1. 10.1 The Nature of Volcanic Eruptions
 Factors that determine the violence of an eruption.
• 1- Composition of the magma
• 2- Temperature of the magma
• 3- Dissolved gases in the magma

2. 10.1 The Nature of Volcanic Eruptions
Factors Affecting Eruptions
10.1 The Nature of Volcanic Eruptions
 Viscosity- is the measure of a material's resistance to flow.
• Factors affecting viscosity
Temperature
Composition
A. High silica—high viscosity
B. Low silica—more fluid

3. 10.1 The Nature of Volcanic Eruptions
Factors Affecting Eruptions
10.1 The Nature of Volcanic Eruptions
Dissolved gases
• Mainly water vapor and carbon dioxide
• Provide the force to extrude lava
- More Viscous magma produces a more violent eruption.

4. 10.1 The Nature of Volcanic Eruptions
Volcanic Material
10.1 The Nature of Volcanic Eruptions
Lava Flows
• Types of lava
- Pahoehoe lava (resembles braids in ropes)

5. Pahoehoe (Ropy) Lava Flow

6. Slow-Moving Aa Flow
- Aa lava (rough, jagged blocks)

7. Slow-Moving Aa Flow

8. 10.1 The Nature of Volcanic Eruptions
Volcanic Material
10.1 The Nature of Volcanic Eruptions
Pyroclastic Materials
particles produced in volcanic eruptions.

9. 10.1 The Nature of Volcanic Eruptions
Volcanic Material
10.1 The Nature of Volcanic Eruptions
• Types of pyroclastic material
- Ash and dust—fine, glassy fragments
- Pumice—, air-filled lava

10. 10.1 The Nature of Volcanic Eruptions
Volcanic Material
10.1 The Nature of Volcanic Eruptions
- Volcanic Bombs

11. 10.1 The Nature of Volcanic Eruptions
Anatomy of Volcanoes
10.1 The Nature of Volcanic Eruptions
• crater is the depression at the summit.
• conduit, or pipe, carries gas-rich magma to the surface.

12. Anatomy of a “Typical” Volcano

13. 10.1 The Nature of Volcanic Eruptions
Types of Volcanoes
10.1 The Nature of Volcanic Eruptions
1- Shield Volcanoes-are broad, gently sloping volcanoes built from fluid basaltic lavas.

14. Shield Volcanoes

15. Shield Volcanoes

16. Cinder Cones
2-Cinder Cones-small volcanoes built primarily of pyroclastic material ejected from a single vent.
- Small in size, Steep slope angle, and often appear in groups

17. Cinder Cones

18. 10.1 The Nature of Volcanic Eruptions
Types of Volcanoes
10.1 The Nature of Volcanic Eruptions
3-Composite Cones/ Strato
• composed of both lava flows and pyroclastic material. - Large size, Most violent type of activity
- Most are adjacent to the Pacific Ocean (e.g., Mt. Shasta).

19. Composite/ Strato Cones
Mt. Rainer
Composite/ Strato Cones

20. Composite/ Strato Cones

21. Mount St. Helens Before and After the May 18, 1980, Eruption

22. Profiles of Volcanic Landforms

23. 10.1 The Nature of Volcanic Eruptions
Other Volcanic Landforms
10.1 The Nature of Volcanic Eruptions
Calderas- are large depressions in volcanoes

24. 10.1 The Nature of Volcanic Eruptions
Other Volcanic Landforms
10.1 The Nature of Volcanic Eruptions
Lava Plateaus
• Fluid basaltic lava extruded from crustal fractures called fissures.