1. Volcanoes & Volcanism

2. Anatomy of a Volcano– Primary Features

3. Anatomy of a Volcano—Secondary Features

4. Anatomy of a Volcano—Tertiary Features
Produced by the collapse of a volcano into its emptied magma chamber

5. Parts of An Eruption

6. Geologic Hazards
associated with
Volcanoes

7. 1. Lava Molten rock released during a volcanic eruption.
Can be mafic (thin, and very fluid), felsic (thick and chunky), or intermediate (a mix of mafic and felsic)

8. 1. Lava
Pahoehoe – hot mafic lava with a smooth, ropy surface

9. 1. Lava
Aa – cooler mafic lava with a sharp, angular texture; also called “clinker”

10. 2. Gases
Form from the mixture of ground water with magma and solid rock below the surface– often acidic

11. 3. Pyroclastics (Tephra)
Solid rock produced during an eruption
Sources – neck, cone, lava cooled in the atmosphere
Size
ash—small (looks like smoke)
blocks—angular up to 6 meters
bombs-rounded up to 6 meters

12. Lahar—mixture of ash and water

13. Types of Volcanoes…

14. 1. Shield Volcanoes Form from oceanic crust; mafic lava
Slope of cone is <5o
Example: Hawaii
Eruption: mostly lava; have few gases or pyroclastics; eruptions can last for months or years

15. 2. Composite (or Strato) Volcano
Form on continental margins with intermediate lava
Moderate slope 15-30o is typical
Example: Mt. St. Helens, Washington
Eruptions– a mixture of lava, gases, and pyroclastics; a delay of years is possible between eruptions

16. 3. Cinder Volcanoes Form from continental crust; felsic
Steep slope >30o
Example: Crater Lake, Oregon
Eruptions: mostly gases and pyroclastics; very little lava (if any); very violent eruptions (often destroy the cone)

17. Where in the world?