1. Chapter 18
Volcanic Activity

3. Magma
A mixture of molten rock, suspended mineral grains, and dissolved gases deep beneath Earth’s surface.
Forms when temperatures are high enough to melt rock
800°C-1200°C

4. Factors That Affect Magma Formation
Temperature and Pressure
As pressure increases the temperature at which a substance melts increases.
Presence of water
Lowers the melting point temperature

5. Three Major Types of Magma
Basaltic magma
Least explosive
Andesitic magma
Rhyolitic magma
Most explosive
Magmas differ in the source rock from which they form, viscosity, silica content, gas content and explosiveness

6. Intrusive Activity Affects Earth’s Crust
Magma can force rock apart and enter newly formed fissures (cracks)
Magma can cause rocks to break off and sink into the magma chamber
Magma can melt rock into which it intrudes

7. Types of Intrusions
Batholiths, stocks, sill, dikes, and laccoliths are plutons that are classified according to their size shape and relationship to surrounding rock.
Batholiths are the largest plutons and often form the cores of many of Earth’s major mountain chains.

8. Volcanoes Lava flows onto Earth’s surface through a vent
Multiple lava flows can accumulate to form a volcano
A crater is a depression that forms around a vent at the summit of a volcano
A caldera is a large crater that forms when a volcano collapses during or after an eruption.

9. Three Types of Volcanoes
Shield volcanoes
Cinder cone volcanoes
Composite cone volcanoes

10. Tephra
Rock Fragments ejected from a volcano

11. Where Volcanoes Form Convergent and divergent plate boundaries
Hotspots
Usually hot areas in the mantle that are stationary for a long period of time
Flood basalts
when lava flows from fissures to form flat plains or plateaus