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Download 042016 Intro to Volcanos
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Introduction to Volcanos Do not adjust your monitor. Introduction to Volcanos: Outline • Sources of Magma/Lava – Three main sources • Features of Magma/Lava – Mafic, Felsic, Other Components – Effects on Eruptions • Typical Volcanos – Five Representative Kinds Sources of Magma/Lava • Convergent Boundaries – IF / ONLY IF OCEANIC CRUST IS SUBDUCTING • Divergent Boundaries – Thinned crust, mantle forms magma • Mantle “Hotspots” – Lava regardless of plate boundaries Sources of Magma/Lava: Convergent Boundaries • Must be subducting oceanic crust – Water encourages rock melt – Does NOT WORK at continent-continent http://en.wikipedia.org/wiki/File:Subduction.png Sources of Magma/Lava: Divergent Boundaries • Spreading boundaries thin out the crust – Can be cont.-cont. or ocean-ocean – Takes pressure off the mantle • Mantle material melts making magma – Can form new oceanic crust – Can also ERUPT! http://geomaps.wr.usgs.gov/parks/pltec/diverge229x88.gif Sources of Magma/Lava: Hotspots • Hot liquid mantle rises in a single spot, while plates move over it • Can happen in the middle of a plate! – Competing theories as to why this happens • Ex: Hawai’i chain http://en.wikipedia.org/wiki/File:Hotspot%28geology%29-1.svg Getting to Know Your Lava: What to Look For • Is it mafic? (Think dark basalt.) – It will be runny, flows easily • Is it felsic? (Think white rhyolite or pumice.) – It will be VISCOUS, will not easily flow – Can get backed up, build pressure, and explode • Are there complicating factors? – Sea water, glacier, extra dissolved gases Getting to Know Your Lava: How Composition Affects Eruption • Basaltic Lava (Low Viscosity) – Watch: http://www.youtube.com/watch?feature=player_ embedded&v=6J6X9PsAR5w – Typical magma/lava of “hotspots” and some rifts • Rhyolitic Lava (High Viscosity), Presence of Gas – Watch: http://www.youtube.com/watch?v=1bsmv6PyKs0 (Start at about 2:45) – This is an extreme example (“Plinian” eruption) Some Typical Volcanos 1. 2. 3. 4. 5. Shield Volcano Cinder Cone Stratovolcano (a.k.a. Composite) Lava Dome Caldera Shield Volcano Example – Sierra Grande, NM Photo by Joel Barton Shield Volcano Example – Sierra Grande, NM Photo by Joel Barton Shield Volcano Example – Mauna Kea, HI http://en.wikipedia.org/wiki/File:Mauna_Kea_from_Mauna_Loa_Observatory,_Hawaii_-_20100913.jpg Cinder Cone Example – Capulin, NM Photo by Joel Barton Cinder Cone Example – Capulin, NM Photo by Joel Barton Cinder Cone Example – Layers of Scoria and Ash, Capulin, NM Photo by Joel Barton Stratovolcano/Composite Basics http://en.wikipedia.org/wiki/File:Stratovolcano.jpg Stratovolcano/Composite Example – Mount St. Helens, WA http://en.wikipedia.org/wiki/File:Sthelens1.jpg http://en.wikipedia.org/wiki/File:MSH82_st_helens_plume_from_harrys_ridge_ 05-19-82.jpg Lava Dome Example – Close-up of Mount St. Helens, WA http://volcanoes.usgs.gov/vsc/images/image_mngr/500-599/img541.jpg Caldera Basics “Drawing” by Joel Barton Caldera Example – Valle Grande, NM Photo by Joel Barton Caldera Example – Valle Grande, NM Photo by Joel Barton Introduction to Volcanos: Check Yourself • What will the source of the magma help determine? • Why will different lavas erupt differently? • How is the lava/eruption related to the final shape of the volcano?
