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Lecture 5

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Environmental Science
Nick Eyles

60 anniversary of ‘god save the queen’ How oceans die nd when oceans close Pacific ocean dying,surrounding continents encroucthing in Pacific rim-most dangerous,place on earth,most dangerous volcanoes nd earthquake..populated areas megacities endangered Steep-sided volcanoes-magma have silica in it.stiff gas cant come out,sudden release of gas ..cud find pyroclastic debris..these volcanoes produce a lot of ash..pyro is fire nd clastic is to break..since these volcanoes break the magma by the faults of eruption The blue line in the rim-are deep water trenches which mark the floor of the pacific ocean and pushed /buckled down in surrounding landmasses–trenches identified as subduction zone,..this is how earth recycle natures crust…deepest on whole ocean on earth.. Japan,Vancouver(BC) threatened by major earthquake…Canada has a rim,Chile (volcanoes) Continents surrounding the rim are growing at the expense of the ocean cause the oceanic crust(subducted) is melting nd magma erupt around the continents becomes the part of the continents Figure(process) 5:26  Blue/yellow stars are the epicentres of the earthquake  A lot of friction  Bout 100km of depth the magma starts to melt as result of basalt moves up of the continental crust nd gets contaminated ..picks up silica  Eruptive volcanoes  Continents grows as a result  Accretionary wedge-Seafloor sediments tht are literally being scraped off of the descending plate so that advancing continent is like a giant snow plow..those sediments are being added to the the continental plate..contains a lot of gas  This is what happens in the subduction zone  Imp. pnt-adding to the continent when recycling oceanic crust Subduction ll fig 2.26 7:06  Thts why oceanic crust is going down the continent crust  Density is dricing the plate underneath.the older heavier one is going down  Generating volcanic island arc…japan/indonasia- all volcanoe joining together  Creating embryonic continent-protocontinent(how first continent created)  Island arc will grow thru time  Conditions on early earth 4 billion years ago –where earth consisted of magma ocean (giant red ball water)  Next stagethe formation of ocean… the red ball came out of the mantle result of dewatering deep with in the mantle,the water vapour degasses and forms ocean..then magma cools and begins subduction process  If it wasn’t for wateror was the Cooling of magma ocean very imp in generating the first continent  Acreation wedge ..Sediment unstable…when get earthquake a lot of it collpases and triggers lrg tsaunamies cause seafloor failing..nd displaces it  Tsuanamie-Massive displacement of the seafloor Pacific rim of fire-tectonics of a closing ocean (not so specific ocean)  New Zealand  Idonesia  Japan  California  Chile Merapi volcano-most active volcano in Indonesia Volcanic island arc-where oceanic crust is subducted below othr oceanic crust Made up of joined volcanoes (some are dead some are not) very steep being built up of pyroclastic eruptions then collapse thts why so dangerous Proto-continent Jab-jacarter-sultans endanger by the volcano (royal palace) Krist-symbol of power,made up of iron meteriotes,knife 13:40 fig-  bombs,-lrg piece of magma thrown in the air  pyroclastic flow-where side slope collapse  lateral-blast-a lot of the stuff don’t go vertically,a lot go sideways  very dangerous cause ppl living here  best soils on volacano,relatively wet climate..these ashes undergo weathering nd produce very fertile soil nd many ppl will farm here..the pyroclastic flow (stiff,viscous flows not flood basalt)  lahar- refer to remobilization of ash by heavy rain..enormous volumes of ash blown up in the air and blanket the slopes,=nd coat are quite stable.then ropical cyclone will turn these ash into heavy mud then flow down slope producing disastraous lahrs tht bury cities 17:24 marapi volcano,very activice, …sulphur gas coming up more nd more releaseas u get closer to an eruption..measure to predict when volcano might blow.. 18:20 nd the top of the volcano will collapse..pyroclastic an avalanche w/ hot gas 450 pyroclastic rock..density is very great for it to carrylrg boulders..happen very quickly… lazer beams are there nd is recorded..ppl don’t want to leave because of their farms 19:40 deposit of the pyroclastic flow-cud see lrg boulders..killed 53 ppl Japan-most dangerous place on the rim,challenger deep Pic-bullet train Fig.subduction 20:46 Japan lie in intersection of four major plates On right is pacific ocean and under there is the pacific plate, moving to the will see bony trench subduction zone where tht plat is pushing down japan Philipine plate,old ridge is the spreading centr of this plate… pacific plate is going under this When see japan u can see on left hand side of poorly define plate margin of Asian plate on left nd American plate on the right..theres a fault in the plate boundary 22:08 Tokyo found on intersection of all four plates  In march pacific plate was locked in subduction …firction,whole plate margin was locked..buildup ofstress2…nd plates suddenly unlocked caused an..sudden slippage of the pacific plate down into the subduction zone 23:05 March Honshu Tsaunami produced spreading out on pacific..timelines (meteres..80cm,60cmon the scale) nd the hours on the map across the pacific..etre barely notice in mid-ocean when the waves meet at coast nd get focused they increase in height-baywave..nnd get concentrated increase in height..concern in opp side of pacific 24:12 GPSmoniter plate movement quite accurately ;deformation and slip during march earthquake  Uplift nd subsidence of ocean floor; eastward movement of Japan..  Seafloor of Tokyo-sealvl rise 7metres on outr coast ; inner coast has gone down..has tilted down  japan has rised up to accommodate tht pacific plate;thts why wave so destructive 1896 earthquake didn’t eveneven get reported because it was tht common Uplift and then subsidence in all the dykes/seafloor were dropped nd waves were was slip on the fault Japan Moved east-25metres as quick split sec. South America/north moving to slowly pacific ocean dying Pop increase-risk 27:27-shield volcano…Mount fuji/haven’t had major volcanic eruption for 700 million yrs..but actually it is a very dangerous volcno w/ pyroclastic flow nd have major city underneath 28:24 Have shento temple beneath .. 28:50 Replica of volcano every august…godess inside…if she likes what she sees then volcano will not erupt 29:37 light tires…fire festival to prevent volcano erupt 29:47 out-crop…sediments exposed,each bed is a pyroclastic thing is burnt tree trunk (cud be dated by looking at the beds get sum idea of the freq of the eruption) 31:11 Shimabara city-lays below mount unizen-site of deadliest volcanoe disaster in 1972  part land,cities  huge fragments of the volcanoe tht came down from slope from the past  huge landslide tht collapse that triggred the volcanoe was an earthquake  named after Japanese prince 32:31 those land masses are huge masses of rock that came down an landslide 32:47 The legend of the giant catfish(kashima)..when catfish brittle there will be a earthquake Japan-earthquake nation 33:47 1891-neonardi earthquake-offset by a scab..a block went down..picking out a fault..a fault scab.- pic actual plate boundary of asia and America 34:46-seismology,became a science evr since this ancient scabs to date the earthquakes/frequncy 35:53 middle line of the picture is a falut plane/plate boundary-blocks
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