Volcanoes
Objectives:
1. Be able to explain the process that leads to volcanic activity at:
a. Subduction Zones (Covergent P.B.)
b. Mid-ocean ridges and rift zones (Divergent P.B.)
c. Hot Spots.
2. Be able to predict the volcanic eruption pattern (Quiet, intermediate, or explosive)
based on the amount of silica and temperature of the magma (melt)
Review of Concepts: Circle the correct word or fill in the blank.
A. SILICA: The more silica there is in magma, the (less/more) explosive the eruption
will be.
Rocks that make up the CRUST have (less/more) silica than MANTLE ROCKS.
Continental Crust:
__________% silica
Oceanic Crust:
__________% silica
Mantle Rock:
__________% silica
B. Temperature: As magma gets hotter, it becomes (less/ more) viscous. Viscous
magmas produce explosive eruptions.
Subduction Volcanoes
o
o
o
Ocean plate collides with another plate (ocean or land)
Ocean plate sinks back into mantle (denser)
Subducted plate is “dewatered” (water leaves it)
This lowers the melting temp. of the crust above.
Crust above melts to make magma
Mid-Ocean Ridge Volcanoes
o Formed by Seafloor spreading
o 2 ocean plates move apart as magma fr. mantle
pushes through.
o Magma originates in SHALLOW MANTLE;
Ocean crust melt gets added.
Rift Valley Volcanoes
o Formed when 2 plates of continental crust separate.
o Magma originates in SHALLOW MANTLE;
C.Crust melt gets added.
Hot Spot Volcanoes
o Can be in the middle of a plate or @ plate boundary
o Magma originates from a plume in the DEEP MANTLE.
o Overlying crust gets added to the melt.
1. Rank the rock type based on the amount of silica (most  least)
 Oceanic Crust
 Continental Crust
 Mantle Rock
2. Melts that form from _____________________ would have the highest temperatures
 Oceanic Crust
 Continental Crust
 Mantle Rock
3. Volcanoes at these locations have magmas that originate in the SHALLOW MANTLE.
a. Subduction zone
b. Mid Ocean Ridge (Sea floor spreading)
c. Rift zone
d. Hot spots
4. Volcanoes at these locations have magmas that originate in the deep mantle.
a. Subduction zone
b. Mid Ocean Ridge (Sea floor spreading)
c. Rift zone
d. Hot spots
5. Volcanoes at these locations have magmas that may originate from the melt of
continental crust (Pick more than one)
a. Subduction zone (oceanic – continental plates)
b. Subduction zone (oceanic – oceanic plates)
c. Mid Ocean Ridge (Sea floor spreading)
d. Rift zone
e. Hot spot on ocean plate
f. Hot spot on land
6. Which location would you expect to have the least explosive volcanoes:
a. Subduction zone (oceanic – continental plates)
b. Subduction zone (oceanic – oceanic plates)
c. Mid Ocean Ridge (Sea floor spreading)
d. Rift zone
e. Hot spot on ocean plate
f. Hot spot on land
7. Defend your choice for #6 with reasons.