Download CHAPTER 9 STUDY GUIDE Test Date: 11/15

CHAPTER 9 STUDY GUIDE
Test Date: 11/15
1. Define Vocabulary
 Volcano a vent or fissure in the Earth’s surface through which magma and gases are
expelled.

Active Volcanoes are currently erupting or show signs of erupting in the near future.

Vent an opening at the surface of Earth through which volcanic material passes.

Dormant Volcanoes are currently not erupting but the record of past eruptions suggests
they may erupt again

Magma chamber the body of molten (melted) rock that feeds a volcano.

Extinct Volcanoes have not erupted in recorded history and probably will never erupt
again

Crater funnel shaped pit near the top of the central vent of a volcano

Mantle Plumes columns of rising magma

Caldera large, semi-circular depression that forms when the magma chamber below a
volcano partially empties and causes the ground above to sink.

Rifts cracks

Lava plateau wide, flat landform that results from repeated nonexplosive eruptions of
lava that spread over a large area.

Pyroclastic Material is material that forms when magma is blasted into the air and
hardens

Rift zone area of deep cracks that form between two tectonic plates that are pulling
away from each other (divergent boundary)

Hot Spot volcanically active area of Earth’s surface far from a tectonic plate boundary.
2. Why do volcanoes form at subduction zones? Describe the process and include a simple
picture.
The denser, thinner oceanic crust slides under the less dense crust. This movement of
tectonic plates scraping against each other causes the temperature and pressure to
increase. This in turn causes the water to be released from the oceanic plate which lowers
the melting point and allows the rock in the mantle to melt. This new body of magma can
rise, because it is less dense than the surrounding rock, and form a volcano.
3. What is a major cause of geological events on the Earth’s surface?
Movement of lithospheric plates.
4. What are some examples of how volcanic eruptions impact the Earth’s surface?
The following landforms my result: islands, calderas, craters and lava plateaus
5. How do volcanoes form new land?
Lava that flows out of mid-ocean ridges forms new sea floor/land. Lava flows form new
land (for example, Hawaii)
6. Where do volcanoes usually form?
Along plate boundaries → convergent and divergent.
7. How does silica content affect lava? (page 252)
High silica content = stiff consistency, slow flow
Low silica content = runnier consistency, quicker flow
8. How does water content affect magma?
High water content leads to increased pressure = explosive eruptions
Low water content leads to decreased pressure = non-explosive eruptions
9. Name the two types of volcanic eruptions.
Explosive and non-explosive
10. Describe each type of volcanic eruption
a. Non-explosive: relatively calm flows of lava. The most common type of eruption.
Can release huge amounts of lava. Vast areas of the Earth’s surface are covered
with lava from non-explosive eruptions.
b. Explosive eruptions: hot debris, gases and volcanic ash explode into the upper
atmosphere. Much rarer than non-explosive but much more destructive. In an
explosive eruption molten rock is blown into tiny particles that harden in the air.
The dust sized particles (volcanic ash) can reach the upper atmosphere and circle
the Earth for years. Explosive volcanoes can blast millions of tons of lava and
rock – in a matter of seconds it can demolish an entire mountainside.
11. Describe the 4 types of lava: how it forms, what it looks like, etc. (page 253)
a. Aa Lava:
Lava pours out quickly
Forms a brittle crust
Crust is torn into jagged pieces
b. Pillow Lava:
Forms when lava erupts underwater
Lava forms rounded lumps in the shape of pillows
c. Pahoehoe Lava:
Flows slowly, like dripping candle wax
Its glassy surface has rounded wrinkles
d. Blocky Lava:
Cool, stiff lava that does not travel far from erupting vent.
Usually oozes from volcano forming jumbled heaps of sharp-edged chunks
12. How does viscosity affect lava (page 253)?
Low viscosity lava is more fluid/ flows more easily. (Aa and Pillow)
High viscosity lava is stiff and flows more slowly (Blocky and Pahoeoe)
13. Describe the four types of pyroclastic material in detail. How it forms, what it looks like,
etc.
a. Volcanic bombs:
Large blobs, harden in air, shape caused by magma spinning in air as it
cools.
b. Lapilli:
Means “little stones” in Italian, pebble-like bits of magma that hardened
before they hit the ground.
c. Volcanic Ash:
Forms when the gases in stiff magma expand rapidly and the walls of the
gas bubbles explode into tiny, glasslike slivers. Ash makes up most of the
pyroclastic material in an eruption.
d. Volcanic Blocks:
The largest pieces of pyroclastic material. Solid pieces of rock erupted
from a volcano.
14. Name the 3 types of volcanoes and describe each one in detail:
a. Shield volcano:
Built of layers of lava released from repeated non-explosive eruptions.
Lava is runny so spreads out over wide area creating gently sloping sides.
Although not steep, shield volcanoes can be enormous – the tallest
mountain on Earth is taller than Mt. Everest. (Mauna Kea in Hawaii)
b. Cinder Cone Volcano:
Made of pyroclastic material usually produced from moderately explosive
eruptions. The pyroclastic material forms steep slopes. Cinder Cones are
small and usually erupt for a short time. They often occur in clusters,
commonly on the sides of other volcanoes. They usually erode quickly
because the pyroclastic material is not cemented together.
c. Composite Volcano:
Sometimes called stratovolcanoes, are one of the most common types.
Form from explosive eruptions of pyroclastic material followed by quieter
flows of lava (non-explosive eruptions). The combination of both types of
eruptions forms alternating layers of pyroclastic material and lava with
broad bases and sides that get steeper toward the top.
15. How can volcanic eruptions affect climate?
Volcanic ash and gases can block enough sunlight to cause global temperatures to
drop.
16. Where does magma form?
Forms in the deeper regions of the crust and upper mantle where temperature and
pressure are very high.
17. How does magma form? (page 260)
Changes in pressure and temperature cause magma to form.
18. What kind of rock forms from cooling magma or lava? (page 93)
Igneous Rock
19. True or False – The most likely place to gather samples to study the composition of
material from the mantle is volcanic vents on the ocean floor.
20. What instrument do scientists use to detect small changes in the angle of a volcano’s
slope?
Tiltometer