Download What causes volcanoes

Notes: Volcanoes
What causes volcanoes?
Magma under heat & pressure is less
dense than rock. It flows out of vent and
cools quickly becoming solid, igneous
rock that builds up around the vent. The
crater is the steep walled depression
around the vent. Volcanoes may vent
from the top or laterally (on the side)
Where are volcanoes located?
They are related to the Earth’s plates:
Diverging plates-create rifts where
magma flows and cools quickly in
seawater. Can build up above sealevel
and become island- Ex Iceland
Converging plates-magma created in
subduction zone is less dense than
surrounding material and is forced
outward. Ex-Mt. St. Helens (Cascade
range)
Hot spots- places in the mantle that are
unusually hot. Magma from deep in
Earth’s mantle has melted the crust to
form volcanoes. Ex- Hawaiian Islands
Types of Eruptions:
Explosive, violent
(1)Trapped gases (water, carbon dioxide)
Under pressure eventually escape.
Mt. St. Helens
(2)Composition magma- granite converging plates, subduction zones,
dense, thick, lots of silica. Gets trapped
in vents, pressure builds beneath itexplosive eruption, gases expand rapidly
often carrying pieces of lava in explosion
Mt. St. Helens
If the water content is high the eruption
is more explosive.
Composition magma- basalt –
Less silica, less dense, more fluid
produces quiet, nonexplosive eruptions.
Mt. Kilauea
Form or shape of volcano has to do with
type lava: basaltic, granitic, intermediate.
Shield Volocano
Quiet, spreads basaltic lava in flat layers
which build up to be broad volcano with
gently sloping sides. Ex-Mauna Loalargest active volcano on Earth.
Cinder cone Volcano
Explosive, throws lava in the air which
cools, hardens and falls as cinders,
rocks(bombs) Becomes steep sided,
cinder cone. Ex-Paricutin, Mexico
Composite- has explosive period and
quiet period. Forms at convergent plate,
lava and rock forms in layers.