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Standard 3.e – Students know that there are 2 kinds of
volcanoes: one with violent eruptions and the other kind
with voluminous lava flows producing gentle slopes.
• Crater – circular opening in the top of the volcano
where magma erupts
• Main Vent – Magma conduit or pipe; magma
travels through this to reach the surface
• Magma Chamber – large magma reservoir of
molten rock (1-6 miles beneath earth’s surface)
• Pyroclastic Flow - a fast moving volcanic cloud of
extremely hot gases, ash, lava, and rock
(temperatures of about 1830° F and can travel at
speeds of 450 mph)
• Lava Flow – when lava flows at the surface; thick
or thin
1. Shield Volcano
2. Composite Volcano
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Largest volcanoes
Gentle and broad slopes
Fueled by Basaltic Magma
If the magma is thin and runny, the gas can escape
easily and there will not be an explosion.
• The magma just comes out of the mountain and
flows down the sides.
• Shaped like a bowl with long gentle slopes made
by the lava flows.
• Example: Hawaii
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AKA - Stratovolcanoes
Smaller than Shield
Steep-sided
Made from alternating layers of lava and ash
Fueled by Andesitic/Rhyolitic Magma
Gas cannot escape from thick, sticky magma.
Pressure builds until it explodes violently.
• Pyroclastic flow
• Lahars (mud fows)
• Example: Mount St. Helens, Mt. Shasta, Mt.
Rainier, Mt. Etna
Chaiten Volcano
Chile
Mt Peleé, Martinique (1902)
An eruption of Mt Peleé in 1902 produced a pyroclastic flow
that destroyed the city of St. Pierre.
29,000 people died….
Only 2 survived! Why?
before
after
• Rhyolitic eruptions can result in a total collapse of
a volcano
• Caldera – Large crater that forms from a volcano
collapsing into the magma chamber during a
violent eruption.
Crater Lake,
Oregon
Once called Mount
Mazama erupted
violently 7,700
years ago
Krakatoa Caldera 1883
• Tephra – rock fragments thrown into the air
during an eruption
• Ash – fine particles of mineral matter
• Lapilli – small, hardened fragment of lava
• Volcanic Bombs – chunks of lava that cools in the
air and can be thrown great distances (2.5 inches
to size of cars)
• Pyroclastic flow – extremely fast moving clouds of
superheated gas, ash, and tephra (up to 400 mph)
• Lahars – destructive mudflow
• Fast-moving Lava flows
• Landslides
• Toxic Gases
• Ash
a) Seismicity (earthquake activity) – indicates
magma moving upward and breaking crust
• Earthquake activity is measured by Seismographs
– Seismographs are stationed on the flanks of the
volcano
– These record the frequency, duration and intensity of
the earthquakes and report it back to the volcano
observatory.
b) Deformation – volcanoes will bulge in areas
(deform) as pressure builds within
• Measured with a tiltmeter
c) Gas Output – noxious gases are released as
magma rises; gas output can also cause plants
and animals to die
• Gas levels are collected at active vents and by
remote sensing
Positive effects:
• Geothermal energy: hot water, electric power
• Resources: sulfur, building materials, pumice, granite,
gravel driveways
• Formation of our climate: Outgassing
• Soil rejuvenation: Fertile soils
• Building topography: Islands, Mountains, New Land