Download How do volcanoes form?

Volcanoes
Mr. Fetch’s Earth Science Classroom
Volcano History
The word volcano
comes from Vulcan,
the Roman god of fire
and metalworking
who “lived”
lived” under Mt.
Etna.
The study of
volcanoes is referred
to as volcanology.
volcanology.
Volcano
Landform that develops where lava, ash, and gas erupt.
Mr. Fetch’s Earth Science Classroom
Volcanoes
How do
volcanoes
form?
Mr. Fetch’s Earth Science Classroom
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How do volcanoes form?
There are two major ways volcanoes form:
1. Convergence of tectonic plates
2. Hot spots
Mr. Fetch’s Earth Science Classroom
Convergence
When two tectonic plates collide:
1. There is Subduction of a plate into the asthenosphere.
2. The plate begins to melt rock, forming magma.
magma.
3. The hot, low density magma rises toward Earth’
Earth’s surface.
Mr. Fetch’s Earth Science Classroom
Convergence
When two tectonic plates collide:
4. Pressure pushing up on Earth’
Earth’s crust gets higher and higher.
5. Eventually, magma pushing up forms a crack called a fissure.
fissure.
6. Magma erupts through the fissure and onto Earth’
Earth’s surface.
7. Magma that is above Earth’
Lava.
Earth’s surface is called Lava.
After several
eruptions,
lava builds
up and a
rocky hill
called a
volcano is
formed.
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Hot Spot
A hot spot can also form a volcano:
1. A hot spot is an area in the lower mantle that is really hot.
hot.
2. Since it is so hot, parts of the mantle melt and form magma.
3. Hot magma rises because it is less dense.
4. Pressure is put onto the surface of the Earth, forming a fissure.
fissure.
6. A volcano is formed over many eruptions.
Examples:
Hawaii
Yellowstone
Hot spots are
normally
found inside
of plates, not
at boundaries.
boundaries.
Mr. Fetch’s Earth Science Classroom
Hot Spot Example: Hawaii
1. Hawaii sits on the Pacific Plate,
Plate, which is moving Northwest.
Northwest.
2. There is a hot spot under Hawaii causing magma to rise.
3. The hot spot is located in the mantle, and is not moving
4. The plate moves over the hot spot, forming a line of volcanoes.
Which islands
are the oldest,
the northern
or the
southern
islands?
er
th
r
No
n
Mr. Fetch’s Earth Science Classroom
Volcanoes
1. While volcanoes form in similar ways, all volcanoes are not alike.
alike.
2. Some are tall, steep, violent, gentle…
gentle… Why so different?
different?
To understand what makes
one volcano different from
another we need to look into
the heart of the volcano: ITS
MAGMA.
MAGMA.
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Volcanoes
The type of volcano
and how it erupts
depends on…
Mr. Fetch’s Earth Science Classroom
Magma and Viscosity
The type of volcano and how it erupts depends on magma’
magma’s
Viscosity: how easily a liquid will flow.
flow.
Thick / Viscous magma
- Honey or Molasses
- Does not flow very easily
Thin / NonViscous magma
- Water
- Flows very easily
Why is Magma Viscous?
- Low temperatures
- High Silica content
Why is Magma Nonviscous?
- High temperatures
- Low Silica content
Mr. Fetch’s Earth Science Classroom
Why Silica ???
The more Silica in magma, the thicker and more viscous it is.
% Silica
High
Low
Viscosity
High
Silica tetrahedrons link
together in long chains that
stop magma from flowing
easily.
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What about the Magma?
Magma with Silica content that is:
High
Granitic Magma
Medium
Andesitic Magma
Low
Basaltic Magma
Viscous Magma
- Low temperature
- High Silica
- Called Granitic Magma
Medium Viscous Magma
- Medium temperature
- Medium Silica
- Called Andesitic Magma
Nonviscous Magma
- High temperature
- Low Silica
- Called Basaltic Magma
Mr. Fetch’s Earth Science Classroom
Why is Viscosity so important anyway???
What happens to a fly in honey?
Mr. Fetch’s Earth Science Classroom
Why is Viscosity so important anyway???
Thick and Viscous Magma
1. There are gasses in magma, such as Water Vapor and CO2.
2. Gasses rise up toward Earth’
Earth’s surface with the magma.
3. If the magma is thick,
thick, it does not flow up easily. GETS STUCK!
STUCK!
4. Rising gasses also get stuck and can not escape.
5. The gasses build up pressure until they explosively erupt.
erupt.
Mr. Fetch’s Earth Science Classroom
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Why is Viscosity so important anyway???
Thin and Nonviscous Magma
1. If the magma is thin,
thin, it flows up easily.
easily. DOES NOT GET STUCK!
2. Rising gasses also flow up and can easily escape.
3. Pressure does not build up and magma gently erupts.
erupts.
Mr. Fetch’s Earth Science Classroom
Volcanoes
The type of volcano and how
it erupts depends on…
MAGMA’S VISCOCITY
Mr. Fetch’s Earth Science Classroom
What about the Magma?
Viscous Magma
- Low temperature
- High Silica
- Called Granitic Magma
Medium Viscous Magma
- Medium temperature
- Medium Silica
- Called Andesitic Magma
Nonviscous Magma
- High temperature
- Low Silica
- Called Basaltic Magma
VERY EXPLOSIVE
ERUPTIONS
MODERATELY
EXPLOSIVE
ERUPTIONS
GENTLE
ERUPTIONS
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Volcanoes
You must MEMORIZE the entire
previous slide. Know the types of
Magma, their temperature,
viscosity, silica content, and
eruption style. Make a chart or
something to commit this to
memory. You will have to fill out a
chart on the test. KNOW IT!
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