Basic Geology/Volcanism

There are three types of lavas formed by volcanoes. Mafic, Intermediate, and Felsic

Mafic (Basaltic)

• %SiO2: < 50%
• %FeMg: 4%
• Temp: up to 1500C
• Viscosity: Low
• Eruptive Behavior: gentle
• Distribution: divergent plate boundaries, hot spots, convergent plate boundaries

Intermediate (Andesitic)

• %SiO2: ~60%
• %FeMg: ~3%
• Temp: ~1000C
• Viscosity: Intermediate
• Eruptive Behavior: explosive
• Distribution: convergent plate boundaries

Felsic (Rhyolitic)

• %SiO2: >70%
• %FeMg: 2%
• Temp: 700C
• Viscosity: High
• Eruptive Behavior: explosive
• Distribution: hot spots in continental crusts (Yellowstone National Park), convergent plate boundaries