Download Volcanic Activity

Volcanic Activity
EQ: What occurs when a volcano erupts?
How do the different type of eruptions differ?
How Magma Reaches Earth’s
Surface
• Magma rises because it is less dense
that the surrounding solid material
What happens when a volcano erupts?
• As the less dense magma rises, the pressure
decreases
• The dissolved gas separates out and bubbles
form
• A volcanic erupts when an opening develops
in weak rock on the surface
• During a volcanic eruption, the gases
dissolved in magma rush out, carrying the
magma with them
• Once magma reaches the surface and
becomes lava, the gases bubble out
Inside a
Volcano
Magma Chamber
• The pocket beneath a
volcano where
magma collects
Pipe
• A long tube through
which magma moves
from the magma
chamber to Earth’s
surface
Vent
• The opening through
which molten rock
and gas leave a
volcano
Where are vents located?
• Usually there is one central vent at the
top of the volcano
• Often times there are additional vents
that open on the volcanoes sides
Lava Flow
• The area covered by
lava as it pours out of
a volcano’s vent
Crater
• A bowl-shaped area
that forms around a
volcano’s central
opening
• Lava collects there
How does magma rise through the
lithosphere?
• Liquid magma in the asthenosphere is less
dense than the rock in the lithosphere above
it, so it flows upward through cracks in the
rock
– The magma is stored in the magma chamber
• It continues upward (through the pipe) until it
reaches the surface (exiting through a vent)
or it is trapped beneath layers of rock.
Silica
• A material that is found in
magma,formed from the elements
oxygen and silicon
• The more silica the magma has the
thicker it is
Three factors contribute to how
forceful a volcanic eruption is .
• Amount of gas present
• How thick or thin the magma is
(Temperature)
– Thinner (hotter) is more fluid
• The silica content
– If the silica content is high, magma is thick
– This causes the pressure to build
Types of Volcanic Eruptions
Quiet Eruptions
• Classified as a quiet eruption if its
magma flows easily
• The gas in this magma bubbles out
gently
• Quiet eruptions produce two types of
lava:
– Pahoehoe – (pah HOH ee hoh ee)
– aa – (Ah ah)
Pahoehoe
• A hot, fast-moving
type of lava that
hardens to form
smooth, ropelike
coils. Cools slowly
resulting in a
smooth texture
Aa
• A cooler, slowmoving type of lava
that hardens to form
rough chunks; cooler
than Pahoehoe.
Cools more quickly
What accounts for the differences
between these two types of lava?
• The temperature of the lava
• The speed at which the lava flows
Explosive Eruptions
• Magma that is thick and sticky causes a
volcano to erupt explosively
• Magma can not flow freely causing
pressure (gas) to build up until it
explodes
Pyroclastic flow
• The expulsion of
ash, cinders, and
bombs from a
violent volcanic
explosion
How do the two types of volcanic
eruptions differ?
• Quiet eruptions occur when the lava flows
more easily because gas dissolved in the
magma bubbles
• When the lava is thick and sticky the gas
continues to store increasing pressure
– When the pressure becomes so great an
explosion takes place when the gas pushes the
magma out with incredible force
Three Stages of Volcanoes
• Active
– A volcano that is erupting or has shown
signs that it may erupt in the near future
• Dormant
– A volcano that is not currently active, but
may become active in the future
• Extinct
– A volcano that is unlikely to erupt again
Hot Spring
• A pool formed by
groundwater that
has risen to the
surface after being
heated by a nearby
body of magma
Geyser
• A fountain of water
and steam that
builds up pressure
underground and
erupts at regular
intervals
Geothermal Energy
• Energy from water and steam that has been heated by magma
• Geothermal energy is produced by drilling a well into the ground
where thermal activity is occuring.
• Once a well has been identified and a well head attached, the steam
is separated from the water, the water is diverted through a turbine
engine which turns a generator.
• Usually the water is injected back into the ground to resupply the
geothermal source.
Monitoring the activity of a volcano
• Measure tilt caused by magma
movement underground using tiltmeters
& laser-ranging devices
• Monitor temperature underground
• Monitor small earthquakes that occur in
the area around a volcano
Hazards of Volcanoes
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Fire
Bury entire towns
Damage crops
Landslides
Avalanches of mud
Damage car and jet engines