Tectonics enq 1 Flashcards
Four types of plate margins with examples
Destructive - Montserrat, Constructive - Mid Atlantic ridge, Conservative - San Andreas Fault, Collision - Himalyas.
What is Ridge Push and Slab Pull?
- As the lithosphere thickens with distance away from the MOR, it cools and the boundary becomes deeper and slopes away from the ridge due to gravity, this weight produces a downward force, so the asthenosphere ‘pushes’ the older part of plate in front of it.
- With distance the lithosphere becomes cooler and denser, after subduction the cool, dense lithosphere sinks into the mantle under its own weight, pulling the rest of the plate down with it.
What 5 factors is Plate tectonic theory driven by?
- Mantle Convection
heat rises from core as it rises it cools becoming denser before sinking back into core to be heated again - Slab Pull
- Seafloor Spreading/ Palaeomagnetism
as new crust is formed at MOR plates are pushed apart as convection currents are the crust apart them apart, magnetic orientation evidences this. - Subduction
the earth isn’t expanding despite new crust being created as it is being destroyed by subduction as the end plate sinks beneath the continental plate.
Evidence for Plate tectonic theory
Continental drift, Palaeontology, Palaeomagnetism, Climate Change, Geography and Geology.
Intra-plate Earthquakes and Volcanic Hotspots
EQ - near the middle of plates as a result of solid crust cracking as it travels over millions of years
VH - result of upwelling of magma (mantle plume) forming volcanic hotspots
Name three different types of volcanoes
Basaltic, Andestic, Rhyolitic
Basaltic Volcano properties
1200 degrees, Very hot iron rich and silica poor, low gas content, can erupt continuously and not very explosive
Andestic Volcano properties
800 degrees, Hot iron poor silica rich, increased gas content, sticky, can be very explosive
Rhyolitic Volcano properties
600 degrees, Cooler lava iron poor and silica rich, very high gas content = very combustible, devastating but erupt rarely
Name 4 volcano primary hazards
Lava flows, Pyroclastic flows, Ash fall, Gas eruptions
Name 2 volcano secondary hazards
Lahars and Jökulhlaup
Case study: Montserrat Volcano
- minor eruptions preceded swarm of eqs
- pyroclastic flows meant that people had to evacuate the capital
- the ash covered two thirds of island
- social environmental and economic damage
What are lava flows
Stress of molten rock that pour from an erupting vent. The speeds at which it moves depends on type of lava and its viscosity
What are Jökulhlaups
‘Glacial outburst floods’
They occur when volcanoes and glaciers interact, they can occur anywhere where water accumulates in a subglacial lake beneath the glacier filling a caldera (volcanic crater). The ice cap can push the water out of the caldera
Case study: Jökulhlaups at Eyjafjallajökull, Iceland
- erupted April 2010
- disrupted flights across Europe - global impact
- Further eruptions generated more jökulhlaups that inundated an Icelandic town resulting in its evacuation
Define pyroclastic flows
Dense, fast moving flow of solidified lava pieces, volcanic ash and hot gases can be extremely dangerous and result in flooding.
Define ash fall
A rain of airborne ash resulting from a volcanic eruption
Define Gas eruption
eruption of carbon and sulphur dioxide with can poison people and animals in extreme cases. Occurs at subduction zones
What is the VEI (Volcanic Explosivity Index)
A numeric scale that measures the relative explosivity of historic eruptions.
What three factors does the VEI take into account
- volume of products
- eruption cloud height
- qualitative observations
What are earthquakes caused by
The rupture and sudden movement of rocks that have been deformed beyond their elastic limit, they occur along fault line.
What is the focus in an earthquake
The point on the fault where the rupture begins
What is the epicentre
The point on the earths surface directly above the focus.
What are primary waves
Waves that arrive first, fast, move through solid rock in a push and pull motion
What are secondary waves
Slower than P waves, only move through solid rock, have an up down movement
What are Rayleigh waves
only travel through surface of the crust in a Rolling motion. ground is moved up and down and side to side
What are love waves
only travel through surface, fastest surface wave, move sided to side as it moves forward
What is the Benioff zone
The active seismic zone on a subduction plate
Name three secondary hazards that can result from earthquakes with examples
Tsunamis - boring day 2004
Liquefaction - Christchurch 2011
Landslides - Kashmir 2005
Tsunamis causes
The shifting of the sea floor during an eq is the most common cause, however undersea landslides and volcanic eruptions can also cause this
Where do the most destructive tsunamis occur and why
The Pacific Ocean as it is dominated by active subduction zones such as Hawaii
How are tsunamis created
Two overlapping tectonic plates become ‘stuck’ and seismic energy starts to accumulate, the stuck area ruptures and releases the seismic energy this creates a water column and the waves spread out.
What is liquefaction
Soil so severely shaken that they liquify, if the ground consists of loose sediment this can occur.
Define Landslides
The movement downslope of a mass of rock, debris earth or soil caused by the vibrations created by an eq.
What are the two earthquake scales
The Richter scale
The moment magnitude scale
Japan tsunami 2011 general physical info
- magnitude
- extremity
- cause
M9.0
Preceded by two earthquakes
Occurred on the subduction ion zone plate boundary between Pacific and North America
Boxing Day tsunami 2004 general physical info
- magnitude
- extremity
- cause
M9.3
Longest eq ever recorded traveled 5000km
Caused when the Indian Plate was subducted by the Burma Plate
After effects of Boxing Day 2004
socio-economic
Deaths 220,000 - 280,000
Displaced - 1.75 million
Missing - 146,000
GDP loss up to 20%
After effects of Japan tsunami 2011 socio-economic
Deaths 16,000
Displaced - 131,000
Missing - 4500
GDP loss less than 4%
Preparations for Boxing Day tsunami
NONE
Preparations for Japan tsunami
- high tech warning system in 8 seconds after first wave detected messages sent to 52 million phones
Response to Boxing Day tsunami
- humanitarian aid needed because of widespread damage
- nations all over world provided over 14 billion dollars in aid
- took years to recover
Response to Japan tsunami
- after 6 days motorway was repaired
- 6 months back to normal
Environmental consequences of Japan tsunami (3)
- land subsidence
- irrigation dam = flooding
- damage to crops and sewage systems
Evrionmetanl consequences of Boxing Day tsunami (3)
- poisoning freshwater supplies and soil by saltwater infiltration
- plant biodiversity damaged
- spread of solid and liquid waste
Which tsunami event was able to bounce back and why
Ultimately Japan was able to bounce back much quicker than the countries around the Indian Ocean as it was more prepared, its buildings were better built, it has a strong economy and high levels of insurance.
