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volcanism:any activity that
includes the movement of
magma toward the surface of
the Earth
volcano: place where magma
reaches the surface
magma: liquid, molten rock
underground
lava: magma that reaches the
surface
•lost gas, gained rock
MID-OCEAN RIDGE: occurs
where plates are moving apart
•lava flows out smoothly and
fluidly from cracks
SUBDUCTION ZONE: occurs
at subduction boundaries
•usually explosive and erupted
material is mostly lava
HOT SPOTS: areas of volcanic
activity in the middle of a
lithospheric plates
Hawaiian Islands are an example
two types of lava:
•felsic: much silica (Rhyolitic),
light-colored, slow moving
(viscous), continental crust
•mafic: low silica (basaltic),
dark-colored, fast moving (least
viscous), oceanic crust
• Pahoehoe (puhHOEEE-hoeee):
thin mafic lava.
– usually hardens
with wrinkled
surface
– means “ropey” in
Hawaiian
Pahoehoe Lava
• Aa (AH-ah):
sharp block
shapes of
hardened mafic
lava.
– caused by rapid
cooling on surface
of lava
– breaks into
jagged chunks
Aa Lava
Aa Lava
Pahoehoe
Lava
Pahoehoe
Aa
Pillow lava from Hawaii
•many magmas contain dissolved
gases that are given off
•water vapor, carbon dioxide
(CO2), sulfur (S)
•magmas with more gases have
more explosive eruptions
tephra:solid fragments ejected
from a volcano
ash (<2mm)
bombs
lapilli (<64mm)
blocks
Sometimes called pyroclastic
material
lapilli
bombs
bombs
blocks
•Vent: opening from which lava
flows
•Crater: funnel-shaped pit or
depression at top of volcano
•Caldera:craters whose walls
have collapsed
•composed of quiet lava flows
•form gently sloping, domeshaped mountain
•basaltic (mafic) magma
largest = Mauna Loa in Hawaii
•Made mostly of tephra and other
rock particles
•Formed from explosive eruptions
•Not very high, narrow base,
steep sides
•Rhyolitic
(felsic) magma
•built up of alternating layers of rock & lav
•explosive eruptions at first with tephra
then quiet with lava
•forms large, cone-shaped mountains
•made of rhyolitic & basaltic magma
Mount Fuji