plate tectonics and volcanoes.gdoc

internal structure of the earth 1. (continental) crust → thin outermost later, consists of solid rock 2. upper/lower mantle → solid rocks and a layer of molten rock called magma, >2000ºC 3. outer/inner core → innermost part of the earth >3000ºC summary of earths internal structure...

internal structure of the earth 1. (continental) crust → thin outermost later, consists of solid rock 2. upper/lower mantle → solid rocks and a layer of molten rock called magma, >2000ºC 3. outer/inner core → innermost part of the earth >3000ºC summary of earths internal structure layer thickness (km) temperature (ºC) composition crust continental 10-70 -14 to 1200 less dense minerals (such as aluminium) oceanic 5-10 denser minerals (such as magnesium) mantle (upper and lower 2900 1400 to 3000 mixture of solid and mantle) semi-molten rocks (magma) solid core outer 2100 3000 to 5000 mostly iron and nickel (forming an inner 1370 alloy) plate tectonics theory states that the earth is in constant motion convection current in the mantle drives the movement of plates ○ created by heat from the earths core (much of which is generated by the radioactive decay in the core) plate movements creates major landscape and landforms such a volcanoes, for mountains and many more plate movements also cause earthquakes convection currents in the mantle 1. magma gains heat from the core (heat source) 2. magma rises to the crust as it is less dense 3. semi molten rock spreads out, carrying the above plate with it 4. could cause crust to crack and drag *tectonic movement can destroy old crust and create new lithosphere made up of the crust and the very top of the mantle asthenosphere semi-fluid layer that lies below the lithosphere, which allows the plates to move most tectonic plates have both continental and oceanic crust continental crust → thicker but less dense (makes up continents) oceanic crust → thinner but more dense (forms ocean floors) plate movement types 1. towards each other (converging, destructive) → convergent plate boundary, subduction occurs movements ○ continental-continental convergent (2 continental plates collide, creating mountain ranges) ○ oceanic-oceanic convergent (2 oceanic plates converge, one is subducted under the other, forming deep ocean trenches and volcanic islands) ○ oceanic-continental convergent (oceanic plate forced under continental plate, creating subduction zone) result ○ oceanic trenches ○ volcanic arcs ○ fold mountain ○ earthquakes 2. away from each other (diverging, constructive) → divergent plate boundary, magma escapes into ocean movements ○ oceanic-oceanic divergent (2 oceanic plates move apart, creating mid-ocean ridge) ○ continental-continental divergent (2 continental plates move apart, leading to rift valleys) result ○ mid-oceanic ridges ○ rift valleys ○ volcanoes 3. slide past each other (conservative) → transform plate boundary movements ○ oceanic transform boundary (2 oceanic plates slide past each other horizontally) ○ continental transform boundary (2 continental plates slide past each other horizontally) result ○ faults ○ earthquakes ** when there are 2 plates sliding past each other, the plate with the higher density will sink (slide under the other plate) plates (15) 1. african plate 2. antarctic plate 3. arabian plate 4. caribbean plate 5. cocos plate 6. eurasian plate 7. indo-australian plate 8. juan de fuca plate 9. nazca plate 10. north american plate 11. south american plate 12. philippine plate 13. pacific plate 14. scotia plate 15. okhotsk plate recap → continents and oceans 1. atlantic ocean 2. arctic ocean 3. pacific ocean 4. southern ocean 5. indian ocean  a. south america b. north america c. asia d. europe e. australia and oceania f. antarctica g. africa 1. plate boundary _ is a _____ plate boundary where the ______ ridge is formed 2. (describe process), in the process, the plates above it are pulled along and they move toward/away from each other 3. this results in ____ in the ____ plates 4. as shown in figure, when the (process), the ____ is formed in the ___ plate boundary at _ plate movement types (again aha) 1. oceanic-oceanic divergent plate boundary ○ two oceanic plates move away from each other ○ rising convection current below lifts the lithosphere, producing a mid-ocean ridge, rows of submarine mountains ○ tensional forces stretch the lithosphere and produce a deep fissure forming the spreading center ○ when the fissure opens, pressure is reduced on the super-heated mantle material below, which responds by melting and the new basaltic magma flows into the fissure ○ the magma then cools and solidifies to form new seafloor (process is called seafloor spreading) ○ as it is less dense than the surrounding older rocks, the new sea floor rises in elevation, resulting in gravitational sliding that pushes the older rocks away from the spreading center (this is known as the ‘ridge push’ force ○ shallow earth quakes are often associated with this crustal stretching basaltic magma from the asthenosphere wells up along any crustal fractures to form submarine/undersea volcanoes 2. continental-oceanic convergent plate boundary ○ when a thinner and denser oceanic plate converges with a thicker and lighter continental plate, the former descends beneath the latter due to ‘slab pull’ force into the asthenosphere ○ a long, narrow and deep oceanic trench is formed where the oceanic plate dips into the asthenosphere ○ movement of the subductingplate is not smooth, producing vibrations called earthquakes along the subduction zone ○ tip of the subduction oceanic plate melts due to friction with the overriding continental plate, and heat at great depth, producing silica-rich magma ○ magma moves up any breaks or fractures on the overriding continental plate to form a magma chamber as it is less dense than the asthenospehre and as gases in the magma expands ○ build up of pressure in the magma chamber forces magma to escape through the vent on the land surfaces as lava ○ lava cools and solidifies around the vent and overtime, through repeated eruptions, it accumulates and builds up to form a volcano ○ edges of continental plate, and sediments near the edges of continental shelf and on the the seafloor are contorted and folded to form fold mountains 3. continental-continental plate convergence  ○ when both continental plates collide, neither tends to sink as their densities are similar ○ instead, the continental crust buckles and folds, forming fold mountain ranges ○ little volcanic activity occurs because rocks from the rust do not sink deep into the mantle volcanoes a landform produced by magma emerges via an opening in the crust as lava flow lava cools and solidifies to form a layer of volcanic material with each eruption, layer upon layer built up to form a volcano lava continues to rise through a passageway pipe, lava ejected at a top opening crater parts of a volcano distribution in relation to plate boundaries along convergent plate boundary where subduction takes place, produce chain of volcanic islands (e.g: pacific ring of fire) along divergent plate boundary where new sea flow materials produce submarine volcanoes (e.g: mid-atlantic oceanic ridge) away from plate boundary, a plate moving over fixed ‘hot spots’, which are localised heat sources in the mantle to produce groups of volcanoes (e.g: the hawaiian island) classification  1. active: erupts frequently and in recent times 2. dormant: has not erupted for quite some time but is not considered extinct 3. extinct: has not erupted in historic times; solidification sealed off vent and volcanic shape may disappear types of volcanoes (6) 1. fissure volcano 2. shield volcano 3. dome volcano 4. ash-cinder volcano 5. composite volcano 6. caldera volcano factors influecing shape of volcanoes basic lava low viscosity, is hot and runny (1200ºC) has lower silica content takes a longer time to cool and solidify, flows considerable distances as rivers of molten rock produces extensive but gentle sloping landforms eruptions are frequent but relatively gentle lava and steam ejected found at constructive plate margins where magma rises from the mantle acid lava (dome-shaped, step, convex slopes) viscous, less hot, flows slower and shorter distances (800ºC) has higher silica content soon cools and solidifies, flowing very short distances produces steep-sided, more localised features eruptions are less frequent but are violent due to build up of gases ash, rock, gases, steam and lava ejected found at destructive megan’s where oceanic crust is destroyed (subducted), melts and rises statovolcano/composite volcano (acid lava) → concave → cone-shaped → alternate layers of acid lava and ash-cinder shield volcano (basic lava) → broad based → cone-shaped → gentle slopes similarities → cone-shaped pyroclastic flow a fast-moving current of hot gas and volcanic matter which reaches speeds moving away from a volcano up to 700 km/h gases can reach temperatures of about 1000ºC volcanic eruption affects the environment through: lava flows  emission of toxic gas mudflows of rocks and ash pyroclastic materials of ash and cinder bombs disturbances on ocean floor may trigger tsunamis volcanic hazards primary effects 1. pyroclastic flow → fast flowing clouds of volcanic ash and rock 2. tephra → small volcanic stones 3. lava → liquid rock that reaches very high temperatures 4. gas → often poisonous gases released from the mantle during an eruption secondary effects 5. lahars → a fast flowing river of volcanic mud 6. acid rain → rain mixed with volcanic gases that can damage crops 7. flooding → melting of glaciers and ice caps 8. tsunamis → giant sea waves 9. climate change → ejection of vast amounts of volcanic debris into the atmosphere can reduce global temperatures and is believed to be in an agent in past climate change 10. volcanic bombs → large volcanic rocks 11. landslides c collapsing mountain material benefits of vulcanicity // why do people stilll live near volcanoes? 1. formation of soil → economic reason: fertile soils for agriculture lava that has weathered down to form soils and ash that has settled on the ground are rich in nutrients to aid plant growth people have a livelihood by earning an income through the sale of crops as food grows, access to food and food security is provided 2. precious stones and minerals → economic reason: mining of minerals, sulphur → employment opportunity working as sulphur miners is employment for people to earn income sulphur sold for revenue industrial uses include making fertilisers, disinfectant and black gun powder 3. tourism → economic reason: tourism e.g: geysers and hot springs tourism industry makes use of scenic beauty and attractions provided by volcanic landscape people can be employed (e.g: hotel employees, tour guides) and earn a livelihood earn revenue from tourist attractions and recreational activities provided 4. geothermal energy → economic reason: harnessing of geothermal energy, power for development + energy resource geothermal energy is heat within the earth, a renewable energy source and heat is continuously produced in the earth used for bathing, to heat buildings, to generate electricity necessary for industrial and commercial development for domestic consumption (e.g: drive machinery and electrical appliances for heating and cooling in homes) 5. other: → cultural rootedness: sense of belonging, generations live there → do not have the financial resources to move  → attachment to the place and protection of their livelihoods as well as capacity to adapt to natural hazards and reduced perception of risk that involves impacts of volcanos 1. primary and secondary effects pyroclastic flow may destroy cities and kill its inhabitants deadly lahars may destroy cities and kill its inhabitants 2. destruction of primary industry eruption may destroy many agricultural crops ○ cause unemployment to increase following eruption 3. destruction of property and infrastructure eruptions may destroy houses, and damage roads and communications 4. threats to health those with chronic lung diseases such as asthma may be disproportionately affected after eruptions due to exposure to volcanic ash, suffering from acute effects including bronchitis, wheezing and eye irritation people may also die due to various diseases such as diarrhoea, measles and bronchi-pneumonia how to reduce 1. predictions → using a variety of techniques to monitor and predict and issue timely warnings for an impending blow, through sirens and media broadcasts to evacuate people from dangerous places around the volcano 2. prevention → reduce vulnerability by relocating people most at risk from tectonic hazards, undertake hazard mapping and create exclusion zones 3. preparedness → know the level of risk and plane, e.g: have a shelter and evacuation plan involving ensuring evacuation strategies are in place along with emergency supplies, stay connected and listen carefully to local emergency information