Understanding volcanic eruptions

• What are volcanoes?

  Openings in the earth's crust through which lava and ash erupt
• What is lava?

  Magma which has been forced up from the mantle, where it cools and becomes volcanic rock
• What are lava flows?

  Primary volcanic hazards where lava erupts from a volcano
• What are pyroclastic flows?

  Primary volcanic hazards where a mixture of lava, ash, and gases erupts from a volcano, with these also being much faster than lava flows
• What are tephra falls?

  Primary volcanic hazards where tephra, pieces of volcanic rock, fall around the volcano
• What are gas eruptions?

  Primary volcanic hazards where poisonous natural gases are released into the atmosphere from an eruption
• What are lahars?


  Secondary volcanic hazards where a mixture of rock, ice and mud flow down the side of a mountain, caused when an eruption melts snow
• What are glacial outburst floods?

  Secondary volcanic hazards where the heat of a volcanic eruption melts the snow and ice in a glacier, causing heavy flooding
• How can volcanoes be measured?

  Using the Volcanic Explosivity Index to describe or compare the size or magnitude of volcanic eruptions
• What are the main factors used to assign a number on the VEI?

  The amount and height of tephra ejected, and how long the eruption is
• How can volcanoes be predicted?

  By monitoring small earthquakes, changes to the surface of the volcano, and changes to the tilt of the volcano