GLG 112 1st Edition Lecture 21Outline of Last Lecture I. 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 name3. Color4. Temperature5. Viscosity 6. Max volatile contentB. Intermediate magma1. Silica2. Rock name3. ColorThese 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.4. Temperature5. Viscosity6. Max volatile contentC. Felsic magma1. Silica2. Rock name3. Color4. Temperature5. Viscosity6. Max volatile contentOutline of Current Lecture I. Introduction to volcanoesA. Active volcanoesB. Deadliest EruptionsII. ExplosivityA. Volcanic Explosivity Index (VEI)B. Controls on explosivity1. Viscosity2. Volatile contentCurrent LectureThere are thousands of active volcanoes in the world. An active volcano is one with the potential to erupt. It can be constantly erupting, but it does not have to be.The deadliest eruption was in 1815 at Mt. Tambora (Indonesia). There were 92,000 deaths.Explosivity- Measured with the Volcanic Explosivity Index or VEI. It is based on plume height and volume. It goes from 0 to 8 with zero being nonexplosive (effusive) and eight being very explosive. - Viscosity and volatile content control explosivity.1. Viscosity*high viscosity=explosive and low viscosity=effusivea. Viscosity is based on silica content.Low silica=low viscosityHigh silica=high viscosityb. Viscosity is also based on temperature.High temperature=low viscosityLow temperature=high viscosity*Felsic Magma has a high silica content and low temperature.*Mafic Magma has a low silica content and high temperature.2. Volatile
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