Download Volcanoes

 http://www.youtube.com/watch?v=BcFtpWjZwlE
 Volcano – opening in Earth’s surface that often forms a
mountain when layers of lava and volcanic ash erupt
and build up.
 Dormant volcano -
volcano that is not
“active”
 1. Divergent Boundaries-
location where two plates
are moving apart
 Long deep cracks are present
and lava flows up and quickly
cools
 2. Convergent Boundaries -
location where plates are
moving together
 One plate may slide under
the other and partially melt =
subduction zone
 http://www.youtube.com/
watch?v=kQES0ALjUoI
 The magma may then get
forced upward and form a
volcano
 Ex. Pacific Ring of Fire (Mt.
Saint Helens)
 3. Hot Spots
 Occur because mantle is
hotter in some areas
than others and the
magma is closer to the
crust and can
sometimes melt the
Earth’s crust.
 Ex. Hawaiian Islands
 1. Amount of water vapor and other gases that are
trapped in the magma.
 2. If the magma is basaltic or granitic
 Basaltic (dark) magma contains less silica and is very
fluid
 Granitic (light) magma contains higher levels of silica
and is very thick
 The type of volcano is determined by the type of
eruption
 The type of eruption is determined by the type of
magma
 There are three types of volcanoes.
 Formed by eruptions




that vary between quiet
and explosive.
Made from andesitic lava
Composed of layers of
tephra and lava.
Tall, steep-sided cones
Ex: Mt. Saint Helens &
Mt. Vesuvius
 Explosive eruptions
 Composed of tephra –
volcanic material (ash,
cinders, rocks, lava
bombs)
 Small, steep-sided cone
 Ex: Paricutin, Mexico
 Gently sloping sides
 Basaltic lava
 Quiet eruptions
 Ex. Hawaiian Islands