Volcanoes
Chapter 6
6.1 Volcanoes and Plate Tectonics
plate boundaries
• Volcanoes from along _________________
divergent and convergent
– Both __________________________
• Divergent:
– Plates fracture
_______ and allow magma to reach surface
• Convergent:
sinks under the other
– One plate ______________________
Water
– __________
is brought down with the plate and
eventually forms magma that rises to the surface
6.1 Volcanoes and Plate Tectonics
• Island arcs
convergent boundary
– Result of ____________________
Older, denser
– _______________
plate subducts into deep ocean
trench
– Water in the sinking plate leaves and causes
the mantle to melt and form magma
____________________________________
rises and breaks through ocean floor to
– Magma ______________________
form volcano
a string of islands
– These volcanoes form ___________________
6.1 Volcanoes and Plate Tectonics
• Hot Spots
– Hot spots _______________________
remain in the same place for millions
of years while the earth’s plates move over them
– Some lie close to plate boundaries and some are
____________________
in
the middle of plates
– ________________
Hawaiian islands
formed from a plate
moving over a hotspot
6.2 Volcanic Eruptions
crater
vent
side vent
pipe
lava flow
magma chamber
6.2 Volcanic Eruptions
• Eruptions:
Magma
– ____________
rises to surface
– Dissolved gases in magma ___________________
expand and bubble
falls
– Pressure in magma __________
and size of
bubbles ____________
increase
pushes magma up
– Force of expanding gases __________________
the volcano to the surface
• Two types of eruptions
Quiet
1. _______________
Explosive
2. _______________
6.2 Volcanic Eruptions
• Quiet Volcanic Eruptions
low in silica
– Magma is _______________
– Gases bubble gently
can flow many kilometers
– Lava oozes quietly and ______________________
– 2 types of lava produced and form 2 types of rock:
Pahoehoe
1. _________________
forms from lava that is fastmoving, thin, and runny. Looks like ropelike coils
Aa
2. _________
forms form cooler, thicker lava. Has a
rough texture with jagged chunks of lava
6.2 Volcanic Eruptions
• Explosive Volcanic Eruptions
high in silica
– Magma is _________________,
thick, and sticky
– Magma blocks the volcano pipe like a cork
trapped behind
– Gases are _______________the
magma and build
up ____________
until the force is great enough
pressure
to push the magma out volcano
– Throws lava in the air that cools
• Smallest pieces are called _________________
volcanic ash
• Pebble-sized pieces are ________________
cinders
• Larger pieces that range from gold ball to car size are
bombs
called ______________
6.2 Volcanic Eruptions
• Volcano Hazards
Quiet eruptions
– __________________
cause fires and can bury
everything in their path
– Explosive eruptions send out hot rock and ash,
pyroclastic flow
and __________________
landslides
– Explosive eruptions can also cause ____________
of mud, rock, and melted snow
6.2 Volcanic Eruptions
• Stages of activity:
live
1. Active (___________):
– erupting or will erupt in the near future
2. Dormant (_____________):
sleeping
– Expected to become active in the future
3. Extinct (_________):
dead
– Unlikely to ever erupt again
6.3 Volcanic Landforms
• Landforms from Lava and Ash:
Shield volcanoes
– ________________
Cinder cone volcanoes
– ___________________
Composite volcanoes
– ___________________
Lava plateaus
– _________________
• Other Landforms:
– ______________
Calderas
• Huge holes left from a volcano that has collapsed
6.3 Volcanic Landforms
• Cinder Cone Volcanoes
an explosive volcano
– Formed from ____________________with
magma that had high silica content
– Ash, cinders, and bombs ____________________
build up around the vent
in a steep, cone-shaped hill or mountain
6.3 Volcanic Landforms
• Composite Volcanoes
The silica content varies
– ________________________
lava flows
– Eruptions alternate between _____________
and
explosive with ash, cinders, and bombs
– Tall, cone-shaped mountain with layers that
lava and ash
alternate with _______________
– Can be more than
4,800 meters tall
___________________________
6.3 Volcanic Landforms
• Shield Volcanoes
vent
– Thin layers of lava come out of a ________
– The lava hardens on top of previous layers
– Wide, gently sloping mountain
– ____________________
on the ocean floor are
Hot spot volcanoes
usually formed
this way
6.3 Volcanic Landforms
• Lava Plateaus
– Lava flows from several cracks in the earth’s crust
thin and runny
– Lava is ___________________
so it travels far
before it cools and solidifies
Millions of years with this type of lava flow
– ________________
form high, level plateaus
6.3 Volcanic Landforms
• Landforms from Magma:
Volcanic necks
– ________________
Dikes and sills
– ________________
Dome mountains
– ________________
– ________________
Batholiths
6.3 Volcanic Landforms
• Volcanic Necks
magma that hardens in the pipe of
– Forms from ___________________
a volcano and then the surrounding rock wears
away
6.3 Volcanic Landforms
• Dikes
– Magma forces itself
across rock layers
___________________
and then hardens
• Sills
– Magma squeezes
between horizontal
____________________
rock layers and
hardens
6.3 Volcanic Landforms
• Dome Mountains
– Forms when a large body of hardened magma is
pushed towards the Earth’s surface
__________________________________
bend upward
– The magma forces rock layer to ____________
into a dome shape
– Rock above the dome
mountain wears away,
leaving the hardened
magma exposed
6.3 Volcanic Landforms
• Batholiths
– A mass of rock formed by a large
body of magma
_________________
cooled
inside the crust
– Millions of years or weathering
and erosion wear away the
overlying rock
____________________
and the
batholith moves upward
Ice and water
– _______________
carve the
batholith into a mountain
Volcanic Eruptions