1. Volcanoes
Chapter 12

2. Section 1: Volcanoes and Earth’s moving plates
How do volcanoes affect people?
What conditions cause volcanoes to form?
What is the relationship between volcanoes and plates?
Section 1: Volcanoes and Earth’s moving plates

3. Most active volcanoes Hawaii
Kilauea (kee low AY ah) is the world’s most active volcano
May 1990 eruption destroyed the town of Kalapana Gardens
Eruptions on and off since January 1983
Iceland
Hekla eruption February 2000
Iceland sits on an area where Earth’s plates more apart
Known as the island of fire and ice

4. Effects of Eruptions
Human
Environmental
Evacuations occur with enough warning – people must leave their homes. At times, everyone in the path is completely destroyed, homes, cars; towns are buried in ash.
Sulfurous gases from an eruption mix with water vapor to form acid rain. Vegetation, lakes and streams are devastated by acid rain.

5. How do volcanoes form?
Deep inside Earth, heat and pressure changes cause rock to melt
This magma is slowly forced upward toward the Earth’s surface
After many, many years of this process, magma reaches the surface and flows out through an opening called a vent
As the lava flows out and cools, it forms igneous rock around the vent. The steep walled depression around the volcano’s vent is the crater.

6. Where Do volcanoes occur?

7. Divergent boundaries Plates moving apart
Iceland is part of the Mid-Atlantic Ridge and located in the Artic Circle
Plate separate forming rifts
Lava flows from the rifts and as it cools, builds layers of rock
Sometimes, the eruptions rise above sea level, forming new islands (like Iceland)
Island of Surtsey was formed in 1963

8. Convergent boundaries
Plates move together
Oceanic plates slide underneath continental plates
Andes Mountains in South America
Volcanoes at convergent boundaries tend to erupt more violently than others
Island of Monteserrat Volcano
July 1995
Destroyed towns, vegetation and killed people

9. Hot Spots
Hot rock at areas between Earth’s mantle and core is forced toward the crust where it melts partially (this is NOT a plate boundary)
Hawaiian Islands (p. 333 Figure 5)
Formed from volcanic activity over a period of 5 million years
Five of the islands are volcanoes
Hot spot is stationary while the pacific plate moves (causing the islands to actually change locations)

10. Hanauma bay, Hawaii
Formed through a series of violent volcanic eruptions, it is now a flooded crater.

11. Hanauma Bay, Hawaii
A nature preserve popular among tourists for the beautiful coral reefs and wildlife

12. For Tomorrow Define “tephra” in your notes
Read Section 2 pg. 336 – 343
Bring a few colored pencils to diagram volcanoes!

13. Section 2 Types of volcanoes
How is the explosiveness of a volcanic eruption related to the silica and water vapor content of its magma?
What are the three types of volcanoes?
Section 2 Types of volcanoes

14. Eruptions
When you think about a volcanic eruption, what do you see in your head?
Two major factors influence how an volcano erupts:
Water Vapor & Trapped Gases Present in the Magma
Silica content in the magma

15. Eruptions
Trapped Gases
Water Vapor
Example: What happens when you shake a can of coke and then open it? Gases can escape quietly or explode all at once, like a shaken Coke.
At convergent plate boundaries, oceanic plates are involved. The more water vapor present in the magma, the more explosive the eruption.

16. Silica poor Magma Quiet eruptions
Basaltic Magma
Fluid & quiet; lava pours from the vents and runs down the sides of the volcano
Types of lava (pg. 338)
Pahoehoe- rope like, smooth
Aa- chunks of rocdk, shapr
Pillow- pillow shape chunks, most common type.

17. Silica Rich magma explosive eruptions
When plates slide underneath each other and the rock melts, the magma is forced upward
Thick magma with lots of trapped gases
Andesitic magma
Granitic magma

18. types of volcanoes

19. Shield volcano Broad volcano with sloping sides
Example – Hawaiian Islands
Basaltic Lava
What type of eruption?
Can flow onto Earth’s surface through cracks called fissures
Creates flood basalts, which is where most of the material inside the volcano comes out at

20. Shield volcano

21. Cinder Cone Volcano Steep sided, loosely packed
Forms from tephra falling to the group from explosive volcanic eruptions
Paricutin
February 1943
Farmed noticed a large hole in his cornfield suddenly had hot, glowing cinders in it. Over the next few days, cinders were thrown into the air from the opening, creating a cinder cone volcano

22. Cinder cone volcano

23. Composite volcano
Some volcanoes alternate between quiet and explosive eruptions
Formed from a cycle of explosive and quiet eruptions, causing lava and tephra to layer on top of each other
Found mostly where Earth’s plates come together
Example – Mount Rainer in Washington

24. Composite volcano

25. Three types of volcanoes

26. upcoming
Section 1 & 2 Review Worksheet Bill Nye “Volcanoes” PROJECT RESEARCH DAY FRIDAY. You need to have chosen your volcano by Friday. Section 3 –Monday Test – Wednesday PROJECTS DUE THURSDAY, 1/16 AND FRIDAY, 1/17.

27. Section 3 igneous rock features
What are igneous rock features and how do they form?
How does a volcanic neck and a caldera form?
Section 3 igneous rock features