13.2 Volcanic Eruptions
Volcanic Eruptions
Section 13.2
Volcanic Eruptions
· volcano - vent (opening) in Earth's surface
through magma and gases are expelled
· viscosity - measure of a material's resistance to flow
thicker material, greater viscosity
affected by temperature, silica content, and dissolved
gases
· quiet or explosive
· factors that determine the violence of eruption
composition of magma
temperature of magma
dissolved gases in magma
Types of Magma
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MAFIC
low in silica
thin
dark in color
rapid movement
dissolved gases escape
easily
smooth-flowing eruptions
creates broad-based
volcanoes
FELSIC
high in silica
thick
light in color
slow movement
dissolved gases do
not easily escape
· explosive eruptions
· creates steep-sided
volcanoes
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1 All of the following influence how
violent a volcanic explosion will be
EXCEPT
A composition of magma
B dissolved gases in magma
C depth of magma chamber
D temperature of magma
2 MATA: Describe felsic lava.
A
high in silica
B
explosive eruptions
C
smooth flowing
D
light color
E
dissolved gases escape easily
F
thick
Materials Associated with
Volcanic Eruptions
· lava flows
pahoehoe lava - looks like rope
aa lava - jagged chunks
blocky lava - large chunks
· gases
water vapor, carbon dioxide, sulfur, hydrogen, chlorine
· pyroclastics - "fire fragments"
ash, dust, lapilli, bombs, blocks (increasing in size)
13.2 Volcanic Eruptions
Types of Volcanoes
· shield
broad base w/gentle sloping sides
quiet eruptions of mafic lava
ex. Hawaiian Islands
· cinder cone
steep sloping sides
explosive eruptions w/large pyroclastics
· composite (stratovolcano)
form large volcanic mountains
alternate btwn quiet and explosive eruptions
most violent eruptions
most active found in Pacific Ring of Fire
4 MATA: Which volcano(es) could erupt
with felsic lava?
A
shield only
B
shield and composite
C
composite only
D
composite and cinder cone
E
cinder cone only
F
cinder cone, composite, and shield
Predicting Volcanic Activity
· NO reliable way
· methods of prediction
1. change in earthquake activity around volcano
2. bulging - areas of magma pushing against volcano
3. volcano's past behavior
3 Ash, lapilli, and bombs are all examples
of
A
pyroclastics
B
lava flows
C
volcanoes
D
lava viscosity
CAlderas
· like a crater
· magma chamber below a volcano empties and
the cone crumbles inward
· may fill with water and form lakes
5 A change in a volcano's behavior is a
reliable indicator that the volcano is
about to erupt.
True
False