gen-define-volcanism-and-magma-composition-and-give-one-short-wo-949f

Define volcanism and magma composition and give one short worked example.

# Volcanism and Magma Composition ## Volcanism **Volcanism** (or volcanic activity) is the process by which molten rock (magma), gases, and solid fragments are expelled from Earth's interior onto the surface or into the atmosphere. This occurs through vents, fissures, or volcanic structures. ## Magma Composition **Magma composition** refers to the chemical makeup of molten rock, primarily defined by: - **Silica (SiO₂) content** - the most important factor - Other elements: Fe, Mg, Ca, Na, K, Al ### Three Main Types: 1. **Mafic (Basaltic)**: 45-52% SiO₂ - low viscosity, hot (~1000-1200°C), fluid lava 2. **Intermediate (Andesitic)**: 52-63% SiO₂ - moderate viscosity and temperature 3. **Felsic (Rhyolitic)**: 63-75% SiO₂ - high viscosity, cooler (~650-800°C), explosive --- ## Worked Example **Question:** A volcano in Hawaii produces fast-flowing lava that travels several kilometers, forming broad shield volcanoes. What type of magma is this, and why? **Answer:** This is **mafic (basaltic) magma** because: - Low silica content (~50% SiO₂) creates **low viscosity** - Low viscosity allows lava to flow easily over long distances - This produces the characteristic **shield volcano** shape - Typical of **hotspot volcanism** like Hawaii