Download Volcano

Chapter 9…
Volcano – an opening in Earth’s crust through
which molten rock, gases, and ash erupt and the
landform that develops around this opening.
3 Conditions Allow Magma to Form:
• Decrease in pressure (lowers the
melting temperatures of materials in
asthenosphere)
– Takes place along rift valley at midocean ridge (lithosphere is thinner and
exerts less pressure)
• Increase in temperature (causes
materials in asthenosphere to melt)
– Occurs at a hot spot
• Increase in the amount of water
(lowers the melting temperatures of
materials in asthenosphere)
– Occurs at subduction boundaries
Where are volcanoes found?
• Mid-ocean ridges where plates move apart
(Occurs at. . Divergent Boundaries ).
Where are volcanoes found?
• At subduction boundaries where plates are
forced under other plates.
Where are volcanoes found?
• Over hot spots
Characteristics of magma/lava:
Types of Magmas:
•
•
•
•
Felsic
Intermediate
Mafic
Ultra mafic
High Silica rocks are called Felsic
Igneous Rocks and are light in color.
Silica-Rich, or Felsic Lavas
Igneous rocks and lava that have a
Silicate composition of 65% or more
are considered to be Felsic .
Low Silica rocks are called Mafic
Igneous Rocks, and are dark in color.
Mafic Rocks
Silica-Poor, or Mafic Lavas
Igneous rocks and lava that have a
Silicate composition of 45-50% or
less are considered to be Mafic .
Igneous rocks that have a Silicate
composition of 50-65% are considered
to be Intermediate or Andesitic (named
after a rock made from a mixture of
Mafic magma and minerals from Felsic
“country rock”).
High Silica content causes
Felsic Magma to be thick , or
viscous, and slow -flowing.
Felsic Dome
Felsic Dome
Low Silica content causes
Mafic Magma to be thin or
low-viscosity, and fast-flowing.
Lava Flows/Eruptions:
Pahoehoe lava– basaltic lava with high temperatures
and quickly flowing. Lava has smooth, ropelike
surface. (Mafic lava flow)
Aa lava– cooler basaltic lava, moves a bit
slower. Lava has rough jagged surfaces.
Pillow lava– lava that flows underwater.
Lava has rounded, pillowlike shape.
Pyroclastic flow- dense, superheated cloud of
solid fragments and ash – it is a VIOLENT
eruption!
Tephra or Ash Deposits
Volcanic Landforms
Shield Volcano – broad base volcano with gentle
sloping sides
- (basaltic lava builds up sides because of low
viscosity and lava flowing long distances before hardening).
Eruption is fast moving, non explosive.
Cinder Cones – a smaller type of volcano, can
form in groups and on sides of larger volcanoes.
Molten lava is thrown into the air from a vent and
as it falls the lava breaks into fragments which
accumulate into a cone-shaped mound. Eruption
involves lava thrown into the air.
Capulin Mtn., New Mexico is a Cinder Cone
(we did the topographic profile of this earlier in year)
Composite Volcano (also know as Stratovolcano) –a
taller, steep volcano. Eruption is lava and pyroclastic
material. (lava and Tephra)- Felsic
• Mt. St. Helens in Washington
•Mt. Shasta in California
•Mt. Fuji in Japan
Do Volcanoes Exist Anywhere Outside
of Earth? - Yes!
• Moon – maria, are the
dark lower areas of
basaltic lava flows on
the moon. (occurred ~
3-4 bya)
– The moon is cold now
and no longer
volcanically active.
Do Volcanoes Exist Anywhere Outside
of Earth? - Yes!
• Mars – has shield volcanoes (Olympus
Mon, the larges volcano in the solar
system).
– Volcanic activity is relatively recent (about 2060mya), scientist wonder if erupts are still
taking place, or if they will take place in future.
Do Volcanoes Exist Anywhere Outside
. - Yes!
of Earth?
• Venus – has more than 1,600 large
volcanoes, most are shield volcanoes.
– Scientist think volcanic activity here may still
be active and that’s why surface temperatures
are so high there
Do Volcanoes Exist Anywhere
Outside of Earth? - Yes!
• Io (Jupiter’s 3rd largest moon) – is one of
the most volcanically active places in the
solar system. Scientist believe that lavas on
Io may resemble those of early Earth.
Name that picture:
Cinder Cone
Shield Volcano
Composite/Stratovolcano
Aa Lava
Pahoehoe Lava
Pillow Lava