Tectonics Flashcards
(16 cards)
Basaltic lava
Basic magma
Very hot
Iron rich
Silica poor
Low gas content, runny lav
Can erupt almost continuously
Not explosive
Andesitc lava
Intermediate
Hot
Iron poor
Silica rich
Sticky, can take decades/centuries between eruptions
Very explosive
Rhyolitc
Cooler lava
Iron poor
Silica very rich
High silica + low temperature = very high gas content
Erupt rarely but devastating
What is forecasting
When, where, likely magnitude
Limited to return periods
Hazard profiles
Past experience
What is prediction
Where hazard may occur - EQ only occur on plate boundaries, spatially only, seismic gap theory
Tsunamis partially predicted - seismometers locate, ocean monitoring equipment detects
Seismic gap theory
Based on the assumption that all parts of fault will eventually move
Means area that hasn’t had any seismic actuivity in a while will be next
Hazard management cycles
Response, Recovery, Prevention = Mitigation, Preparation ~ everything important
Important because…
Saves lives and allows countries to have a plan so they can cope, adapt and recover from natural hazards. Gives people increased awareness so they know what to do. Decreases vulnerability due to good management/governance.
Mitigation
Actions and interventions that a community can use to help reduce vulnerability in advance of a tectonic hazard
Apadtation
Ways in which communities may be able to live with a tectonic hazard by making adjustments to help communities reduce risk
Constructive plate boundary
2 plates move apart, can cause mid ocean ridge
Hazards: basaltic volcanos, minor shallow EQ
African rift valley
Destructive plate boundaries
2 plates collide, ocean subducts
Hazards: andestic eruption, major shallow EQ
Soufrierre hills Montserrat
Conservative plate boundary
Plates slide past each other
Hazards: major shallow EQ
No volcano as plate not being created or destroyed therefore no subduction to melt rock that forms magma
San Andreas Fault
Hazard CSs
EQ 2ndry:
- liquefaction - Christchurch 2011 (movement from shaking can cause loose sediment act like liquid)
- landslide - Kashmir 2005 (vibrations from EQ cause debris move downslope)
Volcano primary:
- ash falll - eyjafyjallajokull
- lava flow - Hawaii (streams of molten rock as volcano erupts)
- pyroclastic flow - montserrat
- gas eruption - mt st Helen
Volcano 2ndry:
- lahar - pinatubo
- jokulhlaup - eyjafjyallajokull (pressure from volcano breaks ice cap and pushes water out caldera)
Pressure and release model PAR
suggests socio-economic context of hazard is important.
In poor, badly governed places (root causes) with rapid change(dynamic pressures) low coping capacity (dynamic pressures) and low coping capacity (unsafe conditions), disasters are likely.
root causes (ltd access to power, resources etc due to political systems), dynamic pressures and unsafe conditions combine with a natural hazard to create a disaster.
Haiti:
Root causes:
- corrupt, poor governance
- Per capita GDP (PPP) US $1200
- 50% of the population is under 20 years old
Dynamic pressures:
- Lack of education, training and investment
- Rapid population change and urbanisation
Unsafe conditions: (physical)
- 25% of people live in extreme poverty
- 80% of Port-au-Prince’s housing is unplanned, informal slums
Root cause - ltd access to power, resources etc due to political systems
Tsunami occur
Overlapping plates get stuck as subducted and seismic energy builds up which releases and creates a water column that gets disrupted and forms waves.
Waves gain height and energy due to friction from sea bed. Top of wave moves faster than bottom so sea rises
Eg: Boxing Day 2004
50ft high, +200,000deaths, Indian plate subducted by Burma plate
Hotspots
Mantle plumes: Isolated plumes of convecting heat
- rise towards the surface = basaltic volcanoes(erupt continuously)
A mantle plume is stationary, but the tectonic plate above moves slowly over it.
Over timeproduces a chain of volcanic islands,
