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Chapter 9 Answers for “Set”!
Section 1: Volcanic Eruptions
1. What is a volcano? Volcanoes are areas of Earth’s surface through which magma and volcanic
gases pass.
2. Explain what makes a volcano erupt. During an eruption, molten rock, or magma, is forced to the
Earth’s surface.
3. What are the creative forces of volcanoes? they help form fertile farmland and create some of the
largest mountains on Earth.
4. What is the most common type of eruption? Nonexplosive eruptions are the most common type of
eruption.
5. Fill in the venn diagram comparing and contrasting explosive and non-explosive eruptions.
Minimum two facts per section.
Explosive Eruptions
* rarer than
nonexplosive
*desructive
*produces
pyroclastic
*clouds of hot
debri, ash, gas
* mils of tons; lava
& rock
Non-Explosive Eruptions
*both are eruptions
and release stuff from
a volcano
*both occur around the
world
* most common
* relatively calm
flows of lava
* release huge
amounts of lava
*produces mostly
lava
6. If the water content of magma is high, an explosive eruption is more likely.
7. Explain how water and magma create explosive eruptions.
Because magma is underground, it is under intense pressure and water stays dissolved in the
magma. If the magma quickly moves to the surface, the pressure suddenly decreases and the
water and other compounds, such as carbon dioxide, become gases. As the gases expand
rapidly, an explosion can result.
8. Magma that has a high silica content also causes explosive eruptions.
9. Explain how silica-rich magma creates explosive eruption.
Silica-rich magma has a stiff consistency. It flows slowly and tends to harden in a volcano’s
vents. As a result, it plugs the vent. As more magma pushes up from below, pressure increases.
If enough pressure builds up, an explosive eruption takes place.
10. What is pyroclastic material? Pyroclastic material forms when magma is blasted into the air and
hardens.
11. What is viscosity? How lava flows: milkshake has high viscosity and a glass of milk has low
viscosity. Lava that has high viscosity is stiff. Lava that has low viscosity is more fluid.
12. Fill in the four types of lava and describe each one:
Type of Lava
Description
Aa
Pours out quickly and forms brittle crust. Crust is torn into jagged pieces as
molten lava continues to flow underneath
Pahoehoe
Flows slowly. Glassy surface has rounded wrinkles.
Pillow
Forms from lava erupting underwater. Forms rounded lumps.
Blocky
Cool stiff lava that doesn’t travel far. Forms jumbled heaps of sharp edged
chunks.
13. Label the volcano with the following terms: magma chamber, vent, lava flow, pipe
Vent
Lava Flow
Pipe
Magma Chamber
14.
Fill in the chart about the different types of pyroclastic material
Type of
Pyroclastic
Material
Description of Material
Size of Material
Small
Medium
Volcanic blocks
Largest pieces of pyroclastic material. Pieces of solid
rock erupted from a volcano
Large
Volcanic bombs
Largest blobs of magma that harden in the air.
Large
Lapilli
Means “little stones”. Pebble like bits of magma that
hardened before they hit the ground.
Medium
Volcanic Ash
Formed when the gases in stiff magma expand rapidly
and the walls of the gas bubbles explode into tiny glass
like slivers. Makes up most of the pyroclastic material in
an eruption.
Small
Large
15. Describe a pyroclastic flow. Pyroclastic flows are produced when enormous amounts of hot ash, dust,
and gases are ejected from a volcano. This glowing cloud of pyroclastic material can race downhill at
speeds of more than 200 km/h—faster than most hurricane-force winds! The temperature at the center
of a pyroclastic flow can exceed 700°C.
Section 2: Effects of Volcanic Eruptions
16. Fill in the chart below about different types of volcanoes!
Type of Volcano
What is it made of?
Shield
Built of layers of lava
released form
repeated non
explosive eruptions.
Made of Pyroclastic
material usually
produced from
moderately explosive
eruptions.
Form from explosive
eruptions of
pyroclastic material
followed by quieter
flows of lava.
Cinder Cone
Composite
Describe what is it
shaped like and draw
a simple picture.
Gently sloping sides.
Can be very large and
very tall.
Very Steep Slopes!
Steeper towards the
top - layering
Provide an example.
Hawaii’s Mauna Key.
Mexican volcano,
Paricutin.
United States: Mount
Hood, Mount Rainier,
Mount Shasta, and
Mount St. Helens.
17. Using the volcano identification document on Mrs. Poole’s Blog, identify the type of
volcano in each figure:
Figure 1: ____Shield_____________
Figure 4:_____Shield____________
Figure 2:_____Cinder Cone_______
Figure 5: _____Cinder cone________
Figure 3:_____Composite_________
Figure 6: _____Composite_________
Volcanic Landforms
What are the 3 types of landforms produced by volcanic activity?
18. Crater
19. Caldera
Type of What is it and
Volcanic what does it
Landform look like??
Crater
Caldara
Lava
Plateau
Provide an
example.
A funnel-shaped pit
near the top of the
central vent of a
volcano.
Kamchatka in
Russia formed
around the central
vent of a volcano.
A large,
semicircular
depression.
Much of
Yellowstone Park is
made up of 3 large
calderas that formed
when volcanoes
collapsed.
A wide, flat
landform that results
from an eruption.
The Columbia River
Plateau formed from
a massive
outpouring of lava
that began 17 years
ago.
20. Lava Plateau
Describe how
it forms.
During a less
explosive eruption,
lava flows and
pyroclastic material
can pile up around
the vent creating a
cone with a central
crater. As the
eruption stops, the
lava that is left in
the crater can drain
back underground.
A caldera forms
when the magma
chamber below a
volcano partially
empties and causes
the ground above to
sink.
In other words: they
form from the
collapse of the roof
overlying a magma
chamber.
A lava plateau
results from
repeated
nonexplosive
eruptions of lava
that spread over a
large area.
Answer the
random
question
If lava hardens in
the crater, what
happens during the
next eruption?
If the lava hardens
in the crater, the
next eruption may
blast it away. This
can cause craters to
become larger and
deeper.
How are hot
springs heated?
Hot springs, such as
Old Faithful, are
heated by the
thermal energy left
over form those
events.
Provide an
interesting fact.
Answers will very
Section 3: Causes of Volcanic Eruptions
21. Magma forms in the deep regions of the Earth’s crust and in the uppermost
layers of the mantle where the temperature and pressure are very high
22. What is the upper mantle made of? Very hot, puttylike rock that flows slowly.
23. The rock is hot enough to melt but remains puttylike solid because of pressure
24. The most common cause of magma formation is a decrease in pressure
25. Where does magma often form? The boundary where separated tectonic plates
Where pressure is decreased
26. What does the magma do because it is less dense? Rises toward the surface
27. Where do a large number of volcanoes occur? Directly on tectonic plate
boundaries.
28. Where is the Ring of Fire located? Around the Pacific Plate
29. At plate boundaries plates either: collide, separate, or slide past each other
30. 80% of volcanoes form where plates collide , 15% of volcanoes occur where plates
separate
31. Complete the chart below:
Type of Boundary
Divergent
Convergent
How plates move
Away from each other
Towards each other
32. What is happening at the mid-ocean ridges? Lava flows from undersea rift zones
and produces volcanoes and mountain chains
33. What is formed at mid-ocean ridges? New crust
34. Most volcanic activity on Earth occurs at mid-ocean ridges
35. What happens when the oceanic plate collides with a continental plate?
The oceanic plate slides under the continental plate.
36. Why does the oceanic crust go under the continental plate?
The ocean crust is less dense.
37. Identify the type of boundary and describe what is happening in each picture in the chart
below:
Convergent
Two oceanic plates collide, one plate
goes under another creating volcanic
arc islands
Convergent
Oceanic and continental plates
collide, ocean plate subducts/goes
under continental plate. Heats
magma, it rises to form land
volcanoes
Divergent – Sea floor spreading
Two ocean plates move away from
each other creating new sea floor
Hot Spot
Tectonic plate moves over a mantle
plume or crack in the earth’s crust
forming a volcanic island