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 Divergent 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! Barton beats boredom beneath big blue boundary boxes! 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) First vid is Kilauea in Hawai’i, hotspot Second vid is Vesuvius in Italy, ocean-continent convergence, similar eruption type killed people at Pompeii in 79 CE

Some Typical Volcanos Shield Volcano Cinder Cone Stratovolcano (a.k.a. Composite) Lava Dome Caldera

Shield Volcano Example – Sierra Grande, NM Notice very gradual slope, large size Photo by Joel Barton

Shield Volcano Example – Sierra Grande, NM Notice very gradual slope, large size Photo by Joel Barton

Shield Volcano Example – Mauna Kea, HI Resembles an ancient shield http://en.wikipedia.org/wiki/File:Mauna_Kea_from_Mauna_Loa_Observatory,_Hawaii_-_20100913.jpg

Cinder Cone Example – Capulin, NM Exposed scoria in the foreground Photo by Joel Barton

Cinder Cone Example – Capulin, NM Significantly smaller than Sierra Grande, e.g. Photo by Joel Barton

Cinder Cone Example – Layers of Scoria and Ash, Capulin, NM Pyroclastic rock – on the boundary of sedimentary and igneous Photo by Joel Barton

Stratovolcano/Composite Basics Many LAYERS of different erupted material, hence “strato-” http://en.wikipedia.org/wiki/File:Stratovolcano.jpg

Stratovolcano/Composite Example – Mount St. Helens, WA Left side – day before eruption in 1980 Right side – two years after eruption, notice lava dome in middle 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 535 feet high and almost ¼ mile wide, seen from ½ mile away 1 year after 1980 eruption http://volcanoes.usgs.gov/vsc/images/image_mngr/500-599/img541.jpg

Caldera Basics Very large, very violent “Drawing” by Joel Barton

Caldera Example – Valle Grande, NM The entire valley is the caldera crater, and the hills are the rim. Photo by Joel Barton

Caldera Example – Valle Grande, NM The entire valley is the caldera crater, and the hills are the rim. 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?