Download How do volcanoes form?

What Causes Volcanoes?
• 9-3 pgs. 230-235
11/9/15
IN: What causes
volcanoes?
Formation of Magma
Solid rock may become magma
when:
–pressure is released,
–when the temperature rises above
its melting point,
–or when its composition changes.
Nonexplosive Volcano
• Lava flows come from nonexplosive
eruption.
Explosive Volcano
• Clouds of hot debris and gases shoot
out from the volcano often at
supersonic speeds.
• Shield volcanoes  nonexplosive
• Cinder cone volcanoes  explosive
• Composite volcanoes
 explosive and then nonexplosive
Where do volcanoes form?
• Near tectonic plate boundaries.
Where do volcanoes form?
• Divergent Boundaries - when
tectonic plates separate.
Rift – deep crack between plates
Not this
Divergent,
Lexi!

Where do volcanoes form?
• Convergent Boundaries - when
tectonic plates collide.
Subduction Zones
Where do volcanoes form?
• Hot Spots – places on the Earth’s
surface that are directly above
columns of rising magma, called
mantle plumes. 
Hawaii
• Animation
Predicting Volcanic Eruptions
•
•
•
•
Measuring Small Quakes
Measuring Slope
Measuring Volcanic Gases
Measuring Temperature
Classifying Volcanoes
• Extinct – will never erupt
• Dormant – may erupt
• Active – are erupting
•OUT: Why are most
volcanoes on
tectonic plate
boundaries? 