1. Volcanic Eruptions

2. Mafic Lava Dark colored Rich in magnesium and iron
Formed from oceanic crust
Cools rapidly

3. Felsic Lava
Light colored
Rich in silica
Formed from continental crust

4. Eruptions
Composition of lava determines the force of the eruption

5. Oceanic Eruptions Erupt on the ocean floor and oceanic islands
Mafic lava
Very hot
Very thin (watery)
Flows easily

6. Continental Eruptions
Erupt on the land
Felsic lava
Cooler
Thicker
Contains large amounts of gases
Carbon dioxide and water vapor
Explosive

7. Mafic Lava
Pyroclastic material (tephra)-rock fragments ejected from volcanoes
Volcanic ash- less than 2 mm
Volcanic dust- less than .25 mm
Both can travel around the Earth in the atmosphere

8. Volcanic Cones
Piles of volcanic material around the vent

9. Volcanic cones Shield cones Cover wide areas Broad at the base
Gentle slope
Quiet eruptions
Example Hawaiian Islands

10. Shield cones

11. Volcanic cones Cinder cones Explosive eruptions Very steep slopes
Rarely more than a few hundred meters high

12. Cinder cones

13. Volcanic cones Composite cones Develop into high volcanic mountains
Alternating types of eruptions
Examples: Mount Fuji, Mount Hood, Mount St. Helens

14. Composite cones

15. Crater
Funnel shaped pit at the top of a volcanic vent

16. Caldera Large basin shaped depression caused by an explosive eruption
Magma chamber below a vent, causing the volcanic cone to collapse

17. Predicting Volcanoes Earthquakes
Temperature changes in rock around vent
Bulging of the surface of the volcano
Change in gases given off