6.2 – Volcanic Eruptions

Essential Questions:
1.
2.
What Happens When a Volcano Erupts?
What Are the Stages of Volcanic Activity?
How Does a Volcano Form?


Magma, which is
hotter and less dense
than other rock in the
mantle, rises through
any cracks it finds.
When the magma
reaches the surface, a
volcano can form.
 Ignore
the numbers.
Anatomy of a Volcano





Magma chamber – A pocket of magma beneath the
surface.
Pipe – A long tube that extends from the magma
chamber, up through the volcano, to Earth’s surface.
Vent – Opening(s) in the volcano through which molten
rock and gases escape.
Crater – A bowl-shaped area that may form at the top
of a volcano around a central vent.
Lava flow – The spread of lava as it flows out the vent.
Anatomy of a Volcano
Central Vent
Crater
Lava Flow
Side Vent
Pipe
Magma Chamber
A Volcanic Eruption


Just like a can of soda, magma contains trapped
gases.
As the magma reaches the surface, the pressure
decreases and the gases expand.
 This

produces huge forces!
When a volcano erupts, the force of the expanding
gases pushes magma from the magma chamber
through the pipe until it flows or explodes out of the
vent.
A Volcanic Eruption (Sarychev as seen from the ISS)
Russia
Silica

Silica (SiO2) is a
material found in
magma that helps
determine its viscosity.
 Viscosity
is a fluids
natural resistance to
flow.
Types of Volcanic Eruptions
Quiet


Hot, low silica magma
is thin and runny.
Gases escape easily.
Explosive



High silica content.
Magma is thick and
sticky.
Gases become trapped
Photographed from space!!!
Volcanic Tephra

Tephra is the general term for volcanic ejecta.
 Ash
– Less than .1 inch in diameter.
 Not
good for breathing!
Volcanic Tephra

Tephra is the general term for volcanic ejecta.
 Lapilli
 Latin
– Between .1 and 2.5 inches in diameter.
for “little stones”.
Volcanic Tephra

Tephra is the general
term for volcanic ejecta.
 Block
– Larger than 2.5
inches.
 Also
not good for your
health.
Volcanic Tephra

Tephra is the general
term for volcanic
ejecta.
 Bombs
– Molten
fragments that harden
in mid-air.
Volcanic Hazards

Lava flows.
Volcanic Hazards

Pyroclastic flows, which are fast moving clouds of
ash, gas, and dust.
Volcanic Hazards

Toxic gases such as CO2, SO2, and H2S.
Volcanic Hazards

Lahars – Mudflows that result when snow melts.
Stages of Volcanic Activity




Anywhere from less than 10 years to more then
10,000,000 years.
Active volcanoes are ones that are erupting or show
signs of eruption in the near future.
Dormant volcanoes may erupt in the future, but do
not currently show signs.
Extinct volcanoes are unlikely to ever erupt again.
Eruption Precursors




Ground movements measured by tiltmeters.
Earthquakes measured by seismometers.
Changes in heat output measured with thermometers.
Volcanic gases detected by air analysis.