Transcript Section 2: Volcanic Activity - SS. Peter and Paul Salesian

Section 2: Volcanic Activity
Friday, March 12, 2010
Pages 183 -- 192
Arenal Volcano -- Costa Rica
Objectives
• Describe what happens when a volcano
erupts.
• Explain how the two types of volcanic
eruptions differ depending on the
characteristics of magma.
• Identify some hazards of volcanoes
• Identify types of volcanic activity other
than eruptions.
Vocabulary Words
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Magma chamber
Pipe
Vent
Lava flow
Crater
Silica
Pahoehoe
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Aa
Pyroclastic flow
Active
Dormant
Extinct
Hot spring
Geyser
Geothermal energy
Origin of Magma
• Lava begins as magma in the mantle.
• The magma is under great pressure
• Magma flows upward because it’s less
dense than surrounding materials.
• Magma will continue to rise until it
reaches the surface or until it becomes
trapped beneath rock.
Volcanic Eruptions
• The trapped gases found in magma are
under great pressure.
– Ex: soda bottle
• As the magma reaches the surface, the
pressure decreases.
• The gases begin to separate out, forming
bubbles.
• During volcanic eruption, the gases dissolved
in the magma rushes out, carrying the
magma with them.
Stromboli -- off the North coast of Sicily.
Exploring a Volcano
Dust Cloud
Crater
Vent
Pipe
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Side Vent
Lava Flow
Lava
Magma
Magma Chamber
Characteristics of Magma
• There are many types of magma.
– Some are thick and flows slowly.
– Some are fluid and flow very easily.
– The temperature of the magma will
determine how it flows.
The Role of Silica
• The amount of silica in magma also
helps to determine how easily the
magma flows.
• What is silica?
– It’s a material formed from 2 different
elements -- oxygen and silicon.
– There are lots of silica found on the Earth’s
crust and mantle.
The Role of Silica -- Cont’d
• The more silica
magma contains,
the thicker it is.
• Magma with a lot of
silica produces lightcolored lava.
• Rhyolite is an
example of a rock
formed from magma
with lots of silica.
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Rhyolite
Role of Silica -- Cont’d
• Magma that is low in
silica flows easily
and produces darkcolored lava.
• Basalt is an
example of a rock
with very little silica.
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Types of Volcanic Eruptions
• The type of magma that flows from a
volcano will determine whether the
eruption is quiet or explosive.
Quiet Eruptions
• If the magma flows easily, the eruption will be
quiet.
• This is because the gases in the magma
bubble out slowly.
• The lava is usually thin and runny.
• There are 2 types of lava produced this way.
– Pahoehoe
– aa
Pahoehoe
• Fast moving
• Looks wrinkled,
rope-like
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aa
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• This type of lava is
cooler.
• It is slower-moving.
• When cooled, the
surface is jagged
and chunky.
Explosive Eruptions
• Eruptions are explosive if the magma is
thick and sticky.
• The thick magma prevents the lava from
flowing freely.
• Instead, the magma builds up slowly in
the pipe and acts as a plug.
• The trapped gases build up until it
explodes.
Explosive Eruptions -- Cont’d
• The lava is pushed out violently.
• The lava is broken into fragments that
cool quickly.
– Can be as small and fine as volcanic ash
– Can be as large as a car
• This type of flow is called pyroclastic
flow.
Mount St. Helen
• This is an example
of pyroclastic flow.
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Stages of a Volcano
• Active
– The volcano is alive.
• Dormant
– The volcano is asleep.
• Extinct
– The volcano is unlikely to erupt again.
Other Types of Volcanos
• Hot Springs
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Mt. Princeton Hot Springs, CO
– Formed from the heating
of underground water by
a nearby body of magma
– This water may contain
dissolved gases and
other substances found
deep within the Earth.
Other Types of Volcanos
• Hot Springs
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decompressor
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Mt. Princeton Hot Springs, CO
– Formed from the heating
of underground water by
a nearby body of magma
– This water may contain
dissolved gases and
other substances found
deep within the Earth.
Other Types of Volcanoes
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Old Faithful -- Yellowstone
• Geyser is a fountaiin
of water and steam
that erupts from the
ground.
• This is a result of
water and steam
that is trapped
underground.
Geothermal Energy
• This is a form of alternative energy.
• This form of energy is clean and
reliable.
• Is energy source is used in Iceland,
northern California and New Zealand.
Homework
• Workbook 6.2 (3/15)
• Vocabulary quiz 6.2 (3/17)
• Workpacket 6.2 (3/17)