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Section 13-1 Review
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#1
Describe three conditions that affect
whether magma forms.
Magma forms when . . .
• the temperature of the rock rises above the melting
point of the minerals that compose it,
• the pressure of the rock decreases faster than its
temperature does,
• when it is mixed with fluids that decrease its melting
point.
#2
Explain how magma reaches Earth’s
surface.
Magma reaches Earth’s surface because the
rising magma is less dense than the
surrounding rock of the crust.
#3
Compare magma with lava.
Magma is melted rock beneath Earth’s
surface; lava is magma that erupts onto
Earth’s surface
Magma
Lava
#4
Describe how subduction produces
magma.
The denser, subducted plate releases fluids
to the surrounding crust and mantle
materials, thus lowering their melting
points and causing magma to form.
Subduction creating Magma
#5
Identify three tectonic settings
where volcanoes commonly
occur.
 subduction zones
 mid-ocean ridges
 hot spots
Subduction Zone
Mid-Ocean Ridge
#6
Summarize the formation of hot
spots.
The hot spot lies above a column of solid,
hot material from the mantle. When the
mantle material spreads out at the top of
the plume, its pressure drops and the rock
melts. The resulting magma forms
volcanoes at the hot spot.
Hot Spot
#7
Describe how the presence of ocean
water in crustal rocks might affect
formation of magma .
Ocean water in ocean rock can lower the
melting point of the rock and aid the
formation of magma.
#8
Yellowstone National Park in
Wyoming is far from any plate boundary.
How would you explain the volcanic
activity in the park?
The volcanic activity in Yellowstone National
Park would be due to mantle plume that
cause a hot spot within the continental
crust.
Yellowstone Magma Chamber
Yellowstone Volcano History
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