Download volcano type.sxi - Milan Area Schools

All About Volcanoes.....
What is a volcano?
- A volcano is an opening in Earth that
erupts gases, ash & lava
- FYI – There are over 600 active
volcanoes on Earth right now! Especially
in Hawaii and Iceland
How do volcanoes form?
A. Deep inside Earth, heat & pressure
changes cause rock to melt
B. Melted rock is less dense than solid rock
so it is slowly forced up
C. After a long period of time, the magma
reaches the surface & flows out of a vent
D. When the lava flows out, it cools, forming
layers of igneous rock around the vent
E. The steep walled depression around the
vent becomes a crater.
Where do volcanoes occur?
Volcanoes usually occur :
A. Where tectonic plates are moving apart
(divergent plate boundaries)
example: Mid-Atlantic Ridge
B. Where plates move together (convergent
plate boundaries)
example: Andes Mountains (these type
of volcanoes tend to be more violent)
C. Hot Spots – Thin spots where magma
comes to surface in middle of plates ex. Hawaii
The Hawaiian Islands form as they move
over a Hot Spot (or thin area of crust
where magma rises)
Volcano Parts
Volcanoes have an opening at the summit
and depending on its size, it can be:
A. a crater (steep walled depression at summit)
or
B. a caldera ( summit depression > 1 km
diameter)
They also have a Vent ( the tunnel that connects
the crater to the magma chamber
Crater Lake –
with remnants
of Mt Mazama
(OR)
2 Calderas (in
Galapagos
Islands)
3 Main Volcano Types
1. Shield Volcano
- broad, slightly domed
- primarily made of basaltic (less viscous)
lava
- generally very large (& flat) & produce a
lot of lava
example: Mauna Loa in Hawaii
Shield Volcano - Hawaii
3 Main Volcano Types
2. Cinder Cone
- built from ejected lava fragments
(pyroclastics)
- steep slope with loosely packed fragments
- usually small & often occur in groups
- Can form quickly
ex. Paricutin in Mexico
In 1943 a a farmer noticed a hole in
his field spewing smoke. A few days later,
a cinder cone several hundred meters
covered his field!
Cinder cone –
Mojave Desert
California
3 Main Volcano Types
3. Composite cone (Stratovolcano)
- most are in Ring of Fire (encircle Pacific
Ocean)
- large & most violent
- produce granitic (more viscous) lava
- erupt a mix of lava & pyroclastics
ex. Mt. St. Helens in Washington
Kanaga stratovolcano - Alaska
Relative sizes of the 3 volcano types. Cinder
cones are tiny, shield volcanoes are huge
Remember not all magma reaches the
surface and erupts