1. Inside Earth: Chapter 3- Volcanoes
Section 2: Volcanic Activity

2. Guide For Reading What happens when a volcano erupts?
How do the two types of volcanic eruptions differ?
What are some hazards of volcanoes?

3. How Magma Reaches Earth’s Surface

4. Why does magma rise?
Magma rises because it is less dense that the surrounding solid material

5. Guide For Reading: What happens when a volcano erupts?
As the less dense magma rises, the pressure decreases
The dissolved gas separates out and bubbles form
A volcanic erupts when an opening develops in weak rock on the surface
During a volcanic eruption, the gases dissolved in magma rush out, carrying the magma with them
Once magma reaches the surface and becomes lava, the gases bubble out

6. Inside a Volcano

7. Magma Chamber
The pocket beneath a volcano where magma collects

8. Pipe
A long tube through which magma moves from the magma chamber to Earth’s surface

9. Vent
The opening through which molten rock and gas leave a volcano

10. Where are vents located?
Usually there is one central vent at the top of the volcano
Often times there are additional vents that open on the volcanoes sides

11. Lava Flow
The area covered by lava as it pours out of a volcano’s vent

12. Crater
A bowl-shaped area that forms around a volcano’s central opening
Lava collects there

13. Checkpoint (page 94): How does magma rise through the lithosphere?
Liquid magma in the asthenosphere is less dense than the rock in the lithosphere above it, so it flows upward through cracks in the rock
The magma is stored in the magma chamber
It continues upward (through the pipe) until it reaches the surface (exiting through a vent) or it is trapped beneath layers of rock.

14. Characteristics of Magma

15. Silica
A material that is found in magma,formed from the elements oxygen and silicon
The more silica the magma has the thicker it is

16. What three factors contribute to how forceful a volcanic eruption is
What three factors contribute to how forceful a volcanic eruption is? Explain how each determines this.
Amount of gas present
How thick or thin the magma is (Temperature)
Thinner (hotter) is more fluid
The silica content
If the silica content is high, magma is thick
This causes the pressure to build

17. Types of Volcanic Eruptions

18. Quiet eruptions like the ones that take place on _______ have built up the big island over _______ of _______ of years.
Mount Kilauea
Hundreds
Thousands

19. Pahoehoe
A hot, fast-moving type of lava that hardens to form smooth, ropelike coils

20. Aa
A cooler, slow-moving type of lava that hardens to form rough chunks; cooler than Pahoehoe

21. What is the difference between the two types of lava?
Pahoehoe is a faster flowing lava that cools slowly resulting in a smooth texture
Aa is a slower flowing cooler type of lava that hardens into rough chunks

22. Figure 7 Inferring (page 97) What accounts for the differences between these two types of lava?
The temperature of the lava
The speed at which the lava flows

23. Checkpoint (page 97): What types of lava are produced by quiet eruptions?
Quiet eruptions produce two types of lava: pahoehoe and aa
Pahoehoe is a fast-moving, hot lava
Aa is a cooler, slower-moving lava

24. Pyroclastic flow
The expulsion of ash, cinders, and bombs from a violent volcanic explosion

25. Checkpoint (page 98): What causes an explosive eruption?
Magma that is thick and sticky causes a volcano to erupt explosively
Magma can not flow freely causing pressure (gas) to build up until it explodes

26. Guide For Reading: How do the two types of volcanic eruptions differ?
Quiet eruptions occur when the lava flows more easily because gas dissolved in the magma bubbles
When the lava is thick and sticky the gas continues to store increasing pressure
When the pressure becomes so great an explosion takes place when the gas pushes the magma out with incredible force

27. Stages of a Volcano

28. What are the three stages of a volcano? Explain each stage.
Active
A volcano that is erupting or has shown signs that it may erupt in the near future
Dormant
A volcano that is not currently active, but may become active in the future
Extinct
A volcano that is unlikely to erupt again

29. Other Types of Volcanic Activity

30. Hot Spring
A pool formed by groundwater that has risen to the surface after being heated by a nearby body of magma

31. Geyser
A fountain of water and steam that builds up pressure underground and erupts at regular intervals

32. Geothermal Energy
Energy from water and steam that has been heated by magma
Geothermal energy is produced by drilling a well into the ground where thermal activity is occuring.
Once a well has been identified and a well head attached, the steam is separated from the water, the water is diverted through a turbine engine which turns a generator.
Usually the water is injected back into the ground to resupply the geothermal source.
academic.evergreen.edu/g/grossmaz/heidtken.html

33. Monitoring Volcanoes

34. How do geologists monitor the activity of a volcano?
Measure tilt caused by magma movement underground using tiltmeters & laser-ranging devices
Monitor temperature underground
Monitor small earthquakes that occur in the area around a volcano

35. Volcano Hazards

36. Guide For Reading: What are some hazards of volcanoes?
Fire
Bury entire towns
Damage crops
Landslides
Avalanches of mud
Damage car and jet engines