Download Chapter 5 Atoms to Minerals

Chapter 9
Volcanoes
9.1
How and Where Volcanoes Form
How and Where Volcanoes Form
The term volcano
refers to both the
opening that the lava
escapes from and the
landform that develops
around this opening.
Magma Formation
A volcanic eruption occurs when magma rises to
the surface.
Solid rock beneath the surface can become
magma one of three ways…
- Decreased pressure
- Increase in temperature
- Increase in amount of water
Once magma forms it raises up because it is
less dense.
e
At Subduction Boundaries
Subduction boundaries are where plates collide.
When an oceanic plate collides with a
continental plate mountain ranges form like the
Cascades.
Click to see animation of Himalas Form
When an oceanic plate collides with another
oceanic plate - volcanic island arcs form like the
Aleutians.
Click to see Volcanic Island Arcs form
The oceanic plate carries water with it to depth.
This allows the melting point to lower forming
magma.
http://www.classzone.com/books/earth_science/terc/content/visualizatio
ns/es0902/es0902page01.cfm?chapter_no=visualization
Pompeii
Subduction zone volcanoes can produce violent
eruptions that can burry whole cities like Pompeii
(79 AD) with little warning.
At Divergent Boundaries
Where plates move away from each other,
pressure is lowered.
This allows for magma to form, raise and create
new crust.
This also creates a ridge or raised area that runs
for thousands of miles below the oceans.
http://www.classzone.com/books/earth_science/terc/content/visualizatio
ns/es0903/es0903page01.cfm?chapter_no=visualization
Over Hot Spots
In some places the magma gets so hot it burns
through the crust.
The Hawaiian Islands were created from the
Pacific plate moving slowly over one of these hot
spots.
Over millions of years this process has created
an island chain over a 1000 miles long.
http://www.classzone.com/books/earth_science/terc/content/visualizatio
ns/es0904/es0904page01.cfm?chapter_no=visualization
State Standards
3b Students know the principal structures that form
at the three different kinds of plate boundaries.
3f* Students know the explanation for the location
and properties of volcanoes that are due to hot
spots and the explanation for those that are due to
subduction.
Quiz
1. A volcanic eruption occurs when _______ rises
to the surface.
2. Magma can form from a decreased in pressure,
increase in temperature, and an increase in _____
3. What is created at the surface when an oceanic
plate collides with another oceanic plate?
4. A __________ boundary is where plates move
away from each other.
5. Hawaii was formed by a ______ spot.
End