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NAU GLG 112 - Volanoes
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GLG 112 1st Edition Lecture 20Outline of Last LectureA. Wave characteristicsB. What does it look like?C. How far do they travel?1. In the ocean?2. On land?D. Warnings?Outline of Current Lecture VolcanoesI. Introduction to MagmaA. What is magma?B. How does it form?1. Decrease in pressure2. Addition of volatiles3. Increase in temperatureII. Types of magmaA. Mafic magma1. Silica content2. Extrusive igneous rock nameThese 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.3. Color4. Temperature5. Viscosity 6. Max volatile contentB. Intermediate magma1. Silica2. Rock name3. Color4. Temperature5. Viscosity6. Max volatile contentC. Felsic magma1. Silica2. Rock name3. Color4. Temperature5. Viscosity6. Max volatile contentCurrent LectureA. Magma is underground liquid rock with volatiles H20, CO2, and SO2. Because pressure is high underground they are liquid until they reach the surface and become gas. It forms in subduction zones, divergent plate boundaries, and hot spots.B. Most magma comes from the asthenosphere. There are three ways it can form with the first way being the most common.1. Decrease in pressure (also called decompression melting). This happens at hot spots and divergent plate boundaries. Low melting temperature rocks rise first. Occurs in the asthenosphere. 2. Addition of volatiles occurs in subduction zones. Water causes melting temperaturesto lower and create magma. Occurs in the asthenosphere.3. Increase in temperature is the least common way of magma forming. It happens in the crust instead of the asthenosphere. Magma forms when temperatures rise in thecrust. Types of MagmaClassification: based on silica content. Silica makes rocks form.Viscosity: resistance to flow. High viscosity means it does NOT flow. Water has a low viscosity and honey has a high viscosity.A. Mafiic Magma-has the lowest silica content (50%)-its extrusive igneous rock name is basalt (which is the most common)-it is black or dark colored-has the highesttemperature (1100-1200 degrees C)-low viscosity (like shampoo)-has the lowest max volatile content (0-2%)B. Intermediate Magma-medium silica content (60%)-its extrusive igneous rock is andesite (2nd most common)-has a medium grey color-medium temperature (800-1000 degrees C)-medium viscosity-max volatile content between 0 and 4%.C. Felsic Magma-highest silica content (70%)-its extrusive igneous rock name is rhyolite (rare)However, pumice is a form that floats in water because of all the vesicles (air bubbles)-it is light colored (light grey or pink like feldspar)-temperature is the lowest (600-800 degrees C)-highest viscosity (like toothpaste)-maximum volatile content is the highest


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NAU GLG 112 - Volanoes

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