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September 16

September 16 - Volcanoes and volcanism essentially conduits...

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September 16, 2008 Volcanoes and volcanism essentially conduits from the interior of the earth to the surface of the earth through which material comes out. - lava (sometimes) - pyroclastics magna can be fragmented into bits and pieces - gas comes out. can cause global cooling in large scale eruptions. use volcanoes to sample what is in the earth (crust and mantle) represent venting of the earth's interior. molten magma rises within the earth and is erupted either quietly (lavas) or violently (pyroclastic) sacragema- volcano that erupts every half hour. kids go to school with their knapsacks and hard hats incase anything falls. why some eruptions are quiet and not? quiet eruptions produce lava flows. dangerous, erupt in explosive fashions. high columns that go out into the atmosphere. some volcanoes do both, difficult to understand because the transition is not so clear, and it's not predictable. some volcanoes that grow lava domes and these domes sometimes blow up. (very disturbing) 2 controls on the explosivity of magmas 1- chemical composition volcano rock- magnesium, aluminum, sodium, potassium, but most of it has silicon. the more silicon in the rock, makes for a very sticky magna and those magmas can commonly create explosive eruptions because of its' high amount of silica and the stickiness. magna- mushy under the earth sometimes so sticky that it's practically a solid. is pressure develops somehow within volcano, it can erupt in an explosive fashion. some magmas have a lot of gas, some don't magna's without gas, are less explosive. if you're looking at a particular volcano, make undergo changes, 1 point gas rich, another, lost it's gas. potential for explosive eruptions is reduced. 3 important type of volcanic rocks basalts- low silica and low gas, erupt as lava flows, runny and less explosive
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andosites- more silica, higher gas contents rilites more silica, high gas contents some of the largest eruptions, commonly referred to as super volcanoes are very gas
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