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Notes #2 Types of volcanoes
Know there are two kinds of
volcanoes: one kind with violent
eruptions producing steep slopes and
the other kind with voluminous lava
flows producing gentle slopes.
1. The viscosity of magma determines
what type of volcano forms and how
hazardous it will be.
• Viscosity is the
resistance of a liquid
to flowing.
• What are some
examples of viscous
liquids?
1. The viscosity of magma determines
what type of volcano forms and how
hazardous it will be.
• Less viscous magma erupts from volcanoes and flows easily
• More viscous magma does not flow easily and traps gas
• When gas reaches the surface it can expand and explode
2. Shield volcanoes are formed from basaltic/low
viscosity lava flows.
• Creates large volcanoes with low slopes
2. Shield volcanoes are formed from basaltic/low
viscosity lava flows.
2. Shield volcanoes are formed from basaltic/low viscosity lava flows.
•Are made from layers of lava flows
•Are made from mafic magma that is rich in iron and magnesium
•Are found at hot spots and on divergent plate boundaries where the mantle is melting
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3. Cinder cones are small volcanoes made
from magma that is viscous enough to trap
some gas.•Have steep sides•Are made from mafic lava that shoots out of the vent creating a pile of pyroclastic material (pieces of rock)
Mt Lassen
4. Composite or stratovolcanoes are large volcanoes that
have violent, hazardous eruptions because they are made
by viscous magma.
•Have
moderately
steep sides
4. Composite or stratovolcanoes are large volcanoes
that have violent, hazardous eruptions because they
are made by viscous magma.
• Are made of layers
of felsic lava flows
and pyroclastic material
• Occur as a result
of subduction
• Are most explosive
when gas is trapped in the
magma
Mt Lassen
4. Composite or stratovolcanoes are large volcanoes
that have violent, hazardous eruptions because they
are made by viscous magma.
Before
During
After
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Pyroclastic
material: ash and
rocks are thrown
into the air
Pyroclastic flow: an avalanche of rock, ash and gas
Lahar: a mudflow (pyroclastic materials mixed
with water)
Lahar: a mudflow (pyroclastic materials mixed
with water)
Fumarole
A crack in
the crust
that emits
gases
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Bubbling Mud Pots