Download Volcanic Eruptions 3.3

Volcanic Eruptions 3.3
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Objectives:
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Explain what happens when a volcano erupts.
Describe 2 types of volcanic eruptions
Identify stages of volcanic activity
Volcanic Eruptions 3.3
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What comes out of volcanic explosions?
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Magma forms in the asthenosphere
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Ash, lava, steam, rock, gases, dirt
Convection currents in the mantle bring
magma towards the surface
Magma tries to flow into any open crack
When magma reaches a weak spot in the
crust, a volcano forms
Lava is magma that has reached the
surface
Magma Reaches Earth’s
Surface
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Volcanoes are systems of passage ways
through which magma moves.
Inside a Volcano
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Magma collects below the volcano in the
magma chamber
Magma flows upward through a tube (pipe)
that connects the magma chamber to the
surface.
Magma Reaches Earth’s
Surface
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Inside a Volcano
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Gas and magma leave through vents
Central vent is the opening at the top
 Side vent anywhere along the side of the volcano
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Lava pours out of the vents and creates a
lava flow
A bowl shaped area called a crater may form
around the central vent
Crater
Vent
Pipe
Side Vent
Lava Flow
Magma Chamber
Magma Reaches Earth’s
Surface
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A Volcanic Eruption
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Dissolved gases are trapped
in magma under extreme
pressure (CO2 in a soda bottle)
as magma flows
, pressure
because
there is less rock on top of it.
the dissolved gases expand and form bubbles
When a volcano erupts, the force of the
expanding gas forces magma up the pipe until
it explodes out the vent
Content checkpoint… think/pair share…take two
minutes to answer these questions with a partner nearby…..
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What common everyday occurrence
can we relate to a volcanic eruption?
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What happens to the pressure in the
magma as it rises toward the surface?
Kinds of Volcanic Eruptions
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Volcanic eruptions can be quiet or
explosive.
Eruptions depend on the properties of
magma
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Silica content
Viscosity
Kinds of Volcanic Eruptions
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Quiet Eruptions
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Magma has low silica content = low viscosity
Magma flows easier so gases bubble out
gently
Lava can flow many kilometers from the vent
Produce both pahoehoe and aa lava
Example: Hawaiian Islands – Mount Kilauea
Kinds of Volcanic Eruptions
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Explosive Eruptions
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Magma has high silica content = high
viscosity
Magma doesn’t always flow out of vent and
so it builds up (like a cork in a bottle)
Trapped gases build up pressure until they
explode
Magma is pushed out of the vent with
incredible force
Kinds of Volcanic Eruptions
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Explosive Eruptions
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Lava breaks into fragments that cool quickly
and harden into different sizes
Ash – fine, dust sized particles of lava
 Cinders – pebble sized particles
 Bombs – baseball to car sized chunks of lava
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Pyroclastic flow: when an explosive
eruption hurls out gases, ash, cinders and
bombs.
Pumice forms when lava cools quick and traps
air bubbles inside
Obsidian forms when lava cools quick leaving
the surface smooth and glass-like
Kinds of Volcanic Eruptions
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Volcano Hazards
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Quiet eruptions cause lava to flow far --burning and burying everything in its path
Explosive eruptions can bury entire towns in
ash, cause landslides, avalanches, cause
damage from gases and cinders/bombs.
Content checkpoint…
think-pair-share take
two minutes to answer these questions with a partner nearby
.
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What is pyroclastic flow?
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How does volcanic ash cause damage?
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What is the main difference between
a quiet eruption and an explosive
eruption?
Stages of Volcanic Activity
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Life Cycle of a Volcano
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Scientists use historical records and monitor
volcanoes to determine what stage of activity
a volcano is in
A volcano can be active, dormant or
extinct
An active volcano is erupting or showing signs of
near future eruptions
 A dormant (sleeping) volcano can awaken in the
future and become active
 An extinct (dead) volcano is unlikely to erupt ever
again
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Stages of Volcanic Activity
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Monitoring Volcanoes
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Geologists use tiltmeters to detect slight
changes in surface elevation cause by magma
moving underground
They monitor gases escaping from a volcano
Increase in temperature might mean magma is
nearing the surface
The changes detected may give a short
warning time BUT
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We cannot be certain the type of eruption or how
powerful it will be
Think and Discuss….
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Which is more likely to be dangerous –
a volcano that erupts frequently or a
volcano that has been inactive for a
hundred years? WHY?