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Essential Question:
Chapter 9: Volcanoes power point notes
a
A volcano is: an opening in the Earth’s surface through which molten material or volcanic gases
are erupted.
A volcano can occur as:
1. Classic Cone
2. A simple crack in the ground, though which lava erupts
3. or a simple volcanic vent
Volcanoes occur at:
1. subduction boundaries(converging tectonic plates)
a. Ocean-ocean subduction
examples: Aleutian Arc Volcanoes or Lesser Antilles
b. ocean-continental subduction
examples: Cascade Mountain range volcanoes
2. Divergent boundaries (plates moving apart)
Examples: Mid-Atlantic Ridge or the African Rift
3. Hot spots
examples: Hawaii and Yellowstone
Volcanoes can be classified as either:
1.Active-actively erupting
2.Dormant-currently not erupting but does have a magma source and could erupt anytime in the
future
3. Extinct-there is not magma source. The magma has since cooled and formed an igneous rock
Summary:
Parameters of Volcanism:
1. Viscosity
2. Chemistry of magma
3. gases within the magma
4. water content
Types of Magma/Lava:
1. Felsic Magma
a. light in color,
b. high silica content which cause the magma/lava to be thick and slow flowing
c. Associated with composite type volcanoes and continental hotspots
d. Found at continental-oceanic subduction boundaries
2. Mafic Magma
a. dark in color,
b. low silica content which cause the magma/lava to be thin and fast flowing
c. Associated with shield volcanoes, rift zones and oceanic hotspots
d. Found at divergent boundaries
Gases in Magma/Lava include:
Water vapor, carbon dioxide, carbon monoxide, sulfur dioxide, hydrogen sulfide. Water vapor is
what makes a volcano explosive, the more water vapor the more explosive the eruption.
Lava flows (types) would be described as:
1. Pahoehoe – smooth rope like
2. Aa – rough jagged lava
3. Pillow Lava – forms when hot lava flows into water
Types of Lava Fragments found include (these are part of pyroclastic materials and flows):
1. Ash
2. Tephra
3. Breccias
4. pumice
5. cinders
6. bombs
7. blocks
8. Pyroclastic flows
Essential Question:
Volcanic landforms include:
A. Shield Volcanoes: formed by basaltic (mafic) lava that flows long distances, usually
associated with oceanic hotspots and divergent boundaries.
B. Cinder cones: are formed when molten lava is thrown into the air from a vent and breaks
into drops. These drops harden into cinders that form a steep cone around the vent
C. Composite Volcanoes: are formed by layers of pyroclastic materials and lava that have
erupted in the past.
D. Lava Plateaus: continuous eruptions that build up on each other
E. Caldera: is a large crater-shaped basin that forms when the top of a volcano collapses.
Types of Volcanic Eruptions:
A. Explosive Eruptions:
• Found at subduction zones
• Magma low temp (800 degrees C), high viscosity, does not flow easily, more felsic
mineralogy, gases trapped, hard to predict explosions
• Forms composite volcanoes, cinder cones, calderas, aerial bombs, pyroclastic flows,
very destructive
B. Effusive Eruptions:
• Generally at hots spots, spreading centers
• Mantle comes directly to surface
• Hot lava; low viscosity, very mafic, flows easily, gases escape easily
• Forms shields, flood basalts
Summary: