Lecture-11-F10 - EAS 111 General Announcements 10/6/09 •...

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Unformatted text preview: EAS 111 General Announcements 10/6/09 • Today: Igneous Rocks II: Volcanoes and hazards • This week and next week: – Bring your textbooks to lab – it will help! – Keep up on your reading in Chapter 5 & 6 – see directed readings at the end of this PowerPoint and online on Blackboard – it will help! • Next Monday – October Break – no class! We DO have lecture Weds 10/13. • Next week – October Break – NO LABS! Earth and Atmospheric Sciences 111 Fall 2010 Igneous Processes II -Volcanoes and Plate Margins -Volcanic Processes -Volcanic Hazards Lecture 11 05.10.c1 Granite Diorite Gabbro 05.02.b1-8 Felsic Rhyolite Intermediate Andesite Mafic Basalt Gabbro Basalt Mafic Mantle Mantle Peridotite Ultramafic = silica = partial melting = other refractory (usually mafic) minerals that stay Granite Rhyolite Felsic Diorite Andesite Intermediate Gabbro Gabbro Basalt Mafic = silica = partial melting = other refractory (usually mafic) minerals that stay Eruption as lava or ash Forming Forming Igneous Rocks Rocks Forms magma chamber (solidifies or rises) Accumulates into rising magma body Partial melting of source 05.03.a1 What regions have a high risk for volcanic activity? 06.12.c Composite Composite volcanoes volcanoes Calderas Shield Shield volcanoes volcanoes USGS Volcano Hazards Program http://volcanoes.usgs.gov/ Observe these types of eruptions 06.02.a Lava flow Lava fountain Dome Eruption column How Do Gases How Affect Magma? Affect What happens when What you open a soda? you Propels eruption Propels and forms ash and Under less Under pressure, gas forms bubbles forms Dissolved gas held in Dissolved magma by pressure magma 06.02.b Viscosity: Resistance to Flow Low viscosity: lava Low spreads out spreads High High viscosity: lava piles up up Higher temp. Higher and fewer and silica chains silica Lower temp. Lower and abundant and silica chains silica 05.09.c1 CPS: Igneous Rock Texture CPS: Which type of magma would you predict would give the most explosive volcanoes? volcanoes? A. Ultramafic B. Mafic C. Intermediate D. Felsic How Does Viscosity Affect Eruptions? More viscous: Felsic More difficult to flow Intermediate and traps gas lower T and higher silica 06.02.c1-2 Mafic Less viscous: Less higher T flows easier and lower silica gas can escape gas Basalt (Mafic) volcanic systems Settings for Basaltic Eruptions Divergent margins Hot spots Scoria Cones and Basalt Flows Early formation of a Early scoria cone scoria Switch to lava Switch flows flows 06.03.b Scoria cones Lava flow Observe hazards associated with basaltic eruptions, Observe noting if a hazard only affects areas near the vent Lava fountain Lava Lava-caused fire Volcanic ash Lava flow 06.06.b1 Shield Volcanoes Mauna Kea Can have small Can summit craters Mauna Loa Kilauea 06.04.a Fluid magma from fissures and scoria cones fissures Fissures fed Fissures by dikes by Observe these eruptions from shield volcanoes Fissure eruption Eruption into water Lava flow Pillow basalt 06.04.b Rhyolite (Felsic) volcanic systems Role of Source Area Cont inent al Cr ust Man tle Melting Melting continental crust forms felsic or intermediate magma magma 05.03.b2 Melting mantle Melting forms mafic magma magma Why do hot spot associated caldera volcanic systems (like Yellowstone) usually have both basalt flows and rhyolite domes? rhyolite Because partial melting of the mantle yields both Because rock types directly rock B. Because the basalt is always from a much more Because recent phase of activity recent C. Because partial melt from the mantle erupts directly as basalt but also melts continental crust to give rhyolite magmas and lavas to D. Because old intermediate magma from prior subduction has separated to form these subduction A. Magmatism with Hot Spots Magmatism Some basalt derived Some from decompression melting of the mantle reaches the surface. reaches Partial melting of the Partial continental crust by that basalt magma gives the rhyolite magma that erupts to form a caldera erupts Yellowstone Yellowstone Caldera Caldera Cross section through caldera 06.11.c Extent of ash Extent from prior eruptions from Yellowstone Hot Spot Track 06.11.m1 Observe the stages of formation of a caldera Stage 1 Stage 2 06.10.c1-4 Stage 3 Stage 4 and Repeat! Features Formed by Features Caldera Eruptions Caldera Long Valley Caldera Ash-rich sediment Welded ash The next figures show The a sequence of rocks from top to bottom in a caldera caldera Granite Bishop Tuff from the caldera 06.10.b-c Andesite (Intermediate) volcanic systems Granite Diorite 05.02.b1-8 Felsic Rhyolite Intermediate Andesite Melting in a Ocean-Ocean Convergent Boundary Melting (Subduction Zone) (Subduction Mostly Mostly intermediate rocks rocks 05.07.a Add water to Add hot mantle hot How could melting occur along an ocean-continent How convergent boundary? convergent Mostly intermediate Mostly and some felsic rocks and Mafic magma Mafic melts crust melts Adding water Adding melts mantle melts 05.07.b1 Observe the plate tectonic setting of the region and Observe consider what type of volcanoes are common in this setting consider 06.14.b1 Famous Composite Volcanoes Mount Fuji Mount Etna Mount Kilimanjaro Mount Vesuvius 06.07.m Mount St. Mount Helens Helens 06.08.c1 Composite Composite Volcano Volcano Eruption column Pyroclastic flows Lava flows Lava and domes and 06.07.a1-5 Landslides and mudflows Composite Volcano Rock Types Andesite Mudflow deposits Various types of Various ash, lava, mudflows ash, Tephra from Tephra eruption column eruption Tuff from Tuff pyroclastic flows pyroclastic 06.07.b1-6 How could we assess the danger posed by this volcano? Shape Rock types Age History Other data 06.12.a What areas around this volcano have the highest risk? Proximity Valleys Wind direction History Others 06.12.a EAS 111: Assignments for 10/13/09 • Reading in Exploring Geology Chapter 7 – Sedimentary Rocks and Environments 7.0, 7.3 – Seds. & Weathering Basics optional - for more detail, see 15.1, 15.2, 15.3 7.1, 7.2 – Sedimentary Environments 7.4, 7.5, 7.6, 7.7 – Sed. Rocks basic overview 7.12, 7.13 – Layering, change through time FOR LAB THE WEEK AFTER OCTOBER BREAK: 7.8 through 7.11, 7.16 ...
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This note was uploaded on 01/12/2011 for the course EAS 111 taught by Professor Dr.ericriggs during the Spring '10 term at Purdue University.

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