Transcript Volcanoes A volcano is a mountain that forms when molten

A volcano is a mountain that forms when
molten rock is forced to the Earth’s surface.
Volcanoes can by active, dormant, or extinct.
Active Volcano…
Kilauea Volcano is presently one of the most
active volcanoes on Earth.
Dormant “Sleeping” Volcano
Mt. Hood, Oregon
Dormant Volcano: A volcano which is presently inactive but which
may erupt again. Most of the major Cascade volcanoes are believed
to be dormant rather than extinct.
Extinct Volcano
Kohala Volcano
Extinct Volcano: A volcano that is not presently erupting and
is not likely to do so for a very long time in the future.
Where do volcanoes form?
1. Volcanoes form when hot material from below rises and leaks into the
crust.
2. Eventually, but not always, the magma erupts onto the surface. Strong
earthquakes accompany rising magma.
Parícutin, Mexico, 1943
• In the winter of 1943, the countryside near
Parícutin, Mexico was rocked by a series of
earthquakes. The tremors lasted for nearly two
weeks when a fissure open in a farmer's field
and the birth of cinder cone was underway.
Within 12 hours of the initial eruption, the fissure
was ejecting pyroclastic material as well as huge
clouds of gas and ash. Lava began to spill from
the base of the cone building the volcano
laterally.
Parícutin,
Mexico, 1943
• Within 24 hours a 40
meter high cone hurling
volcanic bombs several
kilometers away had
been built.
• After nine years of
activity, two villages
had been buried
Anatomy of a Volcano…
Crater- A bowl-shaped
depression at the mouth of a
volcano
Magma chamber -A large
underground pool of molten
rock lying under the surface of
the earth's crust
Vent - The opening through which
the molten rock flows onto the
surface.
What is the difference between
magma and lava??
Lava – molten rock on the earth’s
surface.
Magma – molten rock deep inside the
earth.
II. What erupts from a volcano?
• Gases:
Water Vapor, Carbon Dioxide, Sulfur Dioxide,
Nitrogen, Hydrogen, Argon
• Rock Fragments:
Dust, ash, bombs, and blocks
• LAVA!!
IV. Types of Lava
and Rock
Fragments
aa – Sharp, jagged lava
Pahoehoe - Smooth,
wrinkled lava
Pillow Lava…
Pillow lava – forms on
the ocean floor and cools
into rounded blobs.
In Greek:
Pyro – “fire”
Clastic – “Broken”
Mt. St. Helens
Mt. Pinatubo
Pyroclastic material - avalanche of
hot ash, pumice, rock fragments,
and volcanic gas that rushes down
the side of a volcano
Rock
Fragments
Lapilli – less than 64
mm in diameter
Volcanic ash – 2 mm in diameter
Volcanic dust - < 0.25 mm in
diameter
Volcanic blocks – greater than 64 cm
in diameter
Volcanic bombs – greater
then 64 mm in diameter
III. Types of Volcanoes
Shield Volcanoes
a. Nonexplosive
b. Thin, runny lava
c. Gently sloping
d. Dome-shaped
mountains
Stratovolcano or Composite
a. Alternating layers
of rock particles
and thick lava.
b. Violent eruptions
c. Large coneshaped mountain
d. Most common
type.
Cinder Cone
a. Different sizes of
volcanic material
b. Explosive
eruptions
c. Large bowlshaped craters
d. Steep sides with
loose rock
particles
Mafic Lava
Felsic Lava
What type of volcano am I?
Stromboli Volcano in Italy
Mt. St. Helens, WA
Kanaga Volcano in Alaska
Sunset Crater, Arizona
Mauna Loa Volcano, Hawaii
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Water (steam) 77.0%
Carbon dioxide 11.7%
Nitrogen 3.0%
Carbon monoxide 0.5%
Hydrogen 0.5%
Sulfur dioxide 6.5%
Sulfur 0.3%
Chlorine 0.05%
Argon 0.05%