1. Factors
Affecting
Eruptions

2. 1. MAGMA COMPOSITION • Viscosity (Viscous = Thick)
Defined: A measure of a material's resistance to flow.
• Composition (silica content) affects viscosity
- High silica - high viscosity (rhyolitic lava)
- Low silica – Low viscosity (basaltic lava)
High or Low Viscosity?

3. 2. MAGMA TEMPERATURE
High Temperature Magma: Flows easily, therefore has a low viscosity
Low temperature Magma: Resists flow, therefore has a high viscosity
Hot spots have the highest temperature magma!

4. 3. DISSOLVED GASES • Mainly water vapor and carbon dioxide
• Gasses expand near the surface
• Violence of eruption = how easily gases escape from magma
- Viscous magma = a more violent eruption.

5. Magma Composition

6. Volcanic Material • Two Types of lava flow
- Pahoehoe lava (resembles braids in ropes)
- Aa lava (rough, jagged blocks)

7. Pahoehoe (Ropy) Lava Flow

8. Slow-Moving Aa Flow