EESA05 - Environmental Hazards - Lec 3: Plate Tectonics (near-verbatim)

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Environmental Science
Mandy Meriano

EESA05 Lecture 3: PY Date: Lecture 3: Plate Tectonics How do we get the mountain formations, volcanoes etc; plate tectonics Development of plate tectonic theory Consequences of tectonics Slide : Internal Energy Whenever you have something moving, have to have NRG to actually move it Early on, when planets formed, pretty much there were many rock masses that collided; these collisions had to do with formation of planets Each mass has lots of kinetic NRG associated w/ it, once collide w/ each other, the kinetic NRG changes to thermal NRG; very hot Thru heat differentiation and mass differentiation > Earth became bigger; middle = very hot; then surrounding it cooled down; as you get to surface = cooler o Density differentiation is what actually facilitates this; there are things that are less dense than the iron core thats in the middle o The NRG of radioactive decay of core is whats running the engine (plate tectonics) Slide : Cross-Section of Earth Very dense very hot = inner core As you move out, get less dense and less hot materials Radioactive heat thru mantle and the mantle sends that heat to the top layers Top of mantle = asthenosphere o Asthenosphere = hot but its not a liquid; its a very hot solid and because its under so much pressure, even though its hot, it acts as plastic plasticity quality o Heat rising, goes thru asthenosphere thats very plastic and on top of the asthenosphere is the lithosphere which is brittle and hard (not plastic) o b/c asthenosphere is very hot and under pressure and has plastic quality, the lithosphere rides on top of the asthenosphere lithosphere = broken into bits = lithospheric plates and these plates float around on top of the asthenosphere on top of lithosphere = crust = what we walk on o crust = 2 diff kinds oceanic continental inner core outer core mantle top of mantle = asthenosphere (plastic) lithosphere = broken into bits at the very top, what we see is the crust radioactive NRG drives the bits of lithosphere and pushes them around Lithospheric plates: various lithospheric plates: African plate etc; 1 EESA05 Lecture 3: PY Date: lithospheric plates are moving around o some places where theyre moving away from one another = divergent boundaries o some places where theyre moving towards one another = convergent boundaries o its the moving away and towards one another thats creating everything that we see in the oceans, we have the oceanic crust; in the ocean, have mid-ocean ridges/rifts where in the ocean, hot stuff comes up from the asthenosphere and comes onto the ocean floor and pushes these oceanic crusts away from one another o somewhere else, the oceanic plates may actually be colliding o as plates hit, a lot may happen and it changes based on what kinds of plates we have colliding o whether 2 oceanic plates, one continental + one oceanic or 2 continental plates colliding raw materials of the plates are constantly being recycled = this is part of the tectonic cycle mid ocean ridge, for ex: Atlantic mid-ocean ridge and also have big one in pacific ocean o also west coast of south America and North America o mid-ocean ridge = not very high mountains but have volcanoes magma comes up and out and pushes plates away o stuff comes out of the ocean floor = basalt basalt = really dark, lot of iron/magnesium, very dense the rocks that we see on the continents arent as dense and heavy as the oceanic crust the differences in density is very impt for what happens Physics: To see how heat is actually distributed which movement of NRG is actually impt for tectonic plate mvt? Conduction o At the molecular level, you have NRG thats being passed on from one molecule to the next o In this way, get NRG transfer from one location to the next o Vibration of atoms/mocs o When adding heat to the pot, youre increasing the vibration of the atoms of the moc in that object Convection o By moving of anything that can flow, whether air/water/something plastic thats how you get the heat moving thru convection Latent heat o Very impt when considering heat transfer of ocean and atmosphere o Water has the largest heat capacity of all the liquids/solids on the planet with the exception of liquid nitrogen/ammonium o Heat capacity: if you want to heat 1 kg of water (change it from liquid to vapour), you have to add a LOT of NRG to change the phase of the water a wonderful quality of water means that we can transfer that NRG 2 EESA05 Lecture 3: PY Date: In oceans, within the depths of the ocean, hold a certain amount of NRG and they distribute that NRG around the globe thats how climate gets moderated o So, the water has all this heat and changes into vapour to change it back to liquid form, it has to give away that heat thats the latent heat thats being transferred o When it snows, actually feel that its not as cold; the waters actually giving away that latent heat to freeze up Which heat movement is impt 4 plate tectonics? o Convection o Convection is whats driving the transfer Atlantic ocean is getting wider by 5cm/yr; opening up by 1mm every week o The amount of NRG needed and the force = tremendous o Arrows show the relative mvts of these plates and along some boundaries = moving away from one another, or towards one another o One place where you can see it colliding = Indian plate India and Himalayas; have 2 continental plates colliding and giving rise to the continental crust where you get the Himalayas o Another place with collisions: West coast of South America Normasca plate = part of the Pacific Ocean is hitting West coast of South America to form the Andes (oceanic plate hitting continental plate) Convergent Margins o 2 plates colliding Divergent Margins o Two plates are actually moving away from one another; can get this in the middle of the ocean have hot magma from the asthenosphere coming out thru lithosphere & oceanic crust and pushing apart the 2 plates o Get destruction of crust o Where you have divergence, youre actually making new crust; deep down in mid- oceanic ridge, have the basalt, magma coming out new crust formed Transform Margins o When you have some sort of change in the movement, where theyre not hitting or moving away from one another o Rather, theyre sliding/slipping past one another o Along the mid-oceanic ridges, sometimes you get breakage (due to pressure etc;) that ends up as transform faults o Can have active or inactive transform faults At one end, theres destruction of crust, the other end = construction of new crust balance In terms of aging: 3
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