Download 7.3 Volcanoes continued

Volcanoes
7.2 Volcanic Eruptions
Types of Lava
• Mafic Lava: rich in magnesium and iron
– Forms much of the oceanic crust
• Felsic Lava: rich in silica (less magnesium and
iron)
– Forms much of the continental crust
What determines the type
of Volcanic Eruption?
Composition of lava (mafic or felsic ) determines
the type of eruption.
• Mafic Lava- hot and thin, flows similar to
water
– Creates quiet eruptions
• Felsic Lava- thick, viscous and cooler. Contain
large amounts of trapped gasses. These gasses
boil out explosively.
– Creates explosive eruptions
– Pyroclastic Material: rock
fragments ejected into the air
Journal
• Which lava flows easily creating quiet volcanic
eruptions?
• Which lava erupts violently?
Pyroclastic Material Classified
based on size:
• Lapilli- less than 64 mm in diameter
• Volcanic ash – less than 2 mm in diameter
• Volcanic dust – less than 0.25mm in diameter
Types of Volcanoes
• Shield
• Cinder-Cone (or Dome)
• Strato-volcanoes or composite volcanoes
Shield Volcanoes
• Broad base and gentle sloping sides
• Formed by mafic lava
Cinder-Cone Volcanoes
• Steep slopes
• Formed by felsic lava
Strato-volcanoes
(or composite volcanoes)
• Formed by both smooth lava flows and
explosive pyroclastic eruptions
• Form high volcanic mountains
1. Create a quick sketch of the following
Volcanoes.
2. Name each Volcano type.
Craters and Calderas
• Crater: funnel shaped pit
• Caldera: large depression that occurs when a
volcanic cone collapses
Predicting Volcanic Eruptions
• seismographs monitor small earthquakes
– number of earthquakes increases prior to volcanic
eruptions
• slight bulging of the surface of the volcano
• composition of gasses given off by the volcano
Journal:
What might an increase in earthquakes near a
volcano indicate?
7.3 Volcanoes not on Earth!!!
The moon: Basaltic lava flow on the near side of
the moon
• No tectonics or convection
currents…..
so how could the volcanoes
have formed….
• May have been caused
by intense heat due to
meteorite collisions
Mars: Seismically active and Crust is not shifting,
produces very large volcanoes
• These volcanoes may
still be active.
Io: moon of Jupiter, has active volcanoes. The lava is
sulfur based.
• The cause of its warm core is the friction as its
surface is pulled back and forth
due to gravitational pull from the
other moons and Jupiter.
The End