1. 10.1 – The Nature of Volcanic Eruptions

2. Do Now
What are the three different types of volcanoes?

3. Do Now What are the three different types of volcanoes? Shield Volcano
Composite Cone (Stratovolcano)
Cinder Cone

4. Key Words
Explosive
Eruption
Dissolved
Extrude

5. Vocab Words Caldera Cinder Cone Composite Cone Crater
Pyroclastic Material
Shield Volcano
Vent
Viscosity
Volcano

6. Factors Affecting Eruptions
Factors that determine the violence of an eruption.
Composition of magma
Temperature of magma
Amount of dissolved gases in the magma.

7. Viscosity A substance’s resistance to flow.
Ex: Maple Syrup is more viscous than water and flows more slowly.
Magma from an explosive eruption may be thousands of times more viscous than magma that is extruded slowly.

8. Viscosity Factors affecting viscosity: Temperature
Hotter magmas are less viscous
Composition (silica content)
High silica—high viscosity (e.g., rhyolitic lava)
Low silica—more fluid (e.g., basaltic lava)

9. Dissolved Gases
During explosive eruptions, the gases trapped in magma provide the force to eject molten rock from the vent of the volcano.
The vent is the opening in the volcano.
These gases are mainly water vapor and carbon dioxide.
These same gases expand as they reach the surface.
Violence of an eruption is related to how easily gases escape from magma.
Viscous magma produces a more violent eruption.

10. Magma Composition

11. Volcanic Material Lava Flows Basaltic lavas are more fluid.
Types of lava:
Pahoehoe lava (resembles braids in ropes)
Aa lava (rough, jagged blocks)
Gases
One to 5 percent of magma by weight
Mainly water vapor and carbon dioxide
Pyroclastic Material
Name given to particles produced in volcanic eruptions.
The fragments ejected during eruptions range in size from very fine duct and volcanic ash (less than 2 millimeters) to pieces that weigh several tons.

12. Pyroclastic Material Types of pyroclastic materials:
Ash and dust—fine, glassy fragments
Pumice—frothy, air-filled lava
Lapilli—walnut-sized particles
Cinders—pea-sized particles
Particles larger than lapilli
Blocks—hardened lava
Bombs—ejected as hot lava

13. Pahoehoe Lava Flow

14. Aa Lava Flow

15. Types of Volcanoes
The three main volcanic types are shield volcanoes, cinder cones, and composite cones.

16. Anatomy of Volcanoes
A volcano is a mountain formed of lava and/or pyroclastic material.
A crater is the depression at the summit of a volcano or that which is produced by a meteorite impact.
A conduit, or pipe, carries gas-rich magma to the surface.

17. Anatomy of Volcanoes

18. Shield Volcanoes
Shield volcanoes are broad, gently sloping volcanoes built from fluid basaltic lavas.

19. Cinder Cones
Cinder cones are small volcanoes built primarily of pyroclastic material ejected from a single vent.
Steep slope angle
Rather small in size
Frequently occur in groups

20. Cinder Cones

21. Composite Cones
Composite cones are volcanoes composed of both lava flows and pyroclastic material.
Most are adjacent to the Pacific Ocean (e.g., Mt. Rainier).
Large size
Interbedded lavas and pyroclastics
Most violent type of activity

22. Composite Cones

23. Other Volcanic Landforms
Calderas
Calderas are large depressions in volcanoes.
Nearly circular
Formed by collapse
Size exceeds one kilometer in diameter
Lava Plateaus
Fluid basaltic lava extruded from crustal fractures called fissures.

24. Group Activity
Fill in the chart on the worksheet. (page 281, Table 1) Also, draw an example of each type of volcano; cinder cone, shield volcano and composite cone.

25. Videos