1. 10.1 The nature of volcanic eruptions

2. What causes a Volcano?
Volcanic activity often starts when a crack develops in the crust. Magma is then forced toward the surface.
Repeated eruptions of lava or pyroclastic materials eventually build a mountain which is called a volcano

3. Factors Affecting Eruptions
The primary factors that determine whether a volcano erupts violently or not include:
Magma Composition
Magma Temperature
Amount of dissolved gasses in the magma

4. Viscosity – is a substance’s resistance to flow
Ex- Syrup is thicker than water
Magma from a more explosive volcano can be 1000x more viscous than that of a “quieter” volcano
Higher Temperature = less viscous
Lower Temperature = more viscous (hardens) = mobility decreases
More Silica in magma = higher viscosity

5. Dissolved Gases
Gases are mostly water vapor and CO2
As magma gets closer to the surface, the pressure of the magma is reduced, which allows for the dissolved gases to be released

6. Volcanic Material Lava Flows Gases Pyroclastic Materials
Depends on silica content
High silica = harder to flow
Low silica = more fluid like
Gases
Pyroclastic Materials
Particles that are produced in a volcanic eruption
Fragments ejected during an eruption range in size from extremely fine dust & ash to pieces that weigh several tons

7. Types of Volcanoes
Shield Volcanoes
Cinder Cones
Composite Cones

8. Shield Volcanoes Produced by the build up of fluid basaltic lava
Shape = broad & slightly domed
Have “grown up” and from the sea floor and have formed islands
Examples: Hawaiian Islands & Iceland

10. Cinder Cones
Cinder cones are built from ejected lava fragments which harden in the air
Fragments range in size
Typically a result of gas rich basaltic magma
Composed mostly of Pyroclastic material
Occasionally releases lava

11. Shape: simple & smaller; determined by the steep sided slopes
Usually the result of a single eruption that lasts only a few weeks and very rarely more than a few years
The eruption only occurs once due to the fact that the pipe connecting the vent to the magma chamber hardens

13. Composite Cones Large & symmetrical
Composed of layers of lava & pyroclastic material
Viscous lava (travel short distances)
Beautiful & possibly the most dangerous
Located in a narrow zone along the Pacific Ocean “Ring of Fire”

17. Other Volcanic Landforms
Calderas – a large depression in a volcano
Form in 1 of 2 ways: collapse of the top of a shield volcano OR collapse of the top of a composite volcano
Necks & Pipes
In most volcanoes, magma travels through pipes that connect the magma chamber to the surface

18. Lava Plateaus The greatest volume of material comes from fissures
Basaltic lava flows from the fissures (which covers a large area)

19. Resources

20. Sources Google Prentice Hall Earth Science Book National Geographic
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