1.
Volcanoes I

2. What determines whether a volcano extrudes magma violently or gently?

3. Composition
Temperature
Dissolved gasses (amount)

4. Composition Shield volcano- basalt lava flows
Stratovolcano- Highly variable; alternating basaltic to rhyolitic lavas and tephra with an overall andesite composition

5. Temperature
It can reach up to 700-1,200 °C (1,292 to 2,192 °F).

6. Dissolved gasses H2O- Water vapor CO2- Carbon dioxide
SO2- Sulfur dioxide

7. Which factors affect viscosity?
Higher temperature, less viscous; lower temperature, more viscous
Greater silica content, greater viscosity; lower silica, lower viscosity
Higher amount of volatiles (dissolved gases), lower viscosity; Lower amount of volatiles, greater viscosity

8. How does a magma chamber form?
rocks closer to the surface become less dense
the magma stops rising
minerals with high melting temperatures 
magma enriched with silica 

9. How is a Hawaiian-type of eruption triggered?
A Hawaiian-type of eruption is quiet or gentle
eruptions are triggered by the arrival of a new batch of magma
The magma chamber swells
The basaltic magma becomes more mobile 

10. What are lava fountains and how are they produced?
Fluid basaltic magmas
These pressurized gases are easily released
These gases may propel lava hundreds of meters

11. What is the role of dissolved gases in explosive or violent eruptions?
Because of its high viscosity, dissolved gases in silica-rich magmas
These dissolved gases begin forming tiny bubbles
These tiny bubbles build up over a long period of time
When the pressure overcomes the strength of the overlying rock
The sudden release of pressure may generate an explosive event

12. What materials are extruded during an eruption?
Lava flows
Gases
Pyroclastic materials

13. Lava Flows
AA lava flow- Basalt characteristically form flows known by the Hawaiian names pahoehoe and aa.
Pahoehoe lava flow-  Are characterized by smooth, gently undulating, or broadly hummocky surfaces.

14. Pyroclastic materials
ash and dust
welded tuff
Cinders
Block and bombs
Scoria and pumice

15. References