Transcript Volcano types and projectiles

Volcano types and projectiles
Eruptions and prediction
Lava types
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Lava is the material that erupts from volcanoes, and has
many different types.
Mafic lava is rich in iron and magnesium, and
usually found on oceanic crust.
Felsic lava contains silica and is usually from
melted continental crust.
Pahoehoe lava is a rapidly cooling lava that
gives a ropey, wrinkly look.
Aa is jagged and blocky.
Pillow lava is circular and cools quickly.
Lava types (continued)
Aa lava flowing in Hawaii
Pillow lava on the midocean ridge
Eruption differences
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Volcanoes that erupt can do so
explosively or quietly.
Explosive eruptions tend to
happen on continental
volcanoes because there are
many trapped gases in the
lava.
Quiet eruptions tend to happen
on oceanic volcanoes
(including island volcanoes)
and are because mafic lava is
very hot and thin, allowing
gases to escape easily.
A 10 meter high lava fountain from an
explosive eruption
Volcanic rock fragments
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Tephra particles are rock
thrown from volcanoes
during eruptions.
It is classified in the
following ways, and are
all based on the size of
the particles.
Tephra is also called
pyroclastic material.
Tephra classification
Size
Name
0 – 0.25 mm
Volcanic dust
0.025 mm – 2 mm
Volcanic ash
2 mm – 64 mm
Lapilli
64mm >
Volcanic bombs
64mm >
Volcanic blocks
Volcano cone features
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Shield volcanoes cover a wide area and result
from quiet eruptions. Mafic lava forms a
gradually sloped cone.
Cinder cones cover smaller areas but are higher
and steeper, made from solid fragments ejected
from a volcano.
Composite cones/Stratovolcanoes are formed
from both types of eruptions, usually alternating.
Volcano cones
Shield volcano (top
left)
Cinder cone (top right)
Stratovolcano (left)
Craters and calderas
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The vent on the top of a
volcano is called a crater.
A caldera is the remnants
of a volcano whose cone
has collapsed.
Krakatau is the most
well-known caldera,
sporting a diameter of 6
km.
Volcanic eruption prediction
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Predicting volcanic eruptions is somewhat possible and
semi-reliable.
Small earthquakes near volcanoes usually occur before an
eruption, and the more frequent they are, the more likely a
nearby volcano will erupt.
Gas emission from craters may indicate an imminent
eruption as well.
Geologists also watch for surface bulges on a volcano,
usually a sign that lava is building pressure in the crater.