VOLCANIC ERUPTIONS

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

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 temperatureMore silica = higher viscosity, less silica = lower

viscosityLower temperature = higher viscosity, higher

temperature = lower viscosity

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)

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

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

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