1. What is going to happen next?

2. What type of volcano is this?

3. Nature’s pyrotechnics
Volcanic Eruptions
Nature’s pyrotechnics

4. Types of eruptions
Nonexplosive
Explosive

5. What determines how a volcano erupts?
The answer is viscosity!
What is viscosity?
A fluids ability to resist flow.
What changes the viscosity of a fluid?
Let’s take a look.

6. What is the connection with those three factors and explosive eruptions?

7. Why Explosive? Silica rich magma = high viscosity
Highly viscous magma traps gasses.
Trapped gas = high pressure in magma chamber.
Eventually the pressure is too much and the vent is fractured and all of the rocks are ejected as pyroclastic material.

9. Rhyolitic magma Highly viscous
Found at subduction zones because the magma comes from melted crust.
Can lead to a caldera.

10. Andesitic Magma Medium Viscosity
Volcanoes of andesite have both pyroclastic material and thick lava flows.
Over time the pyroclastic flow and lava create layers = stratovolcano.

11. Basaltic Magma Low viscosity Move through the vents very easily.
Gasses escape easily.
Associated with divergent boundaries.
Tend to form thin layers of lava.

12. Water and Magma Explosion
Common on islands with volcanoes.
Steam in magma expands rapidly
Erupts with great force
Krakatoa 1883.

13. Lava Types
High Viscosity = slow flow
Block lava formed

14. Lava Types
Low Viscosity = fast flow,
Pillow lava formed

15. Let’s examine our lab. Which lava had the greatest silica content?
Rhyolite
Which lava had the greatest viscosity?
Which lava was most resistant to releasing gas?