1. Volcanic Eruptions

2. What causes volcanoes to erupt?
Magma is hot, so it is less dense than surrounding rock and it rises to the surface
Volcanic eruptions occur when the dissolved gases in the magma produce enough pressure to force the magma out of the volcano
Magma on the surface is called lava

3. Viscosity of magma
Viscosity depends on friction between particles of a fluid.
More friction = greater viscosity and slower movement, less friction = lower viscosity and faster movement
The viscosity of magma depends on silica content and temperature
More silica = higher viscosity, less silica = lower viscosity
Lower temperature = higher viscosity, higher temperature = lower viscosity

4. Types of eruptions Depends on viscosity of the magma
1. Quiet eruptions – low viscosity, lava flows gently out of the volcano
2. Explosive eruptions – high viscosity, lava is forced out of the volcano as a pyroclastic flow (which includes gases, ash and various size chunks of rock being shot out of the volcano)

5. Types of volcanoes Shield – quiet eruptions, gentle sloping mountains
Cinder-cone – explosive eruptions, steep mountain
Composite – alternating quiet and explosive eruptions, tall mountains – alternating layers of lava and ash

6. Stages of volcanic activity
Active – erupting, shows signs it may erupt in the near future
Dormant – not erupting, no signs, but COULD
Extinct – unlikely to ever erupt again

7. Why live near volcanoes?
Dangers: (suffocation due to ash and poisonous gas, property damage)
Benefits: Volcanic eruptions cause soil to be extremely fertile, which is great for farming, geothermal energy can be harnessed