1. Volcanoes

2. Classification of Volcanoes
Structure
Tectonic Region
Type of Eruptive Material
Level of Activity
Location
Dangers Posed

3. Volcanoes
Volcano: anywhere magma, ash, and gas erupts onto the surface

4. Factors Affecting Eruptions
Magma Composition
Magma Temperature
Amount of Dissolved Gases

5. Magma Types
Rate at which magma moves is determined by its silica content
Felsic: High silica content, light colored, slow moving  Bigger Eruptions
Mafic: Low silica content, dark colored, fast moving  Calmer Eruptions

6. Volcanic Material Lava (magma that reaches the surface)
Gases: H20, CO2, Nitrogen, Sulfur…
Tephra: fragments of lava
Ash (less than 2mm)
Lapilli (2-64mm)
Bombs (larger than 64mm)

7. Lava Flows
Mafic
Pahoehoe: Flow with smooth ropelike surface, quick flowing basalt
AA: Rough jagged surface
Pillow Lava: Rounded pillow shaped
Felsic
Pyroclastic Flow: Superheated flow of gas and rock from the eruption

8. Eruption Types
Depending on the eruption type, different volcanoes are formed

9. Rift Eruptions
Occur at long, narrow fractures in the crust where lava flows out smoothly (mafic)
In the ocean, it occurs at spreading centers (mid-ocean ridges)

10. Hot Spots Areas of volcanic activity in the middle of a plate
Caused by heat source in the mantle that makes magma rise
Creates a chain of volcanic islands  overlying plate moves over it.

11. Shield Cone Volcanoes
Rift Eruptions & Hot Spots make Shield Cone Volcanoes
A broad base and gently sloping sides
Usually low amounts of gas, mafic lava that flows long distances before it cools

12. Shield Cone Volcanoes

13. Subduction Boundary Eruption
Magma is thick and gas-rich.
Plates are subducted, they melt, which floods the mantle with silica, making it felsic
Explosive eruptions of mainly tephra and pyroclastic flows
Form cinder cone volcanoes and stratovolcanoes

14. Cinder Cone Volcano
A volcanic, circular cone with steep sides that is mainly made of tephra
Gas rich, felsic lava

15. Stratovolcano
Tall with gentle slope near base and steep slope near summit.
Alternating layers of felsic lava and tephra deposits.
Usually gas rich, felsic lava
Lots of pyroclastic flows

16. Anatomy of a Stratovolcano

17. Plutons and Volcanism
Volcanoes and lava flows are the surface activities of volcanism
Magma below the crust, and its “behavior” impacts the earth in a variety of ways
Plutons: the rock masses that form when magma cools inside other rocks

18. Dikes
Sheets of igneous rock that cut vertically through the rock layers they intrude

19. Sills
Sheets of igneous rocks that are parallel to the layers they intrude

20. Laccoliths
When magmas bulge upwards forming domelike masses

21. Volcanic Necks
When an extinct volcano is almost completely eroded, a volcanic neck may be left
Plugs of hardened magma

22. Batholiths Largest of the plutons
Form the core of many mountain ranges
Erosion of the mountain will expose them