3.1.5.2 Plate tectonics Flashcards
Name the structure of the earth form the inside out towards the surface, explain what is at each layer
Inner core - outer core - mantle - asthenosphere - lithosphere - crust
inner core - Solid ball of iron/nickel. Very hot due to pressure and radioactive decay
outer core - semi-molten layer, made up of iron/nickel
Mantle - mainly solid rocks, rocks are high in silicon. The top layer of the mantle is semi-molten magma ( the asthenoshpere), the lithosphere sits on top.
Asthenosphere - semi-molten layer that is constantly moving due to flows of heat / convection currents. Lithosphere is above.
Lithosphere - Broken up into plates, majority of the lithosphere is within the mantle. The top of the lithosphere is the crust.
Crust - the thin top of the lithosphere.
-Oceanic crust is dense and is destroyed by plate movement, continental crust is less dense and is not destroyed.
Plate tectonic theory
what is the plate tectonic theory
what causes convection currents to occur
what are the edges of where plates meet called
-the plate tectoic theory is that the lithosphere is broken up into large slabs of rock called tectonic plates. These plates move due to convection currents in the asthenosphere, which push and pull the plates in different directions.
-convection currents are caused when the less dense magma rises, cools and then sinks.
-the edged of where plates meet are called plate boundaries/plate margins
Plate boundaries:
what happens at a destructive (convergent) plate boundary
what hapens at a contructive (divergent) plate boundary
-at a destructive plate boundary, plates move towards each other
-at a consructuve plate boundary, plates move away from each other
Destructive plate boundary:
what happens when a continental and oceanic plate, what 3 things cna it create, how are they formed?
what happens at an oceanic and oceanic plate, what 3 things can it create?
what happens at a continental continetal plate boundary, what 3 things can it create?
-at a continental oceanic plate boundary, the denser oceanic plate subcucts below the continental plate. The plate subducting leaves a ocean trench. Fold mountains are formed when sediment is pushed upwards during subduction. As the oceanic crust subdicts into the asthenosphere it melts, the extra magma created causes pressure to build up which forces through weak areas in the continental plate, causing composite volcanoes to occur.Can create fold mountains/composite volcanoes/earthquakes.
-at an oceanic oceanic plate boundary, the heavier plate subducts leaving an ocean trench. Fold mountains will also occur. Built up pressure causes underwater volcanoes bursting through oceanic plate.Lava cools and creates island arcs. Can create underwater volcanies/ocean trenches/earthquakes.
-at a continental continental plate boundary, both plates are not as dense as oceanic so lots of pressure builds. No crust subducts, there is a pile up of continental crust on top of lithosphere due to pressure between plates.Fold mountains formed from the pile up of continental crust. Can create earthquakes/fold mountains
constructive plate boundary:
what happens at an oceanic oceanic plate boundary, what is formed?
what evidence is there to support this idea of plate movement and sea floor spreading? what is paleomagnetism
what happens at a continental continental plate boundary, what is formed
-at an oceanic oceanic plate boundary, magma rises between the gap left by the 2 plates seperating, forming new land when it cools, via sea floor spreading.. Less explosive underwater volcnoes form as a result. Creates underwater volcanoes, ocean ridges and earthquakes
-Harry Hess theory in 1940 supports this, it uses the idea of paleomagetism (this is the stdy of rocks that show the magnetic fields of the earth) On the ocean floor, either side of constructive plate boundaries, geologists observed that there are symmetrical bands of rock with alternating bands of magnetic polarity. This is evidence of sea floor spreading.
-at a continental continental plate boundary, any land in the middle of the seperation of the 2 plates is forced apart, this forms a rift valley. Volcanoes form where the magma rises within the valley. Creates horsts (lifted rock) and graben ( valley). Can create rift valleys/earthquakes/volcanoes
what are the 2 processes that influence how convergent (destructive) plate boundaries occur?
explain each one
-ridge push - this is when the slope created from when plates move apart has gravity acting upon it as it is at a higher elevation. Gravity pushes the plates further away, widening the gap (induced by gravitational sliding)
-slab pull -when a plate subducts, the plate sinking into the mantle pulls the rest of the plate (slab) with it, causing further subduction
Conservative plate boundary:
what happens at a conservative plate boundary?
-at a conservative plate boundary, the plates slide against each other horizontally, this can be in different directions and at different speeds. No plates are destroyed so no landforms are created, a lot of pressure is built up when plates move.
-On oceanic crust, this can displace a lot of water.
- On continental crust, fault lines can occur where the ground is cracked by the movement.
Hotspots:
what is a hotspot
what can hotspots create, give an example
- a hotspot is an area of volcanic acitvity that is unrelated to plate boundaries.Hot magma plumes from the mantle and burn through weaker parts of the crust.
-this can create volcanoes and islands, the plume stays in the same place, but the plates contune to move, sometimes leaving a chain of island ( e.g hawaii)
Volcanic hazards:
where can volcanoes occur, what type of lava is formed at each plate margin
what are the 4 main primary hazards of a volcano, how can they impact people
what are 3 secondary hazards of a voolcano, how do they impact people
-volcanoes can occur on both constructive and destructive plate boundaries, as well as on hotspots
-at a constructive plate margin, balsatic lava is formed
-as a destructive plate boundary, andesitic and rhyolitic lava is formed
-pyroclastic flows/Nuees ardentes - this is a mixture of super heated ( 800 C*) gas,ash and volcanic rock that flows down the side of a volcano. It travels at high speed ( more than 80 kmh) and a long distance (near 10-15km). Because they travel fast and can happen with relatively little warning
-Lava flows, the speed at which lava flows is dependent on its viscosity. However, silica makes lava viscous and slow, which is common in explosive eruptions. The slow paced lava makes lava flows relatively not a threat t ohuman life as people can be warned and evacuated, however it can damage and destroy buildings.
-Volcanic gases - some eruptions release toxic gases, such as carbon dioxide,and sulphur dioxide. These can cause respiratory issues with some poeple.
-Ash clouds and fallout - volcanic ash ejected into the atmoshpere can lead to ashfall. It can cause structural collapse, dirupts air travel and damges machinery. Can also lead to some respiratory issues.
secondary hazards:
-Lahars (volcanic mudflow) - a mixture of volcanic ash, rock debrs and water that flows rapidly downhill, they are highly destructive, as they bury settlements,infrastructure and farmland under thick mud. They pose a great thret to life since due to their fast nature, they are difficult to evacuate. (50mph)
-flooding - can occur when volcanic activity melts glaciers, releasing large volumes of water, can damage property as well as pose a great threat to human life.
-climate change and atmospheric hazards - large eruptions release toxic gases into the atmosphere, these gases form aerosols, reflecting sunlight and causing short-term global cooling. E.g the eruption of Mt Pinatubo 1991 led to a temporary drop in temperature globally by about 0.5C*
what is the area called that has a high prevelance of volcanic and earthquake activity
The pacific ring of fire
Magnitude of a volcano:
how is vulcanicity measured?
what is the VEI, what does it go up to, what factors does it take into account?
-vulcanicity is measured using the VEI
-the VEI is a measure of the vucanicity of a volcano.it goes up from VEI1 to VEI8,
-the VEI takes intgo account the plume height, the height of the tephra ejected, and how long the volcanic eruption lasts
Frequency of a volcano:
What tends to be the case for volcanoes that are frequesnt and those that are infrequent
-frequently active volcanoes tend to have effusive eruptions, whilst infrequent volcanoes tend to be more explosive.
Regularity of volcanic activity:
Not a fashcard just info.
volcanic eruptions are regular in that the eruptions on each type of boundary are similar.
Sometimes there may be irregular eruptions that do not fit the pattern
Predictability of volcanic activity:
What helps estimate when eruptions will take place?
Are there any definite predicitins to a volcanic eruption
-the regularity of volcanic activity
-seismic activity
-gases releasing
-there are no definite predictions to a volcanic eruption
Primary effects/impacts of volcanic activity:
Environmental impacts.
Economic impacts.
social impacts
political impacts
Environmental:
-ecosytems damaged through variou volcanic hazards
-wildlife killed
Economics:
-business and industries destroyed or disrupted
Social:
-people killed
-homes destroyed from pyroclastic flows
Political:
-Government buildings and other important areas destroyed or disrupted
Secondary effects/impacts of volcanic activity:
Environmental impacts.
Economic impacts.
social impacts
political impacts
Environmental:
-water acidified through acid rain
-volcanic gases contributing to the greenhouse effect (global warming)
Economics:
-jobs lost
- profit from tourism industry
Social:
-fires can start which puts lives at risk
-mudflows or floods pose a threat to human life
-Trauma
-Homelessness
Political:
-Conflicts concerning government response, food shortages, insurance etc
Responses to volcanic hazards:
what are the 4 categories that responses can be sorted into, which one can be both short/long term and which are long term.
-give 3 examples of short term responses to volcanoes
-what is the aim of long term responses, what 3 categories do they fall in
-what is the disadvatnage about prevention with volcanic activity, provide an example of a prevention response
-what is preparedness, provide 2 responses
-what is adaptation, provide 2 responses.
-mitigation, prepardness, prevention, adaptation. Mitigation is the short term one.
Short term responses:
-evacuating people, providing emergency food supplies, providing immediate aid
-the aim of long term repsonses is to reduce the impacts of future eruptions by managing the risk. they tend to fall into the categories of adaptation,prevention, and preparedness.
-the disadvatnage with prevention is that volcanic eriptions cannot be prevengted. One prevention measure that may be taken, is to prevent people from living/builidng or being near volcanoes.
-preparedness is what takes place prior to an eruption to minimise risks and vulnerability. One response is installing monitoring aystems, which help predict when an eruption might occur, allowing authorities to plan to evacuate people and protect certain areas. Another response is that individuals can make sure that they are protected, e.g. by knowing where their closes emergency shelter is and creating emergency kits.
-adaptation is about how people change their behaviour or surroundings to minimise the risks and maximise the benefits of living near a volcano. One response may be capitalisiing on the booming tourism industry/ also agriculture industry, as ash makes soil very fertile.. Another response may be relocating away from the active volcano
Seismic activity:
what is the process of seismic activity occuring
what is the focus
what is the epicentre
-Due to plates not perfectly fitting into each other, when the plates move friction builds up between them, when the plates are stuck the convection currents in the asthenoshphere continue to push, which builds the pressure. It builds so much pressure that can no longer be sustained, and the plates eventually give way.Causing seismic waves ( shock waves) to occur
-the focus is the point underground where the earthquake originates form
-the epicentre is the area above the ground that is directly above the focus
Seismic activity:
what is the spatial distribution of earthquakes:
where do most of the worlds eathquake occur, what proportion does this account for.
-earthquakes occur across all boundaries.
-the pacific ring of fire accounts for 90% of the worlds earthquakes.
sesicmic activity:
what is seismicity
what are the 3 main measure of an earthquake, which is more accurate than the richter scale. (RS,MMS,MS)
what impact does the depth of the focus have on the magnitude of an earthquake. which one causes more damage. what boundaries have shallow and deep focuses
-seismicity refers to the occurence, frequency and distribution of earthquakes in a particular are over time
- Richter scale, which is a measure of the magnitude of an earthquake, it doesmt have an upper limit and it is logarithmic. Major earthquakes are above 7
-Moment magnitude scale (MMS) is based on total amount of energy released by an earthquake. It is logarithmic and has no upper limit. It is more accurate than the richter scale, especially for larger earthquakes
-the mercalli scale measures the impacts of an earthquake using bservations of the event (e,g reports and photos), the scale is between 1 and 12. wth 12 being total destruction
-the depth of the focus impacts the magnitude directly. Deep focus earthquakes tend to be higher magnitude than shallow focus earthquakes, however deep focus earthquakes geenrallydo less damage than shallow focus earthquakes. due to the seismic waves having to travel further reducing their power.
-conservative boundaries have the shallowest focuses, destructive boundaries usually have deeper focuses.constructive boundaries tend to be shallow focused.
Seismic activity:
what is the frequency pattern for large earthquakes and smaller ones
-small earthquakes are frequent and occur everyday at boundaries, hundreds occur daily, but these cannot be felt by humans
-larger, damage-reaping earthquakes are rare and less frequent.
seismic activity:
what is the regularity of earthquakes, do they occur regularly
what is the predictability of earthquakes, can they be predicted, what can give some indication, is their strength able to be predcted or is that random too
-earthquakes are not regular, they follow no pattern and are random, so there is irregularity between event - this makes managing them difficult.
-earthquakes are almost impossible to predict, microquakes may give some indication but magnitude cannot be predicted as how strong they are is random
sesimic hazards:
what other hazards are caused by seismic events (4)
how are tsunamis caused, what is its process, what determines the power of a tsunami, how can they imapct people
what are shockwaves, how are they caused,what determines their strength.
how do earthquakes cause landslides and avalanches (2 ways for lamdslides,1 shared with avalanches)
what is soil liquefaction
-tsunamis, shockwaves(sesimic waves), liquefaction, landslides and avalnches
-tsunamis are large waves caused by the displacement of large volumes of water, they are triggered by underwater earthquakes, which cause the seabed to move, displacing the water.waves radiate out from the epicentre of the erathquake. the greater the movement of the sea florr, the more water that is displced, the larger the wave.
-the power of a tsunami is determined by the distamce to the coast, those that start close to the coast are more powerful, this is due to the smaller distance travelled, preventing the amount of energy lost before making contact with the land.
-tsunamis are very fast, as waves travel quickly in deep water, so they can hit the shore without much warning, they can cause the death toll to be high.
-shockwaves occur when thwo plates move side by side and friction builds up, dur to convection currents in the astheonoshphere, the pressure continues to increase until the pressure can no longer be withheld, the potential energy then transfers to kinetic energy which is released causing vibrations in the ground. The further away from the focus the weaker the shockwaves
-the shaking of the ground can dislodge rocks, soil or snow, causig landslides or avalanches that move downslope quickly. The shaking can also loosen ground material making infiltration easier. The weight of the extra water may trigger a landslide veen after the ground has stopped shaking
-when soil is saturated with water, the vibrations of an earthquake can cause it to act like a liquid. this makes the soil weaker and easier to deform, so its more likely to subside, especially where it has a heavy weight on top of it (e.g in urban locations underneath buildings)
seismic hazards:
primary impacts of a seismic hazard:
what are the environmental impacts
what are the economic impacts
what are the social impacts
what are the political impacts
environmental:
-earthquakes can cause fault lines which destroy the environment
-liquefaction can kill wildlife and damage ecosystems
economic:
-business are destroyed
-government spending is very high
social:
-loss of life
-buiildings collapse, killing/injuring/trapping people
-loss of homes/homelessness
political:
-government buildings destroyed
-no matter how the matter is handled the government will be scrutinised for a poor job
