Transcript volcano - Cloudfront.net

November 4, 2013
Agenda
1. Roll
2. PowerPoint: What Causes
Volcanoes?
3. Possible Video
Test is on Wednesday
Subject Area: What Causes Volcanoes?
EQ: How does the heat from the Earth’s
interior reach the surface?
Questions:
1. How does magma form and move?
2. Where does magma form?
3. How does plate tectonics relate to
volcanoes?
4. What methods do scientists use to
predict volcanic eruptions?
What Causes Volcanoes?
Scientists have studied volcanoes for years
and understanding why a volcano forms is
very difficult. There is no way to see deep
into the Earth so they have to rely on
models. There are many uncertainties
about why a volcano will form.
The Formation of Magma
Magma collects in pockets in the deeper
regions in the Earth’s crust and in the
uppermost layers of the mantle. This zone
of magma is between 25 and 160 km
below the surface.
Partner Share:
Where does magma form?
Magma forms …
The Formation of Magma
Mantle is hot and pliable; it is still considered
to be a solid. The mantle is hot enough to
melt any rock. The reason it doesn’t melt
the crust is because of pressure. The
pressure keeps the atoms tightly packed
so the rock will not melt.
Partner Share:
1. How does pressure determine whether mantle is solid or
liquid?
Pressure determines whether the mantle is solid or liquid by …
The Formation of Magma
Rock will melt when the heat
is increased and the
pressure is decreased. The
temperature of the mantle
Partner Share:
is fairly constant so the
1. What two factors may cause solid rock to become magma?
decrease
of …
pressure will
The
two factors are
cause magma to form.
Magma will sometimes melt
solid rock or make its way
through cracks and
fissures.
The Formation of Magma
Once the magma is formed it will rise to the
surface because it is less dense than the
surrounding rock. Not all magma will come
to the Earth’s surface. Some will cool and
solidify while still in the Earth’s crust.
Where Volcanoes Form
A large number of
volcanoes lie directly
on tectonic plate
boundaries. The
boundaries in the
Pacific Ocean have
many volcanoes this
is called the Ring of
Fire.
Where Volcanoes Form
It is easier for magma to rise up through the
crust where the plates collide or separate.
When Tectonic Plates Separate
When tectonic plates separate a deep crack
or rift will form. Decrease in pressure
causes the mantle rock to partially melt
and become magma.
When Tectonic Plates Separate
Magma rises through the rift between the
separating plates creating new crust. Most
diverging plates are on the ocean floor.
When Tectonic Plates Collide
In a subduction zone the oceanic crust will
contain water which will lower the melting
point in rock it comes in contact with. As it
sinks deeper into the mantle it gets hotter
and hotter.
When Tectonic Plates Collide
The combination of increased pressure and
heat will cause the water to be released. It
then mixes with the mantle rock.
When Tectonic Plates Collide
Heat from rising
magma will cause
some of the overlying
continental crust to
melt which is rich in
silica.
When Tectonic Plates Collide
This gooey thick
silica rich
magma is very
likely to cause
an explosive
eruption.
Hot Spots
Not all volcanoes are formed
on a tectonic plate
boundary. The volcanoes
of Hawaii and several other
places on Earth are called
hot spots. Hot spots are
places within tectonic
plates that are directly
above columns of rising
magma.
Hot Spots
The columns of hot rising
magma are called
magma plumes.
Scientists are not sure
what causes these
plumes. Some think
that a combination of
heat and radioactivity
keep the plumes rising.
Partner Share:
What is a Hot Spot?
A Hot Spot is …
Predicting Volcanic Eruptions
It is very difficult to predict when a volcano
will erupt. Scientists will use the history of
the volcano to classify them. The three
classifications are extinct, dormant, and
active.
Extinct Volcano
Extinct Volcanoes are those that have not
erupted in recorded history and probably
never will.
Dormant Volcano
Dormant Volcanoes are those that are not
currently erupting but have erupted some
time in recorded history.
Active Volcano
Active Volcanoes are those that are in the
process of erupting or show signs of
erupting in the near future.
Partner Share:
1. What are the three classifications for volcanoes?
The three classifications are …
Predicting Volcanic Eruptions
Dormant and active volcanoes keep
scientists guessing. One sign they look for
is, sometimes when a volcano is getting
ready to erupt there will be a series of
small earthquakes.
Predicting Volcanic Eruptions
Scientists will look for bulges in the slope of
a volcano. These bulges might be magma
pushing against the inside of the volcano.
Scientist will use a tiltmeter to detect small
changes in the angle of the slope.
Predicting Volcanic Eruptions
Scientists will also look for outflow of gases.
As magma rises it will push gas out small
holes in rock, when this happens the
scientist know an eruption is not far away.
Predicting Volcanic Eruptions
Scientist will also use satellite images that
record radiation that can tell if magma is
rising closer to the surface.
Partner Share:
1. Describe a technology scientists use to predict volcanic
eruptions.
The technology scientists use is …
Movie
Summary
1. Answer the essential question “How does the
heat from the Earth’s interior reach the
surface?
2. Your answer needs to be in complete sentences.
3. Place your answer at the bottom of the notes we
did today.
4. Make sure you include the two factors that
cause solid rock to become magma from your
notes.
Earth Science Volcanoes
Questions for your
Science Notebook
Earth Science Volcanoes
What did you know?
Skip 3 lines
What did you learn?
Skip 3 lines
What do you want to know?
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