Quiz The most important factor affecting the size of crystals in an igneous rocks is the: A. Water pressure around the magma B. Rate of cooling C. Size of magma D. Mineral composition of the magma

Quiz Of the more than 4000 minerals that exist, only ____ of them compose over 95% of all igneous rocks. A. 3 B. 7 C. 11 D. 16

Quiz The two igneous rock types that make up the oceanic crust are: A. basalt and gabbro B. granite and rhyolite C. granite and gabbro D. andesite and granite

Quiz According to Bowen’s reaction series, which ferromagnesian mineral will crystallize first in a cooling basaltic magma? A. pyroxene B. olivine C. quartz D. calcium-rich plagioclase

Quiz The basaltic magma that emerges from the mid-ocean ridge is produced by the partial melting of the: A. lithosphere B. asthenosphere C. outer core D. continental crust

Volcanism What is a volcano? Where do volcanoes occur and how do they erupt? Materials produced by volcanoes and kinds of volcanic structures Forecasting volcanic eruptions Effects of volcanoes on global climate

Volcanoes on line volcanoes.usgs.gov Volcanic hazards in the United States 53 active volcanoes (3rd most volcanically active nation)

Anatomy and Setting of a Volcano Volcano: place where magma, gas, ashes erupt Vent: cylindrical-shaped outlet for magma Lava: magma that reached the surface Crater: bowl-shaped depression

Anatomy and Setting of a Volcano Caldera: larger than crater, formed by collapse Feeders: network of vents

Geometry of volcano and style of eruption What factor(s) control the slope of a volcano? Why are some eruptions quiet while others are explosive and extremely destructive? Is there a correlation between slope of a volcano and its eruptive style?

Materials of eruptions Magma viscosity depends on silica content, temperature, gases, ev. water depth and reactions with country rocks (e.g., limestone) Lavas fine-grained textures with microscopic crystals, glass, bubble cavities; porphyritic texture (basalts, andesites, obsidian) basaltic and silicic lava flows

Materials of eruptions Pyroclastic material ash, cinders, lapilli, blocks, bombs air fall (tephra) or surge deposits (nuée ardente - ignimbrite) mudflows (lahars) Volcanic gases carbon dioxide, water vapor, sulfur dioxide, hydrogen sulfide

Volcanic structures and eruptive styles High-silica eruptions explosive eruptions abundant pyroclastic debris steep cone Basaltic volcanoes quiet eruptions broad, gently sloping cones

Volcanic structures and eruptive styles 2/3 of all volcanoes on the Ring of Fire (Pacific subduction zones) Divergent (basalt) and convergent (andesite, rhyolite) margins Fissure eruptions and lava plateaus flood basalts: Columbia Plateau and Deccan Traps Mount Saint-Helens

Forecasting eruptions Procedures for predictions Study the geologic setting: field study and radiometric dating Establish a monitoring system (earthquakes, tiltmeters, gas composition and quantity, heat, groundwater temperature and composition)

Vesuvius Pompeii 79AD http://www.harcourtschool.com/activity/pompeii/pmpMain.html Risk assessment for Vesuvius: Vulcan.fis.uniroma3.it/vesuvio/vesuvius_risk.html

Effects of volcanism Volcanism and climate Atmosphere and climate (dust particles and acid droplets, CO2 and other gases) Eruption of Mount Pinatubo in 1991 Carbon dioxide and the greenhouse effect Volcanism can cause both warming and cooling Positive aspects of volcanism

Summary Volcano, vent, caldera, lava, feeders Tectonic settings of volcanoes Magma viscosity and eruptive styles Names of volcanic rocks and composition of lava Forecasting eruptions Volcanism and climate