Volcanoes - when magma reaches the earth's surface, it is called lava.  An eruption occurs when lava forces its way to the surface.

    Active - erupted in the last century

    Dormant - no eruption for hundreds of years

    Extinct - no eruption in thousands of years

Parts of a volcano

    Magma chamber - large pockets of magma underground
    Pipe - long vertical crack through which magma moves
    Vent - the opening through which the magma or lava exits
    Crater - hollowed out area surrounding the vent
 

Types of Volcanic Eruptions

    Lava flows - a stream of lava that flows from a vent

    Volcanic explosions - a very explosive eruption of debris containing rock particles:
                                        Types of particles: (from smallest to largest) dust, ash, cinders, bombs.
 

Types of Volcanoes

    Cinder cone volcanoes - form from explosive eruptions.  Ash and debris build up around the vent.  They are
    steep near the top, but their bases slope gently.

    Shield volcanoes - have flat tops.  Lava coming out of these is runny.  As the lava cools it thickens and collects.

    Composite volcanoes - have alternating layers of debris and lava.
 

Areas of volcanic activity

    The Ring of Fire
    The Oceanic Ridge Systems
    Hot Spots