Transcript Volcano Types (39)

Volcano Types (39)
• Volcanoes are either
explosive of non
explosive.
• Ex.
• Explosives- Mount
St. Helens
• Non-explosiveKilauea
What Controls Eruptions?
• Two factors
• 1. The amount of water vapor and other
gases, which are trapped in the magma.
• 2. Amount of silica in the magma
• Silica is a compound of silicon and
oxygen.
• http://www.bbc.co.uk/science/earth/surface
_and_interior/lava#p00h1dn1
• http://www.youtube.com/watch?v=jRfEGvp
6wDU
Trapped Gases
• Water vapor and carbon dioxide are trapped
in magma by the pressure of the
surrounding magma and rock.
• As magma nears the surface, it is under less
pressure, which allows gases to escape,
causing non explosive volcanoes.
• Gas that builds up to high pressures
eventually causes explosive eruptions
Water Vapor
• Magma at some
convergent plate
boundaries contains
water vapor
• The trapped water
vapor in the magma
can cause explosive
eruptions.
Non-explosive Eruptions
• Magma with low silica
levels called basaltic
lava.
• It is fluid and produces
quiet, non-explosive
eruptions
• As pahoehoe (pa-HOYhoy) lava cools, it forms
a ropelike structure.
• Lava flows at a lower
temperature, a stiff,
slowly moving aa (AHah) lava forms.
Pillow lava
• Quiet eruptions form
volcanoes over hot
spots such as the
Hawaiian volcanoes
• Lavas that flow
underwater form
pillow lava formations
• http://www.youtube.co
m/watch?v=gn_IW5V
sxaw
Explosive Magma
• Silica-rich, or granitic,
magma produces
explosive eruptions
• Magma is forced upward
by denser surrounding
rock, comes in contact
with the crust, and
becomes enriched in
silica
• Silica-rich granitic
magma is thick, and gas
gets trapped inside,
causing pressure to build
up
Types of Volcanoes
• The three basic types of volcanoes are
shield volcanoes, cinder cone volcanoes,
and composite volcanoes.
Shield Volcanoes
• Basaltic lava spread
out in flat layers.
• Forms a broad
volcano with gently
sloping sides.
• Example- Hawaiian
Islands
Cinder Cone Volcanoes
• Explosive eruptions throw
lava and rock high into the
air.
• Bits of rock or solidified
lava dropped from the air
are called tephra.
• Tephra varies in size from
volcanic ash, to cinders, to
larger rocks called bombs
and blocks.
• When tephra falls to the
ground, it forms a steepsided, loosely packed
cinder cone volcano
Paricutín
• On February 20, 1943, a
Mexican farmer noticed
that a hole in his cornfield
that had been therefore as
long as he could remember
was giving off smoke.
• Throughout the night, hot
glowing cinders were
thrown high into the air.
• In just a few days, a cinder
cone several hundred
meters high covered his
cornfield.
Composite Volcano
• Some volcanic
eruptions can vary
between quiet and
violent.
• An explosive period
can release gas and
ash, forming a tephra
layer.
• Quieter period,
erupting lava over the
top of the tephra layer
The __________ the pressure on the gases
in magma, the __________ explosive the
volcanic eruption.
• A. greater, less
• B. greater, more
• C. lower, more
• D. pressure doesn’t affect the eruption
• Which of the following types of magma is
most likely to produce violent eruptions?
• A. basaltic
• B. pahoehoe
• C. silica-poor
• D. silica-rich
• 3. Explain the difference between an
explosive and non-explosive eruptions.
• Explosive volcanoes have magma which is
silica rich, with large amounts of trapped
gases. Magma is thick.
• Non-explosive volcanoes have magma
which is silica poor, with minimal amounts
of trapped gases. Magma is fluid and
liquid and spreads out.