1. The Dangers and Benefits of Volcanoes video 9.16
A volcano is a weak spot in the crust where molten material, or magma, comes 
to the surface. The landforms that we call 
volcanoes are created by repeated 
eruptions of lava.

2. Magma is the 
molten mixture of 
rock-forming 
substances, gases, 
and water that 
makes up part of 
Earth's mantle.
video
Most volcanoes occur along diverging 
plate boundaries, such as the mid-ocean 
ridge, or in subduction zones around the 
edges of oceans.

3. When magma reaches the surface, it is called lava
When magma 
reaches the 
surface, it is called 
lava. After lava has cooled, it forms 
solid rock. The lava 
released during 
volcanic activity 
builds up Earth's 
surface. Volcanic 
activity is a 
constructive force 
that adds new rock 
to existing land and 
forms new islands.
video

4. Volcanic Eruptions
During volcanic eruptions, many rock 
fragments are blown into the air. The smallest 
particles are called volcanic dust. (less than 0.25 mm)
Volcanic Ash ( mm) falls to the Earth 
and forms small rocks.
Volcanic bombs (a few cm to several meters) 
are molten and harden as they travel through 
the air.

5. Parts of a Volcano
pipe - a long tube in the ground that connects the 
 magma chamber to Earth's surface
crust - the crust is Earth's outermost, rocky layer.
lava - lava is molten rock; it usually comes out of 
 erupting volcanoes.
magma chamber - a magma chamber contains 
 magma (molten rock) deep within the Earth's crust.
vent - a vent is an opening in the Earth's surface 
 through which volcanic materials erupt.
caldera - the depression created when the roof of a 
 magma chamber collapses.
Subduction, Magma Chambers
Volcanic Mountains 5.46

6. Label a Volcano
ash
vent
lava
pipe
crust
magma 
chamber

7. Parts of a Volcano ash vent side vent pipe lava crust magma chamber
Magma Inside the Earth 4.45

8. Types of Volcanoes
Different types of volcanic eruptions form 
different types of volcanoes.
 Cinder cones
 Shield volcanoes
 Composite volcanoes

9. Composite Types of Volcanoes
Tall, cone-shaped 
mountains that are 
typically steeply-sided, 
symmetrical volcanoes in 
which layers of lava 
alternate with layers of 
ash.
Examples of composite 
volcanoes include Mount 
Fuji in Japan and Mount 
St. Helens Washington 
state.
video

10. Composite

11. Mt. Vesuvius

12. Mount Vesuvius
Images of 
victims in 
eruption of 
Vesuvius in 
79 AD. Most 
died as a 
result of 
suffocation 
from the ash.
video

13. Cinder Cone Types of Volcanoes
Cinder cone volcanoes 
are the most common kind 
of volcanoes.They are 
steep sided cones. 
Streaming gases carry 
liquid lava blobs into the 
atmosphere that fall back to earth around a single 
vent to form the cone. The 
volcano forms when ash, 
cinders and bombs pile up 
around the vent to form a 
circular or oval cone.
video

14. Cinder Cone

15. Types of Volcanoes Shield Volcano
At some places on 
Earth's surface, thin 
layers of lava pour out of 
a vent and harden on 
top of previous layers. 
Such lava flows 
gradually build a wide, 
gently sloping mountain 
called a shield volcano. Shield volcanoes rising 
from a hot spot on the 
ocean floor created the 
Hawaiian Islands.
Shield Volcano
video

16. Shield

17. Crater/Caldera
There is often a funnel-shaped pit or 
depression at the top of a volcanic cone. 
This pit is called a crater. If the crater becomes very large as a result of the 
collapse of its walls, it is called a 
caldera. A caldera may also form when the top of a volcano explodes or when 
the magma chamber collapses.

18. Volcanic Crater

19. Caldera

20. Volcanic Activity
Volcanoes are rather unpredictable . Some erupt 
regularly, others have not erupted in modern history. 
Scientists classify them as active, dormant or 
extinct.

21. Active Volcanoes
An active volcano is one that 
erupts continually or periodically 
such as Mount Katmai in Alaska 
and Mount St. Helens in the 
Cascade Range.
active =
constant

22. Dormant Volcano dormant = sleeping
A volcano that has been known 
to erupt within modern times but 
is now inactive is classified as a 
dormant volcano. Mount Rainier in 
Washington state is an example of 
a dormant volcano in the United 
States.
dormant =
sleeping

23. Extinct Volcano
A volcano not known to have erupted within 
modern history is classified as an extinct 
volcano. They have been worn away almost to 
the level of their magma chamber. Mount St. 
Helens was considered to be dormant but 
erupted after long periods of inactivity 
which proves that scientists can be wrong 
about a volcano.
extinct =
never

24. Where are the Volcanoes?
Count the 
total 
amount of 
active 
volcanoes.

25. The Ring of Fire
Most volcanoes 
occur along 
diverging plate 
boundaries, such 
as the mid-ocean 
ridge, or in 
subduction zones 
around the edges 
of oceans.
video

26. Hawaii A hot spot is an area where magma from deep within the
mantle melts through the
crust like a blow torch. Hot
spots often lie in the middle of 
continental or oceanic plates
far from any plate boundaries. 
Unlike the volcanoes in an island arc, 
the volcanoes at a hot spot do not 
result from subduction.
video

27. References
Plate map and labeling diagram: World Book Encyclopedia Volcanoes Interfact
Animated Volcano:
Types of Volcano images: 

Total active volcanoes: 

NA total:
Ring of Fire total: 

Country totals: 

SA Total:
Ring of Fire Image: 

Hawaii image: biology.usgs.gov/.../ PacificIslandPIERC.htm

28. Attachments
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Volcanoes_and_Lava video 2.10.asx
Yellowstone_Crater__Supervolcano.asf
Subduction__Magma_Chambers__and_the_Eruption_of_Volcanoes.asf
Volcanic_Mountains 5.46.asx
Magma_Inside_the_Earth 4.45.asx
Deadly_Eruptions video 6.49.asx
Mount_Vesuvius_and_Pompeii video 5.12.asx
Volcanoes 5.31.asx
Lava_Junkies 5.42.asx
The_Fire_Goddess asx
The_Ring_of_Fire.asf
Hot_Spots__The_Formation_of_the_Hawaiian_Islands.asf