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 temperature More silica = higher viscosity, less silica = lower viscosity Lower 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