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Volcanoes:
Don’t get all steamed about it…
A: Main Concept #3: Any place where heat and “molten material”
From deep in the earth reaches the surface of the crust!!!
The basic process of an eruption is listed here:
3. When it breaks through
the surface, we get a
Vent
volcanic eruption!
4. Lava and other super hot
Pyroclastic
material
flow out of the
Flow
volcano
and onto the sides
2. Molten material
fills up every
crack Lava
it can find
Lava Flow
1. Pressure increases
as molten material fills
Magma Chamber
up the “magma chamber”
Q: What
is a
Volcano?
Where you’ll
likely find a
Volcano
• Convergent plate boundary (large volcanoes)
• Divergent plate boundary (small volcanoes)
• “Hot spot” (various sizes but can be the biggest by
far. This includes SUPERVOLCANOES!!!!)
Volcanoes & Plate
Boundaries
• Divergent & Convergent Plate Boundaries
As the crust goes deeper, it gets melted!
As we have learned, hot stuff goes up!
If the melted crust (magma) gets to the surface…we get a volcano!
You can see that volcanoes are forming where
ocean crust dives under other crust
Hot Spots
A hot spot is where a large amount of molten material
Is trying to push it’s way up to the surface FAR FROM
A PLATE BOUNDARY!!!
Hawaii is a CLASSIC
example of a hot spot
We are not sure
why they occur…
Why do volcanoes form at hot spots?
Because there is hot material that wants to move up!
Why do hot spots form?
Now that’s a good question!
You can identify hot spots in two ways:
We can learn a lot from hot spots!
Volcanoes in the middle of nowhere (not near a plate boundary)
We can see the direction a plate is
moving by the line of volcanoes!
Older
Younger
A long line of volcanoes that get older in one direction
Plate Boundary
You can see that the Pacific plate has changed
it’s direction of travel sometime in the past!!!
Hot spot
Volcanic Hazards
Hey!
Where
did my
car go?!
Volcanic Hazards
Quiet Eruptions
• Quiet Eruptions:
Great.
– Lava flows from
vents, setting fire and
how are
burying Now
everything
in we
its path.
gonna get home?
– Covers large areas with a thick layer of lava.
Volcanic Hazards
Quiet Eruptions
Fig. 7.23a
Stephen
Teachers, Please
Marshak
don’t mark your
students tardy – we
have a bus that’s
running late.
*
Mt. Saint Helens
Mt. Saint Helens
Mt. Saint Helens
Mt. Saint Helens
Mt. Saint Helens
The Aftermath
You can see stumps
that were trees sliced
in half by the
force of the wind!
Here is an entire forest that was
destroyed by the energy released
from the volcano!
Now we also have a river of
hot mud instead of water!
It wasn’t just a small section of
forest that was destroyed!
The Aftermath
The Aftermath
The air was so hot, these trees
just started to burn spontaneously!!!
The amount of ash the volcano
expelled almost covered this house!
Rabaul Caldera on September 19, 1994
The ash can travel 100’s of miles!!!
U.S. Clark Air Base, Philippines, about 25 km east of Mount Pinatubo
Pompeii was destroyed by
Mt. Vesuvius in Italy
The people died before they could
run away and their bodies left a
body shaped hole in the ash.
If you fill in the hole with cement, and
then removed the ash, the cement
shows the person who died there!
There is volcanic
danger in Utah!!!
Here is a map
What about Yellowstone National Park?
There are geysers…
showing
the areas
that are in
danger if
There are extinct
Yellowstone
volcanoes all over Utah
has a major
of hot springs…
There areAnd
hot lots
springs
eruption
all over Utah
again!!!
How do you explain all this if there isn’t hot
material under the ground?
Monitoring Volcanoes
• Because volcanoes have a lot of energy,
we can use instruments to detect that
energy to determine when she’s gonna
blow!
Tilt Meter
Seismograph
Measures the shaking
of the ground
If the ground begins to bulge
Volcanic Eruption
Indicators
• Bulging & Tilt
• Increase in Earthquakes
• Increase in Temperature from
underground water
• Out-gassing
• Many other indicators…
Main Concept #4: We can use indicators to determine if a volcano is likely to erupt
Dormant volcano (basically
no molten material at this time)
Notice a bulge forming
where the molten material
is trying to punch through
Fig. 7.15abc
Potentially active volcano
(Magma fills chamber,
signs of possible eruption)
W. W. Norton
Active volcano
(Molten material has
punched through)
Graphing the energy of a
volcano
Energy builds up over time
Eruption releases most
Earthquakes release some
Energy of a volcano
40
35
Energy
30
Volcanic Eruption
Earthquake 2
Earthquake 1
25
20
Energy
15
10
5
0
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20