1. 10.1 The Nature of Volcanic Eruptions
Factors Affecting Eruptions
• magma composition
• magma temperature
• amount of dissolved gases

2. 10.1 The Nature of Volcanic Eruptions
 Magma Composition
• Viscosity (Viscous = Thick)
Defined: A measure of a material's resistance to flow.
• Factors affecting viscosity
- Composition (silica content)
High silica - high viscosity
(rhyolitic lava) (thick)
High or Low Viscosity?
Low silica – Low viscosity
(basaltic lava) (thin)

3. 10.1 The Nature of Volcanic Eruptions
 Magma temperature
• Factors affecting viscosity
Temperature
High Temperature Magma: Flows easily, therefore has a low viscosity
Low temperature Magma: Resists flow, therefore has a high viscosity
Magmas with the highest temperatures can be found around the world near mantle hot spots.

4. 10.1 The Nature of Volcanic Eruptions
Dissolved gases
• Mainly water vapor and carbon dioxide
• Gases expand near the surface
• Violence of eruption = how easily gases escape from magma
- Gases escape easily from fluid magma. (low viscosity)
- Viscous magma = a more violent eruption.

5. Magma Composition

6. 10.1 The Nature of Volcanic Eruptions
Volcanic Material
Lava Flows
• Types of lava
- Pahoehoe lava (resembles braids in ropes)
- Aa lava (rough, jagged blocks)

7. Pahoehoe (Ropy) Lava Flow

8. Slow-Moving Aa Flow