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Volcanoes
8th grade Physical Science
How are Volcanoes Formed?
O Gases force magma, melted rock in the
Earth to rise. If magma breaks through the
Earth’s surface, a volcano is formed.
Three Different Types of
Volcanoes
O Shield Volcano
O Composite Cone Volcano
O Cinder Cone Volcano
Shield Volcano
O They release relatively fast-moving less
gassy lava, and tend to have less explosive
eruptions than other types of volcanoes.
O People often walk fairly close to these
erupting volcanoes.
O They usually form large, broad volcanoes.
Mount Bachelor in Oregon
Composite Cone Volcano
O These volcanoes have explosive eruptions
as a result of more gassy magma.
O They are formed from layers of lava and ash.
O Composite Cones are also known as
stratovolcanoes.
Mount St. Helens in Washington
Cinder Cone Volcano
O These are the smallest and most common
volcanoes
O They are formed from explosive eruptions
that shoot small pieces of magma and ash
into the air.
O The magma then cools and hardens as it
falls back to the Earth, forming a cinder
cone.
O In many cases, cinder cones form on the
sides of a larger volcano.
Mt. Etna in Italy
Active Volcano
O Active volcanoes is one that has erupted
since the last ice age approximately in the
past 10,000 years.
Dormant Volcano
O Dormant volcanoes would then be one that
hasn’t erupted in the past 10,000 years, but
it is expected to erupt again.
Extinct Volcano
O Extinct Volcanoes would be one that nobody
expects to ever erupt again.
Two Types of Eruptions
O More gassy eruptions
O Less gassy eruptions
More Gassy Eruptions
O Explosive and violent eruption and magma
shoots out of the volcano.
Less Gassy Eruptions
O More quiet eruption. The magma just flows
smoothly out of the volcano.
Ring of Fire
O Many volcanic eruptions have occurred
worldwide.