Download Volcanoes

Section 6.1
• Vocabulary to know:
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Volcano
Quiet eruptions
Explosive eruptions
Crater
Central vent
Dike
Lava
Pipe
Magma chamber
Magma
Aa
Pahoehoe
Pillow lava
Blocky lava
Pyroclastic
Volcanic bombs
Lapilli
Volcanic ash
Volcanic blocks
What is a Volcano?
• Volcano–a
mountain
that
forms
when
magma
(As well
as
volcanic
gases)
reaches
the
surface
How do volcanoes form?
Magma reaches Explosive
the surface
eruption. Boiling
through a vent
mud and ash
are hurled into
the air
Hot lava then
flows out through
the vent. The
lava cools and
hardens
The process keeps on
repeating itself making the
volcano grow larger
Types of Eruptions
• Quiet (Non explosive)
eruptions– Have very hot, low
silica, low viscosity
magma
• Explosive eruptions– High amounts of water
– High silica, and high
viscosity magma
• Clogs a volcanic pipe…
• Enormous pressure
builds up…
• Steam gets trapped…
• Volcano explodes!!!
Non explosive volcanic eruptions
• 4 different types of lava:
Aa- forms brittle
crust…crust gets torn
into little pieces as lava
flows underneath
Pahoehoe- flows very
slowly…like wax
dripping from a candle
Pillow lava- forms when
eruptions occur
underwater
Blocky lava- cool and
stiff. Doesn’t travel far
from the erupting vent of
the volcano
Volcano Structure
1. Crater•
bowl shaped pit at top of
central vent
2. Central vent•
magma escapes to the
surface
3. Dike•
leads to side vent
4. Lava•
magma that has reached the
surface
5. Pipe•
narrow vertical channel
6. Magma chamber•
pocket where magma
collects
Explosive volcanic eruptions
• Produce pyroclastic material– Forms when magma explodes from a volcano and solidifies in
the air
– 4 types:
Volcanic blocksVolcanic bombs•Large blobs of magma that
harden in the air
Lapilli•Pebble-like bits of
magma that harden
before they hit the
ground
Volcanic ash•Majority of pyroclastic
material
•Solid pieces of rock
erupted from volcano
What are pyroclastic flows?
• Pyroclastic flow– Very dangerous
– produced when
enormous
amounts of hot
ash, dust, and
gases are ejected
from volcano
– can race downhill
at speeds of more
than 200 km/h
– temperature at the
center can exceed
700°C
Section 6.2
• Vocabulary to know:
• Shield volcano
• Cinder cone volcano
• Composite volcano
Shapes of Volcanoes
• Shield
volcano:
– Broad
– Gently
sloping
• Eruptions:
– Hot, flowing
basaltic lava.
– Travels a
long way
before it
solidifies
Mount Kilauea (Shield Volcano)
• Located in Hawaii
• Presently the most active
volcano on the planet
• Can be walked up to
because of its non-violent
explosions
Shapes of Volcanoes
• Cinder cone
volcano:
– Small
– Steep sides
• Form from:
– Ash and
cinders that are
ejected into the
air and fall
back onto the
volcano
Shapes of Volcanoes
• Composite
volcano:
– Tall
– Steep sides
• Built up from
viscous
lava, ash,
and volcanic
bombs
• Eruptions:
– High silica
– High viscosity
Mount St. Helens
• Composite volcano
• Erupted on May 18,
1980
• Killed over 55 people
• Blast removed 1000 ft off
the top of the volcano
• The explosion could be
heard as far away as
Canada
• Notice the trees…
Krakatau
• Composite volcano
• Erupted on August 26, 1883
in Indonesia
• Explosions were heard 2200
miles away in Australia
• Ash was propelled 50 miles
into the air
– This ash blocked the sunlight
for 2 ½ days
• Created a tsunami 120 feet
tall
• Killed 36,000 people
Mount Vesuvius
• Composite volcano
• Erupted in Pompeii in 79
AD
• 10 feet of ash piled on
top of the buildings after
the explosion
• Considered to be one of
the most dangerous
volcanoes in the world
– 3,000,000 people live
close to it
Mount Pinatubo
• Erupted in 1991
• A 7.7 Richter scale
earthquake caused
the volcanic
eruption
• Scientists predicted
the eruption, and
the residents were
evacuated
• Caused the entire
world’s
temperatures to
drop by 1 degree
Section 6.3
• Vocabulary to know
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Plate boundary
Ring of fire
Divergent boundary
Convergent boundary
Hot spot
Most Volcanoes Occur at Plate Boundaries
Ring of Fire
• Mostly
found along
the edge of
the Pacific
plate
• Contains
nearly 75%
of the
worlds
active
volcanoes
found on
land
Divergent Boundary
• Magma
escapes to the
surface as the
plates move
apart
– Magma rises
to fill the gap
between the
two separating
plates
– Mid ocean
Ridge
Convergent Boundary
• Oceanic plate is
subducted into the
mantle…
• This causes
melting…
• Magma forms and
rises to the surface…
• Volcano created!!!
• Why does the
magma rise?
– It’s less dense
than the rocks
around it.
Hot Spot
• Hot spot stays
in one place…
• Plates move
over the top of
it…
• Over time, a
chain of
volcanoes is
formed!!!
• Is Kauai an
active volcano?
Iceland
• Above sea level
because there is a
hot spot that works
with the mid ocean
ridge
• What rocks would
be the oldest?
• What would
happen to a
house built on the
mid ocean ridge?