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Lecture 6

Lecture 6

4 Pages

Environmental Science
Course Code
Nick Eyles

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EESA06 Lecture 5: When Oceans Close Subduction: getting rid of oceanic crust Rheology: the ability to flow, how easy is it for something to flow o Volcanic eruptions- how easy does magma flow o Magma more vicious, they throw up, very dangerous o Pyroclastic: broken by fire Rocks shattered by eruption and blown up either as volcanic bombs or as ash Lots of volcanoes in Italy, thought volcano that was product of coal underground burning o Ashes are finely rocks Wax in lava lamp warms up when heated by bulb, get plumes Earths mantle- get rising plumes of hot, plastic rocks Pacific Ocean Slowly disappearing Floor being encroached on by surrounding continents South America and North America moving to left Australia moving up northwards- 70 millions years, Australia will be where modern day Tokyo is Pacific rim ring of fire o Get dense concentration of volcanoes o Major earthquakes- tsunami (sea floor raised or lowered) Subduction Oceanic crust going down Different colour stars are earthquakes Deepest earthquakes occur about 700km down Takes long time to melt slabs going down Magma come up to generate magmatic arch- line of volcanoes directly above subduction zones Oceanic crust made up of basalt, sea water and sediment, when we melt that lot, silicic magma- has effect of reducing viscosity of magma Deep water trenches- where ocean floor starting to go down into seduction zone- get very deep water trenches New Zealand Small island Is the exposed tip of a much larger land mass, called Zealandia The light blue is continental crust and deep blue is oceanic crust Teeth like marks on red line- direction of subduction o Bottom, Australian plate being subducted below pacific plate o Top, pacific plate going down below Australian plate o Middle, dangerous, has volcanoes, earthquakes o No subduction across continent of New Zealand- only on waters Oceanic crust gets subducted into the lighter continental crust Continental crust being collided together- obduction o Huge collision zone o The Himalayas, the alps How can we have subduction when colliding oceanic crust together- older oceanic crust gets subducted below warmer, younger oceanic crust On North island, pacific crust older than Australian plate Southern alps in New Zealand result of uplift along pacific rim where colliding continental crust together o Mt. Cooke- highest point in southern alps
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