Download Chapter 8: Volcanoes The Big Idea: Volcanoes form as a result of

Chapter 8: Volcanoes
The Big Idea:
Volcanoes form as a result of tectonic plate motions and
occur where magma reaches Earth’s surface.
Section 1: Why Volcanoes Form
VOCABULARY:
1. Volcano: a vent or fissure in Earth’s surface through
which magma and gases are expelled.
2. Magma: liquid rock produced under Earth’s surface, in
the crust and mantle. Igneous rocks form from magma.
WHY VOLCANOES FORM:
Main Ideas:
Notes:
-Where do volcanoes
form?
-Mostly on tectonic plate boundaries
(plate boundaries that surround the
Pacific Ocean have so many
volcanoes that the area is called the
Ring of Fire).
-Volcanoes at
-Plates pull apart creating fractures
Divergent Boundaries: called fissures. Most volcanoes at
Divergent boundaries form under
water. Ex: mid ocean ridge (chain of
mountains).
-Volcanoes at
Convergent
Boundaries:
-Plates collide, the denser plate
sinks. As the plate sinks a trench is
formed. As the plate subducts into
the mantle (subduction), the rock is
subjected to heat and pressure,
which causes the rock to melt.
-Hot Spots:
-Volcanically active places not
located at tectonic plate boundaries.
-Thought to lie directly above
columns of hot rock that rise through
Earth’s mantle.
Ex: Hawaiian Islands.
-Hot Spots: as tectonic plates move over a mantle plume,
rising magma may cause a chain of volcanoes to form.
Hot spot (mantle plume)
HOW MAGMA FORMS:
Main Ideas:
Notes:
-Where does magma
form?
-In the deeper parts of Earth’s crust
and the uppermost parts of the
mantle, where the temperature and
pressure are extremely high.
Changes in the temperature and
pressure cause magma to form.
-Magma forms when temperature of
the rock increases and pressure
decreases, or when water lowers the
melting temperature of a rock.