Tectonics Flashcards
What are properties of the inner core?
- solid iron
- hottest section at 6000°
What are properties of the outer core?
- semi molten
- liquid iron and nickel
- medium temperature of 4500-6000°
What are properties of the mantle?
- widest layer
- upper part is solid but lower part is molten and forms aesthenosphere
What are properties of the crust?
Outer shell of solid rock
- oceanic plate is thin and dense
- continental us older, thicker and less dense
What is Wegner’s theory?
- 1912, continental drift, conversion currents with the mantle
- around 200 million years ago the continents were merged in a supercontinent called Pangea
- these moved and now assume the position we see today (Laurasia which moved north = North African Asia and Europe) and (Gondwanaland which moved south = south Africa, Australia, Antarctica and India)
- Wegner’s also suggested mountains formed when the edge of a drifting continent collided with another causing the floor to crumple and fold
What was Wegner’s opposition?
-took 150 years to be accepted as scientists still believed mountains are caused by cooling of the earth as well as it being difficult to find variable evidence
What was Wegner’s proof?
- fossil records showed desert biome species were ready for the artic so the continents must have moved biomes
- many animals shared home structures and were too alike to have developed separately
- mountain ranges had been separated leading to rock correlations
- land masses fit like a jigsaw
What was Hess’s theory on paleo magnetism ?
- ocean floor is getting progressively older the closer to the coast and that newer crust must be produced by molten rock rising inside as when more molten rock came to the surface the crust is pushed outwards
- pushing at the ridge and pulling at the convergent margin resulted in the sea floor spreading
- at the Benioff zone, oceanic crust is heavier and gravity pulls it under the continental crust. Gravity helps as once cooled it sinks because it gets heavier
Evidence for Hess’s theory
- as the world isn’t getting bigger he knew the crust must be destroyed at the edge
- used sonar to survey the sea floor discovering it wasn’t flat but rather there were mountain ranges in the middle
Examples of Hess’s discovery?
- the magnetic poles flip back and forth often over a long time
- when magma cools tiny magnetic minerals cool in the magnetic field direction
- this means there are parallel strips of cooled magma on the sea floor. A series of magnetic crevasses prove that the ocean floor is spreading because the stripes have been pulled apart
What is the theory about subduction and slab and pull?
- a magma plume heated by the core rises to the aesthenosphere where it slowly pulls the slabs of crust apart as it cools
- in the centre ridges form
- eventually the slabs are subducted by another, less dense of heavy slab forming a trench
- these currents operate as cells
What happens when an oceanic plate meets a continental?
- oceanic plate is subducted as it is less dense which creates deep oceanic trenches
- fold volcanos may also be made as the continual crust is pushed up
- Benioff zone creates friction adding to the melting of the mantle which creates an eruption
What happens when an oceanic plate means another oceanic?
- denser or faster plate is subducted beneath the other
- the subducted plate melts creating magma which can rise through faults
- this creates ocean trenches and submarine volcanoes which can sometimes grow above sea level
What happens at a divergent plate margin?
When two plates move away from each other
- in ocean magma can break through and build up to make new islands and continents. This creates rift valleys as the crust stretches and land between faults collapses
- it can also form submarine shield volcanos and shallow focus earthquakes
What happens at a conservative plate boundary?
Two plates found last each other or in the same direction at different speeds
- no crust is made or destroyed here yet powerful earthquakes are created due to a shallow focus
- major breaks in crust can occur however when they move (on a large scale this is a transform fault)
What are intraplate earthquakes?
- earthquakes that occur in midplate settings usually associated with major ancient fault lines being reactivated by tectonic stresses
- collisions if plates can also fracture crust that is far from the focus
What are intraplate volcanos (hot spots)?
- volcanos at a distance from boundaries
- isolated plumes of convicting magma (mantle plumes) rise towards the surface creating basalt volcanos that erupt continuously
- the plume is stationary but the plate moved slowly above it
- this produces a chain of volcanic islands called a toll
what is the risk damage threshold?
refers to the classing of different natural hazards based off their magnitude and scale of damage
- at what point does a risk lead to damage and therefore must be mitigated
what us physical and economic vulnerability?
- physical vulnerability is when people live in hazards prone areas in buildings that offer little protection
- economic vulnerability is when people risk losing their jobs, assets and money
what is social, knowledge and environmental vulnerability?
- social is when a household or community Is unable to support the disadvantaged people within it (e.g. political isolation)
- knowledge vulnerability exists when people lack education and training, therefore understanding
- environmental vulnerability Is because of things like population pressure which forces people into riskier areas
why is mitigation harder than reduction of vulnerability?
it is dependent on the physical environment which is harder to change and alter
-yet vulnerability is predominantly to do with people which are easier to educate and alter
where must the greatest initiative for mitigation come from?
- largest power and influence to implement reforms
- money to maximise their effectiveness and ability
- for example individuals may not have the social influence to make their ideas widespread or the money to successfully enforce them
what is a hazard?
a natural process becomes a hazard when people are affected
what is a disaster?
when a hazard affects a vulnerable population causing over 500 deaths
what is vulnerability?
how susceptible a population is to the impacts of a hazard
examples of recent megadisasters
- Tohuku (15,900 dead)
- Haiti (230,000 dead)
what’s the hazard risk equation?
risk reduction = mitigation of hazard x reduction of vulnerability and increase capacity to cope
what is the mercalli scale (MMIS)?
- measures the intensity of the quake using the amounted damage caused by shaking
- usually the stringer the shaking the greater the magnitude yet local factors can modify this
- very subjective based off observation
- measures from X to XII
what is the moment magnitude scale?
- based on energy released from all shock waves, the area of rupture and also movement
- more accurate than the original Richter scale as that was only based on P and S waves measured on a seismograph
- logarithmic
- equivalent to Kg of explosive
what us volcanic explosively index?
- open ended yet exists from 1-8 at the moment
- logarithmic
- calculated from the volume of ejected tephra
- generally the greater the VEI the less frequent the event occurs
what are hazard profiles?
a way of comparing the physical processes and impacts that all hazards share
why might hazards profiles be useful?
- they can help areas see what they are most at risk of
- this means they can plan and prepare more effectively helping to mitigate the effects
- this can help to rank hazards which need most attention advising decision makers
- breaks the event down into a variety of factors (e.g. frequency and duration). this means we can critically compare similar hazards in different locations based off more than one way
- if hazards are measured in the same way they will have broadly the same impacts
why might hazard profiles not be good?
- difficult to compare two different hazards because it doesn’t provide specific values for factors leaving it somewhat open to interpretation
- they have varying impacts and spatial and temporal distributions
- doesn’t take sub areas into account
what is governance?
the sum of the many ways individuals and institutions manage common affairs
- it is a root cause of vulnerability
- there are three strands of governance; economic, political and administrative
what are the effects of poor governance on overseas initiatives?
-concerns about political corruption and mismanagement means organisations are unwilling to channel aid money through it directly instead bringing their own staff at huge costs. This can hamper their ability to be self sufficient
what are the effects of poor governance of preparation?
- reduces investment into preparation meaning officials didn’t know what to do reducing efficiency
- less money invested into preparation because developing counties spend money on debt to previous colonies (e.g. Haiti)
- poor governance can lead to less prediction systems increasing knowledge vulnerability
what is the effect of poor governance on social aspects?
- lack of controls and regulations meant slums were poorly built and lacked structural integrity and couldn’t withstand the shaking
- dense urban environment made it harder for evacuation teams to work effectively
- poor investment into social spending and exploitation of the environment is rife which can lead to unsafe living conditions poor infrastructure and lack of preparedness
- leads to high inequality so poor have less of a political voice
counter point for influence of governance?
- a country needs to be developed to have good governance and development controls how resilient the economy is
- some hazards will also make a place more vulnerable regardless of governance
why are earthquakes more disastrous than volcanic eruptions?
- volcanic eruptions cover a relatively small areas and occur in narrow belts
- small proportion of of human population exposed (1% vs 5%)
- volcanoes are more visible so location of eruption is easier to predict compared to earthquake epicentres
- visual signs tend to be given off when a volcano is erupting
why might volcanic eruptions be worse than earthquakes?
- volcanic eruptions can go on for years
- can have global impacts (e.g. Iceland)
- can have long geographical reaches (e.g. ash clouds)
what is a fault line?
the boundary between two plates or a crack
epicentre
directly above the hypo centre on the surface (the shaking tends to be worse here)
hypocentre
the point at which tension and fraction releases seismic waves
seismic waves
ripples of energy released from the hypo centre
facts about earthquakes
- 95% of earthquakes occur along tectonic boundaries
- 10,000 deaths a year as a result
what are the different types of seismic waves?
- p (primary/pressure) waves are caused bay compression pushing and pulling the direction of travel. they are fastest and have side to side weak movements
- s (secondary/shere) waves are 60% of the speed of p-waves and only more through solid rock (up and down movement)
- L (longitudinal/love) waves only travel through the surface of the crust. unlike the other two body waves these are surface waves moving from side to side as to forward