Tectonics Flashcards
give and example and describe a constructive plate boundary and what features a common of constructive plates
-Iceland, Mid Atlantic ridge
-American and eurasian plates moving apart
-chain of sub-oceanic volcanoes
-new crust in made as material is pushed up from the mantle
Common features:
-Dykes- intrusive igneous rocks–> cut into bedding planes where they have been intruded
-Sills- lie with the bedding planes
-Transform faults- opposite faults that have been offset on either side of the ridge
e.g. Eldfell volcano, 1973
-huge lava flow eruption, lasted 5 months. village saved by barriers and jets of seawater- rock dam
give example of and describe a oceanic/continental destructive plate boundary
- e.g. South american and Nazca plate (oceanic)
- oceanic subducts- wadati benioff- series of earthquakes with deepening epicentres along zone
- hydration meting- helps decrease melting point
- ocean sediment
- peru-chile trench
- fold mountains–> Andes
- explosive volcanoes- viscous lava type, high silica content- Andesitic lava
give an example of and describe a oceanic and oceanic plate boundary
- e.g. Mariana Islands, Pacific ocean
- denser pacific plate subducts beneath Philippine plate
- volcanoes v. explosive, usually low threat as under the ocean
give an example of an describe conservative plate margins
- e.g. Pacific plate moving faster than N.American plate
- earthquakes where plates lock and there is a build up of pressure
- e.g. Loma Prieta, 1989
- no subduction so no volcanoes
give an example of and describe continental/continental plate boundary
- continental Eurasian and continental indo-australian plate
- Fold mountains e.g. Himalayas
- Himalayas still growing today, theoretically, however denudation
give an example of and explain intraplate earthquakes and volcanoes
- hot spots
- occur in the middle of the plate where there is a thermal anomaly-mantle plume- stationary plume
- e.g. Hawaii on a hotspot e.g. mt kilavea, worlds most active volcano
- runny lava e.g. pahoehoe or pillow lava when flows into sea water
- chain or Islands form as the plate moves across the mantle plume
what is the structure of the earth?
- inner core
- outer core
- mantle
- crust
- lithosphere- upper mantle, solid rock
- aesthenesphere= lower mantle, allows the plates to move
- inner inner core has been detected by seismic waves
give an overview of the development of the theory of plate tectonics
- continental drift theory - wegener- suggested continents once joined
- Sir Francis Bacon- fossil evidence- wegener then suggested these species were seperated when plates moved
- e.g. coal deposits in Antarctica, laid down under tropical conditions, plates moved apart since the carboniferous period
- e.g. sandstone in west kirby, laid down during desert conditions, evidence of glaciation e.g. striations in India, Australia, Africa
- theory of plate tectonics, Holmes- convection currents in the mantle
- theory of sea floor spreading, Hess
- Drummond and Vine- identified paleomagnetism
- recent theory of slab pull, older and colder plates sink, pulling newer crust down with it
give examples of volcanic eruptions
- mount pinatubo, philippines- 1991
- The big E, 2010
- Lake Nyos, Cameroon, 1986
give an overview of the case study for Mt Pinatubo
-1991
PRIOR
-prior, sulfur dioxide emissions detected. being monitored by USGS, enabled scientists to accurately predict eruption, evacuation
-hazard map completed
-14,000 people evacuated
-daily alerts issued
ERUPTION
-no deaths from primary hazards, surprising considering GDP, population density and enormity of the eruption
-800 deaths by secondary- 300 by collapsing roofs and 100 by lahars
-lahars from huge Typhoon after eruption- rainwater and ash
-pyroclastics flowed for several km
LONG TERM
-construction of dykes and dams to control post eruption lahars
-houses built on stilts–> lahars don’t bury them
-local indigenous people had to be relocated as their villages were destroyed
give an overview of the big E
- 2010
- jokulhaups washed away bridges
- about 25% of the ice cap melted, prompted evacuation of locals
- major problems was ash and the ash plume–> ash ejected high into the atmosphere
- fine ash caused problems for airplanes
- global economic costs due to flights affected- businesses losing up to $30 million/ day
- ash contaminated water supplies- farmers warned not to let livestock drink from water
give an overview of lake Nyos
- Cameroon, 1986
- lake in crater of the volcano
- volcanic gases e.g. CO2 seep upwards
- an earthquake triggered a landslide, causing landslide, disrupting the lake and releasing gases
- huge outflow of gas suffocated people and livestock
- nearly 2,000 people killed
- happened during the night
give examples of monitoring volcanoes
- ground deformation e.g. Mt St Helens, 1980- bulge on the side of the volcano before eruption
- seismic monitoring- e.g. monserrat–> location of worlds most closely monitored volcanoes- continuous seismic monitoring by the BGS
- glacial outburst floods e.g. big E–> heat given off by volcano
- GPS monitoring e.g. in soufriere hills–> detect any ground deformation
give an overview of the Christchurch earthquake
- liquidfaction as secondary hazard
- infrastructure damaged
- foundations disturbed
- up to 100,000 buildings damaged
give an overview of the japan earthquake, 2011
- 9.0 mag
- japan- v. physically vulnerable
- almost 20,000 dead/missing
- over 130,000 made homeless
- Tsunami- predicted 3 mins after the quake, gave people 30 mins to esacape
- over 100,000 troops distributed within 24 hrs
- after the quake, media coverage kept people updated
- quickly accepted aid from 20 countries
- exclusion zone around Fukushima- locals given iodine tablets
- strict building codes- low corruption, regulation
- well developed disaster plans- e.g. 10m sea wall, however insufficient.
- majority killed by seawater, buildings designed to withstand earthquakes, quickly destroyed by tsunami
- earthquake drills regularly practised by schools and businesses
