Chapter 6, Lesson 2 (pgs. 180-187)
Pg. 180
How does Pele’s hair form?
Drops of lava are spewed out by a volcano. The drops then stretch in the
wind and harden.
Pg. 181
Vocabulary: It consists of parts that function together to move magma to the surface.
Figure 1:
Central Vent
Crater
Lava Flow
Side Vent
Pipe
Magma
Chamber
Pg. 182
Do the Math!
1. Silica, other solids and other oxides
2. High-silica magma has more silica. It is composed of about 70 percent silica
3. The high silica magma will erupt explosively. It is thick and sticky, so gases
cannot easily escape. When it erupts, it erupts with a lot of force.
Pg. 183
Figure 2
Sample Answer: Aa forms a dark mass like the top of a burnt crumb cake. Pahoehoe
forms a broad mass that looks like huge strands of spaghetti.
Pg. 184
Outline: 1b. Low-silica magma
2a. Mount St. Helens
Pg. 184
Figure 3
Gases inside the volcano could not escape the thick, sticky lava. So the gases became
trapped inside. When the magma could no longer contain the gases, the volcano
erupted explosively.
Pg. 185
Figure 4
Lava could set fire to houses and buildings. Ash could bury house and people. The
pyroclastic flow could destroy everything in its path. Landslides could bury people
and buildings. Ash and gases could make breathing difficult.
Review
1a. Quiet and explosive
1b. The ice in the glaciers might melt causing massive landslides.
Pg. 186
Figure 5
1. Circle Mount Rainier, Mount St. Helens and Mount Shasta
2. Because the Juan de Fuca plate is still sinking under the North American
plate.
Pg. 187
Figure 6
As the Juan de Fuca plate sinks below the North American plate, part of the mantle
can melt and rise as magma. The magma will have a medium level of silica content
(60%)—high enough to cause explosive eruptions of ash and lava. The lava will
pour down the volcano’s sides. Together, ash and lava will result in a dangerous
pyroclastic flow. Mount Rainier is an active volcano that has erupted many times
and may erupt again.
Assess Your Understanding
2a. Active
2b. Expanding gases push magma up through the volcano’s pipe until it flows out of
a vent. Lava can erupt either quietly or explosively.