Download Causes of Volcanoes

Causes of Volcanoes
pg. 111
Things to know when talking about
Volcanoes…

Volcanoes release material from the
mantle.
Magma- inside the
Earth
Lava- on the surface
Both are made up of the same
mantle material!
The mantle is basically solid, so
how do we get liquid- really liquidmagma / lava?
Two ways to
melt the solid
mantle…
 Add
water
 Relieve (decrease
or lower) pressure.
What are causes of
volcanic eruptions?
1.
2.
3.
Magma rises in
the mantle.
Releases gas.
Gas expands
and increases
pressure under
surface until
finally it erupts.
Where do
volcanoes form?
80% of
volcanoes form
at convergent
boundaries
when oceanic
lithosphere is
subducted.
What is the “Ring
of Fire?”
“ring” of volcanoes
 plate boundaries
of the Pacific
Plate- oceanic
plate subducts
under the
converging
continents.

Why does subduction
1. Oceanic
produce magma?
Trench
crust contains
water, when the
crust melts, the
water is
released,
forming magma
2. The
magma then
rises to form
a volcano.
Where else do
volcanoes form?
15% of
volcanoes
form at
divergent
plate
boundaries.
(like midocean ridges)
How does magma
form at a divergent
boundary?
1. deep cracks
called a
rift
zone form
between the
plates
2. Lowers pressure on
mantle at boundary.
Less pressure at
the boundary
3. Magma forms and
rises.
What about volcanoes that form far
from either type of boundary?
What are Hotspots?
Volcanoes
that form far
away from a
plate
boundary
Hawaii was
formed from a
hotspot
Hotspots stay in the same location
as the plate moves across it…
Yellowstone National Park- Old Faithful

Geyser
Volcanoes are classified
into 3 categories
Extinct
volcanoes—have
not erupted in
recorded history
Dormant—
not currently
active
Active
volcanoes—
currently showing
volcanic activity
Can we predict a
volcano eruption?
Scientists look for:
 Small
quakes
 Volcanic
gases
 Bulging
mountains
 Changes in
surface
temperature