Transcript Types of Volcanoes

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More than 600 active volcanoes on Earth
Kilauea in Hawaii erupts continuously.
Iceland is a country that is made entirely from
volcanoes.
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Volcanic ash and debris can
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Kill crops and forests
Kill people
Destroy habitats
Sulfuric acid from volcanic gases mixes with
water vapor to create acid rain.
 Gases and ash particles can block sunlight
from entering Earth’s atmosphere lowering the
overall temperature of the planet.
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Soufriere Hills,
Montserrat 1995
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Volcanologists knew
it was about to erupt.
Some folks refused to
leave.
Pyroclastic flows
wiped out cities and
towns in its path,
killing 20 people who
ignored the
evacuation order.
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Plates moving apart—divergent boundaries
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Iceland’s volcanoes emerged from seafloor spreading
Eyjafjallajökull eruption 2010
 http://www.youtube.com/watch?v=tGPD_0SCDp4
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Plates moving together—convergent
boundaries
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Soufriere Hills, Montserrat 2007
 http://www.youtube.com/watch?v=8sPyyHY57H4
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Hot Spot Volcanoes
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Hawaii’s Kilauea is the most active volcano in the
world.
 http://www.youtube.com/watch?v=488BkTUsMa4
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Over a period of about 5 million years, the Pacific plate
has moved over a hot spot where mantle material is
particularly hot and blasts through Earth’s crust like a
torch.
The lava that leaks out at the hot spot built up and
formed a volcanic island.
As the plate moves over the hot spot, the magma
punches through a new spot in the crust, forming new
islands.
Volcanoes that are no longer over a hot spot become
dormant or extinct.
The volcanic islands that are quiet begin to erode by
the ocean waves.
1.
Water vapor and other gases
a.
b.
c.
Water dragged under with a
subducting plate turns to water vapor.
Water vapor and other trapped gases
take up more room, creating more
pressure.
Trapped gases such as water vapor
and carbon dioxide build up pressure
in magma.
2.
Silica
a. The more silica present in
the magma, the thicker and
stickier it is.
b. The thicker and stickier the
magma, the more likely it is
to trap gases.
c. Think of blowing a straw
into the bottom of a thick
milkshake compared to a
runny milkshake.
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Silica-poor magma is basaltic magma.
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Produces runnier magma and quiet eruptions
 Pahoehoe is ropelike or hairlike in structure and comes
from hotter lava.
 Aa is rough and jagged and comes from cooler lava.
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Silica-rich magma is
granitic.
Thick, sticky magma
that is good at
trapping gases.
 Gases can expand
rapidly, triggering an
explosive eruption
 Soufriere Hills,
Montserrat
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Amounts of silica can vary in andesitic
volcanoes.
 They often have more silica than basaltic,
less than granitic
 These volcanoes often form at convergent
plate boundaries.
 They an alternate between explosive and
quiet eruptions
 Krakatau, Indonesia is an example.
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Circular, broad
base, gentle
slopes, basaltic,
non-explosive.
Hawaiian Islands
•Alternating layers of
lava and tephra
• Mt. Ranier, WA
• Soufriere Hills,
Montserrat
• Explosive eruptions
throw rock and bits
of tephra into the air.
•Falls to the ground
and collects into a
cone shape.
•Paracutin, Mexico
Types of
Volcanoes
Shield
Volcano
Composite
Volcano
Cinder Cone
Volcano
Kilauea,
Hawaii
Mt. St. Helens,
Washington
Parícutin,
Mexico