EAR 105 1st Edition Lecture 6Outline of Last Lecture I. Rocks vs. MineralsII. Rock TypesIII. Rock CycleIV. Magma vs. LavaOutline of Current Lecture II. Basaltic MagmaIII. Silicate-Rich MagmaIV. Introduction to VolcanoesCurrent LectureRecap:What are Rock and Minerals?Rocks: aggregate of one or more mineralsMinerals: inorganic, naturally occurring crystalline solid, with a specific chemical compositionTypes of Rocks: Igneous, sedimentary, and metamorphicRock Cycle: Sediment  Lithification (sediment is transported, deposited, compacted, and cemented sedimentary rock)Sedimentary Rock heat and pressure  metamorphic rockMetamorphic rock burial, heat, pressure, melting  igneous rockMolten rock is called magma underground and lava at the surfaceShortcuts to rock cycle exist, does not necessarily have to follow the general patternExtrusive- igneous rock formed at surfaceIntrusive- igneous rock formed below surfaceRecap with transition to volcanoesIgneous rocks are classified by texture (size of crystals) phaneritic (can see crystals) or aphenitic (cannot see crystals)Texture can be glassy, porphyritic, course-grained, fine grained, etc.Mineral composition—Bowen’s Reaction Series BRS measures:- How do crystals form out of a basaltic melt?- Basalt—higher percentage or iron & magnesiumThese notes represent a detailed interpretation of the professor’s lecture. GradeBuddy is best used as a supplement to your own notes, not as a substitute.- Helps to predict order of mineral crystallization and resiliency of those crystals to weathering- Minerals that crystallize at higher temperatures crystallize first, removing iron and magnesium from the melt. Melt becomes less mafic, leaving more silica in the melt.Mafic lava has “peaceful” eruptions. Fluid, high temperature, relatively low temperature. “Hawaiian style volcano” Olivine, pyroxene, calcium-rich plagioclase form and settle out (crystallize) along magma body’s cooler margins; leaves more silica in the melt Remaining silica-rich (felsic) magma becomes more explosive, result of chemical comp of silica-rich lava. Magma is all the while cooling down on BRS Felsic magma precipitates Potassium Feldspar, Muscovite Mica, and Quartz (Because magma is constantly cooling, a lot of felsic magma doesn’t make it to the surface and explode. Instead, it forms intrusive granite)Conclusion: Felsic magma (lower temp) produces more explosive eruptions.Mafic magma (higher temp) produces less explosive eruptions.Types of Volcanoes: Cinder cones, shield volcano, composite (strato-) volcanoCinder cones- smallest, shortest life span- Built of ejected lava fragments- Steep slope- Small- Frequently occur in groups- Can compromise more explosive mafic magmaShort lived, short volcanoShield- largest, thin, far traveling streams of slow flowing lava- Basaltic - Very broad, shield shaped volcano, slightly domed- Most of Hawaii is formed in this fashion.- Produces basalt (extrusive) and gabbro (intrusive)Composite- formed of cooled layers of lava. Most violent eruptions since lava is more viscous more pressure- Has many strata or layers, hence called stratovolcanoes- Ejects intermeddled layers of lava or of pyroclastic debris- Ash, cinders, blocks, pyroclastic fragments- Intermediate, but can have explosive episodes- Pop up but don’t last very long because the lava is thin, so expanding gas can pass through more easily, diminishing the pressure within the volcano- Generally large, but small in comparison to shield volcanoes- Most dangerous, explosive, ex. Mt. Fuji, Mt. Shasta- Produces intermediate composition rocks. Not mafic, not felsic andesite (extrusive) and diorite (intrusive)Pacific rim= ring of fire—not coincidence as volcanoes tend to emerge in groupsWhat controls violence of the eruption?- composition: Felsic (silica rich) is more explosive, mafic (iron, magnesium rich) is less explosive- temperature: low temp is more explosive, high temp is less explosive- gases: dissolved in the magma- water, carbon dioxide, silica dioxide, sulfur- viscosity: material’s resistance to flow. More fluid= less viscous. Less viscous, less explosiveFelsic magma is more viscous, lower temperature, making it overall more explosiveMafic magma is more fluid, higher temperature, making it overall less explosiveConclusion: felsic lava and/or intermediate chemistry create the most violent eruptionsConclusion: Gases from volcanoes can contribute to climate change—but burning of fossils fuelseven more