m thick
- 10km^2 forest destroyed by pyroclastic flow
- eruption columns reached 15km, many airports affected
What were the long term effects of the Chiaten eruption?
- government decided residents could not return and housed them in a new town near Santa Barbara, some residents went to court
- residents lost homes and possessions, with very little government compensation
- as of 2011, 400 people lived in Chiaten and the government had not reconnected electricity and water supply
Explain why people live in areas affected by volcanic eruptions (Iceland) background
Lies on a constructive plate margin between North American and Eurasian plates
300,000 people live and work in Iceland, despite hazards
Explain why people live in areas affected by volcanic eruptions (Iceland) benefits
- geothermal energy, generates cheap electricity and used to manufacture aluminium and paper, providing jobs
- geothermal water, cheap and sustainable way of heating houses
- tourists travel to see waterfalls, geysers at Geyser and Blue Lagoon, providing jobs
- extraction of minerals, such as pumice from around Hekla
- unique microorganisms and enzymes from hot springs are used in brewing and baking industry
- fertile soils from ash in south, livestock farming and geothermal greenhouses to grow food for locals
- seas have large fish stocks to support a large fishing industry which employs many
Explain why people live in areas affected by volcanic eruptions (Iceland) conclusion
- people have well-paid jobs, high standard of living
- meat provided by livestock farmers and fruit and vegetables by thermal greenhouses
- homes have cheap utilities (electricity, water, heating)
- some many not want to leave because of heritage
- academics come to study earthquakes and volcanoes
Describe measures that can be taken to reduce risk of living near volcanoes
- network of monitoring stations means scientists can predict when eruptions could happen
- regularly practice evacuation drills
- can issue warnings and evacuate
- volcano survival kit
- dig diversion channels for lava
- wear masks to protect from ash
What is the focus of an earthquake?
The place in the earth’s crust where the earthquake originates from
What is the epicentre of an earthquake?
The point at the surface, above the focus
What are the key facts about the Christchurch earthquake?
New Zealand South Island
10km west of the centre of Christchurch
22nd February 2011
6.3 on the Richter scale and 5km deep
Conservative margin between Pacific and Australasian plates
Causes of the Christchurch earthquake
September 2010, another earthquake at a destructive plate margin. Complex series of fault lines, a slippage of crust on the Alpine fault line was triggered, sudden jolt. Earthquake measuring 7.1 on the Richter scale. Many aftershocks inc. significant one in Feb 2011, which caused more damage, bc the epicentre was closer to centre and focus was shallower
Primary effects of Christchurch earthquake
- extensive damage
- 185 people killed
- 3100 injured
- 100,000 properties damaged
- $28 billion of damage
- liquefaction destroyed roads and buildings
Secondary effects of Christchurch earthquake
- 5 rugby World Cup matches cancelled
- 1/5 of the population migrated from the city
- economists suggest it will take 50-100 years for economy to recover
- many businesses closed
What were the responses to the Christchurch earthquake?
- $6-7 million of international aid was provided
- Red Cross provided aid workers
- more than 300 police officers flown in from Australia to help
- 30,000 residents given chemical toilets
- 10,000 affordable homes built
- water and sewage restored by August 2011
What can be done to reduce risks in earthquake prone areas?
- earthquake survival kits
- earthquake proof technology (rubber shock absorbers, foundations in bed rock, not clay, steel frames that can sway and shutters over windows to prevent glass from shattering)
- education and frequent evacuation drills
- earthquake rescue teams
