1. Science ~ chapter 6 volcanoes
Miss Nelson

2. Section 2
Volcanic Eruptions

3. What comes out of a volcano when it erupts?
Anticipatory set
What comes out of a volcano when it erupts?

4. standards
S 6.1.d – Students know that earthquakes are sudden motions along breaks in the crust called faults and that volcanoes and fissures are locations where magma reaches the surface S 6.2.d – Students know earthquakes, volcanic eruptions, landslides, and floods change human and wildlife habitats

5. The big idea
What happens when a volcano erupts? What are the two types of volcanic eruptions? What are a volcano’s stages of activity?

6. Key terms
Magma chamber – the pocket beneath a volcano where magma collects
Pipe – a long tube through which magma moves from the magma chamber to Earth’s surface
Vent – opening through which magma leaves a volcano
Lava flow – area covered by lava from a volcano’s vent
Crater – a bowl-shaped area that forms around a volcano’s central opening

7. Key terms
Silica – a material found in magma that is formed from the elements oxygen and silicon
Pyroclastic flow – an explosive volcanic eruption of ash, cinders, bombs, and gases
Dormant – a volcano that is not currently active, but that may become active in the future
Extinct – a volcano that is no longer active and is unlikely to erupt again
Geyser – a fountain of water and steam that builds up pressure underground and erupts at regular intervals

8. Read “Volcanic Eruptions” on page 221 of your textbook

9. Magma reaches earth’s surface
A volcano is more than a large, cone-shaped mountain
Inside is a system of passageways through which magma moves

10. Inside a volcano
All volcanoes have a pocket of magma beneath the surface and one ore more cracks through which the magma forces its way
View the figure of a volcano on page 223 of your textbook

11. A volcanic eruption
The explosion of a volcano is similar to shaking a soda bottle and then opening it
You cannot see the carbon dioxide gas in the soda because it is dissolved in the liquid
When you open the bottle, pressure is released
The carbon dioxide expands and forms bubbles, which rush to the surface
Dissolved gases are trapped in magma
Are under tremendous pressure

12. A volcanic eruption
As magma rises toward the surface, the pressure of the surrounding rock on the magma decreases
The dissolved gases begin to expand, forming bubbles
As pressure falls within the magma, the size of the gas bubbles increases greatly
These expanding gases exert an enormous force

13. A volcanic eruption
When a volcano erupts, the force of the expanding gases pushes magma from the magma chamber through the pipe until it flows or explodes out of the vent

14. Magma reaches earth’s surface
Read “Magma Reaches Earth’s Surface” on pages of your textbook

15. Kinds of volcanic eruptions
Geologists classify volcanic eruptions as quiet or explosive

16. Kinds of volcanic eruptions
The properties of magma determine how a volcano erupts
Whether an eruption is quiet or explosive depends on:
The magma’s silica content
Whether the magma is thin and runny or thick and sticky

17. A volcano erupts quietly if its magma is low in silica
Quiet eruptions
A volcano erupts quietly if its magma is low in silica

18. Quiet eruptions Low-silica magma is thin and runny and flows easily
Oozes quietly from the vent and can flow for many kilometers
Can produce two different types of lava that differ in temperature:
Pahoehoe
Fast moving, hot lava that is thin and runny
Surface looks like wrinkles and ropelike coils Aa
Thicker than pahoehoe
Forms a rough surface consisting of jagged lava chunks

19. Quiet eruptions
The Hawaiian islands were formed from quiet eruptions
On the Big Island of Hawaii, lava pours out of the crater on Mount Kilauea

20. Explosive eruptions
A volcano erupts explosively if its magma is high in silica

21. Explosive eruptions High-silica magma is thick and sticky
It builds up in a volcano’s pipe, plugging it like a cork in a bottle
Dissolved gases, including water vapor, cannot escape
The trapped gases build up pressure until they explode
The erupting gases and steam push the magma out of the volcano with incredible force

22. Explosive eruptions
An explosive eruptions breaks lava into fragments that quickly cool and harden into pieces of different sizes
Pumice and obsidian form from high-silica lava

23. Kinds of volcanic eruptions
Read “Kinds of Volcanic Eruptions” on pages of your textbook

24. Stages of volcanic activity
Geologists often use the terms active, dormant, or extinct to describe a volcano’s stage of activity

25. Stages of volcanic activity
An active, or live, volcano is one that is erupting or has shown signs that it may erupt in the near future
A dormant, or sleeping, volcano is expected to awaked in the future and become active
An extinct, or dead, volcano is unlikely to erupt again

26. Hot springs and geysers
Are often found in areas of present or past volcanic activity
A hot spring forms when water deep underground is heated by a nearby body of magma or by hot rock
A geyser is a fountain of water and steam that erupts from the ground

27. Monitoring volcanoes
Geologists use instruments to detect changes in and around a volcano
These changes may give warning a short time before a volcano erupts
Cannot be certain about the type of eruption or how powerful it will be
Geologists use tiltmeters and other instruments to detect slight surface changes in elevation and tilt cause by magma moving underground

28. Stages of volcanic activity
Read “Stages of Volcanic Activity” on pages of your textbook

29. Check for understanding
Describe the order of parts through which magma travels as it moves towards the surface. As magma travels towards the surface it collects in the magma chamber, then moves upward through the pipe, and finally leaves the volcano through the vent. What are the two main kinds of volcanic eruptions? The two main kinds of volcanic eruptions are quiet and explosive.

30. Check for understanding
Describe the order of parts through which magma travels as it moves towards the surface. What are the two main kinds of volcanic eruptions?

31. Guided practice
What do lava flows made of pahoehoe and aa indicate about the type of volcanic eruption that occured?

32. Guided practice
What do lava flows made of pahoehoe and aa indicate about the type of volcanic eruption that occured? Lava flows made of pahoehoe and aa indicate that the volcanic eruption was quiet.

33. Complete Volcanoes 6-2 Independent Practice