Tectonics Flashcards
What are intra-plate volcanoes and why do they occur? - link to hotspots
-they are volcanoes found in both the middle of oceanic and continental plates
-they occur due to magma rising through mantle from outer core, melting its way through forcing molten material to the surface and breaking the crust, creating volcanoes (magma plume)
-intra volcanoes are also hotspots
-example is Hawaii
How are volcanoes formed on convergent plate boundaries?
-when the oceanic plate subduct’s beneath the continental plate, the crust melts turning it into molten material/magma.
-as this is lighter than the material surrounding it, it starts to rise and creates a magma chamber.
-when enough magma builds up in the chamber, it forces itself up towards the surface creating a volcano.
What are intra-plate earthquakes and why do they occur?
-they are earthquakes found in the middle of a plate (not on a boundary)
-they are caused by:
-ancient faults/cracks in the crust (created by previous plate movement) that have built up friction and strain over time which when released causes low magnitude earthquakes
-human activities (fracking of gas, large explosions)
-isostatic readjustment - weight of ice removed after ice age which means crust has less weight on in and is moving up - may cause an earthquake
-example is UK - 25 earthquakes each year - largest was 6.1 in 1931 in North Sea
What is palaeomagnetism and how does it show evidence of sea floor spreading?
-when outer core convects, it creates a magnetic field for the earth
-direction of this magnetic field changes every 100,000 years
-when crust separates at divergent plate boundaries, it forms new rock - when this rock cools, it locks in the magnetic field at that given time
-this means that as the crust continues to spread apart, and new rock forms through the plate boundary it creates magnetic strips in the oceanic crust of the sea bed going from normal polarity to reversed
What is slab pull?
-cold, dense oceanic plate is subducted beneath less dense continental plate
-the density of the the oceanic plate pulls itself into the mantle
-this occurs at destructive margins.
What are the 2 types of body waves (earthquake shockwave) are what are their properties?
-both travel through the earth
-primary waves (P waves) - first wave to arrive, fast, moves through solid rock and fluids, pushes and pulls in the direction of travel.
-secondary waves (S waves) - slower than P wave, only moves through solid rock, up and down movement
What is an example of a surface wave and what are its properties?
-surface waves travel through the top of the crust
-love waves (L waves) - fastest surface wave, moves from side to side as it moves forward
What is crustal fracturing?
-when shockwaves from an earthquake travel fast through solid rock and can increase stress in it
-stress causes strain until the rock fractures
Why are ash falls a volcanic hazard?
-smallest fragments erupted from volcano is ash
-these are forced to high altitude and are so light they are carried around in the atmosphere
-ash can then heavily fall in certain areas, causing roofs to collapse and electronics to fail
-also poses big threat to planes
What are pyroclastic flows?
-consists of a dense mixture of superheated solid particles (tephra) and poisonous gases erupted from the crater
-moves down sides of volcano and into surrounding area at great speed
-anything in its way is instantly destroyed
How are gas eruptions a primary hazard of volcanos?
-common volcanic gas is sulphur dioxide which is poisonous in high concentrations and can cause ‘acid rain’ when mixed with water vapour
-this damages buildings and plants
-sulphur dioxide may also cool earth when carried in the atmosphere- blocks suns heat energy
What is a lava flow?
-molten magma that erupts flows down side until it cools
-not very dangerous as people can usually get out of the way in time but if it does get to settlements it will set fire to it.
What is a lahar?
-these are a mixture of water and erupted volcanic material of different sizes that create a dangerous mud flow in river valleys
-flows very fast and poses big hazard to people living in settlements on river- may be long way from volcano
What is a jokulhlaup?
-devastating floods caused when volcanoes erupt beneath glaciers and ice caps, creating huge volumes of meltwater
-hot meltwater melts surrounding ice until it can burst out
What is a natural hazard?
-a natural event that causes a disruption to daily lives or death/destruction
What is the Benioff zone?
An area of seismicity corresponding with the slab being thrust downwards in a subduction zone
Primary hazards - volcanic
-lava flows
-gas eruptions
-ash falls
secondary hazards - volcanic
-lahars
-jokulhlaups
What makes a natural hazard a disaster?
-when the scale of impact of natural hazard is great
-measured by number of deaths (UN suggests 500+) or the cost of damage
What is a mega disaster?
-disaster with over 2000 deaths and a GDP reduction of 5% or more
What is the hazard risk equation?
risk= (hazard x vulnerability) / capacity to cope
-risk- potential loss of life and injury and damage to infrastructure
-hazard can be measured in magnitude/type
What are 2 ways a country can be resilient (with examples)?
-adapting things so future hazards have less impact
ex: identifying risks of potential hazard, planning what do before it occurs and implementing plans to reduce impact
-recovering nation after hazard to get back to normal
ex: stock pilling essentials, resources for repairing and rebuilding
What is the PAR model and what is each step of it?
-the PAR (pressure and release) model is a way of summarising the links between natural hazards, risk and vulnerability
-the steps are:
-root causes (poor gov, economic and political systems, lack of resources)
-dynamic pressures (lack of education, rapid urbanisation, ethical problems)
-poor living conditions (weak infrastructure, poverty)
-linked to geography of hazard (location, strength, timing) and what tectonic hazard it was
CASE STUDY: Tsunamis - 2004 Indian Ocean - developing
-general info
(compare to Tohoko)
-Magnitude 9.2
-24 m tsunami height
-Megathrust subduction zone
-off the west coast of Indonesia- affected India and Sri Lanka
CASE STUDY: Tsunamis - 2004 Indian Ocean - developing
-social impacts
-230,000 deaths
-125,000 injured
-1.7 million people displaced across 15 countries
CASE STUDY: Tsunamis - 2004 Indian Ocean - developing
-economic impacts
$15 billion in economic losses
CASE STUDY: Volcanos - Nyiragongo - developing country
-general info
-2002 Nyiragongo in DRC
-Constructive margin, continental rift zone
-Basaltic magma
-Composite cone volcano (a..k.a. stratovolcano)
-VEI = 1
CASE STUDY: Volcanos - Nyiragongo - developing country
-social impacts
-147 deaths
-120,000 made homeless
CASE STUDY: Volcanos - Nyiragongo - developing country
-economic impacts
-15% of the city of Goa destroyed by lava flows
-US $1.2 billion in economic losses
CASE STUDY: Volcanos/mega disasters - Eyjafjallajökull - developed country
-social and economic impacts
-environmental impact
Social Impacts:
No injuries
No deaths
Economic Impacts:
Major disruption to European and transatlantic air travel affecting 10 million passengers and costing $10 million in economic losses - ash cloud- aviation industry making sensors so planes can better detect ash clouds and fly through them
-fruit and veg could not be transported from Africa - it rot and cost them an est £65 mill
Environmental Impacts:
Ice melt on the volcano caused some flash flooding
