1. Bell Ringer
The ___________ eon is divided into 3 eras: Paleozoic (“_______”), Mesozoic (“middle life”), and Cenozoic (“__________”)
Phanerozoic
old life
recent life

2. Volcanoes

3. Anatomy of a Volcano
Volcano – a mountain or hill with a vent through which lava, rocks, and gas erupt from the Earth’s crust
Summit – sides of the volcano
Vent – opening through which lava erupts

4. Anatomy of a Volcano
Crater – bowl-shaped opening (< 1km wide) around the vent
Caldera – large crater formed when the summit collapses during or after an eruption
Crater
Caldera

5. Caldera Lake (Oregon)

6. Anatomy of a Volcano
Famous Calderas -- Santorini Caldera in Greece and Yellowstone Volcano in the US

7. Yellowstone is an example of a dormant (inactive) supervolcano
If it ever erupts, it could potentially change all life on Earth

8. Anatomy of a Volcano
Magma chamber – pool of magma below the volcano that fuels the eruption
Magma – mixture of molten (hot, melted) rock, suspended minerals, and gases

9. Magma
Magmas are named after the igneous rocks that form from the magma
Three types of magma:
Basaltic (Mafic)
Andesitic
Rhyolitic (Felsic)
Basaltic Lava

10. Magma
Viscosity – a substance’s internal RESISTANCE to flow

11. Magma
The HIGHER the viscosity, the more a substance resists flowing. This means the substance is thicker, flows slowly, and is more like a milkshake’s consistency
The LOWER the viscosity, the less a substance resists flowing. This means the substance is thinner, flows easily, and is more like milk or water’s consistency

12. What Affects Viscosity?
1. Temperature – the warmer the substance, the lower the viscosity
Ex: you can heat up honey to make it flow better
Hotter magma has lower viscosity (flows more quickly) than cooler magma
As magma cools, it slows down and hardens into volcanic rock

13. What Affects Viscosity?
2. Silica Content – the higher the silica content in a substance, the higher the viscosity
Magma with lots of silica has higher viscosity (flows more slowly) than magma with little silica
The higher the silica content, the more explosive the eruption

14. Type of Magma
Silica Content
Viscosity
Eruption
Basaltic (Mafic)
Quiet, Not Explosive
Andesitic
Medium Eruptions
Rhyolitic (Felsic)
Highly Explosive
Low
Low
Medium
Medium
High
High

15. Types of Volcanoes
Three types of volcanoes (that correspond with the three types of magma)
Shield
Cinder Cone
Composite

16. Shield Volcanoes
Broad, gently sloping sides with a nearly circular base
Non-explosive eruptions (lava just flows out the vent with no real “eruption”)
Lava has low amounts of silica and low viscosity
Example: Hawaiian Islands

17. Cinder Cone Volcanoes Steep-sided, generally small (< 500m high)
More explosive eruptions than shield volcanoes
Lava has more silica and higher viscosity than shield volcanoes

18. Composite Volcanoes Tallest of all volcanoes
Highly explosive eruptions, most dangerous to humans

19. Composite Volcanoes
Lava has high amounts of silica and a high viscosity
Examples: Mount St. Helens and Mount Rainier, both in Washington State

20. Summary Volcano Type Appearance Eruption Strength Silica Content
Viscosity
Shield
Broad, sloping sides
Cinder Cone
Steep sides and small
Medium
Composite
Tallest
Not explosive
Low
Low
Highly explosive
High
High

21. Based on this information, match the types of magma with the types of volcanoes:
Shield
Cinder Cone
Composite
Basaltic/Mafic
Andesitic
Rhyolitic/Felsic

22. Questions about the Quiz?

23. Quiz Put MC answers in blanks. Attempt every question!
Turn in when done
I will pass out progress reports as you finish
IF YOU WANT YOUR MAKEUP WORK: PUT YOUR NAME ON A PIECE OF PAPER, WRITE DOWN THE ASSIGNMENTS YOU ARE MISSING, TURN IT IN; I WILL GIVE THEM TO YOU TOMORROW

25. Dante’s Peak -- Background
Fictional volcano Dante’s Peak hasn’t erupted in over 7,000 years.
Two people were swimming in hot springs when the springs began to boil, killing the people.
Geologists were called in to investigate.

26. The head geologist (Harry) is concerned, but doesn’t have any scientific proof that the volcano is going to erupt.
The town decides to keep it quiet for two reasons: 1) the volcano hasn’t erupted in 7,000 years and 2) the last threat was a false alarm that really hurt tourism and the town’s economy
The geologists are about to leave town when they notice that the tap water is brown and smells like sulfur…

27. As we’re watching, keep the following questions in mind:
Why didn’t the people evacuate?
If you had been a resident of that town, would you have evacuated?
What real-life disaster have we talked about in class where people did not follow the advice to evacuate?
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