Volcanoes
Chapter 8
Section 2
Class Outcomes
Describe a volcano
Name and describe the 4 types of
volcanoes
Differentiate between Pahoehoe and Aa
lava
Volcano
Area where magma and gases are released to
the Earth’s surface.
Area where magma becomes lava
Magma = under surface
Lava= above surface
Have circular shaped openings called craters
Release Tephra, or solid lava, that enters the
air during an eruption.
Subduction Zone Volcanoes
Oceanic plate dives under and melts. The newly formed magma rises
to the surface and creates a volcano.
4 types of volcanoes
Shield Volcanoes
Cinder Cone Volcanoes
Composite Volcanoes
Fissure Eruptions
Shield Volcanoes
Made from basaltic lava
Thin and easy flowing
“pahoehoe”
Gradually sloping sides
Broad/ largest volcanoes on earth
Hawaiian Islands/Iceland
Mauna Loa
Cinder Cone Volcanoes
Short in height (less than 300m)
Made of tephra
Violent eruptions from gas buildup
Lava and gas shoot high in the air and cool
to form volcano
Short eruption time
Composite Volcanoes
Steep sided mountain
Composed of alternating layers of
basaltic lava and tephra
Explosive eruptions followed by lava
flows
Mt. St. Helens, Mt. Ranier, Mt. Shasta
Composite = pyroclastic flows
Hot gases and ashes released at the
beginning of a composite eruption
2000 degrees Fahrenheit
Up to 450 miles/hour
Deadliest event of a composite eruption
Pyroclastic Flow
Composite = “Lahars”
Mud Flows caused by the super heating
of glaciers on the top of these high
mountains.
Water + Ash = Lahar
2nd deadliest aspect of these giants.
Mt. Shasta, California
Fissure Eruptions
Basaltic lava flows from cracks in the
earth’s crust
Thin and flows easily
Form flat landforms known as lava
plateaus/flood basalts.
Volcano Tour on Google Earth
tour
Fissure Eruption, Kilauea Volcano field, Hawaii
“Pahoehoe vs. Aa”
Pahoehoe lava
Thin and flows easily
Aa lava
Thick and chunky and doesn’t flow, but
breaks apart as it moves.
?
Aa
?
Pahoehoe
What kind of volcano would be the best to
have in your backyard?
Extinct
• Have no magma chamber or source.
Active
• Have regular, predictable eruptions that never gain
strength.
Dormant
• Have irregular, unpredictable eruptions and can be very
catastrophic in strength.
Enjoy the Show
Mountains of Fire